Help with Gibson GA-5 Reissue

[valco]

Hi, so I rehoused my Gibson GA-5 Reissue into a 1x12 cab, instead of the stock 1x8. Sounds wonderful. However, it nows sounds a bit too lean on the bass. Does anyone know how I would increase the bass output? Is there a capacitor or something that I can chance to do this?

I'm aware the "trinity mod" thing, but I was not a fan.

I looked for a schematic that I could attach to this post to help you guys, but I could not seem to find one. Here are the links to the guts. Again, its a Reissue Gibson GA-5 with 1 EL84 and 1 12ax7.

http://harmony.demont.net/myharmonies/Jaybird/GA5new2.jpg
http://occupancy1.com/wp-content/uploads/2010/08/DSC01754.jpg

Thanks for any and all help. Its much appreciated!

[spacelabstudio]

Hi, so I rehoused my Gibson GA-5 Reissue into a 1x12 cab, instead of the stock 1x8. Sounds wonderful. However, it nows sounds a bit too lean on the bass. Does anyone know how I would increase the bass output? Is there a capacitor or something that I can chance to do this?

I'm aware the "trinity mod" thing, but I was not a fan.

I looked for a schematic that I could attach to this post to help you guys, but I could not seem to find one. Here are the links to the guts. Again, its a Reissue Gibson GA-5 with 1 EL84 and 1 12ax7.

http://harmony.demont.net/myharmonies/Jaybird/GA5new2.jpg
http://occupancy1.com/wp-content/uploads/2010/08/DSC01754.jpg

Thanks for any and all help. Its much appreciated!

Do you have any other amps or cabinets lying around?  Does a different amp through that cab give you the bass you want?  Is the bass still lacking if you plug the GA-5 into a different amp?  I'd make sure the culprit wasn't your speaker/cab first.

Electronically, making bypass and coupling caps larger can give you more bass.  Stiffer filtering in the PSU could also potentially help.  Rolling off the tone on your guitar will increase the apparent bass by rolling off the highs.

Chris

[valco]

Thanks for your response!

Yeah, the cab certainly makes a difference. The stock ga5 cab was so small that the stock voicing worked great. In a bigger cab and a 12" speaker, its a huge improvement but sounds like it could use some more bass now that is has some more breathing room. And if i run it through my even larger Bruno Cowtipper 1x12 cab, it sound MASSIVE. I'd like to keep this amp in the smaller 12" that i currently have it in, as i plan on using it as my ultra light and portable amp. The BJF EQ I have does the job great, but I'm looking to see if I can boost the bass within the amp itself so I don't have to rely on the pedal. Basically, I want to "tune" the amp to the new cabinet.

The 3 large caps (filtering, right?) are all 22uf 350v. I 1st stage bypass cap is 25uf 50v. Any ideas?

[spacelabstudio]

Thanks for your response!

Yeah, the cab certainly makes a difference. The stock ga5 cab was so small that the stock voicing worked great. In a bigger cab and a 12" speaker, its a huge improvement but sounds like it could use some more bass now that is has some more breathing room. And if i run it through my even larger Bruno Cowtipper 1x12 cab, it sound MASSIVE. I'd like to keep this amp in the smaller 12" that i currently have it in, as i plan on using it as my ultra light and portable amp. The BJF EQ I have does the job great, but I'm looking to see if I can boost the bass within the amp itself so I don't have to rely on the pedal. Basically, I want to "tune" the amp to the new cabinet.

The 3 large caps (filtering, right?) are all 22uf 350v. I 1st stage bypass cap is 25uf 50v. Any ideas?

What are the coupling caps?

Chris

[valco]

Both are .022uf. They are the yellow mallorys.

[spacelabstudio]

Both are .022uf. They are the yellow mallorys.

You can try increasing those to .047 or .1 and see how that sounds.  If it were me I'd experiment with increasing the size of the filter caps as well--maybe try 47s.  The first one will give the most bang for your buck.  Since it's a solid state rectifier you can probably go 100 or 220, even, if you feel like experimenting.  You can just stack multiple caps together to experiment since capacitance adds in parallel.  This will make the whole amp a bit harder/punchier (aka modern) sounding, but might also help give you the bass response you're looking for.

What is the bypass cap on the power tube?  It's probably a 22--I'd experiment with a 100.

Chris

[valco]

Are you talking about the smaller black cap next to the filter caps? Im not sure what the value of that is, as I cant read it with the way it is. I'd have to take it out. However, that is the only cap that seemed to make any difference.

