Power amps

Roger Crawford · From: Griffin, GA USA

With all the different brands and types of rack mounted power amps available, do any have negative or positive affects on tone, or is tone a product of the pre amp only? Just curious!

Gary Dunn · From: near Camel City, NC

I would like to know more about this topic myself. That sweet rich mellow tone I hear every one else playing, is it from tubes or transistors; analog or digital?

David L. Donald · From: Koh Samui Island, Thailand

Rich, Sweet, Mellow... Tubes without a doubt.
I record digitaly, but use tube preamps and
tube mics if at all possible. It warms up the sound and makes it "more natural seeming" even before the digital encoding.
There are some hybrid amps with solidstate and tubes comingled. Not to say there aren't some fine sounding transister amps.

If you go tubes, Class A circuitry, or when the full sinewave test signal passes each amplification stage without change, will sound the best, and be more expensive...
than class B in which 2 tubes split the up and down halves of the waves doubling the power output for each stage,each does half the work at it's full power, but also needing to be recombined beforethe next stage.

This means the signal integrety is dependant on BOTH tubes being as closely matched in age and performance as possible.
Two mismatched tubes will give 2 halves of the wave at different levels and sometimes different phases also. Read : not so good sound sometimes.
There are other amp class types, like AB and C, but this is the basics. They often do the same design thing with transistors.
There is a reason guitar amps are often tubes... warm tone and nice harmonics caused by the analog effects of tubes.
Plus a sort of tonal pumping caused by power being modulated by a heat based electron flow.
It is a more organic gating of the flow.
I hope this wasn't too deep and was helpful.

[This message was edited by David L. Donald on 02 March 2003 at 05:11 PM.]

David Cobb · From: Chanute, Kansas, USA

The Fender I started with had a mellower sound, the Mosvalve seemed brighter with a lot of punch and the Stewart fell sort of in between. These are all solid state and this was with a Profex II and the same patch each time. Even something like guitar cords can be a factor, George L's seem to deliver the goods in the cleanest manner. But that's just my ear and my opinion...

rpetersen · From: Iowa

Just saw John Hughey play this past weekend - I think he has a great tone - Evans preamp, Stewart power amp, Jbl d130's.
I recently pickep up a JBL and am using an evans Preamp along wth a Peavey 750DPC and am very happy with my tone - And I like a warmer tone!

------------------
Ron Petersen &
The Keep'n Tyme Band

[This message was edited by rpetersen on 03 March 2003 at 05:54 AM.]

Erv Niehaus · From: Litchfield, MN, USA

I like the sound of Tube Works stuff. They build a tube preamp and a Mosvalve power amp. If you are interested, there usually is some of their equip. for sale on e-bay. I picked up my last power amp on there. If you can find their reverb for sale, they're also hard to beat. They built a true spring reverb. As far as I know, Herby Wallace still sells their equip. If you want to sweeten up the sound of solid state, Peavey builds the "Tube Steetener".
Erv

[This message was edited by Erv Niehaus on 03 March 2003 at 07:50 AM.]

C Dixon · From: Duluth, GA USA

Roger,

Power amps of a type; solid state versus tubes, just about ampify the sound unaltered. While there may be a tiny bit of difference between different tube amps (or solid state types), it is usually inaudible.

Now, there is a world of difference when you go from tube to solid state (or vice-versa). It can easily be heard by even the novice. And while great strides have been made over the years, tube amps have the greatest dynamic range. That is; the ability to amplify the lowest level tones as quickly as the highest level tones. Engineers call it "rise time". And it is very real and very important to sound lovers.

In a word, solid state tends to be soft like a cello sound. Tubes are instantaneous like a 22 rifle crack. When solid state first came out, NO way could they begin to duplicate the sound of a snare drum using wooden sticks.

Today that is much much improved, but still tubes do win out in the most ardent of tests (dynamic range). But back to your question. It is the preamp that does 99% of the tone coloring. NOT the power amps.

The post about class A versus AB or class B is true ONLY if the amp is not designed properly or if improperly adjusted or the tubes are not matched. In a properly designed Class AB tube amp with the proper amount of necessary feedback, it can emulate in EVERY way the perfomance of a pure class A amp.

Triple blind test at Princeton Labs by RCA proved this to every "test" engineer's satisfaction. And if you knew these cats, you would know how skeptical they were. They would argue with a sign post. They simply had to have irrefutable proof.

carl

Bob Hoffnar · From: Austin, Tx

Power amps make a big difference in sound. I think they are of equal or of more importance than the pre amp part of the signal chain.
Check out a VHT 2/90/2. Nothing else like it. Except for maybe a 70's macintosh.

The other power amp that I like is the tubeworks mossvalve 500. I have tried out a pile of power amps and so far these are the only 2 I would use in a rack set up if I was concerned with the sound. For weight the Stewart is amazing. But after A/B testing the VHT ate its lunch.

Bob

Michael Brebes · From: Northridge CA

For solid state power amps, I recommend the MOSFET ones. They have less coloration of the tone and extended bottom and top. I use Hafler myself and am very pleased with them.

Stephen Gambrell · From: Over there

Hey Erv, what's a "Tube Steetener?"

David L. Donald · From: Koh Samui Island, Thailand

C Dixon
____________________________________________
class A versus AB or class B is true ONLY if the amp is not designed properly or if improperly adjusted or the tubes are not matched. In a properly designed Class AB tube amp with the proper amount of necessary feedback, it can emulate in EVERY way the perfomance of a pure class A amp.
__________________________________________
I was making that point but in a different way, and didn't really touch on AB design other than mention it's existence. It is a hybrid to bridge the gap between Clas A and C.

But you re-enforced my point;
if the amp is not designed properly or if improperly adjusted or the tubes are not matched.
And this last part is more common in road amps, tubes much more quickly go out of wack. and over come the feedbacks potenial balancing function. Class AB is cool but audiophile purists only want class A.
If you use no Eq. a pre-amp SHOULD pass only what it sees coming in.
Ah but when you get into the eq a bit, then it becomes much more individual because of the designer's choices. It seems Peavey has become loved by the PSG community because they have built powefull amps for PSG's with eq circuitry that has very good choices for this instrument.
Myself, I am looking for an old Fender 50 watt to put on my Hartke bass cab. I want the grit, and we don't play loud. But I may modify the eq some.

[This message was edited by David L. Donald on 03 March 2003 at 03:28 PM.]

Erv Niehaus · From: Litchfield, MN, USA

Steve,
The tube sweetener is a unit by Peavey that is used to "sweeten" the sound from a solid state setup. It is a rack mounted unit and I use it in conjunction with my ProFex II and a DPC 750 amp. Do a search on the Forum and you can learn more about it. Mike Brown turned my onto it.
Erv

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