quadpagenewver

(last updated with makeover 28th October 2000)

The views expressed in these pages are the opinions of the author. He can accept no responsibility what-so-ever for any damage caused to equipment or the person of those who undertake to modify their equipment according to the instruction given below. You have been warned!

Click on the links to jump to the appropriate section:

Introduction

What's what and where is it?

Quad mods

Mod 1 - getting rid of the Quad 22 control unit

Mod 2 - an independent mains supply for the Quad II

Mod 3 - new resistors

Mod 4 - new capacitors

Mod 5 - replacing the valves

Mod 6 - changing the output impedance

Mod 7 - changing the valve sockets

What to do when a transformer or choke goes

Making your own interconnects

The benefits of bi- and tri-amping

The Falcon/Focal Antea C800s are built

Quad 303

Coming soon - more on the active crossovers (for now see under bi- and tri-amping).

Links

Sign my guest book?

Contact

The Quad II Mod Pages are my attempt to describe how to bring a pair of Quad II monoblocks up to modern standards. Much has been written about the Quad II and there are several excellent Quad internet sites (see the links section below). I am not an expert at the restoration of valve gear but I have learnt a lot as I have gone along. I obtained three (yes three!) Quad IIs along with mono and stereo control units from the widow of a jazz record dealer. Unfortunately these had suffered from being left in a very damp spot in a basement. One was rusty to the point where it was necessary to strip the paint and re-spray it. There was no way this particular amp was going to work even if I dared to plug it in! In the event it turned out to need re-valving and I also replaced nearly all of the resistors and capacitors. The other two were not in such bad shape and I decided to plug them in along with the control unit and much to my surprise they functioned perfectly! However, that was not the end of the story. I decided that three was an odd number and bought a fourth Quad II from Dennys Trickett at the Hi-Fi Curiosity Shop (a highly recommended Alladin's cave in Kilburn). This final amp was a near perfect and original example of the marque. Many would consider three amps to be over the top, so why did I buy a fourth? Well I decided to go for bi-amping a pair of Falcon C800 MkII (a copy of the JMLabs Anthea) loudspeakers but more of that as the construction of these pages, and that of the loudspeakers, progresses.

My advice on buying old valve amps is that if you know what you are doing (hell, I didn't!) then go to an audio jumble and buy a pair of Quads. Make sure that they are as original as possible. You are probably going to modify them but it is much better to start with a working pair of original amps than have to solve all kinds of problems that may have been caused by someone messing around with them. Look for cases that have not been drilled and for valve sets that include the original or NOS (new-old stock) EF86, KT66 and GZ32/34 valves. If you see a pair of monoblocks without the control unit and the only mod has been to fit phono sockets then snap them up. If you really don't want to take the risk of buying at jumble then go to a reputable dealer in vintage hi-fi (see the back pages of Hi-Fi World). Expect to pay anything between £300 and £500 for a set-up including the control unit. The control unit looks great in a retro sort of way but it is just not up to it from a hi-fi stand point. Indeed the first and really revealing mod that I made to my amps was to remove the Jones plug (a fine connector but a pain to connect to anything but the original pre-amp to), put the 22 control unit in the loft and connect the working pair of Quad IIs to a high quality home-made passive pre-amp. The result was amazing. I had read a lot about the Quad IIs, many critics stating that they were not up to scratch by modern standards, I am now convinced that many such comments must have come from those listening to the amps driven via the 22 control unit. Take it from me scrap it! It was a fine piece of gear 40 years ago but now it is no longer up to it. This is just one of what I hope are fairly objective comparisons between the amplifiers with and without the modifications I have carried out. Because I have listened to the amps as I have 'modded' them I hope that I can offer some advice on the effectiveness of the various changes.

So how do Quad IIs stand up once 'sorted' by comparison to modern valve amps? Well, I have heard quite a few amps, both transistor and valve, and as yet I haven't found anything that sounds as good as the Quads for less than 2 to 3 times the price - so modify the Quads and you'll have a pair of amps that sound as good as anything you can buy for £1000, and possibly £2000. You will find the Quad IIs variously described as being under-powered, lacking in bass, lacking in treble (most agree they are great in the mid-range), coloured, and any number of other things. If you are trying decide whether or not go for Quad IIs try to get to hear a pair driven from a good pre-amp and connected to a pair of sensitive, high quality speakers. Do not listen them connected to ESL 57s......you'll want to buy them as well!

