3-channel gainclone complete, but problems... - diyAudio
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Old 9th September 2003, 05:33 AM   #1
cowanrg is offline cowanrg  United States
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Default 3-channel gainclone complete, but problems...

hey, why else would i post, except for help with a problem!

first off, it works well. it looks good, only 24mv across speakers posts, no hum, and it doesnt clip, no matter how high it goes. BUT, its much softer than my other amps... when i bi-amp my speakers with this amp, and another amp, the tweeter is MUCH louder than the bass/midrange (tweeter being driven by yamaha receiver). when i drive just a single pair of speakers with it (non-bi-amped), i have to turn it up like 10dB or so more just to get same volume out of it. its just softer.

secondly (this is the wierd one), i had a cap bank made for it just to get a little extra punch. i tossed it in (10,000uf or so x 2 per channel), and the sound was awful. but specifically, there was NO bass at all. it was the flattest i had ever heard speakers. it was worse than most boomboxes. everything that was there was ok, but it was missing so much. i took them out and it sounded ok again. its hard to tell because i have to crank it up so high before it gets sounding good.

any ideas? i used peter's schematic, with a 50K ohm resistor across the rca input.
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Old 9th September 2003, 03:53 PM   #2
cowanrg is offline cowanrg  United States
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anyone?
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Old 9th September 2003, 04:57 PM   #3
wchick is offline wchick  United States
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Did you put 18K ohm and 22K ohm resistor from pin 7 and 8, respectively, to signal ground as suggested by master Kuei? My IGC has stability problem without them and and the sound is weird, very unpleasant (especially high frequency range, it hurts my head). At that point, I have 20mV DC offset at both channel (I thought good enough), no hum and very quiet. After I put those resistors in, music sound right now and DC offset drop to 5 mV and the amp is less hot. Oh, I also put a .22 ohm resistor at the output.

Want to take this chance to thanks Kuei Yang Wang (Thorsten) for his valuable suggestion.



Wallace
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Old 9th September 2003, 05:39 PM   #4
cowanrg is offline cowanrg  United States
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ill give it a shot. i there is really no problem with the sound, as much as there is a problem with the volume. its just not loud enough. would changing the 50K input resistor do anything?
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Old 9th September 2003, 05:54 PM   #5
JoeBob is offline JoeBob  Canada
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Up the gain of your circuit, or attenuate the amp powering your tweeter.

What source are you using, normally "gainclone" circuits are built with highish gain...

When you say 50k input resistor, is that a resistor running from input to ground? Or is it running from your signal to the - input?

If it's running frmo input the ground, you don't need it and you can try it without it. If it's from your RCA jack to - input, then it is decreasing gain (which could explain your problem) and you should lower it, 10k is normally a standard value that works well.
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Old 9th September 2003, 06:07 PM   #6
cowanrg is offline cowanrg  United States
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i used peter daniel's schematic, and i think i may have found my problem. i have the 50K resistor going from rca input to the cap, not to ground.

this still doesnt explain why adding the caps made it sound so horrible... anyone have any ideas on that?
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Old 9th September 2003, 07:29 PM   #7
cowanrg is offline cowanrg  United States
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well, i went and fixed the input resistor problem. the volume is right now. HOWEVER, when i play it loud (-30dB on my pre-amp), it starts to just break up. its not clipping because ive been measuring the temp, and its not getting that hot at all. its got a HUGE heatsink on it too.

the treble is ok, but the bass just sounds like its crapping out :-( is this oscilating?
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Old 9th September 2003, 10:59 PM   #8
tiroth is offline tiroth  United States
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It will clip when it runs out of voltage too, you know. That is the most common way to clip an amp.
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Old 10th September 2003, 02:19 AM   #9
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Quote:
Originally posted by cowanrg
well, i went and fixed the input resistor problem. the volume is right now. HOWEVER, when i play it loud (-30dB on my pre-amp), it starts to just break up. its not clipping because ive been measuring the temp, and its not getting that hot at all. its got a HUGE heatsink on it too.

the treble is ok, but the bass just sounds like its crapping out :-( is this oscilating?
You can not say it's clipping by measuring temperature, but through an oscilloscope. Bass is the most likely candidate for clipping usually.

It might be interesting to add a clip indicator level to your amp, adjusted by looking on the screen at which voltage the output clips.

You may also be getting input saturation, but that should appear on the treble too.

If you already know all this please excuse this explanation.


Carlos
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Old 10th September 2003, 03:56 AM   #10
cowanrg is offline cowanrg  United States
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carlmart,

actually, i did not know all that, so it was very welcome information.

i only say its not temperature because my first gainclone would clip only when i got hot (it started melting the plastic clamps that held it to the heatsinks temorarily... after cooled, it was fine again)

tiroth,

you say it will clip when it runs out of voltage? how do you mean... its a triple mono, each has its own 120VA power supply, rectifiers, etc... it should have enough juice for each amp, and my speakers are 92dB sensitive...

to all:

so, how do i fix this? will adding resistors to pins 7 and 8 solve the problem, or will i have to get more drastic? i have done more listening to it, and every minute i think it sounds worse. its the most digital ive heard a cd sound, and everything almost sounds like and MP3. its close to being scrapped as far as a project goes
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