T-amp mod without pot

[Pano]

Originally posted by Puffin
What difference would using 100k resistors make over the 47k I have used ? Does is lower the gain ?

It shouldn't lower gain, as long as your source is good.
What it can do is lower noise. You see, noise may have a high voltage, but it doesn't have much current, or power. If you try to drive a low impendence with noise, it just can't do it. It can, however, drive a high impedance input, because that input requires very little power.

That is why long lines are often low impedance as well as balanced. Your preamp or CD player can provide enough current to drive a load of 10K or less. The noise picked up on the inputs lines can't. A simple way to "Separate the Men from the Noise" so to speak.

[Puffin]

Pano, thanks for that. Initial impressions of the S.I as a power amp (47k resistors) is that it sounds more like the original unmodded S.I. (fairly bright) Maybe the resistors need time to run-in.

[Puffin]

Carried out another mod to my other S.I amp. Took teh 20k pot off and used some 1uf poly caps and 120k resistors as these were all I had knocking around. There does not seem to be any reduction in bass over 2.2uf or 4.7uf and it sounds really good.

[Pano]

All you really need to get down to 20Hz is about 1uF. I suggest 1.5uF as minimum for reasons of phase.

Of course those of us who have speakers that are phase accurate down to 20 Hz are rare! And how many have ears that are phase accurate that low?

For practical reasons I think anything between 1uF-3uF is just fine. Less than that and you start to roll off the bass, more than that and the turn on pop becomes large.

[v-bro]

thats for sure, I read in an article that if you use an electrolite as an input cap you should use a value that's 10 times as high as the value when using an mkc/t/p cap. So I tried and fried 2 little visaton speakers(luckaly my test speakers costing 2.50 euro) on the huge startup BOOM!

What bothers me more is that the amp(built as a power amp long time ago) suddenly made strange hissing an plopping sounds in one channel(just oscillating out of itself, no source connected). This happened while I was listening to it, the caps were working as long as I connected the speakers after switching it on. Could the(20 mfd) blackgates have fried something(the chip :-(....) else?

Made a stepped ladder attenuator as a preamp by the way, for onyone with "pot problems" this really sounds the way it should!
Used an "elna" 24 step 4-deck switch, lovely quality! And matched a series of metalfilm resistors. Maybe a bit expensive for "only" a t-amp, but I thought it would last forever anyway.....