Power Amp to Revelation Pre-Amp Noise Issue

Jeff Rady · From: Colorado, USA

Hi All,

I've got an old Stewart World PA-200 power amp powering a Revelation Pre-Amp running mono to an old re-coned JBL D120.

Basically, If I turn up the Power amp past 9 o clock or 1/4 up it gets really hissy and lots of shhh noise. It sound ok if I keep it at like 9 o'clock, and I run my Master on the Rev at like 3 o'clock or 3/4 up and my Gain way down. Is this normal or is that power amp a dud?

Let me know your thoughts. Thanks,
Jeff
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Jon Light · From: Saugerties, NY

If you unplug the Rev from the Stewart input, how much hiss is there when you turn up the Stewart volume?

Jeff Rady · From: Colorado, USA

Absolutely none.

Tried a different cable from REV out to Stewart in, still hissing'
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Williams Guitar Purveyor, Owner of jeffsguitarandsteel.com

Dave Grafe · From: Hudson River Valley NY

Jeff Rady · From: Colorado, USA

Hi Dave,

Thanks for the reply. Are you saying run the power Amp output wide open?

Basically as soon as I turn the Rev on even with the master down at 4 and the Gain at 6, I'm still getting hiss.

If I take the REV completely out of the chain and just hook the Power Amp to the speaker there's no noise at all. Think I should change the tubes in the REV?

Thanks,
Jeff
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Williams Guitar Purveyor, Owner of jeffsguitarandsteel.com

Dennis Detweiler · From: Solon, Iowa, US

I get no noise from my Rev. I'm powering with a Crown class D. I'm guessing it's tubes? I've tried different tubes in my Rev. I tried vintage RCA's which sound good, but I settled on JJ 12AX7mg(mid gain) tubes. I love them. Clean, but with some hair when pushed.
The gain on the Rev tone will get warmer as you turn it clockwise. So, it adds some tone along with gain. The Master volume has no tone characteristics added.
The treble control also moves the mid frequency (mid shift).
So, while turning the treble up, it also moves the mid frequency up. I set my treble between 2 and 3, which puts the mid frequency around 700hz. Too much treble may be adding some white noise (hiss) to your sound?
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1976 Birdseye U-12 MSA with Telonics 427 pickup, 1975 Birdseye U-12 MSA with Telonics X-12 pickup, Revelation preamp, Carbon Copy Delay and Hall Of Fame Reverb, Crown XLS 1002, 2- 15" Eminence Wheelhouse speakers, ShoBud Pedal, Effects Pedals. 1949 Epiphone D-8.

Dave Grafe · From: Hudson River Valley NY

Glenn Demichele · From: (20mi N of) Chicago Illinois, USA

In two of your notes, it sounds like you're driving the pre-amp with the power amp? It's supposed to go steel=>pre=>power=>Spkr.

If you do have it hooked up right: does the hiss suddenly start as you increase the volume, or does it come up gradually? If is starts suddenly, it is possible that the preamp&Amp combination is breaking into an ultrasonic oscillation. This could toast a lot of things. Make sure you are using shielded cables. You could also see if moving the speaker away from the guitar or see if changing the treble control changes the volume level at which the noise (oscillation) begins.
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Franklin D10 8&5, Excel D10 8&5. Both amazing guitars! Homemade buffer/overdrive with adjustable 700Hz "Fender" scoop., Moyo pedal, GT-001 effects, 2x TDA7294 80W class AB amps, or 2x BAM200 for stereo. TT12 and BW1501 each in its own closed back wedge. Also NV400 etc. etc...

Donny Hinson · From: Glen Burnie, Md. U.S.A.

