Hi,
i have done the "stealth" mod but want to skip the volume pot and use as a poweramp but i´m not shure how to do it. Is it as simple as connecting the input wires with the new caps together for the left/right channel?
Happy for answers!
Aron
i have done the "stealth" mod but want to skip the volume pot and use as a poweramp but i´m not shure how to do it. Is it as simple as connecting the input wires with the new caps together for the left/right channel?
Happy for answers!
Aron
It's just occurred to me that your diagram relates to the "Stealth" mod. I have carried out the "Classic" mod. I assume that I would still need to add the 47k or 100k resistors in addition to resistors already attached to the other end of the capacitors ?
No more hum and pot!
I soldered in the 47k resistors and suddently my poor little amp was back in track again, so quiet(only a faint buzz, not audible at listening spot) even on my horns with 100db spl. I have no enclosure on this amp yet and i plan to make my speakers active and mount it inside.
The other amp with Alps pot in a wooden enclosure was suffering from very audible hum(even audible in my kitchen).
Audio1st adviced me to try grounding the pot, cover walls with foil and ground this to the negative power connection and this helped a lot - quiet as a mouse!
Puffin: you should try the resistors even if you have done the "Classic" mod.
Thanks!
Aron
I soldered in the 47k resistors and suddently my poor little amp was back in track again, so quiet(only a faint buzz, not audible at listening spot) even on my horns with 100db spl. I have no enclosure on this amp yet and i plan to make my speakers active and mount it inside.
The other amp with Alps pot in a wooden enclosure was suffering from very audible hum(even audible in my kitchen).
Audio1st adviced me to try grounding the pot, cover walls with foil and ground this to the negative power connection and this helped a lot - quiet as a mouse!
Puffin: you should try the resistors even if you have done the "Classic" mod.
Thanks!
Aron
Puffin said:
That is correct. The resistors in the diagram posted by Audio 1st serve to set the input impedance. The volume pot does the same thing, as well as acting as a voltage divider. Without the resistors you run the risk of noise on the inputs. Lower input impedances generally have lower noise.
Tuberider. I did it last night as my very small brain realised after I had asked the question, that the resisitors simply take the place of the pot. It was late last night when I got around to doing it, so I will have a listen tonight and see what it is like. I was using a 20k Alps Blue Velvet before.
Panomaniac. What difference would using 100k resistors make over the 47k I have used ? Does is lower the gain ?
Panomaniac. What difference would using 100k resistors make over the 47k I have used ? Does is lower the gain ?
Well, i know what you are talking about. 98% of my diy time and forum time is done in the late hours after work, spending time/fighting with my 3 year old and new born daughters, renovating my house+ trying not to **** off my suspicious wife🙂 i really should get more sleep. "The lights are on but nobody´s home" , a permanent modus that give birth to a lot of stupid questions
Aron
Aron
Puffin said:
Puffin said:
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. 😉
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.
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.
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.
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.
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.....
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.....
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