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Post new topic Power Amp to Revelation Pre-Amp Noise Issue
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Author Topic:  Power Amp to Revelation Pre-Amp Noise Issue
Jeff Rady

 

From:
Colorado, USA
Post  Posted 21 Apr 2024 10:11 am    
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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
Post  Posted 21 Apr 2024 11:58 am    
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If you unplug the Rev from the Stewart input, how much hiss is there when you turn up the Stewart volume?
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Jeff Rady

 

From:
Colorado, USA
Post  Posted 21 Apr 2024 2:10 pm    
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Absolutely none.

Tried a different cable from REV out to Stewart in, still hissing'
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Dave Grafe


From:
Hudson River Valley NY
Post  Posted 21 Apr 2024 3:11 pm    
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Last edited by Dave Grafe on 23 Apr 2024 1:52 pm; edited 1 time in total
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Jeff Rady

 

From:
Colorado, USA
Post  Posted 21 Apr 2024 7:03 pm    
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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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Dennis Detweiler


From:
Solon, Iowa, US
Post  Posted 21 Apr 2024 7:49 pm    
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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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Dave Grafe


From:
Hudson River Valley NY
Post  Posted 21 Apr 2024 11:39 pm    
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Last edited by Dave Grafe on 23 Apr 2024 1:52 pm; edited 1 time in total
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Glenn Demichele


From:
(20mi N of) Chicago Illinois, USA
Post  Posted 22 Apr 2024 4:38 am    
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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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Donny Hinson

 

From:
Glen Burnie, Md. U.S.A.
Post  Posted 22 Apr 2024 7:38 am    
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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
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Glenn Demichele


From:
(20mi N of) Chicago Illinois, USA
Post  Posted 22 Apr 2024 7:45 am    
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First thing is make sure its hooked up right Smile
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Jeff Rady

 

From:
Colorado, USA
Post  Posted 22 Apr 2024 8:40 am    
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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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Ken Metcalf


From:
San Antonio Texas USA
Post  Posted 22 Apr 2024 9:10 am    
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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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Dave Grafe


From:
Hudson River Valley NY
Post  Posted 22 Apr 2024 9:58 am    
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Last edited by Dave Grafe on 23 Apr 2024 1:52 pm; edited 1 time in total
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Donny Hinson

 

From:
Glen Burnie, Md. U.S.A.
Post  Posted 22 Apr 2024 2:14 pm    
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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.
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Bill Hatcher

 

From:
Atlanta Ga. USA
Post  Posted 23 Apr 2024 5:09 am    
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surely you have hooked the rev up to another power amp for a test to see if you are getting the same hiss.
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Jeff Rady

 

From:
Colorado, USA
Post  Posted 23 Apr 2024 6:27 am    
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I don’t have another one. I’ll see if I can find one.
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Jeff Rady

 

From:
Colorado, USA
Post  Posted 23 Apr 2024 6:31 am    
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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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Jerry Overstreet


From:
Louisville Ky
Post  Posted 23 Apr 2024 7:01 am    
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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.
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Ken Fox


From:
Nashville GA USA
Post  Posted 24 Apr 2024 4:55 am     Ground loop
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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
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Ken Fox


From:
Nashville GA USA
Post  Posted 2 May 2024 1:09 pm     Solution
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Did you get this fixed?
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