classic pre partner for Quad 405?

Other than the Quad offerings, were there/are there any preamps that are particularly well suited to the 405?

 

The only real issue with a 405 is the high sensitivity which at 500mv for full output can make the volume control action a little cramped and twitchy with some pre amps.

Passives work well as these are well suited to higher sensitivity.

If I were looking at a non Quad matching pre I'd look at the old and much underrated Audiolab 8000C and the original Cyrus Pre. Both have a good phono stage and are technically squeaky clean.

The input sensitivity can be adjusted on the 405 by changing the feedback network around the input op amp, if it's found to be too hot.

 

Thanks Rob,

I've tried a couple of passives and even on one of those it didn't really go quiet enough.
In simple terms, what's the difference between adjusting the sensitivity internally and putting an external attenuator between pre and power? (particularly when the pre is passive anyway.)
The only real criticism that seems to be leveled at the Quad 44 is that it is too sensitive for CD output. After that you get into the vagaries of veiled sound and so on. A quick search on the Audiolab is not that dissimilar in terms of grey, thin etc.
Does this mean that they both just measure fairly flat?

Would something like a Rega pre not work so well (and yes, having on-board phono is a plus).

 

Better to actually reduce the input sensitivity since this also reduces noise (and distortion FWIW). You are actually reducing gain rather than attenuating the input.

I take internet talk about the sound of technically good kit with a truckload of salt
Not a 44, but I have two files on my site using the very similar 34, one a direct CD rip, ie it's passed through nothing at all, the other with the same CD played on a Meridian CD player then recorded via the output of the Quad 34.

Listen for yourself:

http://www.bakeraudio.org/sample-audio-recordings.html

 

Volume Control for Quad 405

Further to the discussion on suitable pre-amps for a 405 and Rob's observation that, given their high input sensitivity, they are suited to passive pre-amps:

1. What value dual gang pot should be used on the front of a 405, Rob?

2. Is there a way of getting the pot inside the 405 case with wrecking it. Some pots have very narrow spindles. Are any narrow enough to pass through a hole drilled invisibly between the front fins.

Any other ideas? I would quite like to set up a spare 405 I have to take the output from an Android Tablet. and I would be happier if there was a pot between them.

A pot in a box is a rather less tidy arrangement.

 

The 405 has screw access holes on the back which normally have little plastic stoppers fitted. Often these are used to fit additional DIY rca connectors or binding posts but you could also fit a small pot. Not very convenient positioning though, and anything else requires drilling the case.

A 20k log pot should be fine for most sources.

 

Thanks. I have a couple of spare holes at the back. I was hoping to get a knob on the front without being too destructive!

It occurred to me after I had posted that I might get a pot into a wooden base extension to the Tablet dock. That could look quite good.

Wooden ends to the 405 case might also look good - a front facing pot would go in one of those; but my woodworking skills are . . .

Or I drill a hole in the cheap Ikea box that house the lot, and put the volume controls on the side of the cabinet!

£150 for a box with a pot, a switch and a few sockets seems rather a lot, so I am trying to avoid that!

(Reading the 11 pages on iPhone audio - seen no blood yet!)

 

Hmm.....thinking about it some more.......you might just squeeze in a sub miniature pot where the red led is mounted. I'll whip the cover off later and have a close look.

 

Yes. I had been eying up that hole!

I see you have set up in business - good luck.

How about turning Quad Pre-Amps into digital ready products by adding an on-board DAC?

Would one fit on the plug in RIAA card?

Silly idea?

 

Not silly at all - certainly possible with the 44 where a dac card could replace one of the tape cards.

Harder with the 34 since it's phono card is just a gain stage with the RIAA processing sitting on the motherboard.

Thanks for the good wishes.

 

Ah! I didn't know the 44 had such cards. Could be tempted, though it would be overkill since I have no interest in a phono stage.

I actually prefer the look of the 34!

Quad 44D?

 

A question I feel I should know the answer to - but don't is:

what's the correlation between input sensitivity and attenuation? ie.

The standard mod for the Quad appears to be to drop the sensitivity from .75 to 1.5v for full output does that equate to putting eg. a 10dB attenuator in-line?

 

It's not quite the same thing. The input section of the amp will generate it's own base level of noise and this will remain the same regardless of the signal level being fed. On the other hand if you reduce the actual gain of the input section the base noise level will drop correspondingly.

 

The situation with Quads pre amps is slightly more complex than usual, becasue you've got gain on the line inputs when in today's world you don't really need it, but the outputs are padded down to match the sensitive Quad power amps.
So although you've got lots of gain, you've also got a reduced output which actually balances things nicely in most cases.

It's not ideal from a S/N ratio POV as Simon says, but in practice any noise is well down below signal and is inaudible.

For driving non Quad power amps you can just adapt the output padding network on the pre amps since the core output circuit produces enough voltage to run any power amp.

With all Quad pre/power pairings I recommend increasing the output from the pre and reducing the gain on the power amps. This actually reduces noise, and very audibly so on the 405. Quad were always trying to ensure backwards and sideways compatibility with their equipment which often spanned several decades, hence the slightly odd and non optimal gain structures. Effectively electing to sacrifice nth degree technical performance for better cross-range compatibility and user satisfaction. Can't argue with that!

 

yes, I get the principle of reducing gain on the power, but what I'm trying to figure out is:

I have a passive that could probably do with going 3 or 4 steps quieter, I gather the steps are 3dB so that's 10-15dB in total. Would reducing the gain of the 405 to 1.5v do that, and at the other end would I still be fine with the output on my phono stage?

 

Yes reducing the gain on the power will mean your pre-amp volume control needs to go higher for the same level. Whether or not your phono output will still be enough to drive to a good level I don't know.

 

If the phono stage is designed to produce a similar output to a CD player or dac - which most are these days - then it should be ok.

You can set the 405 to 1, or 1.25v sensitivity if you think 1.5 might be too much and get a middle way.

 

I guess what I had in mind is that to try an in line attenuator is very simple, if 10dB turns out to be the right amount then I'd want to know what change in sensitivity of the 405 would give the same amount of difference.

 

Well 6dB is double or half the voltage. You can find a dB to Volts converter online.

 

This site has lots of useful calculators:

http://www.sengpielaudio.com/dB-chart.htm