Quad 405-2 - to upgrade or change?

[julesd68]

Afternoon chaps,

I would appreciate a little advice on my Quad 405-2.

I'm actually really happy with the way my system is sounding on the whole, but have had my head turned by a couple of different "upgrade" options -

http://www.net-audio.co.uk/quad405fullupgrade.html

http://www.ebay.co.uk/itm/Upgrade-your-Quad-405-405-2-405-II-Power-Amplifier-/170623756707?pt=UK_AudioTVElectronics_HomeAudioHiF i_Amplifiers&hash=item27b9f7e9a3

What I am worried about, is that my Quad comes back sounding un-Quad like, with a brighter, more "modern" character. Would this be a real concern or are the upgrades realising more of the potential of the design? :scratch:

My near mint 405-2 cost me the best part of £300 - would I be better off putting the £270 upgrade towards a 909? I would like to stay with the Quad range for the moment as the smooth character of the sound suits my taste and system.

[IHP]

Hi Jules,

Moorgate Acoustics are currently knocking the 909 out at £599 ! That's all I'm saying ;-)

[Lodgesound]

I own 2 of these - each one drives 1 LS 5/8 speaker.

They are fantastic amplifiers and my advice would be to leave well alone - despite the sales patter I really cannot see where the improvements would actually make a difference to the sound you already have.

[Barry]

I own 2 of these - each one drives 1 LS 5/8 speaker.

They are fantastic amplifiers and my advice would be to leave well alone - despite the sales patter I really cannot see where the improvements would actually make a difference to the sound you already have.

Are they 405s or versions specially modified by Rogers for use with the LS5/8 speakers: the AM8/16? If the former, do you use an external crosover network?

To answer the OP, the upgrade kits provided by either Dada or NET are very good and won't spoil the 'sound', but they are not essential and I'm sure the £270 could be better spent elsewhere!

Regards

[DSJR]

All I ask is that the supply caps are checked every few years, as two 405's I owned were leaking badly after eleven years on the first set. Modern, higher rated caps may not suffer so in this design of course.

I think I agree with Barry, as money spent on full updated boards from dada or Net-Audio would be better put towards a 606, which was always more capable, even in mk1 form.

[sq225917]

606 is better built and specced than the new IAG stuff, that straight from someone who works there.

[Barry]

606 is better built and specced than the new IAG stuff, that straight from someone who works there.

Doesn't surprise me at all. The latest IAG - Quad gear is built in China, with a much noticed and commented on, lowering of component quality.

If it's not made in Huntingdon, don't touch it with a barge pole. The Chinese are milking the Quad name for all it's worth. Caveat emptor!

[hifi_dave]

I've asked this question before but didn't get a credible answer.

What do our Chinese friends think they are buying when they buy Quad, Wharfedale, Audiolab, Castle, Kef, Celestion and other good ol' British names, when they are, actually, Chinese owned and manufactured ? :scratch:

[julesd68]

Here are the votes by the AOS jury -

909 - 1 vote
606 - 2 votes
spend budget elsewhere - 1 vote
leave the 405-2 alone - 1 vote
don't buy a 909 - 1 vote

Well I think I am going to hang onto my cash for now!

[RobHolt]

I own 2 of these - each one drives 1 LS 5/8 speaker.

They are fantastic amplifiers and my advice would be to leave well alone - despite the sales patter I really cannot see where the improvements would actually make a difference to the sound you already have.

I run a 405-2 into ESL63s and use one to drive our Kensai monitors and would agree with those comments.

To the OP:

They should be served however.
The amplifiers are physically small for the idling dissipation and maximum output capability, and the case is unventilated. That means the 405 (all versions) runs very warm in normal use and gets quite hot if run moderately hard.

A fresh set of electrolytic caps every 10-15 years is a good idea as caps perish faster in high temperature surroundings.
That is the only servicing required to keep these amplifiers on top form.

Most of the supposed improvements are nothing of the sort.
You can use a faster op amp, but will probably cause ringing unless you mod the PSU, and even after that you'll get no audible benefit since the standard TL071 is more than capable as configured in the 405 circuit. What's more, the following circuit sections and deliberately 'slowed down' so that the current dumping can actually work. £10 on a posh op amp is £10 straight down the drain.

The feedforward circuit and null bridge works well over a wide component tolerance range, so no need to swap-in audiophile parts.

There are only two useful but far from essential mods IME.
The main supply uses 10k uf caps and these can usefully be changed for 15k uf at service. These days, 10k caps are physically top small for the retaining clips and the cap swap brings the PSU to roughly 606 level.

Lower the input sensitivity. 500mv as standard and reducing this to 1 or 1.5v will reduce the rather high hiss levels from the input stage. Quad pre amps can have their output levels raised accordingly and this makes far more sense in terms of SN ratio and distortion. It will also work better with most non Quad pre amps.
The original levels were rightly set by Quad for some backwards (and sideways) compatibility.




I've asked this question before but didn't get a credible answer.

What do our Chinese friends think they are buying when they buy Quad, Wharfedale, Audiolab, Castle, Kef, Celestion and other good ol' British names, when they are, actually, Chinese owned and manufactured ? :scratch:

Good point dave.

To me, Quad finished with the 6 series.
Real PJW period Quad ended with the 34/44/405, though if you look at the 6 series and strip out the flashy remote and displays, the circuit that remains is almost identical to the previous series.

