Advice on new Quad based system

Hi folks, first post here after lurking around for ever...would appreciate your shared wisdom.

After many years of lusting after a set of 34/306 amps, I have finally got some - though I had to buy blind as they do not hang around for long. I have contacted Quad asking if they have any recent service history and am waiting for their reply. While waiting for the amps to arrive, I am wondering what things would you recommend I look out for? I have read about eg the need to set the gain correctly between the pre and power amps, and also set an input up for a streamer.

Also what speakers would you recommend to go with these. The speakers would need to be stand mount or bookshelf designs to suit SWMBO I would quite like to use speakers from the same era but am nervous about condition. One of the things I like about the quad setup is I know I can get them maintained easily

Grateful for your comments.

 

Welcome to our little backwater and well done for de-cloaking

Looking at the 34 first, this came in two versions and I'll assume you've got the later grey faced version if it came with a 306.

They are extremely reliable and the only real issue with them is the phono input which can sound a little light and lacking LF.
After 20+ years they can benefit from new electrolytic caps but I've never seen a 34 that's failed because of bad caps.
The CD and tape input can have the input sensitivity adjusted with plug-in resistors on the main board - Quad call them 'flags' since the ones suppled are packaged into little plastic cases. A 300 or 500mv flag is correct for CD. Without the flag it's 100mv which is too hot.

The 306 is also very reliable.
Quite powerful but nonetheless it's a physically small amplifier and not well suited to 4 Ohm loads. It will drive them to reasonable levels but quickly gets hot if pushed hard for long, causing the protection trip to cut in. Great for medium - high sensitivity >5 Ohm loads and in such conditions it's indistinguishable from a 606.

Again they benefit from new PSU caps - especially if they've been pushed hard over the years and run hot.

With both units I'd initially just slip off the cases and look for any leaking or bulging caps. If all looks well they should still work ok and sound good.

You can increase the output on the 34 and reduce the input sensitivity on the 306 to a figure more common today. The former is an official Quad documented modification, the latter isn't. This mod does two things - a very slight lowering of the noise floor and it makes both units more suited to partnering with non Quad gear. This mod is more useful on the 405 models where the noise benefit is immediately audible - and not subtle with higher sensitivity loudspeakers.

 

Thanks Rob. I like this backwater....

You are right that the 34 is the later grey version. Both these are from around 1990. I just heard back from Quad this morning who confirmed that there is no service history, so I am wondering whether to send these back anyway for a once over, since I searched ages to get some good ones. And it could be easy as the dealer can ship them to Quad for service rather than to me.

I assume Quad only return them to original spec - would modifying them affect their future value? If they are ok as they are I am not sure and my ears are getting old...!

I have an pair of Dynaudio Audience 40 speakers in storage, but I ruled these out as they are 4 ohms - so the speaker search is on.

 

Do you play vinyl? If so, the mod is worth doing as new op-amps really provide a benefit here.

If not, then just check the big caps. If you want them serviced regardless for piece of mind and assured future reliability then I'd ask Rob if he can do it for you, as it will be less expensive than Quad and probably done with more pride of work

 

Thanks Simon

Other than the phono stage change I do nothing not in keeping with a Quad service unless asked specifically by the owner - I don't believe in extensively modifying these units.

Capacitors get uprated in places mostly because they've got better over the decades. The phono and sensitivity mods if performed can be reversed easily with no sign of having been done if the units ever require restoring to 'stock'.

On the Dynaudio, remember that even the most aggressively current limited amplifier will drive even a 2 Ohm load - its just a question of how much power you require. So 50w or so max into the Audience 40 may well go plenty loud enough for you. Give it a try if you like them - you can't break a Quad power amp and a 306 will just shut down into protection if you take it too far.

If you want info on my servicing - www.bakeraudio.org
Otherwise Quad uk do a fine job and I'm not knocking them.

 

Thanks Tenson - one of the reasons for this project is to start playing vinyl again.