Before getting down to the nitty-gritty a word about hi-fi nerds. Hi-fi nerds are a weird bunch. Some seem ready to believe in almost everything including little green men. This group believe that they can hear the difference between a silver-plated and a copper wire, a metal oxide and a carbon film resistor, and that little green rings stuck on your CDs will make them sound better. My view is that they may well be right but that their views have to understood to be personal opinion. I cannot hear the differences that these things make but I can hear the difference between a fine valve amp like the Quad and many, so-called hi-fi, transistor amplifiers and the difference that the mods I detail below made to the sound of my amps. Understand that I am not someone who believes that valve amplifiers are in some way magic - there are lots of fine transistor amps it is just that you are unlikely to get a transistor amp that sounds as good as the Quad II for the same price. Besides which I believe that Peter Walker, the founder of Quad and responsible for all their early designs, was a genius and that the Quad II is a monument to his inspiration.

In striving for the best in hi-fi you must make your own judgements but please try to do it without laying out vast sums of money. That solid silver, hyper-slick, inch thick speaker cable at £100 a meter may be better than the heavy duty OFC stuff from Maplin but if it is then I can't hear it and neither can the people I have tried blind substitution tests on. A long while ago Wireless World got some hi-fi gurus together and got them to listen to do truly blind comparisons of high-end amplifiers. The results were very interesting - most could not tell one amplifier from another! No one seems to have convinced any of these gurus to go in for another set of such blind comparisons. Your hearing may warrant spending more money than mine does but I implore you LISTEN before you leap and try to get someone to swap components without your knowledge before you make a judgement.

Inevitably you will also need a circuit diagram (click the thumbnail):

The figure below has all the component values and placements shown superimposed on a picture of the inside of the chassis. Click on the picture to download a bigger version (large file may take sometime to download!).

With these pictures printed and to hand you can consider whether or not you want carry out the following modifications.

OK it's time to decide whether or not to carry out any of the following mods. But first here is a warning:

The voltages in valve amplifiers can be lethal! Do not take this warning lightly. It is not just a nasty to receive a 350V shock, it can be the last thing you ever experience. Careless wiring and/or faulty earthing can also put friends and relatives at risk of lethal shock or fire. If you do not know your Vs from your Is and Rs - STOP and get professional help NOW!

A word of advice - never throw anything away! I have kept all the original parts (bar the resistors). Amps that have not been subject to modifications are generally more saleable than those that have. I have kept the Jones plugs and sockets, capacitor retaining clips and original capacitors so that I can return my amps to their original condition.

Getting rid of the Quad 22 control unit

My opinion is that this is the single most effective mod that you can make. Let me take a moment to let you know what you can expect if you replace the 22 control unit with a passive pre-amp. My passive is an interim measure. A passive does not in my opinion provide sufficient drive, though with good short cables, a decent pot (I used an Alps Black Beauty 100K log) and a high quality selector switch (I obtained a Rotor-Stator 6 way selector switch from Walther Electronics whom I can thoroughly recommend as an extremely helpful supplier - you have to wait a day or two for the mail from Greece but it is worth it!) the improvement is stunning. My Quad 22 control unit let me down because the pot was noisy, the RCA connectors on the back had oxidised and a good base line would start microphonics, as the plugs, which never seem to fit tightly in older phono sockets (a slight change in dimensions when we went metric?), rattled around. There was a very noticeable hiss when there was no signal and the impression when compared with the homebuilt passive pre-amp was that the 22 drew a veil over the treble and had a woolly bass. The passive's bass was, much to my surprise, much better than the 22 could produce and the treble was clear and clean. The passive is a major improvement. Go on...do it! Get rid of the 22 control unit!

