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Need Help with an Amplifier Preamp Power Supply

Thumpin6string

Thumpin6string

Supporting Member
Apr 25, 2013
7,048
12,465
Shoals Indiana
#1
Hopefully I'm posting this in the correct section.

As some TBers have seen my threads about my A.M.P BH220 with a blown power amp that I'm using as a preamp. The preamp runs on 15VDC. I'm looking to see if any of the amp techs out there like Agedhorse can give me a viable option for a 15VDC power supply to run just the preamp section that is lighter than the current transformer. I'm using it with my Peavey power amp, and it is working flawlessly. I would like to get rid of the heavy transformer so that with the peavey it would be a little lighter to transport. I have found some 15VDC switching power supplies that seem like an option, or maybe a 15VDC wall wort? I'm including a picture of my setup and the preamp schematic from a BH420 (See page 11 on this link A.M.P. Manual) since there are none available for the 220. They are similar other than the EQ section. Thanks in advance for any insight.
IMG_0846.JPG
 
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#3
SushiBoxFX Pedals Run High Plate-Voltage Tubes, but only require 9V @ 500 mA, so if yours runs at 15 VDC I would think a 2 Amp supply would be plenty (you might want to add an inline fuse)....

Amazon.com: 15V 2A Power Supply Charger Cable (Input AC 100V-240V, Output DC 15 Volt 2 Amp 30 Watt) Adapter Transformer Converter DC 5.5mm x 2.1mm/5.5mm x 2.5mm Extra Long 6.6FT : Electronics

Buy 15V 2A Power Supply Charger Cable (Input AC 100V-240V, Output DC 15 Volt 2 Amp 30 Watt) Adapter Transformer Converter DC 5.5mm x 2.1mm/5.5mm x 2.5mm Extra Long 6.6FT: AC Adapters - Amazon.com ✓ FREE DELIVERY possible on eligible purchases
www.amazon.com
 
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#4
WRM said:
SushiBoxFX Pedals Run High Plate-Voltage Tubes, but only require 9V @ 500 mA, so if yours runs at 15 VDC I would think a 2 Amp supply would be plenty (you might want to add an inline fuse)....

Amazon.com: 15V 2A Power Supply Charger Cable (Input AC 100V-240V, Output DC 15 Volt 2 Amp 30 Watt) Adapter Transformer Converter DC 5.5mm x 2.1mm/5.5mm x 2.5mm Extra Long 6.6FT : Electronics

Buy 15V 2A Power Supply Charger Cable (Input AC 100V-240V, Output DC 15 Volt 2 Amp 30 Watt) Adapter Transformer Converter DC 5.5mm x 2.1mm/5.5mm x 2.5mm Extra Long 6.6FT: AC Adapters - Amazon.com ✓ FREE DELIVERY possible on eligible purchases
www.amazon.com
Click to expand...
Only need 15vdc and at least 2 amps. Just not sure if it needs a regulated power supply. I see a lot of wall worts and switching power supplies out there, but not sure if they will work.
 
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#8
jthisdell said:
With the rest of that rig you are worried about weight?
Click to expand...
Besides the A.M.P., the only heavy part is the Peavey. The cabs are both super light. I was just hoping to shave some weight from the A.M.P. since it is no longer a full amplifier and is now just a preamp. Being most preamps are pretty light; it was just a thought. Since they are a backup to my Eden WT550, they probably won't leave my home. Sad, because they sound amazing.
 
#9
Why not get the amp fixed properly? An experienced, qualified tech should have access to suitable parts (even from donor units from that era), though is may not be inexpensive.
 
