Ampeg/Fender Practice amp

drew1d

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After working on my friends Ampeg G12, I thought about trying to make a small, no frills, single ended practice amp in the same "spirit". As far as I know, most Ampeg stuff is push pull, so I took the power section from a Tweed Princeton, and did a few tweaks. As for the Ampeg preamp part, I kept the same value Grid and plate resistors, and Coupling capacitor values. I couldn't do a Baxin/James tone stack, so instead I put a Mid control after the second triode. (not the Framus mid control, but not far off.) No inverse feedback. I also had to go down to 500k volume pot because 1 meg oscillated at full volume.

This is a quick video I just did. I started in the "Accordion" input. When I went to the guitar input, it was a little crackly, I'm not sure if it's the dirty power in my house (same outlet as my boiler and pumps) or something to look into. I'll move it to another outlet and check later. Let me know what you think! (Comments for the amp, Not the open G playing, I know that needs work.)

 

drew1d

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for a single knob mid control, it has quite an effect on the tone! diggin it!
Thanks. I figure a mid control would affect the “character” of the amp the most. Often I hear amps described as either “mid-scooped” or has a mid “hump”. I can always roll off some highs with the tone control.
 

drew1d

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id be interested to see the schematic for the "not a Framus" mid control
It’s not my design. I have Merlin Blencowe’s book, he labeled one design “Framus” and the other is a different bridged T design. It didn’t drop the treble as much as I thought. The white wire goes to a pot to ground, which is the tone control.
 

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drew1d

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A little earlier. It may be easier to see. (Other direction)
 

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boxocrap

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After working on my friends Ampeg G12, I thought about trying to make a small, no frills, single ended practice amp in the same "spirit". As far as I know, most Ampeg stuff is push pull, so I took the power section from a Tweed Princeton, and did a few tweaks. As for the Ampeg preamp part, I kept the same value Grid and plate resistors, and Coupling capacitor values. I couldn't do a Baxin/James tone stack, so instead I put a Mid control after the second triode. (not the Framus mid control, but not far off.) No inverse feedback. I also had to go down to 500k volume pot because 1 meg oscillated at full volume.

This is a quick video I just did. I started in the "Accordion" input. When I went to the guitar input, it was a little crackly, I'm not sure if it's the dirty power in my house (same outlet as my boiler and pumps) or something to look into. I'll move it to another outlet and check later. Let me know what you think! (Comments for the amp, Not the open G playing, I know that needs work.)


nice little amp
 

drew1d

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B6EB597B-49E9-4F12-B82E-0FFA74EE84A4.jpeg

I don’t seem to remember if I put the grid leak resistor before or after the mid control.
 
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drew1d

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Also, I did end up putting a 4700 uf cap across the bridge rectifier + -, ( to make the filaments come on slower) and the light may be AC not DC. Also, the 47k input is on ground from a switching jack when not used.
 
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Jewellworks

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I don’t seem to remember if I put the grid leak resistor before or after the mid control.

"before" (as drawn) its seeing 470k. which isnt horrible...

i tried to "fake out" the Fender and Marshall (and Framus) tone controls at the TSC site, but couldn't get it to work.
 

drew1d

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Thanks for the feedback. As I see it, Traditional TMB controls are highly interactive with the signal. The middle being the ground for the other controls, kinda lifting the effectiveness of the other controls. But most discrete middle controls cut high and low too. In order for it to be effective in my circuit, I would need to put it after a bypass capped gain stage. Which is the driver stage in this circuit. I sacrificed negative feedback, but still have a clean sounding amp. Albeit if the mid and vol controls are dimed it breaks up. I’m experimenting with speaker driven reverb now. I’d have to sacrifice one of the inputs to put the switch. But I’ll probably put that as a different post.
 




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