At first sight this would seem to involve simply throwing it away but then things are never as easy as that. The Quad II amp supplies the power for the control unit and is earthed via its connection to it. The cabling to the QuadlI carries the HT and LT supply lines, the input signal to the amp, and the earth connection. All of this is done via the Jones plug. To make safe and sensible connection to the power amp independent of the control unit you will need to get rid of the Jones socket - a pity because the connector is not a bad one. This will involve providing a properly bonded earth for the amp (see under Mod 2 - an independent mains connections), safely diverting the HT and LT power supply wiring and fixing a plate to carry the phono socket in the hole left by the Jones socket. The plate you want can be cut from thin sheet aluminium, it is relatively small so it won't distort when you plug in the RCA connector unless the aluminium is less than about 1.5mm thick. To make the plate cut a sheet about 34mm high by 34mm wide about 15mm from the top draw a line parallel to the top and drill two 3.5mm holes 26mm apart - these take the screws that will hold the panel in place. Dead center between these drill the hole for the RCA socket (precise size varies with make). The panel is asymmetric because there is very little space at the bottom of the amp and the clips that take the base screws can get in the way. If they do file the bottom right hand edge of the plate so that it fits. Fit the RCA connector and its earth tag beneath its nut - grip the outer part of the socket with a pair of mole-grips using a cloth to prevent damage to the socket's finish - tighten up. Use a good quality heavy gold-plated connector but don't spend a fortune - a good connector with Teflon insulation can be had for £3 -5....spending more will bring no further improvement.

I learnt from Matthias Brennwald's web site (http://www.brennwald.matthias.com/) that the Jones socket can be obtained from Jaeger in Switzerland (the part-number is 627.22 and their web site address is http://www.jaegerag.ch/). Matthias' site has many other interesting offerings.

Now you need to take the base-plate off the amp and de-solder all the connections to the Jones socket. The Quad II circuit diagram (see above) shows the wiring to the socket. Divert the HT and LT into seperate sections of a nylon terminal block, do up the screws and make sure there is no way that the cables within the terminal block can contact anything outside. Now using a glue gun (don't worry, it doesn't get hot enough inside a Quad II to melt the glue!) stick the connector to the chassis just to the left of the empty hole where the socket used to go. Fit your panel and phono plug putting a star washer beneath it and beneath the head of one of the bolts that holds the panel. Make sure there is zero resistance to earth, the RCA socket outer case and the chassis - clean paint away as necessary, this must be a zero Ohm connection. Solder a 1.5MOhm resistor between the RCA signal (centre) pin and earth. The old 1.5MOhm resistors should be discarded....they may have shifted a deal from their original value (mine had wandered off to 1.8MOhms). Connect the signal wire to V1 as shown in the circuit diagram and you are done. Be sure to check that there is absolutely no chance of the HT wires ever contacting the chassis - no chance, not now, not ever.

Since I have recommended getting rid of the control unit a number of people have written to me to say that this is a mistake. I have to disagree, particularly if you intend to drive the Quads from a CD player or you are prepared to buy a decent modern phono stage. There is no doubt that the 22 can be modded to improve its performance but in my opinion it just cannot rival driving the Quads via a passive. If you want to update the 22 Chris Beeching of PM Components (suppliers of any valve you could ever want and also of Golden Dragon tubes) says:

"Firstly, having covered rebuilding Quads in articles for Hi-Fi news in the past I can't quite agree that the 22 is noisy. As you said in the bit about resistors, the values change, and the same is true of the many resistors in the 22. The caps suffer similalry, particularly the smoothing caps and the signal caps. If you replace these and carefully clean the swithes (which is a bit of a nightmare) then you can get a quiet 22 which is musical as well. The phono sockets are a bit of a pain, but if you remove the original 'tag-strip' style ones you'll find that the holes beneath then take modern sockets quite happily. You can also reconfigure the phono input layout to be a left and right input either side of a central mono one; that way you can get two modern plugs into a stereo configuration. If you leave the left and right adjacent to one another you can't get one plug in!"

An independent mains supply for the Quad II

This one is also not quite as easy as it first appears. First the amp will need an independent securely bonded earth and second you will need to make a major decision. Are you going to keep the old Bulgin 2 pin mains socket or replace it with a modern Euro-style 3 pin connector there is a lot to be said for the latter because the Bulgin connector is not up to modern safety standards. A Euro-style connector will make offering an earth a simple business BUT you will probably need to cut the chassis to fit it in. For this reason I kept the Bulgin connectors. However, I ran an earth to the a solder tag beneath a washer and atop a star washer on the bolt that holds the Bulgin socket. It is vital the earth is secure. I left enough earth cable free of the end of the three core cable to enable the plug to removed. I admit this is kluge but it works and you do not need to take a hacksaw to the case. My mains cables are screened with the screen connected to earth at the plug end (run an insulated wire out of the plug to the screen, never run a bare screen into a plug). They plug into a socket equipped with a line filter (Maplin product number CT79). The line filter reduces RFI and gets rid of pops and clicks from refrigerators and other electrical gear connected to same ring main. If you fit a euro-style connector you can buy one from Maplin with a built in line filter. Whatever you do, make sure you have a high quality earth to the chassis!

