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Schematics and Layouts / Re: Scholz UDG Schematic
« on: July 01, 2020, 05:32:41 PM »
Yeah, there’s one on reverb.com for $750 (WOW!) but I am interested in seeing the double clipping stages.
News:
SSG-AMP-1 pcbs have arrived, in testing/modification phases.
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2
Schematics and Layouts / Scholz UDG Schematic
« on: June 29, 2020, 09:02:42 PM »
Has anyone traced out the Ultimatum Distortion Generator?
5
Schematics and Layouts / Re: GK Indicator Footswitch
« on: May 02, 2020, 02:38:32 PM »
Boom! Thank you!!!
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Schematics and Layouts / GK Indicator Footswitch
« on: May 02, 2020, 11:08:07 AM »
I haven’t contacted GK yet, but thought I’d ask here first — looking for the schematic for this GK footswitch used on the 112SC, 212SC, 150GT, etc from ~1980. The PCB inside is marked 50033B. The unit I received was DOA and someone disconnected the leads to the B channel switch at some point. I have a 112SC to test with.
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Amplifier Discussion / Re: HH ic 100
« on: April 20, 2020, 10:19:48 PM »
I’d suggest drilling out the rivet that holds the band together, assuming you can fit a drill bit in there, and replace with a nut/bolt. I mention it because I just drilled out a seized screw in a GK400RB two days ago, after trying just about everything else. Super frustrating.
EDIT: you may also be able to use a diagonal cutter to slice through the rivet.
EDIT: you may also be able to use a diagonal cutter to slice through the rivet.
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Schematics and Layouts / Re: Peavey Mixer: PV8USB Schematic and Repair
« on: April 09, 2020, 09:17:16 PM »
Thanks for your posts! - this is a great forum (I’m relatively new) and a wealth of information here.
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Amplifier Discussion / Re: Feng - Mini Amp using PAM8403 (2x 3 Watt)
« on: April 07, 2020, 06:37:55 PM »
Have a look at the NSC (now TI) “Boomer” series LM468x amplifiers. I worked on the test systems for those parts, and I could not believe how much useable power we wrenched out of +5V. We debuted them at an AES show, with a guitar “amp” we made with 4 of them (4W) all running on a 9V battery and VReg, inside of a little plastic box with belt clip. For a 5V platform, these were awesome. I think they still make a few of the models now, all smd tho.
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Schematics and Layouts / IN SEARCH OF: Studio Supply Company
« on: March 16, 2020, 02:44:27 PM »
Well technically not a solid state guitar amp schematic, I figured I would try here to track down schematics by the Studio Supply Company. These two cards came from a distribution amplifier out of a concert hall built in 1974. I believe the distribution amplifier fed individual offices in the bottom of the concert hall. I am trying to track down the schematic for what appears to be a multi band graphic EQ, all discrete which is in the second image. The first image is the backside of the only card that actually shows the logo of the company. Any help would be appreciated as always. Thanks.
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Amplifier Discussion / Re: Peavey Stereo Chorus NEW noise problem
« on: February 10, 2020, 06:37:23 PM »
Yep. That’s it. But you can use 8 ohms or even 16. You won’t need to crank up the amp to see crossover distortion (and you get the noise at relatively low volume I believe).
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Amplifier Discussion / Re: Peavey Stereo Chorus NEW noise problem
« on: February 09, 2020, 09:00:22 PM »
Honestly, if you haven’t used the scope in a while then I would be weary of poking around the output section of a power amp without some guidance. The scope probe has a ground ring and can easily short stuff and damage your amp if you don’t have the protective sleeve (condom) for it. Or if the alligator clip snaps off and drags across the PCB. I’ve done it - not fun. 
To test the power amp alone, you’ll need to run a sinusoid through it via the fx return. Do you have a dummy load to connect to the output of the amp? Then you can run a signal into that rather than the speaker and look with the scope hooked across the dummy load. That will keep you out of the amp chassis and is safer. You can also probe the output jack (speaker leads - be careful) with no load connected, but my old boss (guru) always made us test for that with a dummy load. With the speaker itself you are going to get a noisy signal and the crossover distortion “glitches” do not necessarily occur in the center of the waveform, so might be hard to see, or obscured. Be really careful and get a dummy load if you can.
To test the power amp alone, you’ll need to run a sinusoid through it via the fx return. Do you have a dummy load to connect to the output of the amp? Then you can run a signal into that rather than the speaker and look with the scope hooked across the dummy load. That will keep you out of the amp chassis and is safer. You can also probe the output jack (speaker leads - be careful) with no load connected, but my old boss (guru) always made us test for that with a dummy load. With the speaker itself you are going to get a noisy signal and the crossover distortion “glitches” do not necessarily occur in the center of the waveform, so might be hard to see, or obscured. Be really careful and get a dummy load if you can.
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Amplifier Discussion / Re: Peavey Stereo Chorus NEW noise problem
« on: February 09, 2020, 06:20:53 PM »
Get an oscilloscope to look at the output waveform - crossover distortion will be easy to see. If the output transistors are biased just into conducting at idle, then there should be little/no crossover distortion. While you can measure the voltages across the emitter resistors, the scope will tell all.
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The Newcomer's Forum / Re: Hello and a question about a Line 6 Spider 3
« on: February 06, 2020, 09:15:20 AM »
Cool! 
Bonus - there is no top plate on the chassis. When you pull it out, the top will be open and you can immediately look inside.
Bonus - there is no top plate on the chassis. When you pull it out, the top will be open and you can immediately look inside.
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The Newcomer's Forum / Re: Hello and a question about a Line 6 Spider 3
« on: February 05, 2020, 09:19:18 PM »
The cabinet does not come apart. The chassis of the amp slides out through the slot/back. Take out the two screws, one on each side, near the top. Lay the amp on its side (speaker perpendicular to table) and remove the top 4 chassis screws. Being on its side, the chassis will not fall down. Then you can slide the metal chassis out, like pulling a book out of a library shelf, from the back side. After that you will need a way to support it while working on it. Not sure if the last Spider I took apart was a v3, so the screw locations may be different, but it was pretty easy to work on. Hope that helps.