Rob

[julesd68]

Thanks for all the info Rob!

[DSJR]

I run a 405-2 into ESL63s and use one to drive our Kensai monitors and would agree with those comments.

To the OP:

They should be served however.
The amplifiers are physically small for the idling dissipation and maximum output capability, and the case is unventilated. That means the 405 (all versions) runs very warm in normal use and gets quite hot if run moderately hard.

A fresh set of electrolytic caps every 10-15 years is a good idea as caps perish faster in high temperature surroundings.
That is the only servicing required to keep these amplifiers on top form.

Most of the supposed improvements are nothing of the sort.
You can use a faster op amp, but will probably cause ringing unless you mod the PSU, and even after that you'll get no audible benefit since the standard TL071 is more than capable as configured in the 405 circuit. What's more, the following circuit sections and deliberately 'slowed down' so that the current dumping can actually work. £10 on a posh op amp is £10 straight down the drain.

The feedforward circuit and null bridge works well over a wide component tolerance range, so no need to swap-in audiophile parts.

There are only two useful but far from essential mods IME.
The main supply uses 10k uf caps and these can usefully be changed for 15k uf at service. These days, 10k caps are physically top small for the retaining clips and the cap swap brings the PSU to roughly 606 level.

Lower the input sensitivity. 500mv as standard and reducing this to 1 or 1.5v will reduce the rather high hiss levels from the input stage. Quad pre amps can have their output levels raised accordingly and this makes far more sense in terms of SN ratio and distortion. It will also work better with most non Quad pre amps.
The original levels were rightly set by Quad for some backwards (and sideways) compatibility.


Rob

Wonderful advice on the whole, but I'd suggest the change of op-amp is possibly to reduce noise and distortion at the input - perhaps - since this device is in the circuit on the 405 and not out in the feedback loop? as in the 606 series. This, I believe, is where the main "upgrade" in the 606 comes in - gawd, I wish I was able to discuss it as a knowledgeable engineer, rather than the info-sponge/tart that I am :scratch:

Regarding preamp sonics. The 44 and 66 may have been related, but the 66 did sound a touch more "relaxed" as I remember, and rather better at reproducing the atmosphere of the venue (accepting the later 44's were better than the earlier ones at this). Wonderful for 57's I remember. The 77 pre was almost old-style valve-like in it's sweetness and really brought Quad full circle sonically. I loved this unit, despite the fiddly and unreliable two-way remote, which I believe all but finished the UK side of the brand off financially. The 77 phono stage was good as well I remember, but I digress (again).....

[RobHolt]

Hi Dave,

You can certainly put something like the OPA134 in place of the TL071, plus a 100nf cap across the supply pins to keep it stable. It will only drop noise by a dB or two though as most of the noise is caused by the series input resistors and high gain.

The 606 is quieter because it doesn't use the op amp input stage at all and later ones were also less sensitive. Pull the 405 sensitivity down and you can get it roughly par with the 606.

Again the best way to reduce distortion from the op amp is reduce the amount of gain in that stage. But there is precious little distortion to start with.

The TL071 in most 405s (and the pre amps) is a low noise and distortion op amp with low dc offset and low current draw. Also stable without additional rail caps.
The problems come when you ask it to drive impedances lower than 600 ohms as distortion then increases. In the Quad circuits there is no such problem as impedances are very high.

You can do all sorts to these old pre and power amps but the gains are largely in taking a very good technical performance and making it excellent - most of the technical benefits aren't audible IME. So I'm not saying don't mod them (mine are all extensively rebuilt to satisfy my own curiosity) but you don't have to given the basic performance is fine.

Rob

[julesd68]

My original question was whether to upgrade or change the 405-2 and now I have an answer - neither. It's going to stay as it is, at least for the time being!

Last week I conducted a three-way poweramp shootout -
Unico DM (bought last week) v Croft Series 7 (on demo) v Quad 405-2 :hairmetal:

First up the Unico - I didn't make it through the first side of my Rush "Moving Pictures" test record. Something just wasn't right - it wasn't gelling in my system at all. Trying to be specific, it was the midband I didn't like - it had a slight hardness that I found very unappealing and everything felt a bit flat. Moving onto the Croft - this time I managed to sit through all of side A and enjoyed it. The presentation was not too dissimilar to the Unico, but was definitely more sophisticated and enjoyable to listen to. I wasn't blown away but felt that this is an amp I could live with. So having tried to the two hybrids it was the turn of the solid state Quad. I knew after about 10 seconds of "Tom Sawyer" that this was the amp I would be keeping. All of a sudden I was hearing dynamics that were totally lacking in the other two amps - everything suddenly came to life. Seems that a powerful solid state amp is what I need.

I am not for a moment saying that the Unico and Crofts are bad amps, just that they weren't right for my system - I would be very interested to hear them with their appropriate pre-amps which are also both hybrids - they might well have been more lively as I'm using a valve Audionote M-zero pre.

So that's it - the Quad is staying and the Unico has gone - have invested the proceeds in a new RCM, which I can't wait to get my hands on.

[Old boy]

Can the 405-2 be used safely with quad 57s that have the clamp boards fitted ?

[Barry]

Can the 405-2 be used safely with quad 57s that have the clamp boards fitted ?

Yes - I use a 405-2 with my 57s, and these are not fitted with the clamp boards. Not had any trouble in over 30 years of use. :)