New resistors

This one I found important if you want two amplifiers of similar performance. The original carbon resistors used in the amp show their age by changing their value. This always seems to increase rather than decrease and can lead to them ending up with values well outside their original tolerance ranges. Clearly two amplifiers cannot be a good match if the voltages set by their resistors are widely discrepant. Fortunately amplifiers with similar production numbers seem to wander off in similar directions and are usually of similar performance even many years later. I replaced the resistors in two of my amplifiers using 2 and 1W close tolerance metal oxide resistors. I had to use two different makes to get all the values needed. Click the thumbnail below to pull up the parts-list from the original Quad II manual.

I simply removed each resistor in turn and replaced it with its new counterpart. I found that it made it much easier to do this job if you first snipped through the resistor's leads near their body. It is then easy to heat the tag to melt the solder and pull out the remnants of the lead with a pair of fine-nosed pliers. I am told that more expensive resistors such as Vishays, sound better than standard carbon or metal oxide ones. I cannot tell the difference between the sound of the old carbon resistors and the new metal oxide ones. If you find Vishays sound better then let me know....I must say that I find it unlikely and for one Vishay you can buy all the metal oxide resistors you will need to rebuild a pair of amps!

New capacitors

I found that replacing the Hunts capacitors with polypropylene 'audiophile' versions made a significant difference to the sound. It became less grainy and more fluid....a subtle but discernable difference. I don't know whether this difference was due to the magic properties of the new capacitors or because the old Hunts were in bad shape as most will be in amp of this age! You cannot hook the big new polypropylene caps down with the original clips. I glue-gunned mine to the casework - crude but an effective way of preventing them vibrating around. For good measure I also changed the bipolar capacitors in my loudspeaker crossovers for the same type. I used the Maplin components with the order code VM87. I replaced the component number C5, a 25microF capacitor, with a standard electrolytic. I doubt that it contributes much to the sound. I have considered replacing the 16+16microF pi-network capacitors with more modem types (this had been done for me in one amp which has an RS dual section capacitor as a replacement for the original). I would be interested to hear anything about the effect of replacing C4 and C6 on the sound. Cricklewood Electronics now sells a two section polypropylene capacitor for not much more than you can purchase a Cerafine or other high quality electrolytic, so even if you don't think polpyprops make any difference you can try them without much extra expense. Incidentaly, old electrolytics are often a problem in repairing vintage gear - electrolytics have a finite lifetime (look at the specs in an electronics catalogue), they do not like heat, and can be expected to be on their last legs after 10 or more years.

Recently, Nick Salamouras of Walther Electronics (http://www.walther.cjb.net) made the following suggestions concerning the pi network capacitors:

"The Quad II uses a GZ32 rectifier which can not accept more than 60 mfd before the choke. Some people use solid state rectifiers and huge capacitor banks before and after the choke. They get much bass but they roughen the sound in a VTL manner in my view. What I do is to retain the valve and its fluidity. My trick is to use polypropylene capacitors (a' la Conrad Johnson) that they blend a degree of precision and slam without destroying the musicality as long as we keep the valve rectifier. I would use an SCR 47/400 before the choke plus two or three SCR 47/400 in parallel after the choke. The 1/3 ratio gives the best sound to my ears. I always bypass the paralleled second section bank with 1microFarad 630V SCR tin foil which relaxes the sound and enhances timbre naturalness. The SCR 47/400 costs 14 EURO each and measures 6cmL x 4,5cmD.The tin foil costs 12,23 EURO."

I haven't tried polyprops and I cannot thus comment on what difference they will make in the pi-network. Some think they work miracles in the signal path and others think they make no difference.

eeks time - thanks for the tip Nick!

