Help Wiring a Replacement Potentiometer for Sonic T

[DEQ+TheEnd]

Very nice job audio1st.

Based on previously postet schematic I 'moved' C3 and removed R01 acording to your diagram (see posted image below).
According to other threads it is common to move the inputs to the bridged C3-C4 and bypass both C1 and L1.
Being the nob I am I'm curious as to how this filter now work with the C1 and L1 still in place?

regards
HansR

[audio1st]

Hello HansR,
I have read on other posts of the other mod improving bass but the mid band loses out. Keeping the C1, L1 filter in may prevent this side effect. Panomaniac says, quote(The 100pF cap and the inductor are meant to drain off some of the RF that may be present on the input.) A slight treble roll off may be noticable but if it wasn't a problem in the unmodded Sonic, it shouldn't be a factor here. (it may be a good thing)?
I just thought it was an easier soldering mod than the other, leaves more SMD's intact and may even sound better.???
I'm sure this mod was suggested by SX881663 ( Roger) some time back.??
It sounds OK to me, but I am not as expert as most of you.
Just trying to help..

[audio1st]

Originally posted by sx881663
http://www.diyaudio.com/forums/showt...880#post571880

In this post (#21 in this thread) there is a drawing of the input circuit. As can be seen if you jumper out c3, c4 you will be connecting r01, r02 directly to the input. This causes a DC offset and will shut the chip down. The solution is to remove these resistors and jumper out the caps at the same time. Then put the quality 2.2uf film caps from the volume control wipers to the input connector on the board. The easiest way to do this is to find the wires from the volume control PCB that connect to the main board and cut them in the middle, splicing in the caps there.
Roger

This is where I got the information..

[Eggzy]

Audio1st...you are a star!!!

Those pix are the best "explanation" I've yet encountered! They truly speak a thousand words! you've saved me a lot of headaches.

many regards
Eggz

ps
Re: the stock pot...is it really that bad???? To me it feels nicely weighted and really well made. [anyone agree?] Should a variable resistor really make any noticable impact to the sound quality or am I just being naive? what is the governing factor?

[PCHuggs]

I asked a few of the experts about bypassing the input filters. I was very leary about removing the SMDs (so tiny). A quick solder tack job seemed so much easier. I was politely told that the filter is there for a purpose and shouldn't be removed. C3 and C4 really need to be replaced with higher quality caps of the proper values. I've successfully done two T-Amps now using this method and the results are worth it. The *very* noticable bass roll-off is gone. It sounds just great.

As far as the potentiometer goes - get yourself a 50k Alps RK27 Potentiometer (RK27112AS25C0A503) from TangentSoft. It's very smooth and well balanced. It works perfectly in this setup.

I've been using a 3 amp Astron and a 3 amp Radio Shack power supply with good results. I got the RS PSU in a closeout for $14. The little T-Amp likes an ample supply of electricity! I'm currently researching a 12v regulated power supply to build myself - more to come later........... (c8




Best regards,
PCH

[Pano]

Originally posted by audio1st
Here is a Sonic T Amp, Bass Mod' dia'

Nice job, Audio 1st! You have done what I have been meanng for so long to get up on my site as the "stealth" input mod. No need to duplicate your efforts, I'll just link to your post.

Maybe you'll give me permission to use your diagram on my site? Full credit, of course.

I like this version, as it retains the input RF filters. Good for those big caps that might pick up RF noise.

[Lostcause]

Originally posted by panomaniac


Nice job, Audio 1st! You have done what I have been meanng for so long to get up on my site as the "stealth" input mod. No need to duplicate your efforts, I'll just link to your post.

Maybe you'll give me permission to use your diagram on my site? Full credit, of course.

I like this version, as it retains the input RF filters. Good for those big caps that might pick up RF noise.

Hi Michael, is this exactly your 'Stealth' version or do you jumper the caps onto the board, replacing the originals rather than putting them before the filter?

[audio1st]

Originally posted by panomaniac


Nice job, Audio 1st! You have done what I have been meanng for so long to get up on my site as the "stealth" input mod. No need to duplicate your efforts, I'll just link to your post.

Maybe you'll give me permission to use your diagram on my site? Full credit, of course.

I like this version, as it retains the input RF filters. Good for those big caps that might pick up RF noise.

Thanks for your comments and you are welcome to use any of my pic's..

Panomaniac, after reading one of your replies on another thread, I did the filter bypass version on the 5066 mod thread..
I was concerned that the 100pf cap after the input cap would show a resistance of 80k at high frequency and raise the output voltage to the speakers, or is it not enough to worry about?


Barry...

[Pano]

Originally posted by Lostcause
Hi Michael, is this exactly your 'Stealth' version?

Exactly the same. I just called it "stealth" because we were sneaking in ahead of the filter. Might as well use the filter if it's there. I won't affect the audio, but should clean up some noise.

I don't think the little 100pF cap will hurt the output. It certainly doesn't effect DC offset. As you know, R01/R02 must be removed, they will cause massive DC offset if used in this version.

I'll try to do a little more research on the effect of the 100pF cap. If anyone else does, please let us know. Maybe someone can spice model it.

[jwb009]

I just saw that the 'stealth' version is up and i'd like to try it...however I have already done the 'Version 1' mod, removing R1 and R2.

So my question is can I still do the stealth version somehow, or will I need to put R1 and R2 back in (I already threw em away, or lost em)? Thanks