I tried adding a 100uf 250v cap in parallel with each filter cap (only one at a time though) and it made no audible difference to me. Same with the coupling caps. I doubled both of those and no difference was detected.

However the small black cap next to the filter caps added more bass when I put the 100uf cap in parallel. Not much, but certainly noticeable. All of this stuff is new to me, so I'm not always sure what I'm looking at. Since that seemed to have the most effect, perhaps I should try an even larger cap value there. Again, the 100uf made a very small but noticeable difference in the bass. How high a value can i go with this? Also, what would be a safe voltage to use?

Thanks again for your help!

[FYL]

However, it nows sounds a bit too lean on the bass. Does anyone know how I would increase the bass output? Is there a capacitor or something that I can chance to do this?

The GA-5 is a well designed and built small amp, with all components sized for a 8" speaker unable to deliver lows. Short of boosting the power supply, fine-tuning the tone shaping network before the volume control, changing a couple of caps and fitting a much larger set of xformers, there's very little you can do.

I looked for a schematic that I could attach to this post to help you guys, but I could not seem to find one. Here are the links to the guts. Again, its a Reissue Gibson GA-5 with 1 EL84 and 1 12ax7.

Here you go: http://www.blueguitar.org/new/schem/misc_amp/gibson_ga5_schem.pdf
 

[valco]

Thanks for the info. Fair enough. Perhaps I'll just stick to using an EQ pedal.

[valco]

However, since I did notice a small increase in bass with that one small black cap, NEAR the filter caps, would it be safe to experiment there and increase the value? If so, what would the max be, and what voltage should I use?

Thanks!

[spacelabstudio]

However, since I did notice a small increase in bass with that one small black cap, NEAR the filter caps, would it be safe to experiment there and increase the value? If so, what would the max be, and what voltage should I use?

Thanks!

Which cap are you talking about?  In general I would encourage experimentation.  Even if a change doesn't accomplish something you would consider useful you learned a little something about what the tweak does.

Chris

[valco]

Please excuse my ignorance with this, but I think its the 2nd bypass cap. If you look at the first link I posted at the top of this thread, you can see the guts. Its the small black cap to the left of the 3 larger filter caps.

I found when I added 100uf in parallel to the existing cap, in added a bit of bass. So, I'm wondering if it is safe to add a lot more to that existing cap and see what happens. Perhaps a few 100uf, since 100uf was so minor?

[spacelabstudio]

Please excuse my ignorance with this, but I think its the 2nd bypass cap. If you look at the first link I posted at the top of this thread, you can see the guts. Its the small black cap to the left of the 3 larger filter caps.

I found when I added 100uf in parallel to the existing cap, in added a bit of bass. So, I'm wondering if it is safe to add a lot more to that existing cap and see what happens. Perhaps a few 100uf, since 100uf was so minor?

That is the cathode bypass cap for the power tube.  It is safe to add as much capacitance as you want there, but you are unlikely to hear any difference beyond what you've already done.  At 125uF you're already pretty much beyond the maximum value that will have any noticeable effect.  If you want to play, I would experiment with the coupling caps.

Chris

[phsyconoodler]

Quote:"And if i run it through my even larger Bruno Cowtipper 1x12 cab, it sound MASSIVE."

  No one mentioned the speaker you are using.Maybe swap the Bruno speaker into your cab?
I have built a few 12" champs and the speaker choices were quite dramatic.

[P Batty]

I think you are at a point where you should leave the circuit alone and start auditioning speakers, as many different ones as you can buy, beg or borrow.

[PRR]

> No one mentioned the speaker you are using.

spacelabstudio said: "I'd make sure the culprit wasn't your speaker/cab first."

[valco]

Hi, thanks for the help and suggestions.

Okay, I WAS using a Weber 12F150 in the new cab. Again, sounded really nice but a was bit lean on the bass. I swapped it for a 100 watt Weber Ceramic Blue Dog that I've been trying to find a home for. Big improvement! A bit softer sounding, but with more bass. I added a subtle bright cap (with an on off switch) to the volume pot which helps brighten it up a bit. The amp sounds much more balanced now.

I think I will leave this amp alone for now. If I really want some huge bass frequencies, I can always use the BJFE EQ, as it can really boost the bass without sounding fake. But with this Blue Dog, I don't think I'll need it.

Thanks again!