New valves

One of my amps needed re-valving. This showed itself by smoke coming off R12 which had 38V across it! Martin Ackroyd has gave some excellent advice on the choice of substitutes for the KT66 on the now defunct (?) Andre Jute web pages. Martin described how he had measured the performance of RCA 6L6GCs, Sovtek 6L6WGCs, GEC KT66s, Mullard EL34s and Sovtek EL34s in his Quad amplifers. His conclusions were that the 6L6s seemed a perfectly good substitute for the KT66s. His dad had worked in the GEC labs in 1937 and told him that the valve designers there had aimed to make the KT66 compatible with the RCA 6L6 of the day.

I chose to use a pair of Golden Dragon KT66 retros. These look and sound exactly like the original valves but are quite expensive (~£80 a pair). I bought a matched pair because while the specs say that the amp will take a 25% mis-match, the distortion levels are significantly increased. These valves draw significantly more filament current so I guess that there is more strain on the power transformer. However, since these were designed to cope with addition of the control unit and tuner, you shouldn't have any problems.

Chris Beeching of PM Components has some very helpful advice on revalving:

"Wearing my PM hat, the Golden Dragon KT66 Retro has a filament current draw of 1.3amps, the same as the original GEC KT66. Confusion has arisen because of a (wrong) article which stated that the original GEC only drew 0.9amps. THIS IS NOT TRUE. The majority of the 6L6 family draw 0.9 amps, but the KT66 and KT88 (and particularly the EL34) are exceptions. A very good alternative to the GD KT66-R (if you're on a budget) is the excellent 350B which is shaped similalrly to a Mullard GZ32, but which is an output pentode, and will drop in without alteration. If you're running 6L6s you should raise the cathode resistor value to about 220ohms."

Watford Valve (http://www.watvalve.dircon.co.uk/) can supply you with matched KT66s made by Harma (matched quad sets are about £120). I have not heard these though I understand they too are indistinguishable from the originals. If you buy NOS GEC KT66s expect to pay £100+ for a matched pair.

The EF86s can be substituted by A729s or 6267s. The GZ32 is sometimes replaced by the CZ34 which offers a little more headroom. Other possibilities are the 54KU or the 5V4G. Chris Beeching also has some useful advice on EF86 substitutes:

"The EF86 is a good valve, but it was designed to be a telecomms line repeater. In reality it's almost an RF valve. A really excellent replacement (if you can rewire the base in both the IIs and the 22) is a 6BR7. It's far more musical, much quieter, and far less prone to microphonics. And it's cheaper!"

Changing the output impedance

This is easily done by changing the links on the bottom of the output transformer. To drive speakers with impedances of 4-8Ohms remove the link between tags R and S and instead connect Q to R and S to T.

Changing the valve sockets

A quick inspection showed that the spring connectors within the valve sockets of my oldest amp were turning green! This, I thought, might be the reason why one of my KT66 heaters sometimes failed to warm up. I decided to keep the looks of the amp by buying 'retro' McMurdo bakelite bases similar to the originals. I bought these from Watford Valve. Nicely made sockets with two pressed chromed-steel sheets forming the flange. Unfortunately, a slight doming of the uppermost of these means that they will not fit on the underside of the chassis and a certain amount of iling is required to get them to fit on the top. I guess the best thing is to buy another type. I'll report on what i am able to find another time. When you replace the KT66 bases do them one at a time. The component placements and wiring scheme is identical for both of them and you can use one as a model for the other. Watch that you get the pin numbers correct. The numbers on the originals are a little displaced from the pins and can lead to confusion.

What to do when a transformer or a choke goes!

I learnt the answer to this the hard way! A couple of weeks ago I switched on my amps and sat back to notice a huge hole in the bass output. Inspection showed that the usual glow from the filaments of one Quad II was absent. I took it to my bench and checked the fuse - it had blown. Within a few seconds of replacing it I had two blown fuses. I disconnected all the secondaries on the mains transformer and carefully seperated them and replaced the fuse for the 3rd time. Now I had three blown fuses and the upsetting knowledge that I needed a mains transformer. A search through the back pages of Hi-Fi world revealed a couple of places that advertised second hand transformers. P.G. Hi-Fi (Tel 01428-651554), who also carry spare output trannies and chokes had one on the way to me within days. The cost is roughly equivalent (£80) to buying a new one from Sowter transformers. The Sowter transformer is a fine replacement but doesn't fit in the same case as the original so if you buy it your amp will be very changed in its appearance. A few minutes soldering and I had the new transformer in place...everything came back to life and I breathed a sigh of relief! The bottom line is that 2nd hand transformers are out there still but they are not cheap. It may be a good idea to pick up a cheap amp and keep it for spares. Non-functional Quads are of course an unknown quantity but are relatively cheap and would likely yield the iron you may need one day.

