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Old 22nd July 2003, 12:46 PM   #21
UrSv is offline UrSv  Sweden
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Quote:
Originally posted by Joe Rasmussen


I'd like to know that too... sound degradation. Ideally the 18K should be by-passed, does the fact it isn't create a sonic degradation?

The 18K, if I may answer this, is close in value to 220K in parallel with the 22K. This keeps the DC Off-set on the output low. The bipolar inputs draws current and if you don't balance the circuit it shows up on the output and puts DC into your speakers.

Joe R.
Thanks Joe, I was afraid the answer was already posted somewhere in the thread and I simply had missed it. I knew about the 18 K value being the value of 220 K in parallell with 22 K so my comment should rather have read:

Does the 18 K resistor also degrade the sound quality and if so how do I remedy that?
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Old 22nd July 2003, 12:53 PM   #22
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Quote:
Originally posted by UrSv


Thanks Joe, I was afraid the answer was already posted somewhere in the thread and I simply had missed it. I knew about the 18 K value being the value of 220 K in parallell with 22 K so my comment should rather have read:

Does the 18 K resistor also degrade the sound quality and if so how do I remedy that?
By-passing it with a cap? It would need to be a large value, say 10uF, and not electrolytic, stating the bleeding obvious. But Thorsten reckons increasing 220K to 300K remedies it. Like to know what the thinking is behind that? Or have I missed something already posted?

Joe R.
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Old 22nd July 2003, 12:58 PM   #23
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Joe, actually I think KYW states that increasing the feedback resistor remedies the sound degradation of the 22 K from the negative input. I would also like to know why exactly that is but also as in my previous reply to you the question is how, and if, the 18 K from the POSITIVE input degrades the sound and how to remedy that.
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Old 22nd July 2003, 02:20 PM   #24
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Quote:
Originally posted by UrSv
... and if, the 18 K from the POSITIVE input degrades the sound and how to remedy that.
How about shorting it?
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Old 22nd July 2003, 02:50 PM   #25
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Oh, it is short enough for my liking. About 10 mm..
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Old 22nd July 2003, 03:20 PM   #26
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Konnichiwa,

Quote:
Originally posted by UrSv
Joe, actually I think KYW states that increasing the feedback resistor remedies the sound degradation of the 22 K from the negative input.
Nope, if the feedback resistor is increased to 330k the (noise)gain is always > 10, so 22k and 18k can be removed, Pot is 100k linear. Maximum gain is slightly > 30db.

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Old 22nd July 2003, 03:22 PM   #27
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Quote:
Originally posted by Kuei Yang Wang
Konnichiwa,



Nope, if the feedback resistor is increased to 330k the (noise)gain is always > 10, so 22k and 18k can be removed, Pot is 100k linear. Maximum gain is slightly > 30db.

Sayonara
OK, clear.
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Old 22nd July 2003, 03:30 PM   #28
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I did some listening comparisons, and the sound is different with 250K and 300K (what I used). You might try it yourself and decide which you prefer. I'm also using log pot and the control range is very good, both with average efficiency speakers and horns (100db efficient). So you might also consider using that type of pot instead of linear.
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Old 22nd July 2003, 03:40 PM   #29
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Quote:
Originally posted by Peter Daniel

How about shorting it?
Simple answer, but with the manufacturing drift these chips have you may have from as little as 7~8mv DC Offset to around 50mv.
And I love my speakers.


Quote:
Originally posted by Kuei Yang Wang
Konnichiwa,
Nope, if the feedback resistor is increased to 330k the (noise)gain is always > 10, so 22k and 18k can be removed, Pot is 100k linear. Maximum gain is slightly > 30db.
Sayonara
I did a board with LM1875s and 330k as feedback resistors.
I used the 22k resistor as always, but for initial tests I ommited the 18k (direct wire).
I had almost 40mv DC.
So, I removed the direct wire and put 50k multi-turn pots.
Final resistance of the pots at 0.0mv: 18.9k.
But the 22k resistor remained in place, it's not as you're saying, Kuei.
Maby removing the 22k resistor...
Ahhh... nevermind, the board is finished and looks loovely with the 50k multi-turn pots.
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Old 22nd July 2003, 03:50 PM   #30
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Quote:
Originally posted by carlosfm


Simple answer, but with the manufacturing drift these chips have you may have from as little as 7~8mv DC Offset to around 50mv.
And I love my speakers.


I believe I love my speakers even more, but even 100mV won't make any damage to them.
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