Hey Gang...
Ordered caps. Extras for some spares. Two 47uf & four 22uf. Plan is to replace the two 10's with 22's first and evaluate.
Pulling the 6SN7 kills the 60Hz. So my thinking is that it is not coupling between the PT and OT or anything down stream. I think there is still a grounding issue in the inverter section but, I want to get the caps changed and confirm the suppression of the 120Hz before I start changing things.
As soon as I get the parts (mid next week?) I'll report back.
Also, I wanted to do a little "boning up". I checked on Amazon and there are several books available. Anything not super technical recommended? I'm way more comfortable with an actual book than online.
Again, thanks to all for your help!
Best.
Gibson GA50 Clone Noise Issue
Moderators: pompeiisneaks, Colossal
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Duck Dodgers
- Posts: 24
- Joined: Wed Jul 27, 2022 10:29 pm
- Location: California Central Coast
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Duck Dodgers
- Posts: 24
- Joined: Wed Jul 27, 2022 10:29 pm
- Location: California Central Coast
Re: Gibson GA50 Clone Noise Issue
Hello...
Some unexpected developments but, a good outcome.
While I was waiting for my filter caps I went ahead and built a small board with the pre-amp output circuit. Everything from V1, P8 to V2, P1.
Pic is below. It didn't help but, it pretty much eliminated that part of the circuit as the cause. I'm showing this for "fun" only. Maybe I'll use it to build something else.
Received the filter caps and changed C3 & C4 to 22uf. The 120Hz was still audible but greatly diminished.
Put a 22uf in parallel with the first filter cap but, no further improvement so I didn't change out the first cap for a 47uf.
Noise level was pretty low but, at this point my OCD was getting the better of me.
I recalled that Phil_S, in between (deservedly) shaming me for my lead dress, suggested swapping sections on V2. (Pins 1&4 and 2&5).
I think the intent was to see if the 120Hz was somehow section dependent.
Tried it and, 120Hz completely gone! 60Hz only audible if you stick your ear in the speaker. Absolutely nothing from 2ft away.
To sum up..
All the iron in original positions. Non-optimal but seems to work.
Grounding scheme changed per the suggestions in the first installment. Again, thanks to "didit" for the link to the grounding article.
Pot leads dressed to, I hope, Phil_S' satisfaction.
Changed filtering from 10-22-10-10uf to 4x 22uf.
Swapped V2 sections. (Phil_S, again) Don't quite get it but, I'll take it. Works with both the JJ and Tung Sol.
Tone is very mellow '50's-'60's jazzy. Will breakup at Warp 7 or so but by then it's way too loud. Background hum/buzz basically non-existent.
Next up is building a cabinet and getting some speakers. I'd like to go with the original 12"/8" combination. I also have a 15" Weber in another amp. I'll give it a try as well.
When I finish (not soon) I will post a pic and, hopefully an audio sample.
Again, thanks to the group for help and patience. I learned a lot!
Cheers.
Some unexpected developments but, a good outcome.
While I was waiting for my filter caps I went ahead and built a small board with the pre-amp output circuit. Everything from V1, P8 to V2, P1.
Pic is below. It didn't help but, it pretty much eliminated that part of the circuit as the cause. I'm showing this for "fun" only. Maybe I'll use it to build something else.
Received the filter caps and changed C3 & C4 to 22uf. The 120Hz was still audible but greatly diminished.
Put a 22uf in parallel with the first filter cap but, no further improvement so I didn't change out the first cap for a 47uf.
Noise level was pretty low but, at this point my OCD was getting the better of me.
I recalled that Phil_S, in between (deservedly) shaming me for my lead dress, suggested swapping sections on V2. (Pins 1&4 and 2&5).
I think the intent was to see if the 120Hz was somehow section dependent.
Tried it and, 120Hz completely gone! 60Hz only audible if you stick your ear in the speaker. Absolutely nothing from 2ft away.
To sum up..
All the iron in original positions. Non-optimal but seems to work.
Grounding scheme changed per the suggestions in the first installment. Again, thanks to "didit" for the link to the grounding article.
Pot leads dressed to, I hope, Phil_S' satisfaction.
Changed filtering from 10-22-10-10uf to 4x 22uf.
Swapped V2 sections. (Phil_S, again) Don't quite get it but, I'll take it. Works with both the JJ and Tung Sol.
Tone is very mellow '50's-'60's jazzy. Will breakup at Warp 7 or so but by then it's way too loud. Background hum/buzz basically non-existent.
Next up is building a cabinet and getting some speakers. I'd like to go with the original 12"/8" combination. I also have a 15" Weber in another amp. I'll give it a try as well.
When I finish (not soon) I will post a pic and, hopefully an audio sample.
Again, thanks to the group for help and patience. I learned a lot!
Cheers.
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Re: Gibson GA50 Clone Noise Issue
I'm very glad you got it sorted out and that you think my small contribution was worthwhile.
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Duck Dodgers
- Posts: 24
- Joined: Wed Jul 27, 2022 10:29 pm
- Location: California Central Coast
Re: Gibson GA50 Clone Noise Issue
Promised I'd post finished pictures....
Couple developments;
Went with Weber alnico 12" and 8" per original GA50. Sound was good before with the old Fender Blues Junior speaker. Now it's fantastic (at least to me).
Interior temperature was getting a little warm after I put the bottom on the chassis. Mostly cathode resistors. Added a fan. This is a 60mm x 12mm 24v fan on 12v. Used a $4 amazon p.s. Totally quiet and pushes enough air to keep it cool(er).
Anyway, very pleased.
Thanks again gang for all the help...literally couldn't have done without you.
Cheers
Couple developments;
Went with Weber alnico 12" and 8" per original GA50. Sound was good before with the old Fender Blues Junior speaker. Now it's fantastic (at least to me).
Interior temperature was getting a little warm after I put the bottom on the chassis. Mostly cathode resistors. Added a fan. This is a 60mm x 12mm 24v fan on 12v. Used a $4 amazon p.s. Totally quiet and pushes enough air to keep it cool(er).
Anyway, very pleased.
Thanks again gang for all the help...literally couldn't have done without you.
Cheers
You do not have the required permissions to view the files attached to this post.
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johnnyreece
- Posts: 1072
- Joined: Thu Jan 26, 2012 2:05 am
- Location: New Castle, IN
1 others liked this
Re: Gibson GA50 Clone Noise Issue
Sharp! Thanks for sharing!
Re: Gibson GA50 Clone Noise Issue
Hello --
Best .. Ian
Exceptional. A tidy package faithful to the original, however original in itself.
Really have to get to finishing off my own amp this coming winter when time allows. And I've learned along with you and this project some things to investigate in that. So thank you.Thanks again gang for all the help...literally couldn't have done without you.
Best .. Ian
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Duck Dodgers
- Posts: 24
- Joined: Wed Jul 27, 2022 10:29 pm
- Location: California Central Coast
1 others liked this
Re: Gibson GA50 Clone Noise Issue
Thank You!
Since the chassis/cabinet layout was so different than the original I just tried hard to make it "period correct". Although I'm no industrial designer, it was great fun and I think it came trough with the '50's vibe.
Particular thanks to you, Ian. Your "GA50 Aspirations"" posts (2017?) and our PM's more than a year ago(!) were the beginnings of this build.
Cheers
Since the chassis/cabinet layout was so different than the original I just tried hard to make it "period correct". Although I'm no industrial designer, it was great fun and I think it came trough with the '50's vibe.
Particular thanks to you, Ian. Your "GA50 Aspirations"" posts (2017?) and our PM's more than a year ago(!) were the beginnings of this build.
Cheers