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Old 24th January 2013, 07:37 AM   #3811
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Originally Posted by guitar89 View Post
Yesterday, I apply the input filter using 1 ohm & 1 uF, doesn't changes much for me. IF I TOUCH the input with my finger, it sound really badly, is that normal ? (filter doesn't help)
Is oscilloscope available to you?

Usually there are 50/60 Hz plus harmonics, some local devices interferences like nearby SMPS, LCD, lamps etc in the spectrum. But there shouldn't be clear and strong MHz components present in the output signal when touching live input pin.

Without scope you're blind, electrically speaking.
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Old 24th January 2013, 08:29 AM   #3812
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Quote:
Originally Posted by Lazy Cat View Post
Is oscilloscope available to you?

Usually there are 50/60 Hz plus harmonics, some local devices interferences like nearby SMPS, LCD, lamps etc in the spectrum. But there shouldn't be clear and strong MHz components present in the output signal when touching live input pin.

Without scope you're blind, electrically speaking.
I believe I'm blind now ^^ I'm a blindman touching/feeling an elephant
Will proceed to TSSA when i'm free, and will wait for bad thing happens now. (they are rather obedient now)
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Old 24th January 2013, 08:47 AM   #3813
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Originally Posted by keantoken View Post
I try to keep any cap on the input below 47pF, so the amp can be used with a volume pot. Otherwise you'll have an LP filter that changes with volume. I rather put LP filtering before the pot, where source impedance is much more predictable. My amps typically have a simple input buffer which makes them much more tolerant to a variety of source impedances. This solution is less expensive than creating an amp without an input buffer and then having to buffer the volume pot/attenuator.

Another option is to employ a fancy bootstrapped input LP filter to cancel input impedance, but this must be done carefully or you'll have an oscillator.
Completely omitting input cap is out of an option at CFB, since any HF interference pick-up with input/cable can make output stage to saturate in max HF current, even to oscillate. As you've said from min 20-30 pF directly from input bases to GND is a must.
Good input buffer is also a must to connect higher impedance sources like tube preamps etc. With VSSA I'll try to analyse amp's response and stability if vary input impedance from 10k to 100k.
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Old 24th January 2013, 08:59 AM   #3814
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Originally Posted by Lazy Cat View Post
Completely omitting input cap is out of an option at CFB, since any HF interference pick-up with input/cable can make output stage to saturate in max HF current, even to oscillate. As you've said from min 20-30 pF directly from input bases to GND is a must.
Good input buffer is also a must to connect higher impedance sources like tube preamps etc. With VSSA I'll try to analyse amp's response and stability if vary input impedance from 10k to 100k.
Hm... So it is not wise to direct connect source to input bases of input pair ? Recommendation ? (including volume pot)
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Old 24th January 2013, 09:04 AM   #3815
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I believe I'm blind now ^^ I'm a blindman touching/feeling an elephant
Will proceed to TSSA when i'm free, and will wait for bad thing happens now. (they are rather obedient now)
I apologize for any inconvenience, but scope is a must when DIY fast AC circuits.
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Old 24th January 2013, 10:08 AM   #3816
naf is offline naf  Indonesia
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or you can try to build Shaan's SSA version. it stable good sounding... i've build 2 stereo without any problem at alll.
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Old 24th January 2013, 10:22 AM   #3817
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or you can try to build Shaan's SSA version. it stable good sounding... i've build 2 stereo without any problem at alll.
Compared to some commercial amp? Did you like it? Which speakers?
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Old 24th January 2013, 12:56 PM   #3818
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Yesterday, I apply the input filter using 1 ohm & 1 uF,
???
Please, use 1K in serial and 50 or 100pf to the ground. Are your speaker's cables long ?
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Old 24th January 2013, 04:57 PM   #3819
shaan is offline shaan  India
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stable good sounding...
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Originally Posted by Lazy Cat View Post
Compared to some commercial amp?
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Old 24th January 2013, 05:03 PM   #3820
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Compared to some commercial amp? Did you like it? Which speakers?
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