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kooltubes 3rd January 2013 02:29 PM

Gibson Goldtone amp GA-30 RVS (stereo)
 
Hi,
I am wondering if someone has modified a Gibson GA-30RVS (stereo) and would share some info. It has too much gain and white noise. The noise is probably induced by the chips used to drive the reverb and buffer the effects loop. I am after a clean tone suitable for Jazz. Help and suggestions are most welcome. Thanks.

Schematics are available from here: http://images.gibson.com/Lifestyle/S...cs/GA30RVS.pdf

rongon 4th January 2013 04:06 AM

Well, there are a couple of things.

1) The tone controls are pretty close to a Fender 'blackface' circuit, but with an additional half 12AX7 as a common cathode gain stage (labeled "EXTRA GAIN STAGE"), and then a cathode follower to drive the tone stack. You are probably keeping the switch RL1A and RL1B in the "clean" position, correct?

2) The tone stack has a lot to do with the character of the sound you get. Turnover points, which frequencies are boosted, phase response of the filters, etc. all put their stamp on the tonal character of the amp.

3) The power amp sections are pretty close to a Fender 'blackface' circuit too, except that they're using a 12AX7 as the long-tailed pair (LTP) phase splitter, driving a pair of EL84 output tubes instead of 6L6's, and no global negative feedback loop. The end result is a very sensitive amp that can be overdriven easily.

Making that particular amp suitable for a clean sound like you'd hear from Kenny Burrell or Jim Hall is going to be an interesting project.

Are you sure you wouldn't rather start out with a different question, like, "What kind of amp will give me a clean tone suitable for jazz playing?"

--

kooltubes 4th January 2013 04:16 AM

Hi Rongon,
There are many amps on the market suitable for jazz playing but I just bought the amp; I can understand the mod project can be a hit or a miss.

rongon 4th January 2013 04:20 AM

Well, you could try putting ECC81 (12AT7) in the V3 and V4 positions and see if that puts you closer to what you're looking for.

rongon 4th January 2013 04:22 AM

Also, by a "clean tone suitable for Jazz," do you mean a tone like Jim Hall, Pete Bernstein or Kenny Burrell, or more like John Scofield or Mike Stern? Or maybe you're thinking more like Bill Frisell? Or Herb Ellis? Tal Farlow?

What guitar are you using? Is it an archtop electric? Solid body? Humbucking pickups, or single coil?

eyoung 4th January 2013 04:33 AM

Hi all...

I am assuming you have cleaned all the pots and switches, also inspect for poor solder connections. Just a thought .

Regards, Elwood

kooltubes 5th January 2013 05:42 PM

Quote:

Originally Posted by rongon (Post 3310275)
Also, by a "clean tone suitable for Jazz," do you mean a tone like Jim Hall, Pete Bernstein or Kenny Burrell, or more like John Scofield or Mike Stern? Or maybe you're thinking more like Bill Frisell? Or Herb Ellis? Tal Farlow?

What guitar are you using? Is it an archtop electric? Solid body? Humbucking pickups, or single coil?

Hi Rogon,
I have archtop electric guitars. re: tone, my preferences are: Julian Lage, Jimmy Bruno, Norman Brown, Paul Jackson jr, etc.

rongon 5th January 2013 07:07 PM

I'm only familiar with Jimmy Bruno out of that particular group, but last I looked, he was playing through a Henriksen amp -- Jazz Guitar Amplifier: Henriksen Jazz Amp: light, powerful, inexpensive, small, jazz guitar amplifier -- which is solid state.

Paul Jackson Jr, according to the wikipedia (not sure about accuracy of that), plays Marshall and Mesa amps. High gain, designed for distortion. So I'm confused.

Norman Brown allegedly uses Polytone amps, which are solid state for sure.

In this picture --

http://www.julianlage.com/images/con...rweb-small.jpg

-- Julian Lage is using a 1970s vintage Fender combo amp. That's my amp of choice as well.

So, I'm not sure I have a clear picture of what you're after. Those are four players with very different sounds, and very different amplifiers.

--

My rig, back when I was playing regularly, was a Gibson Howard Roberts guitar (the fully hollow one, not the later "Fusion") and a Fender Deluxe Reverb from the mid-1970s. FWIW...

--

kooltubes 5th January 2013 07:36 PM

Hi Rogon,
I have seen videos on youtube, where Paul Jackson jr uses a GA-15 Rv Paul Jackson Jr. plays with RC Booster - YouTube
Anyway, if I have to start from scratch, which amp kit would you suggest?

rongon 5th January 2013 07:41 PM

I couldn't see or hear that Paul Jackson Jr video. I think you linked me to the Mobile version.

If you start an amp from scratch, then you can make anything you want. The obvious question is, what do you want?

--


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