Help Wiring a Replacement Potentiometer for Sonic T

[blubbo]

Boy am I happy! With pure instincts I bought a new rca plug today, (stupid, eh? How's one of those gonna fail?) and suprisingly it worked after changing it! Have to give a big thanks to audio1st for that "schematic"! It's a new amp really!

By the way I feel quite stupid now, beeing new and all...


Also thanks Eggzy, that I did not know!

[genki]

Hi every body

I have mod my T amp according to Audio1st dia using some cheap stuff. The details as following:
1. replace powe supply cap with Nichicon 3300uf, 16 v. soldered on pcb
2. replace input cap with two cheap oil cap, namely Remix 2.0 uf, 250V (don't know where it comes from, bought on with 20 cent here in my place). I could find the caps that you use here.

3. Replace across caps at the speaker output jacks with two 0.15 uF Corald Jonhson poly propylene caps

4. Bridge c3, c4 and remove R01 and R02.

5. Change cover, jacks but use cheap internal wire and cheap pot
I use 12V DC 3.2 A adaptor.

Result: a lot of bas improvement, better image. its another amp, sure. But.......... there are alot of noise. It should be as quiet as mouse using the said dia, right?

I guess it is because of the cheap pot because if I increase the volum, the noise is bigger until close to the max level, it is suddenly.disappeared. Or is it because of the cheap wire? and I donot have good soldering skill?

thats what I guess and because I'm definitely know nothing about electronics, you might have better idea than me.
Any advice will be appreciated!!

Thanks in advance

[Lostcause]

Hi Genki,
Well this could be a lot of things but the first thing to do is twist the output wires together so the ground acts like a shield.
Do the same on your input wires.

Try shielding the input caps with tin foill (Ensure you dont short anything with it)

get back after you have done this.

[Pano]

Hi Genki,
You don't say what kind of noise you're having, bet I guess it's buzz from your description.

Mostly likely a grounding problem. Are you using sheilded wire on the inputs? Are all your connection points well shielded? It is common to hear the noise increase when you turn up the volume control, then have it go away at some point. That is almost always a ground problem. You may need to connect the amp board or input connectors to ground, or maybe even disconnect it. Grounding problems can be difficult to trace.

Let us know how it goes!

[genki]

Thank you Pano and lostcause

The noise is the background noise, it buzz on my speakers. I think that's the grounding problem. I have tried shielding the input, out put wires with tin foil but there's no change. Finally, I have connected the out tag of the input jacks to ground, using a piece of wire and connect it to the ...........water tab. Then all the noise disappeared

It sounds great now. My Tannoy SRM 12x sings really fantatic. If any body says Tannoy is lack of bass then he should try my T amp...

But there is a small problem, you guess, I cannot connect to the water tab for grounding all the time. Do you experts have any better way to deal with this grounding problem?

[Pano]

Grounding can be very difficult. And just think, you have a very simple system. Image a recording studio or a live show! Big headaches.

Sometimes the amps can work well with no connection to ground at all (think iPod or portable radio) other times you will have to have a ground wire. Is anything else in your system connected to ground? It sounds like it is not, or the water pipe trick would not make a difference.

It is very hard to tell you how to fix it without actualy being there. The very smallest things can make a big difference. Your easiest choice is running a wire from a good ground to your amp. Does your house or building have gounded power mains outlets? Can you run a wire to the water pipe?

[genki]

Thanks Pano

The amp sounds really different. If not connect to the water pipe, the buzz is just hard to accept. You can hear it from 4 metter far from the spearkers. With the water pipe then the sound is even better, not only the noise is away.

But I'm wondering if I did some thing wrong because before that there is no noise, right? and most of you donot have this problem with the same kind of moding. Do you think what and where I can look at on the PCB to check the ground problem?

When I change the case of the amp, i just desoldered the DC jack and connect with a peice of wire to bring it out of the PCB, but I broke the small foot of the jack which connect to the PCB (the grounding foot). When I use wire, I just connect it to the next foot on the PCB(which are inter connected with the broken one). But I'm not sure this is the problem.

Don't have a good camera to show you what I did, hope you can imagine.

[notaclue]

Maybe you could just alter this drawing to show what you did?
Open the picture then right click over it and save it onto your PC, alter it in paint with arrows and text, then save it and upload it back onto the forum.

[cpemma]

Originally posted by genki
But I'm wondering if I did some thing wrong because before that there is no noise, right? and most of you donot have this problem with the same kind of modding.

I've a similar problem, maybe not quite as bad as you, but nearby sources of interference will vary with each person, so don't think you've fouled up the mod. I'm thinking its partly splitting & spreading the ribbon-cable pot leads out (to accommodate the bulkier new input caps) and jamming everything back just to make sure it still works, some are probably too close to where they shouldn't be. I've asked for "best practice" ideas in the SI 5066 Parts List & Modifications thread before spotting your post & the responses, hum is curable.

Mind you, there are warnings about what we're doing...

[Pano]

Originally posted by cpemma

Mind you, there are warnings about what we're doing...

Good link! I can certainly tell you that big caps will pick up noise, just put your finger on one while the amp is running. Buzzzzzz.

Thus you should be careful to used shielded cable wherever possible and keep the caps shielded, if only by the metal chassis. Usually works.