My name is Bobby DeMoss, a Steeler in Kansas City North.
In electronics now 57 years.
I recently acquired 3 Sho Bud Studio Stage 500 amplifiers made in Nashville by Bonitron and have dissected the amp chassis. They are in 3 stages of development. The final stage is really quite good! According to what I have heard they were to compete with the Session 400's. The Peaveys were 210 watts RMS. Well, Bonitron apparently did not want anyone to pump that kind of power through a single speaker(JBL D130F). What their dirty little secret was is to build two 100 watt amplifier modules into one amplifier Chassis. If you notice from my pictures, which include 3 stages of design changes, you will see the 2 amps wired independently through two separate fuses to two speaker output jack's. This way they got out of blowing speakers under warranty and was to get you to use another cabinet/speaker loading both amp modules. Thus power of 200 watts in competition.
Sounds just awesome too. Just think, a true stereo efx loop! Currently working on a buffer stage for this!
See picture.
Trying to decide if I should run a second speaker, which is just something else to carry around, or invert the second amp stage input signal and run the amps in bridge mode?
A Rig-Zumsteel 08 Anti E9th 9x10, Vegas 400's x2 Lemay Mods, B Rig-Zumsteel 99 9x10, Stroborack's X2, Lexicon MPX200's x2.
I can't imagine the need for that much power. I would go for the extra speaker option. Cabinets are available that are light enough and I love the sound stage when it's spread apart.
Jerry, no I do not currently have a schematic but plan on reverse engineering one and possibly drawing one. I may try contacting Bonitron to see if they still have anything archived!
My final design amp sounds killer. Needs an efx loop though. One of the two prototype amps I have has Earl Skuggs Review stenciled on the back of it. The two amp modules are just that, breadboard modules but professionally done!
A Rig-Zumsteel 08 Anti E9th 9x10, Vegas 400's x2 Lemay Mods, B Rig-Zumsteel 99 9x10, Stroborack's X2, Lexicon MPX200's x2.
Played the amp Saturday night here in Kansas City North at the Thirsty Bull Saloon and it had plenty of low growl and crystal clear high end on E9th. Going to love the amp. They had something there. Bonitron should have continued on their own and marketed that amp.
Or maybe if Sho Bud cranks up, they can continue with that design.
A Rig-Zumsteel 08 Anti E9th 9x10, Vegas 400's x2 Lemay Mods, B Rig-Zumsteel 99 9x10, Stroborack's X2, Lexicon MPX200's x2.
Looks like all 3 amp chassis are going to work after a few capacitors. One has a low boost switch as well as a bright switch. I will investigate this! Also they were experimenting with output biasing so I will change all 3 to the final design. Can't get over how good she sounds. Put a 1502 with shiny dust cover in her, the speaker with the ribbed cone,(my favorite), great amp but heavy. Maybe some castors
A Rig-Zumsteel 08 Anti E9th 9x10, Vegas 400's x2 Lemay Mods, B Rig-Zumsteel 99 9x10, Stroborack's X2, Lexicon MPX200's x2.
The output stages are a pair of darlingtons giving 100 watts output from two amplifiers in one chassis. They epoxyed the bias diodes to the devices. Appears to be stable, at least I played fairly loud all night through one amp all night and it's still going. They were finally successful in getting biasing right on the darlington devices. More later!
A Rig-Zumsteel 08 Anti E9th 9x10, Vegas 400's x2 Lemay Mods, B Rig-Zumsteel 99 9x10, Stroborack's X2, Lexicon MPX200's x2.
Bobby DeMoss wrote: 26 Dec 2024 6:08 pm
The output stages are a pair of darlingtons giving 100 watts output from two amplifiers in one chassis. They epoxyed the bias diodes to the devices. Appears to be stable, at least I played fairly loud all night through one amp all night and it's still going. They were finally successful in getting biasing right on the darlington devices. More later!
It was wired w/ one output to chassis which won't work as it's a differential amplifier. Still trying to get it going, I have a later one which works, and i wanted to convert it to the later one, but these are difficult to work on,
Bobby DeMoss wrote: 21 Dec 2024 7:36 am
Jerry, no I do not currently have a schematic but plan on reverse engineering one and possibly drawing one. I may try contacting Bonitron to see if they still have anything archived!
My final design amp sounds killer. Needs an efx loop though. One of the two prototype amps I have has Earl Skuggs Review stenciled on the back of it. The two amp modules are just that, breadboard modules but professionally done!
I tried contacting Bonitron a couple years back, and they told me that they prob still have schematics, but that it would be waay too much effort to find them in their myriad library of electronic prints---
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