Valve Preamp with SS Power Amp

Hi Guys.

I'm currently auditioning a Quad QC Twenty Four Valve Pre Amp with my Quad QSP Solid Sate Power Amp.
Asking the question regarding matching I was assured that it would work ok, and it does. My concern is
that the volume control is a bit hot and it's sufficiently loud at approx 10 o'clock. I am aware that that the
impedance required for the preamp is around 50k ohms and the QSP is 15k ohms, which I guess is the reason
the volume control is hot.
My concern is; Is this doing any damage to anything and is it ultimately affecting fidelity.


Regards

When you say "the volume control is a bit hot", I assume you mean the knob itself.

If so, it's probably picking up a bit of radiated heat from the mains transformer which is right behind it, as can be seen in this photo:

http://i66.tinypic.com/2aj7rjo.jpg

Unless it's ridiculously hot, I'd not worry. As for the impedance match, if it sounds happy enough, I'd not worry about that either.

My knob gets hot as well and it pulses :eyebrows: :)

In this case I believe 'hot' means the control doesn't need to be turned far to get loud volume.

No problem other than convenience.

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Originally Posted by Audio Al

My knob gets hot as well and it pulses :eyebrows: :)

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Well keep it away from mains transformers. :eek:

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Originally Posted by walpurgis

Well keep it away from mains transformers. :eek:

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OK will do ;)

If as Dave says, it gets loud quite quick and its difficult to get several nice levels then i would walk away. It becomes a pain in butt. If its getting excessively warm i would also leave it as its not doing the carbon track any good

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Originally Posted by hifi_dave

In this case I believe 'hot' means the control doesn't need to be turned far to get loud volume.

No problem other than convenience.

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I did wonder. :)

Sorry, didn't mean hot, as in temperature just it don't take a lot of turning from zero before it's load enough.
I guess from Daves' reply, no real problem then and it's not affecting fidelity

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Originally Posted by LittleTone

Hi Guys.

I'm currently auditioning a Quad QC Twenty Four Valve Pre Amp with my Quad QSP Solid Sate Power Amp.
Asking the question regarding matching I was assured that it would work ok, and it does. My concern is
that the volume control is a bit hot and it's sufficiently loud at approx 10 o'clock. I am aware that that the
impedance required for the preamp is around 50k ohms and the QSP is 15k ohms, which I guess is the reason
the volume control is hot.
My concern is; Is this doing any damage to anything and is it ultimately affecting fidelity.


Regards

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It's because your preamp has too much gain for your power amp. It isn't going to damage anything.

You can try some in-line attenuators, like the Rothwell ones, which will give you a lot more volume control.

Could the fact that the preamp has too much gain the reason I am hearing hash/static through the loudspeakers even when the volume is turned right down?
Would attenuators address this as well ?

Yes and yes :)

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Originally Posted by Firebottle

Yes and yes :)

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Thanks for the reply Alan, appreciated. Like the Preamp; shame it's not perfect

Is it under warranty? If not it is probably a simple job to lower the gain.

Do you have a circuit diagram by any chance?

I would doubt very much whethere these two items have even been considered by quad to be a pairing, let alone been designed to work together.

Yes you could fiddle with the insides of one or other to get the gain to match but I'd personally look a bit futher for a pairing with more obvious matching in terms of gain/input sensitivity.

The Preamp is only on demo at the moment. Kindly lent to me by a dealer I've known and purchased items from since the 70's. He kindly obliged my curiosity to try a valve pre. The obvious is I guess is to buy the power amps that do match; but I'm not prepared to spend that sort of cash. I have to agree that Quad would probably not recommend this pairing and as much as I like it, the mismatch is unacceptable .
Anybody recommend a good preamp to front a Quad QSP ( I don,t need a phono input)
Thanks for all your replies guys
Back to the drawing board as they say

Sure quad would say the elite pre. have you tried a passive?

If only after a simple (no Phono) preamp.
A simple Passive comprising: a Pot , Buffer and an Autoformer is as Likely as good a "Preamp" as yet devised by Humans.
Really inexpensive to assemble .. adding insult to injury :eyebrows:

Hope you're well Tony?

The reason that the volume is a little hot may be that the input sensitivity of the power amp and output of the pre are probably not matched (designed to work together) and you probably do have too much gain from the pre. I believe that this amp uses about 15sB of gain from its single 6111WA valve per channel outputting at 1V . However S/N isn't great at >80dB so with sensitive loudspeakers and a more than typical 33dB gain on the power amp you may well hear some hiss/hum. 48dB of gain is quite a lot!

The main issue here for the "hot" volume though is that you can easily over loading the power amp input which only requires 760mV for a full 33dB gain through the power amp. The pre also has much poorer S/N ratio than the power. Personally, I would have matched the power with it's partnering preamp or a passive pre. The QC24 doesn't appear to be a good match. Yes, you can use attenuators or have someone modify the pre-amp circuit with some resistor value changes between the valve gain stage and volume pot but you're still left with pre that can't match the superior S/N of the power so it won't give you the quiet background of a better match especially with any other valves devices in the source or with vinyl sources. Tom's point is valid about the pairing.

If you like what it does, it's what you think that matters, so you could try it with some attenuation and try and get the output down. If it likes to see a load of 50KOhms, that indicates a relatively high oputput impedance from the pre so it may not be suited to driving long interconnects but if it doesn't appear to be rolling off the HF (ie forming a low pass filter) then, again, don't worry about it.

Bottom line: It isn't the best match but the gain can be addressed.