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#10
agedhorse said:
Why not get the amp fixed properly? An experienced, qualified tech should have access to suitable parts (even from donor units from that era), though is may not be inexpensive.
Click to expand...
It can't be fixed, at least at a reasonable price. The traces are almost non-existent from multiple previous repairs. I had it fixed 2 years ago by a highly experienced tech. He spent more time fixing all the damage done in its past than replacing the few bad parts. He had about 20 hours fixing traces and bad solder joints. He told me that if it ever failed again, it would not be worth trying to fix. It would need a new power amp board and they are not available. It is the same power amp that was in the Eden WT heads. I've searched for any dead A.M.P. or Eden heads that might have a good power amp board, but after having no luck, I went with the preamp into a separate power amp route. I'm happy with how it sounds and it kept the A.M.P. out of the landfill. My thread was to just see if there was a way to get rid of the heavy transformer. If not, no problem.

I don't really understand your previous reply. How is 15V+ and 15V- make it a 30 volt preamp board? I assumed it was both sides of 15VDC where one side was the + and the other was the -.
 
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#11
Thumpin6string said:
It can't be fixed, at least at a reasonable price. The traces are almost non-existent from multiple previous repairs. I had it fixed 2 years ago by a highly experienced tech. He spent more time fixing all the damage done in its past than replacing the few bad parts. He had about 20 hours fixing traces and bad solder joints. He told me that if it ever failed again, it would not be worth trying to fix. It would need a new power amp board and they are not available. It is the same power amp that was in the Eden WT heads. I've searched for any dead A.M.P. or Eden heads that might have a good power amp board, but after having no luck, I went with the preamp into a separate power amp route. I'm happy with how it sounds and it kept the A.M.P. out of the landfill. My thread was to just see if there was a way to get rid of the heavy transformer. If not, no problem.

I don't really understand your previous reply. How is 15V+ and 15V- make it a 30 volt preamp board? I assumed it was both sides of 15VDC where one side was the + and the other was the -.
Click to expand...
No, the supply is 30V, it’s derived do that the mid point is the ground. The voltage is 15V above ground and 15V below ground, which totals 30V. This topology is a critical part of the circuits in your preamp.

If you can’t find a donor board, you have a boat anchor. Sure with enough knowledge and ski you COULD adapt a replacement power supply, but you may be able to find a complete used amp for less cost and hassle.
 
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#12
agedhorse said:
No, the supply is 30V, it’s derived do that the mid point is the ground. The voltage is 15V above ground and 15V below ground, which totals 30V. This topology is a critical part of the circuits in your preamp.

If you can’t find a donor board, you have a boat anchor. Sure with enough knowledge and ski you COULD adapt a replacement power supply, but you may be able to find a complete used amp for less cost and hassle.
Click to expand...
It functions as a preamp. So not a boat anchor. I'll just leave it be. If the amp wasn't such a rare model, I'd have scrapped it. Chances of finding another is slim to none. Thanks for your input and explanation. I do appreciate it.
 
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#13
Thumpin6string said:
It can't be fixed, at least at a reasonable price. The traces are almost non-existent from multiple previous repairs. I had it fixed 2 years ago by a highly experienced tech. He spent more time fixing all the damage done in its past than replacing the few bad parts. He had about 20 hours fixing traces and bad solder joints. He told me that if it ever failed again, it would not be worth trying to fix. It would need a new power amp board and they are not available. It is the same power amp that was in the Eden WT heads. I've searched for any dead A.M.P. or Eden heads that might have a good power amp board, but after having no luck, I went with the preamp into a separate power amp route. I'm happy with how it sounds and it kept the A.M.P. out of the landfill. My thread was to just see if there was a way to get rid of the heavy transformer. If not, no problem.

I don't really understand your previous reply. How is 15V+ and 15V- make it a 30 volt preamp board? I assumed it was both sides of 15VDC where one side was the + and the other was the -.
Click to expand...
A guy I used to work with taught Soldering in the USMC and told me they would remove layers and replace traces 7 layers deep!...

I do like your decision to continue to use it "as is".

Cheers,
 
#14
WRM said:
A guy I used to work with taught Soldering in the USMC and told me they would remove layers and replace traces 7 layers deep!...

I do like your decision to continue to use it "as is".

Cheers,
Click to expand...
Naaah, I call BS on that one! Makes for an impressive story though, maybe he was trying to dazzle you with the impossible?
 
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