I have an RP3 with ​Ortofon 520 mkII cartridge in storage - bought used a few years ago. I don't plan on changing this and hope I can bring an end to box swapping.....

I would like to have the peace of mind that everything has been checked over as well some long term reliability. I will get in touch with Rob directly now.

Thanks for the comments on the Dynaudio as well - they are fine little speakers and it would be easier on cashflow if I could use them - for a while at least.

 

Just to update this...

Now received the 34/306 after sending them to Robert for service and tweaking. Rob provided exceptionally fast and helpful service and I cannot recommend him highly enough...Thanks.

Running ok with the Dynaudios so far...I will try something else after xmas when I have saved up a bit more cash.

 

Thanks for the kind comments Phil.

Not sure if I mentioned it but when modifying the phono stage I also reduced the capacitance loading from 220 to 100pf to better suit the Ortofon, and most other modern MMs for that matter

Most arm cable looms will add around 100-130pf.

 

I've owned quad equipment for many years and have realised they perform much better with high impedance loudspeakers They definitely do not like low impedance Indeed the quad amps were deigned to work with quad's electrostatic speakers.

As for the mods you can change the 10kuf psu caps for 22kuf, new bridge rectifier. I purchased a high quality audio grade transformer from cpc, which made a massive difference.

I've always noticed that upgrading the transformer, irrespective of the equipment, makes the most difference. Upgrading the transformer by itself will make more difference than all of your other mods put together, by a long way This should be your first port of call.

 

Yep, just plugged in the RP3 and played vinyl for the first time in almost 30 years - yikes! Sounding very good.

 

Yes, my low impedance Dynaudios are a stop gap for now till funds allow a swap.

I know there are a lot of mods that can be done to these quads, personally I wanted to keep them close to original. Having said that, I like them so much I could easily see myself looking for another set to play with. Are you saying the transformer in the 306 is the weak link?

 

Have to say I disagree with Goodguy.
You can modify the 306 in myriad ways but I don't recommend trying to push more current because it's a physically small amplifier and cannot deal with the heat. Modifying it to work harder will make it run much hotter and that's not good for caps or any other components for that matter. It's already a very warm running amplifier given the 30w idle consumption thanks to the Class A stages.

The capacitor banks are ample for a 2x50w amplifier at 4x6800uf - they are already 50% larger than stock and going larger offers no benefit.
In stock serviced form it's a transparent amplifier - it doesn't get better.
If you want more power to drive low impedance loads and play loud, trade it for a 606 which has the necessary output stage compliment and heat sinking to deal with high power into 4 Ohm loads. You cannot fit a higher VA rated transformer inside the 306 case, nor does it need one.

Any component labelled 'audio grade' should be regarded with suspicion IME.

Above all lets consider some context. A stock 306 will deliver 70w into 4 Ohms which is plenty loud enough for many applications. It won't do so for hours on sine waves but those generally don't make good listening

 

I was really surprised at how small the 306 is - even smaller than the 405. Perfect form and function to my eyes.

Sound wise its doing the job perfectly for me - yes it is running slightly warm, due to the speakers, but no problems so far. It seems to me (as a layman) that quad had perfected their formula with the 306...since then its only been about more power.

AFAIK there were no major design changes to the 306 during its production run, and no pattern of changes made at service? but goodguy's point suggested this might be a misunderstanding on my part?

Contrast this with the 606 where I read that changes had to be made to that in the power supply? Rob you will know this?

 

The 606 became the 606 Mk2 and the only real change was a larger capacity PSU - bigger caps and a switch away from a frame transformer to a toroidal.

The older Mk1 was prone to mechanical hum from it's transformer, so Quad introduced a compliant mounting system which went some way to fixing the issue. Ultimately they switched to a toroid.

Not all Mk1s hum. I serviced a Mk1 606 with decoupling this week and it was silent.
The 306 and 606 share the same circuit - only difference is a larger PSU, higher dc rail voltage and triple dumper transistors to produce and handle the extra power in the 606.
It also has a lot more heat sink real estate to handle the heat when working hard.