Making your own interconnects

It is my opinion that for a few quid you can make a cable as good as any you can buy. I cannot sign up to the notion that spending £100 on an interconnect brings ANY benefit over cables made as I describe below. Bear in mind that cables can only degrade the signals you send along them. An interconnect has the properties of resistance, capacitance and inductance. The biggest problem a cable can present is that it acts as a low pass filter shunting the HF frequencies to earth via the capacitance between signal and earth conductors. This capacitance can be minimised in a number of ways but the simplest is to seperate the signal lead from the earth by the greatest possible distance and use the poorest possible dielectric between the two. Remember the shorter the cable the less the capacitance. Maplin supplies a high quality AV cable (cat # FN74R) which is 8mm in diameter, has oxygen free copper conductors, foamed polythene insulation and a mylar foil and OFC braid. It costs about £2 a metre. This cable has a capacitance of about 60pF/metre. Suitable RCA connectors are Maplin (Cat #s JZ13P, JZ14Q - black and red respectively). These cost about £2 each and are good quality gold plate on brass plugs. Making up a pair of connecting cables from these components takes about 10 minutes and costs ~£10. You will not find a better sounding cable unless you system is too bright in which case I guess you could try using one of those 2mm diameter cheapos that come free with low-end hi-fi - after all in this case you actually want to loose some of your HF signal!

More mods to come!

I will continue to update these pages with Quad mods and projects as they are completed - so come back soon!

The picture below shows one of the amps in which I replaced all the capacitors and resistors. This was necessary because the resistors had wondered way off, the Hunts were faulty (my advice is to replace these capacitors even if they seem OK), and two of the valves required replacing (KT66 and EF86).

And here is a picture of all four Quads housed on a temporary stand:

Those interested in an excellent and detailed account of the benefits of biamping would do well to consult the 'Elliot Sound Products' web pages ((ttp://www.sound.au.com/). Here not only will you find details of bi- and tri-amping, but also how to build active crossovers and many other DIY audio delights.

I have used my four Quad II amplifers to bi-amp a pair of Focal C800/Antea speakers. My arrangements for this are very simple. The Quad IIs consist of a pair whose production numbers are close and one with a much lower, and one with a much higher, production number. The one with the lowest production number has been totally rebuilt and most of the pictures on these web pages are of the refurbished innards of this amp. I used the most closely matched pair to drive the mid-range/treble drivers and the others for the bass. I first used a cheap Maplin electronic crossover to seperate the HF and LF drive to the amps but now have built a 3 way filter to do this and use a Quad 303 for the bass. A comparison of the quality of the output of the paired amps driving the speakers against the bi-amped arrangement showed that bi-amping, even with the Maplin crossover, produced a reduction in the 'muddiness' of the sound. Why is this? When you play music through an amplifier, rather than testing its performance with sine waves of a single frequency, you inject, at the front end of the amp a hugely complex waveform. Fourier showed that any waveform can be repressented by the sum of a series of sine waves (a Fourier synthesis). However, within an amplifer the higher frequency components can be noticeably modulated by the lower frequencies creating a form of distortion that is audible as a lack of clarity and separation between individual instruments/voices.

The Linkwitz-Riley 3-way active crossover that I built based on Rod Elliot's suggestions produced an instantly audible improvement over the high quality all polyprop crossovers that come with the C800 loudspeakers from Falcon. The instructions for such a crossover are to be found on his pages. All I can add to his instructions is that I found it paid to design and etch PCB for what are the 8 similar circuits required. I used Burr- Brown OPA2604APs for the filters, buffers and output matching circuits. You will need 12 of these and they run in at about £2.50 each. I used 1% polyprops from Cricklewood Electronics, 1% metal oxide resistors and Alps blue pots from Farnell, a 19" 3U rack from Maplin was used to house the whole project. I used a reclaimed -/+12V Kingshill power supply to supply the necessary juice. I guess the parts came to about £150. Believe me this is a worthwhile price to pay. Obviously you could use cheaper pots etc. but I think it is better to spend the money and know that you will get a great result. I understand that Rod Elliot is soon to offer PCBs for this and other of his projects. If you have only limited experience in construction of electronic equipment get a PCB - there is a lot of scope for screwing it up!

