New build

Jewellworks

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I started this a while ago. I had an Amp I had built w reasonable success, but it sounded and "felt" alot like another amp I had built, so I decided to make something different from it. So I gutted it, (mostly) and designed something different. I've posted about it on this forum before, but here it is... So far.

Schematic
What's different? Active Tone controls, parallel output.

20220702_104931_1656773518222.jpg

This is also my first turret board build. Cut the material, drilled the holes, set the turrets. I have 2. One for the SS full wave rectifier, and one for the rest of the circuit, with the idea that I keep high power away from the rest of the circuit. In the future, I may combine the rectifier w filter board, and a separate circuit board.

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I'm using all shielded wiring on the pots and input jack. Decided to use radial filter Caps. I have the room and they're so much cheaper...

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I hope to have this finished by the end of this long weekend. Excited to hear it.
 
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Jewellworks

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20220702_170821.jpg
Left:. All power wired in. Rectifier, PT, mains fuse and rectifier fuse, light, switch... All 3 speaker leads landed. Board set in place, but w temp screws until I get longer screws to fit through the turret board. Next time I'll mount the Radial Filter Caps lower on the turret post, rather than through the little hole on top.
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Leads on all pins and pots ready to land. All leads on the pots are shielded.

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Pin leads landed. All that's left is the pots, then double check, double check AGAIN, and plug it in and take measurements!

Almost there!!
 

Jewellworks

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20220703_220731.jpg

It's ALIVE!!
With limited success.
I had to change the way I'm doing the volume pot. Wasn't sure that would work... And I have NO tone controls at ALL. if I turn down way WAY low, I hear a change w the treble, but the bass controls sound very "phasey". My first try w Active tone control... The Baxandal circuit. That was the whole reason I wanted to build this amp. Hhhmmmmm.. .
And right now my bias is WAY off. I'm at about 35W and I should be 9!
It's pretty quiet. Very very slight hum, but I can probably get rid of that w a larger 1st node filter cap. I can go deep since I'm using a SS rectifier.
 

owlexifry

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Feb 10, 2021
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Adelaide, Australia
View attachment 1000774

It's ALIVE!!
With limited success.
I had to change the way I'm doing the volume pot. Wasn't sure that would work... And I have NO tone controls at ALL. if I turn down way WAY low, I hear a change w the treble, but the bass controls sound very "phasey". My first try w Active tone control... The Baxandal circuit. That was the whole reason I wanted to build this amp. Hhhmmmmm.. .
And right now my bias is WAY off. I'm at about 35W and I should be 9!
It's pretty quiet. Very very slight hum, but I can probably get rid of that w a larger 1st node filter cap. I can go deep since I'm using a SS rectifier.


you might wanna look at this
Won't this be phase cancellation?

View attachment 1000128
 

Lowerleftcoast

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california
Isn't it a feedback network for the tone controls?
From my cursory look, I don't see enough resistance to keep the *out of phase* from cancelling too much of the signal. Maybe the caps are supposed to change the phase angle enough to make it work?
Need more resistance or more caps???

Am I missing something here?
 

Jewellworks

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Update:. I re-biased and got both pentodes right at 25mA, @ 8.275W, out of 9.
I also had the volume and tone controls wired wrong, which is why they didn't work right... Fixed that, then tweaked the EQ to get more "tone". Now it sounds great! Especially the treble control. It gets very bright like a Vox. Bass controls can mud up when cranked, but back off a little and it's fat and warm, combined w the top end brilliance... Pretty happy with it.

As for the concerns of the actual circuit and the out-of-phase-ness of it all... To be honest, i don't know how it works. I just copied it. It's a Baxandal active tone control, w dual bass caps. You can find it on the TSC website. Ive also posted a thread on this forum regarding the tone circuit many months ago.
20220705_002209.jpg
It was this tone control that inspired this amp. Glad it works and glad it sounds pretty good! This amp was worth the trouble.

Now the only slightly annoying issue is there is a very very slight hum. Starts when you first turn it on, and otherwise doesn't get any louder as the amp warms up or volume control changes. It's dead quiet except for that low level humm.
I'm thinking I can double the 1st filter cap (from 47uf to 100uf), which should cut the ripple in half from where it is now.
Ive read you can do that with a SS full wave rectifier? But I'm unsure about side effects?
 
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