 

I guess Goodguy was not talking about added power so much as just a 'better' transformer. I'm also sceptical about 'audio grade' parts. I'd want to see measurements taken at the actual outputs of any amp that has supposedly been upgraded before being convinced of benefits. Even then if those changes are below audibility, what's the point? IMO, that needs testing too with blind ABX.

I have seen a difference between transformers in this respect but I must say the older ones are always better! I think this must be due to the ever increasing price of copper and other materials as well as a need to keep prices low in an ever more competitive market. I also wonder if some of this knowledge has been lost along the way, I understand good transformer design to be a rather specialist subject.

I offer modifications for the Behringer DEQ, DCX and SRC units and often have people asking me for things that are commonly said to bring improvements but which I've tested and found to be pointless in this kit. Clock changes, DAC chip swaps, PSU replacements. I've tried them all, and the first thing I do is measure the analog outputs of the kit to see if anything has changed downstream.

 

Thanks for the clarification Rob.

And interesting comments on the quality of components....and from both of you I get the feeling that whilst there are a lot of mods which are possible, few are worthwhile.

I wonder what you think of DACs !

 

Well sure few are worth doing, if it was that easy...

Given the stories I've heard of Peter Walker I don't think he would have used cheap parts if they made his kit perform worse. He sold stuff at a loss you know.

IME good circuit designs don't need expensive parts to work well, that's part of good design. The Quad amps are great for auto correcting themselves from the class-A stage.

However there are a few places which have got more refined with time such as lower noise op-amps. In the case of my Behrigner Mods I change the whole input and output circuits to get an improvement and I confirmed what I was doing with about £20,000 of test equipment kindly loaned by R&S.

 

Hi. Sorry not trying to be funny, i have actually physically upgraded the transformer myself to high quality/audiophile grade and there was a big, big difference.

I think other forum members are talking from a theoretical point of view and not real world. I stand by my statement, changing the transformer to high quality will make the most difference to your equipment, whatever that equipment may be. Just try it for yourself.

I do not have any test equipment but the difference has always been night and days to my ears, it is that obvious.

The next thing you should do is to buy a second amp and use the first amp to drive the mids and tweeters and the second amp to drive the bass units. Sorry, i am not familiar with the speakers you have if they are 2-way or 3-way. But they can be very easily modded up to 3-way if that is something you are considering.

It may not be a good idea to go much further with the modding, you will alter the type of sound the amp is producing. Perhaps they may be a good thing or a bad thing the choice is up to you.

 

I'm afraid that simply doesn't happen - a transformer change of similar VA (can't be higher as it won't fit the case) would at best make a very small change to the measured specification.

You need to compare properly, blind and level matched.
IME most reported 'improvements' of this type by anecdote are questionable, with the difference usually down to lack of controls when the comparison was made.

 

Where to start on that one

Probably the best place to start is to consider the job to be done.
Take the digital input from the transport and convert it to analogue with minimal distortion of all kinds - so low THD, IMD, inaudible noise and a flat response across the audible range, plus a bit further for luck which never hurts. There is no need to dig deeper and examine things like jitter since these things feed and drive the headline distortion and noise figures., so a dac with poor jitter will have relatively poor noise and THD figures. There are £5000 dacs that do this task magnificently, but there are also £200 models (and less) which hold all of these distortions below audibility and so for practical purposes are good enough.

I am personally quite anti dac and want to see them fade into obscurity to join the likes of cassette, 8 Track and quadraphonic. I like the converter to be inside the amp or the transport since I believe their preponderance as a 'must have' system component only encourages needless tinkering and focus on trivia.

Of course many systems need them currently as we are in a transition period from the old days of analogue only amplifiers to the new world of increasing integration are reliance on digital and streaming, but over the medium term I'd like to see the use of dacs very much reduced to a specialist, minority purchase as standalone units.

Simon is a bit less hard line I think