Ga-5 farty when cranked
Moderators: pompeiisneaks, Colossal
Ga-5 farty when cranked
Got my gibson ga-5 finished except for tolex, and handle there's not a lot of headroom after 2 or 3 it start breaking up, if I lower the 10k dropping R inturn raising pre-amp voltages would that help increas headroom , the amp really scream when cranked up but gets kinda farty for lack of a better word. I have NFB hooked up would nfb help with the fairness. Thanks matk
Re: Ga-5 farty when cranked
R12, the 10K in the power supply ladder is for the screen supply on the 6V6. The schematic says that should give you 350V. That isn't the place to increase preamp voltage. You might try to lower R10, 22K. I think I wouldn't go below 5K and I'd start by tacking another 22K in parallel (gives you 11K) to see what it does. I believe higher rail voltage will translate to more headroom. How much? I'm not sure.
You might also go a little more Fenderish on the preamp tube. The first section R/C is 2.2K/20uf and the second section is 2.2K/no cap. I think I'd look at reducing 2.2K on one or both cathodes. It is simple enough to tack another 2.2K across the existing resistor to get 1.1K for testing without so much hassle.
Remember, only do one thing at a time and then check the result.
Fartiness could also be the speaker ;-{
Good luck.
You might also go a little more Fenderish on the preamp tube. The first section R/C is 2.2K/20uf and the second section is 2.2K/no cap. I think I'd look at reducing 2.2K on one or both cathodes. It is simple enough to tack another 2.2K across the existing resistor to get 1.1K for testing without so much hassle.
Remember, only do one thing at a time and then check the result.
Fartiness could also be the speaker ;-{
Good luck.
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Stevem
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Re: Ga-5 farty when cranked
It could be lots-o-things!
First and fore most if your Drive signal level ( AC voltage ) into the grid of the output tube is too much bigger than what the tube is idling at D.C. Wise, that would do it big time!
First and fore most if your Drive signal level ( AC voltage ) into the grid of the output tube is too much bigger than what the tube is idling at D.C. Wise, that would do it big time!
Re: Ga-5 farty when cranked
There it could be any one of 6-or-so different 'Gibson GA-5s'.
So I wonder which 'GA-5' it is?
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He who dies with the most tubes... wins
Re: Ga-5 farty when cranked
or this one?
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He who dies with the most tubes... wins
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Stevem
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Re: Ga-5 farty when cranked
Farting is what happens and or can be made happen to every tube amp under the Sun,( including SS amps ) its excess Bass as you Crank them up more and more , and this makes for farting!
A amp that can provide enough bottom end for rich clean low volume playing is without fail , once again , without fail going to fart out when revved up!
Two simple things to try is to half the value of any of the amps Cathode bypass caps starting with the preamp caps, in a like manor any stage to stage coupling caps bigger than .022 uf may be suspect also.
Marshalls which are near always used cranked make use of a .068 uf Cathode bypass cap in part for this very reason!
Switches to toggle cap values between low volume bottom end needs and cranked bottom end levels are a easy fix.
3 way rortory type switches will allow you to parallel different caps, a six way switch would for example allow you to step up or down in 1uf steps for Cathode caps!
On my amps at low volume playing on the bridge pickup for example I may have the Bass opened up to 8 , when cranking its at no more then 3 on the control!
If you have only a tone control on the amp your only fix is to make use of switches and different caps!
The only thing to watch out for as you add switches is the wiring layout and issues that could make For osscilation!
A amp that can provide enough bottom end for rich clean low volume playing is without fail , once again , without fail going to fart out when revved up!
Two simple things to try is to half the value of any of the amps Cathode bypass caps starting with the preamp caps, in a like manor any stage to stage coupling caps bigger than .022 uf may be suspect also.
Marshalls which are near always used cranked make use of a .068 uf Cathode bypass cap in part for this very reason!
Switches to toggle cap values between low volume bottom end needs and cranked bottom end levels are a easy fix.
3 way rortory type switches will allow you to parallel different caps, a six way switch would for example allow you to step up or down in 1uf steps for Cathode caps!
On my amps at low volume playing on the bridge pickup for example I may have the Bass opened up to 8 , when cranking its at no more then 3 on the control!
If you have only a tone control on the amp your only fix is to make use of switches and different caps!
The only thing to watch out for as you add switches is the wiring layout and issues that could make For osscilation!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Ga-5 farty when cranked
Thanks for responses and its nice too see the site working well, This one has 2.2k with 22 bypass, to a 1 meg pot not sure which exact model i is, a couple .022 coupling caps and a the power supply rounds out the whole circuit, which is per a sch I googled amp does sound good at 4 to 7 cranked on volume but you can tell it has plenty left just gets farty I'll try adjust the second bypass and go from there thanks guys. Mark
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Re: Ga-5 farty when cranked
This is normal for SE amps. The common remedies are either:
1) reducing one of more of the coupling caps by 'a notch' or
2) reducing the size of the bypass Cap(s) in the preamp to 5uF or 2uF or 1uF - depending on how trebly you want the amp to sound or
3) putting a 22k to 47k resistor in series with the grid and the grid leak resistor of the output tube to reduce the onset of blocking distortion.
He who dies with the most tubes... wins
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bluesfendermanblues
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Re: Ga-5 farty when cranked
I have a similar amp (5F1 clone). that I use weekly with a Lollar P90 equipped Ibanez. Off course I never run it past 6 for Jazz.
It's farty alright when cranked. However, don't crank it! unless you want to modify it a la 70s Marshall preamps. Tweed amps just dont sound good when cranked (and IMO neither does blackface or silverface amps). The sweet spot is usually around 11 o'clock, depending on whether you use humbuckers or singles.
Only Spinal Tab run their amps full out.
It's farty alright when cranked. However, don't crank it! unless you want to modify it a la 70s Marshall preamps. Tweed amps just dont sound good when cranked (and IMO neither does blackface or silverface amps). The sweet spot is usually around 11 o'clock, depending on whether you use humbuckers or singles.
Only Spinal Tab run their amps full out.
Diva or not? - Respect for Mr. D's work....)