Hi Paul,
Hope you're well also.
Thanks for all the input guys; definitely gonna knock this one on the head. If I'm gonna spend that sort of money it needs to be
right and this is definitely a mismatch that I don't intend to try putting right. It was a worthwhile exercise; but it's going back to the dealer.
Do all valve preamps exhibit the same 50Kohm ish requirement of a power amp or is it just the Quad. You'll see from my profile that I do have the matching Elite SS preamp but I'm curious about alternatives, and now I don't require any phono input; in fact just a single input from a DAC is all that is required - What are your recommendations ?
The Quad valve pre did add some heft and body to the sound, integrated the bottom end quite nicely, or was the sound of overloading ?????

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Originally Posted by LittleTone

Hi Paul,
Hope you're well also.
Thanks for all the input guys; definitely gonna knock this one on the head. If I'm gonna spend that sort of money it needs to be
right and this is definitely a mismatch that I don't intend to try putting right. It was a worthwhile exercise; but it's going back to the dealer.
Do all valve preamps exhibit the same 50Kohm ish requirement of a power amp or is it just the Quad. You'll see from my profile that I do have the matching Elite SS preamp but I'm curious about alternatives, and now I don't require any phono input; in fact just a single input from a DAC is all that is required - What are your recommendations ?
The Quad valve pre did add some heft and body to the sound, integrated the bottom end quite nicely, or was the sound of overloading ?????

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People often recommend using a valve preamp with a SS power amp, but personally I've had good results working the other way round. The input sections of a valve power amp have better tolerance on the whole for overload than SS, which usually work best with tightly-matched parameters, while a good SS pre can leave the signal pretty much untouched (as you'd want) and can sound great into a valve power amp, while at the same time sorting out the whole impedance matching issue that makes passive preamps such a hit and miss affair (for me they are at least an 80% miss, that's my experience anyway).

If you really like that Quad preamp I'd think about using it with a Class D power amp like some of the Lyngdorfs that work really well with valve input but have lowish (I think 1.2v from memory) input sensitivity. Some of the EAR power amps also have lowish input sensiitivity which make them easy to match with preamps.

There will be people who tell you that you should get a DAC or CDP with a volume control but in my experience 1) this rarely sounds that great mainly due to poor impedance matching - for the most part I see the gain control on a CDP either as a remote control friendly thing or as a gain matching device into a proper preamp, and 2) you might want to add further devices later though if you go for a multi input DAC and they are digital, this won't be an issue. But having said that it may well be worth exploring the main thing you want to be careful of is gain matching, you don't want a DAC or CDP that has 15 DB of gain into the Quad power amp like that preamp or you are back at square one.

Has the OP tried a Croft preamp with a Quad power amp? It's an excellent match; I've heard it with a 405-2 and I'm sure a 909 or one of the more recent ones would be superb. It's a shame you aren't close by or I'd propose an experiment, since I'd really like to hear the QSP with one of my Croft preamps or my ARC LS26.

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Originally Posted by Elephantears

Has the OP tried a Croft preamp with a Quad power amp? It's an excellent match; I've heard it with a 405-2 and I'm sure a 909 or one of the more recent ones would be superb. It's a shame you aren't close by or I'd propose an experiment, since I'd really like to hear the QSP with one of my Croft preamps or my ARC LS26.

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That's a good point and Glenn will tailor the gain to suit whatever you need.

Croft pre into Quad QSP or QMP is a combination I often use for customers with power hungry speakers. It works well.

Well I have bought something. I was looking around on Ebay on Wednesday and came across this.

http://www.eeaudio.com/eeaudio_009.htm.

I've never heard of it before; but after a bit of google'ing, decided it was worth a punt. A bit of a gizmo maybe, but it is a valve line pre-amp in its own right.
The owner had also upgraded the valves to those recommended in the review. ( nice).
It arrived early yesterday and I'm pleased to say that after listening to it, pretty much all day, this item does do what it says on the tin and I rather like it.
I'm currently using it as a preamp between DAC (Mytek) and Power Amp (QSP) and it HAS added the desired characteristics into my system. (nice)

The review is pretty much, spot on.
http://www.dagogo.com/eastern-electr...plifier-review

Thanks for all your previous comments guys, particularly to Tom for taking the time to write such a lengthy response.

Bit like an X10-D with a volume control.

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Originally Posted by LittleTone

Well I have bought something. I was looking around on Ebay on Wednesday and came across this.

http://www.eeaudio.com/eeaudio_009.htm.

I've never heard of it before; but after a bit of google'ing, decided it was worth a punt. A bit of a gizmo maybe, but it is a valve line pre-amp in its own right.
The owner had also upgraded the valves to those recommended in the review. ( nice).
It arrived early yesterday and I'm pleased to say that after listening to it, pretty much all day, this item does do what it says on the tin and I rather like it.
I'm currently using it as a preamp between DAC (Mytek) and Power Amp (QSP) and it HAS added the desired characteristics into my system. (nice)

The review is pretty much, spot on.
http://www.dagogo.com/eastern-electr...plifier-review

Thanks for all your previous comments guys, particularly to Tom for taking the time to write such a lengthy response.

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This is a superb choice for what you outlined as your requirements and kicking myself now for not suggesting it (especially since you said single input). It should provide everything you want from it in terms of both volume control and impedance matching, without throwing additional gain or undue noise into the mix. Perfetto.

Thanks Tom for the vote of confidence. I'm a bit chuffed I actually found it.

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Originally Posted by LittleTone

The review is pretty much, spot on.
http://www.dagogo.com/eastern-electr...plifier-review
.

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That's an interesting read. A pity there is no technical analysis of what it is actually doing, though.