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Old 27th April 2004, 07:31 AM   #11
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Default Not in the datasheet

The feedback network is not in the datasheet.

Your circuit has a gain of 1 at DC and a gain of 20 or so beyond the pole frequency and I really haven't taken the trouble to figure out what it really does.

Since people have found the feedback loop of the gainclone is THE MOST IMPORTANT element required to accomplish great sound, you should first try what has been found to work well and then experiment afterwards. What works well is a good, precision resistor of 20k (for your design) soldered extremely closely between pins 3 and 8. No capacitors on pin 8 at all unless you have really bad DC offset and then you should seek advice first.

Read the huge history here or just follow what BrianGT has done. Copy as much of his schematic as you can.

-Robert
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Old 27th April 2004, 09:56 AM   #12
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I'll have to comment that the 3875 gives great bass...just make sure your source is not clipping...did you use a PC?? I had one that would produce a clipped signal if the eq is set too high for the bass frequencies...
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Old 27th April 2004, 06:42 PM   #13
GregGC is offline GregGC  Canada
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Make R32 1meg and R6 100K. See how it's going to sound then.

/Greg
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Old 27th April 2004, 07:10 PM   #14
lucpes is online now lucpes  Europe
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What are you using for the 0.1uF caps? Change to mylar.
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Old 27th April 2004, 07:22 PM   #15
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I'd like to know how your power supply looks. In your schematic you have 100F caps as rail decoupling. Is that all you have? If so, there's a fair chance that's the source of you problem. 100F into 8 ohms is ~200Hz.

Rune
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Old 27th April 2004, 08:40 PM   #16
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Default 10kuF

The first post indicates he has 10,000uF at the output of the PS. Shouldn't be his problem.

-Robert
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Old 28th April 2004, 01:19 AM   #17
cwteoh is offline cwteoh  Malaysia
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1) I am using 10,000uF caps for both rails but do not have the 100uF and 0.1uF caps at chip.
2) I started the circuit as shown in datasheet but later change to the circuit I posted here because of ringing problem. then I found that is the zobel network that solved the ringing problem and not the feedback loop. Anyway, both version of schematics did not give much bass at all.
3) Do I need to add in tone control to boost the bass? Or, this gc himself is capable to produce "ceiling-booming" bass?
4) I am using a tube preamp which use 5687 as driver tube. Will this caused problem on the bass?

Thanks.
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Old 28th April 2004, 08:30 AM   #18
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If there's a coupling capacitor on the output of your preamp, or if the output impedance is high, you may have a problem. The input impedance of your GC is 11 kOhm. That could be too low. Try multiplying the input resistors by 10.

Rune
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Old 28th April 2004, 11:50 AM   #19
mAJORD is offline mAJORD  Australia
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In response to your bass issue, IF youve setup the feedback/gain correctly so ITs freq range is say 20-20000 at -3db, than it should produce the correct level of bass from thos freqs. ... anything but would afaiak be classed as distortion, should replicate the input signal !


-ed i dont think i made my point quite clear there... I was trying to say you should not need any tone controls to achive correct bass, only to ytailor any fetish you have with 'extra' bass
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Old 30th April 2004, 02:58 AM   #20
cwteoh is offline cwteoh  Malaysia
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Thanks for the info. Allow me to have some times to modify the input impedance and feedback configuration.
Will post the result regarding my finding later. thanks.
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