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.
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.
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
Want to take this chance to thanks Kuei Yang Wang (Thorsten) for his valuable suggestion.
Wallace
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.
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.
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?
the treble is ok, but the bass just sounds like its crapping out :-( is this oscilating?
cowanrg said:
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
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
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
Clipping is when the amp "tries" to output a wave with a value larger than it's maximum (or minimum) voltage. For example if you've got +/- 30V DC suplies and you're amplfying a 5V pk-pk signal 20 times, you've got a 100V pk-pk signal, so it would swing to 30V (well, close, depends on what amp), then sit there until the wave went down under 30V (again, exact value all depends), continue normally until it hit -30V and stay there until it went back up. Then repeat over and over again. What you would see is a waveform with the tops and bottoms chopped off (well, in a gainclone you would). Resulting in DC across your load for short, or not so short bursts.
So in essence, it is when you run out of voltage, not "juice". You could have a huge transformer capable of outputting lots of current, but you can't swing more than the suply rails. Hope that helps.
So in essence, it is when you run out of voltage, not "juice". You could have a huge transformer capable of outputting lots of current, but you can't swing more than the suply rails. Hope that helps.
ok, im going to finally try and get this thing running right...
i think the voltage could be a problem. i misunderstood my xformers. they are only 12-0-12. so my rails are only 12v. this could be the problem. i cant seem to find transformers that are suitable for cheap, so im thinking of just getting 3 more of the ones im using and using them in paralell? this would give me plenty of current and voltage right? if they are the exact same, would this work?
i think the voltage could be a problem. i misunderstood my xformers. they are only 12-0-12. so my rails are only 12v. this could be the problem. i cant seem to find transformers that are suitable for cheap, so im thinking of just getting 3 more of the ones im using and using them in paralell? this would give me plenty of current and voltage right? if they are the exact same, would this work?
No guarantees, but look at PE's #120-225, 129-030 or any of the Avels, such as 122-615. The Avel's I have are really nice and I purchased one of the 129-030's, which came in kind of beat-up, but it works. Have not measured the current, though.
Maybe one of those could help with your voltage issues cheaper than running multiple transformers in series.
Good luck.
Sandy.
Maybe one of those could help with your voltage issues cheaper than running multiple transformers in series.
Good luck.
Sandy.
Check Ebay. A pretty low-cost place to buy power supplies. Just got the following lot this morning:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2562201440&category=32720&rd=1
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2562201440&category=32720&rd=1
well, i got some new transformers in the baby and it works.
im still not thrilled with the sound. of course, now that its working correctly, ive only tested it on maggies, which leaves something to be desired. i will test it on something a little more forgiving when i go back to work. (maybe sonus fabre auditors?)
it runs well though, but for some reason, its still having a clipping/cutting out problem. its only at pretty high volumes after about 30 minutes of playing. if i back it off a few dB, it goes away. i dont think its overheating, because its got a HUGE heatsink, and its clamped to the heatsink with thermal paste... but whatever, it could just be the maggies torturing it.
this will become a bedroom amp, it works alright for that. i did throw a 1khz test tone into it at full volume and tested its max power output. i calculated 59.8 watts. (dont know distortion, only have a multimeter). i guess thats about right into an 8 ohm load.
it runs ok, but im stepping off the gainclone bandwagon though hopefully ill have some pictures of it up soon. my digital camera sucks big time and isnt even worth using.
im still not thrilled with the sound. of course, now that its working correctly, ive only tested it on maggies, which leaves something to be desired. i will test it on something a little more forgiving when i go back to work. (maybe sonus fabre auditors?)
it runs well though, but for some reason, its still having a clipping/cutting out problem. its only at pretty high volumes after about 30 minutes of playing. if i back it off a few dB, it goes away. i dont think its overheating, because its got a HUGE heatsink, and its clamped to the heatsink with thermal paste... but whatever, it could just be the maggies torturing it.
this will become a bedroom amp, it works alright for that. i did throw a 1khz test tone into it at full volume and tested its max power output. i calculated 59.8 watts. (dont know distortion, only have a multimeter). i guess thats about right into an 8 ohm load.
it runs ok, but im stepping off the gainclone bandwagon though
hopefully ill have some pictures of it up soon. my digital camera sucks big time and isnt even worth using.
right now im not using the caps. i took them off. they sound ok with or without them, they dont help.
im using many different types of speaker cable, audioquest, tara labs, and synergistic research. all excellent cables.
im running +- 24V before rectifiers, so i assume like +-30 or so after? its triple mono, each channel having its own 144VA transformer.
im using many different types of speaker cable, audioquest, tara labs, and synergistic research. all excellent cables.
im running +- 24V before rectifiers, so i assume like +-30 or so after? its triple mono, each channel having its own 144VA transformer.
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