[EthanH]

Noob question here...

If a power amp has a variable gain control is a preamp necessary?  I recently experimented with a power amp hooked up directly to my CD player and find that turning the gain about halfway up provides me with more than enough volume in my system.  Is there anything wrong with this? 

The tone and imaging are not as good as my integrated tube amp, but I just figured this is due to the inherent differences between tube and solid state amplification, not to mention these two particular amps.  I don't have much technical knowledge regarding amps though, so I was hoping someone might be able to tell me if not using a preamp is seriously degrading sound quality in some way I'm not aware of - I've just never heard of someone doing it this way (although I supppose this could be attributed to most amps not having variable gain and most listeners using multiple sources). 

Any insight would be appreciated.

 

[Bill Baker]

Hi ethan, There is nothing wrong with using teh gain controls on your amplifiers. A preamp would introduce the characteristics of the whatever model you may choose. Better? Worse? This would depend on how well you chose a preamp to go with your system.
 If you want more from your system "The tone and imaging are not as good as my integrated tube amp....", a preamp might just bring about teh right balance.

 What are the components you mention above?

[EthanH]

Thanks for the response.   I was worried that using the gain controls may raise distortion so it's reassuring to know everything is OK.

The amp is an eighties Yamaha M-60 poweramp my dad gave me.  I believe it makes around 150 watts per channel at 8 ohms and operates in full class A for the first 25 watts or so.   My integrated is a modded Cayin TA-30.  Source is a Onix XCD88 player, and speakers are Totem Arros.

[Bill Baker]

Hey Ethan,
 If you want to experience the best of both worlds (and you want to keep the Yamaha arond for a while since it was given to you by dad), you may want to consider looking into a tube preamp. That could very weel bring much more to the presentation.

[EthanH]

Definitely something to consider; I can see why hybrids like the Unico are so popular, assuming they really can provide the best of both worlds.  I figured the Arros weren't too difficult to drive with their diminutive size, but the beneficial difference in power is obvious at louder volumes or with complex music. 

As far as the Yamaha is concerned, I have no sentimental attachment to it but it's a great backup amp.  Plus it's been waaay too hot for KT88s lately...    

[dado5]

A variable gain control is a volume control. That is, it is a voltage divider (potentiometer) like any other volume control (except of course magnetic, digital or funky 1950's pentode variable screen voltage circuits).

IMO if you can directly drive the amp from the source, do it. Less stuff to worry about viz. cables, etc. But if you like the sound with a pre-amp better that's fine too.

[EthanH]

Thanks for all the info guys.  I'd definitely like to find a way to add some smoothness and image density but don't have the budget for a decent preamp right now, however, I am considering adding a tube buffer or replacing the stock opamps in my XCD88. 
Any thoughts on whether either of these routes might be worthwhile?

[dado5]

Any thoughts on whether either of these routes might be worthwhile?

I would recommend a transformer coupled tube pre.  If a tube pre (or buffer) is not transformer coupled, it uses  a cathode follower output circuit and this is not the best sonic solution IMO (opinions vary of course).

Electra-print audio has the schematic for a transformer coupled single stage pre.  As shown it has an output impedance of 600 ohms and a gain of about 2 (6dB) but you can have the transformer wired for more or less gain (which means higher or lower output impedance respectively).

http://www.electra-print.com/ultrapath.php

[JLM]

Welcome EthanH,

Those little Arro's are power hungry and are best suited for small rooms where room filling bass isn't needed and you listen mostly to small ensemble stuff.  Small speakers tend to be inefficient and lack deep bass (just the laws of physics at work).

Nothing wrong with using the power amp volume pots, in fact several "integrated" amps are really nothing more than power amps with volume pots added (under the premise that one less gain stage is a good thing).  Similarly passive pre-amps only have input selection and volume control (this is what I run with).

Mapletree (see circle below) and SpaceTech are good quality, reasonably priced tube vendors and have pre-amps.  Promitheus offers well received and inexpensive transformer based pre-amps.  Either tubes or transformers will flavor/color the sound.  Most transformer volume control (TVC) pre-amps, like the Promitheus, are passive (no A/C to plug in) which avoids dirty power issues but are typically less dynamic (something that the Arro's already suffer from).

Here's a quick run down of pre-amp tubes:

12B4 - absolutely neutral, cheap, uncolored, transparent, with a pretty glow

5687 - great tone/speed/detail, 10,000 hour life, marginally warm, great presence/musicality, work best in a SRPP circuit

6SN7/12SN7 - natural tone, not the fastest or most detailed, great musicality, highly linear, note that the VT-231 is the military version that can last 20 years, the 6SN7 is most expensive tube here

6CG7 - similar tone to 6SN7, in a cheaper 9 pin design