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Old 15th February 2005, 02:34 PM   #11
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Ok, I'm a newb so I'm gonna ask a couple noob questions. What will the effects be of removing R1/R2 and why are they there? Also, I know L1/L2 is part of a low pass filter, but why are they there?
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Old 15th February 2005, 06:16 PM   #12
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Default Re: Voltage pull down

Quote:
Originally posted by Panelhead



The input of the 2024 is biased up to allow the output to be dc coupled with a single rail supply. Somewhere around 2.5 volts is applied to the input and this is why the c3/c4 is needed where it is at. The 10k shunt resistor is pulling down the 2.5 volt bias and this causes the dc on the output.
I need to dig back in mine, something must be pulling it down to zero to get 9 volts dc. I am back to using a stocker for now.
I have been hesitant to probe around with the chip powered up. All the problems with letting the smoke out of the 2024 chips proves to me that it is easy to kill one if not extra carefull.

George

George,

Why not pull R01/02 and C3/4. Then lay a 10k resistor across each channel of your volume control to ground, followed by your 4.7uF cap? If you're not using a volume control, you can always mount the resistor across your RCAs.
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Old 15th February 2005, 09:13 PM   #13
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motherone, your a genious! Ok, so this is what I'm gonna do.....

R1/R2 Remove and place external 10k resistors across RCA terminals
L1/L2 Remove and jumper
C3/C4 Remove, jumper, and place external elecltrolytics in line with input from RCA terminals.

Does this sound ok? Am I missing anything?

TIA
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Old 16th February 2005, 12:26 AM   #14
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Quote:
Originally posted by theAnonymous1
motherone, your a genious! Ok, so this is what I'm gonna do.....

R1/R2 Remove and place external 10k resistors across RCA terminals
L1/L2 Remove and jumper
C3/C4 Remove, jumper, and place external elecltrolytics in line with input from RCA terminals.

Does this sound ok? Am I missing anything?

TIA
A cleaner signal path is to just remove C3/C4. Then connect the coupling cap to the solder pad that is connected to the 20k resistor. Think is will try this myself. Should be the same and leave room for a better cap than the miniscule surface mounts.

George
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Old 16th February 2005, 01:49 AM   #15
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Quote:
Originally posted by theAnonymous1
motherone, your a genious! Ok, so this is what I'm gonna do.....

R1/R2 Remove and place external 10k resistors across RCA terminals
L1/L2 Remove and jumper
C3/C4 Remove, jumper, and place external elecltrolytics in line with input from RCA terminals.

Does this sound ok? Am I missing anything?

TIA
I don't know about the genius stuff, but hopefully the suggestion'll help.

I'm going to remove R01/R02 and C3/C4. My signal path will then be:

RCA Jack -> 10k noble pot -> 10k 1% dale between pot out and ground -> 4.7uF Solen poly cap -> input on board

L1/L2 along with C1/C2 are probably not neccessary. They seem to prevent RF from coming into the amp, if I'm not mistaken? This isn't specified in the datasheet. Maybe it was something added by SI in order to prevent RF from coming through the little crappy plastic box they put it in.

Quote:
Originally posted by Panelhead


A cleaner signal path is to just remove C3/C4. Then connect the coupling cap to the solder pad that is connected to the 20k resistor. Think is will try this myself. Should be the same and leave room for a better cap than the miniscule surface mounts.

George
Based on the posts above, isn't a DC bias injected by R01/R02?


I agree, but the solder pads are very very weak. I've already lifted 1 pad and 1 trace -- I would bring them to the input and jumper the unneccessary parts on the board. At least the input pads are fairly beefy considering the size of the board.
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Old 16th February 2005, 01:54 AM   #16
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Oh, almost forgot, what type of electrolytics are you using, Anonymous? Most folks are of the opinion that electrolytics are very bad in the signal path. You should take a look for at least some 2uF poly caps. These can be purchased even at radio shack (though they bend you over for it). These would probably sound alot better than electrolytics.
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Old 16th February 2005, 04:20 PM   #17
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Well, success at last. I removed or relocated all but C1/C2 and and the little amp is workin just fine. So does it sound better with these input mods? Who knows..... was that really the whole point of this experiment?

Quote:
Oh, almost forgot, what type of electrolytics are you using, Anonymous? Most folks are of the opinion that electrolytics are very bad in the signal path. You should take a look for at least some 2uF poly caps. These can be purchased even at radio shack (though they bend you over for it). These would probably sound alot better than electrolytics
The only reason I'm using electrolytics is because its all I had laying around. Guess I need to take a trip to ratshack and get some polys.

BTW, should I just go all the way and remove C1/C2 also? Is high frequencies on the input really that big of a problem with a good source?
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Old 16th February 2005, 04:50 PM   #18
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Quote:
Originally posted by theAnonymous1
Well, success at last. I removed or relocated all but C1/C2 and and the little amp is workin just fine. So does it sound better with these input mods? Who knows..... was that really the whole point of this experiment?



The only reason I'm using electrolytics is because its all I had laying around. Guess I need to take a trip to ratshack and get some polys.

BTW, should I just go all the way and remove C1/C2 also? Is high frequencies on the input really that big of a problem with a good source?
If you're putting the amp in a metal enclosure, I would guess that the impact of RF should be less. I'm not an expert at this, but like I said, my theory is that SI did this because of the plastic enclosure.

Do you have an unmodified amp to compare it to?
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Old 16th February 2005, 05:52 PM   #19
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Yes and no. I didn't mod any of the electronics on board, but its in a new enclosure with all new wiring soldered in. I guess I could do a side by side comparison, but unless there is a profound difference in the sound I'm afraid my lead ears won't be able to tell. A bit more low end is pretty much all I was hoping for.
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Old 16th February 2005, 06:32 PM   #20
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Quote:
Originally posted by theAnonymous1
Yes and no. I didn't mod any of the electronics on board, but its in a new enclosure with all new wiring soldered in. I guess I could do a side by side comparison, but unless there is a profound difference in the sound I'm afraid my lead ears won't be able to tell. A bit more low end is pretty much all I was hoping for.
Heh. I'm probably with you right there. I'm sort of modding these things just to mod 'em.. Take them to their "max", even if I can't necessarily hear the difference

I wonder how many folks I made cringe with that statement!
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