Hiss in a tube unit is almost always caused by a bad tube, so the first thing you want to try is to replace the tube. Cool

Glenn Demichele · From: (20mi N of) Chicago Illinois, USA

First thing is make sure its hooked up right Smile

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Franklin D10 8&5, Excel D10 8&5. Both amazing guitars! Homemade buffer/overdrive with adjustable 700Hz "Fender" scoop., Moyo pedal, GT-001 effects, 2x TDA7294 80W class AB amps, or 2x BAM200 for stereo. TT12 and BW1501 each in its own closed back wedge. Also NV400 etc. etc...

Jeff Rady · From: Colorado, USA

Hi Glenn,

No doubt, it’s hooked up right.

Instrument-rev pre-power amp-speaker.

Dave, I definitely get less hiss with the method you describe, but it’s still fairly audible. I’m going to check the tubes.

If I have only the power amp going to the speaker with nothing in the input of the power amp and I turn it up and get 0 noise, is that significant?
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Williams Guitar Purveyor, Owner of jeffsguitarandsteel.com

Ken Metcalf · From: San Antonio Texas USA

I had a Revelation Pre-Amp with a Stewart World PA-400 and it would hiss at very loud volumes.
The hiss was not really auditable at loud volumes or with the volume pedal off.
Definitely keep the Stewart on 10.
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MSA 12 String E9th/B6th Universal.
Little Walter PF-89.
Bunch of stomp boxes

Dave Grafe · From: Hudson River Valley NY

Donny Hinson · From: Glen Burnie, Md. U.S.A.

Unfortunately, high-gain tubes tend to be noisier; fact of life. But here’s the straight story on the low-noise 7025, it actually began life as a 12AX7A. When the 12AX7A tubes were tested at the manufacturer, the really-good ones (the ones with low noise and microphonics) were branded as 7025, and the ones that tested as “average” in noise and microphonics were branded as 12AX7A. This is not to say that they didn’t manufacture special tubes, as in those destined for military and rugged applications. Those were specially designed for ruggedness and extended service life, and they were physically different than standard (consumer electronic) versions.

It was the same with passive components. Normally, they didn’t really manufacture high tolerance resistors and capacitors. They were all made the same way, and those that tested within 5% of their value were branded as such, and those that were within 10% and 20% were marked accordingly.

Bill Hatcher · From: Atlanta Ga. USA

surely you have hooked the rev up to another power amp for a test to see if you are getting the same hiss.

Jeff Rady · From: Colorado, USA

I don’t have another one. I’ll see if I can find one.
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Williams Guitar Purveyor, Owner of jeffsguitarandsteel.com

Jeff Rady · From: Colorado, USA

I think I’m wrong headed about using the Master on the rev. I’ve been cranking it on either the power amp or the pre-amp. I wrote Brad and he basically said to use the power amp master to get an appropriate volume then fine tune with the rev master and keep the gain at least at noon. Rev master should only be maybe 3 at the hottest. So I’ll try that. Plus this power amp is pretty ancient, so could be a contributing factor. Thanks for all the help!
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Williams Guitar Purveyor, Owner of jeffsguitarandsteel.com

Jerry Overstreet · From: Louisville Ky

On my digital amps, both Peavey and Stewart, I run the output level wide open and use the preamp output to set the volume. You want to keep the output ahead of the input to keep from overdriving it.

I have no experience with the Rev, but Brads advice will always be good.

Ken Fox · From: Nashville GA USA

If both the power and and preamp have a grounded power cord you may be getting a ground loop

Try a ground lift on the Revelation
Maybe that will help

I had a Revelation in the shop years ago. It was the best preamp I’ve ever heard
I can’t remember if it had a wall watt or a power cord. Memory ain’t so good

Just checked and it does have a power cord. Ran into this same issue with the Tubefex and Transtubefex a
Preamps. Permanent solution was a Hum-X on the power cord of with the pre or power amp

I do not recommend running the power amp wide open while choking down the preamp. This create a poor signal to noise ratio
A good clean signal need to be created at the preamp. Them the power amp acts as the master volume

Ken Fox · From: Nashville GA USA

Did you get this fixed?

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