Incidentally, I found the 30-day trail version of Spectraplus and my soundcard a brilliant way of testing the crossovers. I found for zero cost in the way of test instruments I could play white noise in the input and get an output spectrum. I made up a couple of test leads that ended in miniature jacks to get the signals in and out of the computer.

The only warning I would issue is that when using transistor amps from the crossovers watch out for switch-thump when you turn the crossover on (ie power up the crossover and then the amps). Remember that with the passive crossover out the way nothing stands between a problem with one of your amps and disaster....it would be wise to look at some kind of speaker protection circuitry. Rod Elliot has several circuits for doing this.

I have in the past bi-wired my speakers. Sorry, but I couldn't hear any change in the sound quality. I have to say the same for changing from big/fat speaker cable bought from Maplin to much more expensive kinds. My conclusion is that the Maplin stuff is as good as anything (oops this will upset some people - particularly the ones who want you to spend a £100 a metre on cable!).

Pictures of the active crossover will appear here soon!!!

I chose the C800s from Falcon Acoustics (http://www.falcon-acoustics.co.uk) because they use outstanding Focal drive units and they have simple cabinetry. I learned some interesting things about loudspeaker manufacture in the process of building these beasts. I have provided a few notes below that are generally applicable to loudspeaker building. I learned the hard way, I only wish I had been able to find some of them out by surfing the web before I started! They are simple statements but by golly they make a difference to how easy you will find it to build a loudspeaker if you are doing it for the first time.

The C800 Anteas are big. They measure 1125 X 320 X 375 cms and have bass and midrange chambers of 86 and 7 L respectively. The component driver units are equisite examples of Focal's technology and when bought with the all polypropylene crossover network provide an incredibly smooth sound as good as I have heard from any loudspeaker...as yet! The kit cost about £750 and the result is something for which you would pay more than £4500 so the {short description of image}

Below is a picture of the modified interior - the black stuff are the dedshete panels. The brace half way down was replaced with a 'toilet seat shaped one before the speaker was finished. Note the back of the midrange chamber is a vertical brace.

{short description of image}

effort of building them is financially very well worth the effort. The diagrams provided by Falcon were easy to follow and they were very good at providing any additional information I needed over the 'phone. A small gripe - the drawings sent to Falcon by Focal contain an error - the midrange chamber will protude into the bass drive aperture unless you move the bass driver down by 25mm. Another minor problem is that the MDF of the thicknes required for some of the cabinetry is not readily available. I used 25mm throughout being careful not to change the chamber volumes. I railed against the Focal notion of single cross braces which are then themselves braced against the back of the drive units. Instead I made the back of the midrange chamber into a vertical brace and added a 'toilet-seat' brace one third of the way up the height of the speaker, again I was careful not to change the chamber volumes. The crossovers are three way and pretty complicated. I decided to build them into the cables outside the cabinet - ugly but sonically a good thing to do. The boards carrying the crosovers can be completely hidden by placing them behind the speaker cabinets.

Here are my tips:

(1) Get all the MDF panels precut to size by a timber yard. My local yard would have only charged £10 for this but my God it would have been worthwhile! The problem is that if you cut MDF by hand, or even with an electric saw, as I did, you won't get the square edge and finish on the edge that a razor sharp electric panel cutter can give. All the joints in the Anteas can be butt joints. The strength and finish both depend on having square edges and a good surface to carry the glue.

(2) MDF in the volume required for these speakers weighs an absolute ton! I cannot lift the finished product in anything but a bear hug. Now think what this means for building them. You will be constantly lifting and turning an enormous assembly of MDF panels. You may well need some help.

(3) I built these speakers in my garden during fine weather. The dust and shavings were terrible. Make sure you wear a mask and do not attempt to build them without a decent bench. I used a good quality 'workmate' bench with a top that can be turned at 90 degrees to clamp big sheets. It was utterly essential. I don't think I would undertake building speakers of these dimensions again without access to a good workshop!

