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Old 16th March 2006, 07:32 AM   #1
Puffin is offline Puffin  United Kingdom
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There was a question posed by jwb009 in September 2005 regarding the "stealth" mod. He asked if the stealth mod could still be undertaken if R1 and R2 had been removed. I cannot see that there was an answer. I would be intersted in that I have carried out Version 1 (the classic) mod, but wonder if I am capable of doing the "stealth" mod. I have an old board with smd's on it and it tried to bridge them and they just came off the board. If R1 and R2 have been removed can you still connect up polypropylene caps (2.2uf) in the same way as shown in the picture posted on Michael Mardis's website which I think came from audio1st ?
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Old 16th March 2006, 09:48 AM   #2
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Hello Puffin,
Unless you can replace R1 & R2 again, you cannot do the "stealth" mod. I don't think IMHO the stealth mod sounds any better than the original mod, it was just meant to be easier to carry out.
If someone knew the value of L1 & L2, you could create the same filter before the 2.2uf blocking caps.
That would be: vol pot, 100pf to ground, L1 or L2 then 2.2uf cap, followed by the 20k resistor.
Hope this makes some sense?
Barry..
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Old 16th March 2006, 12:39 PM   #3
Puffin is offline Puffin  United Kingdom
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Audio1st. Thanks for your reply. I think the classic mod sounds great in any event. I did sacrifice one board when I tried to replace the inductors and the 330uf 25v power line cap.. For some reason all I got was sound coming from the inductors ! any suggestions ?
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Old 17th March 2006, 12:15 PM   #4
Puffin is offline Puffin  United Kingdom
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Does anybody have any ideas re: my previous post ?
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Old 17th March 2006, 04:21 PM   #5
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Quote:
Originally posted by Puffin
I did sacrifice one board when I tried to replace the inductors and the 330uf 25v power line cap.. For some reason all I got was sound coming from the inductors ! any suggestions ?
A little more information about the inductors you used and the noise they made please?
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Old 18th March 2006, 08:13 AM   #6
Puffin is offline Puffin  United Kingdom
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The inductors are from Autocostruire and were recommended as replacements by an article in Hi Fi World magazine. The article is the one on Michael Mardis's website (panomaniac). I used a white noise signal to test the board and as I increased the volume on the pot, the noise came from the inductors. No sound was coming out of the speakers.
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Old 18th March 2006, 04:12 PM   #7
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The only thing that you could have done wrong, is not clean enough lacquer off the legs of the inductors, causing a bad contact. If you didn't change anything else that is all it could be. Changing the 330uf power cap, should cause no problem either.
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Old 19th March 2006, 05:35 PM   #8
Puffin is offline Puffin  United Kingdom
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Thanks for that. After some more tinkering I have got it working and it sounds fantastic. The article in Hi FI World is right when it says that the air-core inductors clean up the treble. They also give it much more air and space. I have found some Kimber Caps 0.1uf caps I used in a crossover to bypass with. I have previously not bothered with using the small caps (across the speaker terminals) that come with the stock S.I. I have fitted these to the current modded amp. I cannot find any information on the forum about using any caps across the terminals. is it worth it ? It doesn't seem to affect sound quality.
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Old 20th March 2006, 08:20 AM   #9
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Good to hear you are up and running.
Quote:
Originally posted by Puffin
I have previously not bothered with using the small caps (across the speaker terminals) that come with the stock S.I. I have fitted these to the current modded amp. I cannot find any information on the forum about using any caps across the terminals. is it worth it ? It doesn't seem to affect sound quality.
I don't use any caps across the speaker terminals. None of the other makes of amps seem to use them either.
The sonic T amp already has 0.1uf smd caps across the speaker outputs on the cct board (c19 & c20).
It is all down to what sounds better, or do the extra caps make it sound worse?
PS, I have just ordered the Autocostruire 2020 amp with the air core inductors and hope I will be able to build it? The sonic T amps are costing about 30 in the UK, add on the inductors and a new pot( 35) and you are getting close to the price of the 2020 amp, about 70. So here goes
Barry..
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Old 20th March 2006, 08:58 AM   #10
Puffin is offline Puffin  United Kingdom
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Having done a couple of Sonic Impact's I would be interested to hear how you get on. The costs do start to rise quite rapidly when you add up the cost of a new box, pot, (I had 3 Alps 20k spare that I picked up at an audiojumble for 1.00each!)connectors and poly caps etc. I reckon each modded S.I has cost me about 55 (without the cost of an Alps pot)

Incidentally I am using 20k pots (because I am tight) which seem to be fine. What's the difference between 20k, 50k, 100k pots. Am i strangling the sound at all ?
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