Author Topic: Need some help with a modified and expanded Sunn Model T Preamp  (Read 343 times)

Need some help with a modified and expanded Sunn Model T Preamp
« on: January 27, 2019, 06:27:25 PM »
Hey all, new here and new to the pcb/schematic side of this stuff so I'd appreciate some tips and advice regarding my first schematic. I'd always like the sound of the sunn preamps but hated their eq section and tended to run them wide open with a heavy treble roll off but wanted more flexibility. I started mucking around with just changing the eq portion of it and ended up with an AMZ presence control after the preamp, a straight rip off of the ROG thunderbolt power amp simulation followed by a baxandall eq and an output buffer. Thats the general gist of it and I should have most of the big moves more or less correct but could use a couple of eyes on things, especially the OpAmp biasing, polarity of the electrolytic caps, and general advise on tuning the various tone controls. I'd wanted to run this at 24v all along and was pleasantly surprised to see the thuhnderbolt has a 24v charge pump as well so I snagged their schematic for that as well and if i'm reading it correctly all the op amp biases just connect to the Vref supply but there's no coupling resistor on the first op amp bias and it for the other two it seems like 47k is small but .... Thoughts? Thanks in advance!



« Last Edit: January 27, 2019, 06:59:23 PM by wannacmypokemons »

PRR

Re: Need some help with a modified and expanded Sunn Model T Preamp
« Reply #1 on: January 28, 2019, 12:14:31 PM »
Welcome.

I think your tone controll connections at U3 are mis-copied.

Re: Need some help with a modified and expanded Sunn Model T Preamp
« Reply #2 on: January 28, 2019, 12:27:16 PM »
I only copied the power amp/phase inverter clipping section from the Thunderbird. I thought a baxandall eq would suit the sound of the preamp more and be more flexible than either the original TMB stack or the thunderbirds active bass/treble/presence setup. 

Does the bax eq's frequency center look right to you though? Im stil pretty new to this.

PRR

Re: Need some help with a modified and expanded Sunn Model T Preamp
« Reply #3 on: January 28, 2019, 09:13:57 PM »
What you have drawn is not a Baxandall.


Re: Need some help with a modified and expanded Sunn Model T Preamp
« Reply #4 on: January 29, 2019, 04:04:41 PM »


Thanks, that was definitely not a bax. Did this get me closer?

PRR

Re: Need some help with a modified and expanded Sunn Model T Preamp
« Reply #5 on: January 29, 2019, 06:37:26 PM »
Your Volume pot wiper now shorts ALL signal to ground before it gets to the output jack.

Re: Need some help with a modified and expanded Sunn Model T Preamp
« Reply #6 on: January 29, 2019, 07:11:30 PM »
A tragedy of the rotate tool, thanks for the heads up. I'm curious if you have any thoughts on the biasing of the LM833 (an area I'm struggling with) and whether or not you'd add an output buffer after the eq. Do you think this circuit would benefit from one in any substantial way?