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Old 2nd January 2012, 09:35 PM   #171
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Uh... shouldn't a 'B' pot be log ('A' is lin)?

Anyway... if you look at the original circuit 1, you'll find that audio gain is set by R7 (4k7) and R5 (470). Q4's quiescent current passes through R7, hence changing that would immediately upset output DC offset. That's why people prefer increasing R5 instead. (Not sure of stability implications, but it seems to work.) These single-ended inputs are a bit tricky to work with.

This was a good design in its day. Well-behaved distortion, low output impedance. It's not exactly a low-noise or PSRR champ though. Without the ability to transition into Class AB, it's not the best for experiments in driving speakers either.
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Old 3rd January 2012, 01:34 AM   #172
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What do R8 (1k) and C5 (330pF) do?

Cheers,
Jeff
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Old 3rd January 2012, 10:57 AM   #173
hotiron is offline hotiron  Scotland
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R8 and C5 form a low pass filter which sets the bandwidth of the amp. Lowering the value of C5 will increase the bandwidth. My amp is still very stable without this filter in place. Try it if you want to hear more top end sparkle.
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Old 6th February 2012, 03:08 PM   #174
xslavic is offline xslavic  Moldova
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Default HEEEEElp

i burned the two 5r1 resistor one after another ,board looks ok
what component should i replace ,after replacing res -not working
sound at the begining than fading to 0
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Old 6th February 2012, 06:27 PM   #175
hotiron is offline hotiron  Scotland
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You need to check your transistors
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Old 6th February 2012, 09:11 PM   #176
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Also check for wrongly installed components and bad solder joints, and the power supply voltages of course. There isn't a whole lot of redundancy in a concept like this.

You have tried to check DC offset on the output, right?
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Old 10th February 2012, 10:43 AM   #177
xslavic is offline xslavic  Moldova
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Default i found it..

It was a 0 ohm resistor ,that broke somehow ,replaced and did all the tweaks
but with 470uF feedback caps (next to 1Uf ones )i get a small buzz (but otherwise much better, volume turned half way...
It almost dissapears with a resistor from one of the tip41 heatsink to ground ,is there another way to compensate ?
.... my 0.1 are in place
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Old 15th February 2012, 06:31 PM   #178
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Quote:
Originally Posted by MilesCampbell View Post
[*]Replace the Zener Diode with 3 x 1N4148 in series (6 off) - Note the polarity is opposite to that of the zener.
Can you please explain this more exactly? I should instead of the zener diode use three 4148 and put them in series?
Cause on the photo of the pcb I see only one diode...
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Old 15th February 2012, 08:51 PM   #179
xslavic is offline xslavic  Moldova
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Default hey sangeet

i found a explanation here Zener diodes : DIODES AND RECTIFIERS
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Old 17th February 2012, 01:33 PM   #180
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Quote:
Originally Posted by MilesCampbell View Post
Stage 2
With a small number of replacement components the design takes another step forward. Using picture 3 as our guide
Implement Stage 1
Change 2k2 for 3k3 resistors (2 off)
Remove the two 10k variable resistors and link as required
Replace 4k7 with 10k (2 off)
Replace 220k with 47k (2 off)
Replace the Zener Diode with 3 x 1N4148 in series (6 off) - Note the polarity is opposite to that of the zener.
Which 4k7 shall I exchange, there are quite a few...
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