(4) Build the midrange chamber seperately and then glue and screw it into the cabinet. It is really hard to get everything right if you fix each midrange panel into the cabinet one after the other.

(5) Find a better glue than I did for 'dedshete' panels. These are 6mm bitumen and will not stay where you put them unless you use a really good adhesive. Falcon recommend Servisol Adhesive 120 from Ambersil Ltd in Bridgewater, Somerset. I tried Evostik's new water-soluble adhesive...it was hopeless. In the end I used a combination of glue and staples to make sure they were rigidly bonded to the MDF cabinet walls. I found microwaving (be careful, there is scope here for a terrible mess and a domestic argument or two!!!) the dedshete for 60 seconds made it pliable and easy to get to lay flat on the MDF.

(6) Do not change the volume of the cabinet. Always calculate what any design changes, however minor, will do to the volume and compensate.

(7) The bass port that Focal show in their drawings is unobtainable. I bought a 110mm diameter one instead and recalculated the length using the formula provide by Falcon (the answer is incidentally that such a port should be 204mm long).

(8) I used Evostick Resin W woodworking glue and a lot of it. You should precoat the edges of the MDF and let this fine coat dry before putting glue between the two edges and clamping with screws. You will need many more screws than you can ever believe - buy 200 2 inch 10s.

(9) You need to make a decision about whether or not to route the drives into recesses so that the driver frame lies flush with the front panel. I used a router and flush mounted the drivers. This brings minor sonic gains - reduced diffraction. This wasn't easy! You will need either to make up a template or do it by hand....my advice is to practice and be aware that the HSS router bits sold in most DIY stores rapidly burn when used in MDF. I found I could resharpen them. I used a rounding-over bit to put a 12mm curve on all the edges of the speaker cabinet.

(10) The original Anthea, as provide by Focal, had solid wood sides. I fooled with the idea of doing this but abandoned it favour of the notion of veneering the MDF. When I looked at the finished cabinet with its rounded edges I decided on a white lacquer 'piano' finish. I used Japlac artic white lacquer on their white undercoat. I think this looks great. I used four coats on each speaker and rubbed each coat down with non-clogging paper in between. If you use a good brush and work this somewhat messy paint the right way you can end up with a near mirror finish. Looking back iam sure it would have been best to practice with using this paint on a piece of scrap MDF. Be sure to that when you rub the coats down you get a completely flat surface on which to apply the next coat. It took nearly a litre of Japlac to do the job!

(11) When you build the crossover be sure to thoroughly check all your wiring. I found I had made an error and I was lucky that the tweeter wasn't damaged - I had inadvertently connected it to the bass output!

(12) I guess I would recommend building the two speakers in parallel to ensure they are indentical. In practice I think you find this very difficult unless you have a huge work shop. I built mine one after the other. It is interesting to note that it took twice as long to build the first as it did the second.

Is it worth the effort. Once or twice during the process I lost heart but at the end when I had the pair wired to the Quads I was just amazingly impressed. There were so many things in my favourite records that I had never heard before. The bass was frighteningly good....a couple of dub tracks threatening the structure of the house!

{short description of image}

I bought the Quad 303 as an amplifier to drive the woofers in the Anthea's. OK so it looks like an army surplus toaster but Peter Walker's design were pretty much all sublime. Whatever you may hear from others, the 303 is a great little amp though it has to be properly set-up, and since the amps are now more than thirty years old, it is quite likely that there will be component failures. In particular, you cannot expect electrolytic capacitors to last for ever. It comes as a bit of a shock to see that the manufacturers guarenteed lifetime for these components is really quite short and the higher the temperature, the shorter the time they last. The relationship of lifetime to temperature is most important to valve amps where things can get too hot to touch but no matter how cool, the electrolytics will need replacing someitme or other.

If you look at the picture above you will see the first modification that I have made to the amp - I drilled the front to place two phone sockets in parallel with the DIN socket. Do get rid of the DIN socket...they are horrible! The picture below shows how nicely made the 'toaster' is. The two amp driver boards fold out once you've undone the neat (but can be fragile) little plastic clips as does the PSU board.

{short description of image}