sanyofreak
03-23-2006, 03:05 PM
A good friend has a part time recording studio and asked if I could solve a problem for him. He needed to be able to run four sets of cans from one headphone out on his console, and wanted volume adjusts for each individual channel. I found this site
http://www.geocities.com/rjm003.geo/rjmaudio/diy_hclo.html
and the author also credits Chu Moy, info that many of You already may be familiar with. These op-amp designs looked like they would be just the ticket I needed, and of course in the true DIY spirit I hacked these basic circuits and made them mine - changed gain, some cap values, etc....No crossfeed circuits, user did'nt want that feature.
I cut my own PCB for the volume pots,and used PC mount panasonic dual types, The pots are nutted down to a metal sub-front, and the PCB is bolted to a mount and to the chassis. This cleaned up the "flywires" I'dve had to run, and gives the unit a very solid feel. The out jacks are mounted to the sub-panel above each volume pot, which leaves just the jack hole through the front panel, with no visible nut, (hey, just like a vintage receiver!!) Input jack on the back. (pretty good hand filing to line up them holes, freak) Oh to only have a CNC mill in the basement !!
The audio breadboard just laid out beautifully with dual op-amps, real clean and symmetrical, and tight as could be on the solder side. The blue caps are really expensive, (coupling and bypass) and the power supply seems about four thousand times overkill. The toroid is a 30VA and the electrolytic filters are Panasonic "FM" types, the lowest ESR, lowest inductance types they offer. (Guess I bought their spiel on them)There's five 2200uf's paralleled per polarity, and the DC runs at an op-amp freindly +/- 11V. With bleeders and a power on LED, music continues to play about 20 seconds after power is removed ! (driving one pair of cans)
The sound ??? All I can say is "OHMYGOSH", I highly recommend this circuit. I cant think of any sonic flaws, I have'nt enjoyed cans for a long time, but I sure could again, using this thing.
I paid no attention to grounding other than the center tap connects to ground at just one point, but the chassis and volume controls have all sorts of ground points -- NO matter, this is absolutely dead nuts SILENT. It is the quietest audio device I've ever DIY'ed. My guess is the real key is that it only has a voltage gain of five. The circuit instantly reveals sonic differences between cans (they are often huge), especially with the single in, you can just connect four pair and cycle through them all live. We mainly tested with Sony 7502 and 7506, niether of which have bass response solid enough for me, but the 06's are some really good phones, and they sound unbelievable behind this thing just hooked up to a walkman.
The case has been in my possesion for over twenty years, I think Dad and I picked it up from electronic surplus in Cleveland, or possibly Lafeyette or Olson's - a real wood vinyl veneered thing, in the pic its still in its cardboard protector. You'll not find anything like it now unless You fab it yourself, but I'd love to do another in a 1U rack enclosure.
Cost about 50 bucks, and I stuck with the OPA2134's, but there are some better BB units You could use that are a few bucks more per. These were about 2 dollars/IC. There are other real worthy designs, and this one wont quite get You to 120dB land before it clips, but it'll get really loud and stays perfectly clean right up until clip.
In the un-nude pic of the front, its sitting on a 1U unit that performs a similar function (a commercial device) - the user tells me my unit is noise-free and uncolored, while the commercial unit he complains is noisy and bright sounding. This of course, pleases me, and is about the ultimate DIY compliment.
I am glad to share it here, and do a little contributing instead of snipping all the time. I hope You all enjoyed - TRY ONE !!
http://www.geocities.com/rjm003.geo/rjmaudio/diy_hclo.html
and the author also credits Chu Moy, info that many of You already may be familiar with. These op-amp designs looked like they would be just the ticket I needed, and of course in the true DIY spirit I hacked these basic circuits and made them mine - changed gain, some cap values, etc....No crossfeed circuits, user did'nt want that feature.
I cut my own PCB for the volume pots,and used PC mount panasonic dual types, The pots are nutted down to a metal sub-front, and the PCB is bolted to a mount and to the chassis. This cleaned up the "flywires" I'dve had to run, and gives the unit a very solid feel. The out jacks are mounted to the sub-panel above each volume pot, which leaves just the jack hole through the front panel, with no visible nut, (hey, just like a vintage receiver!!) Input jack on the back. (pretty good hand filing to line up them holes, freak) Oh to only have a CNC mill in the basement !!
The audio breadboard just laid out beautifully with dual op-amps, real clean and symmetrical, and tight as could be on the solder side. The blue caps are really expensive, (coupling and bypass) and the power supply seems about four thousand times overkill. The toroid is a 30VA and the electrolytic filters are Panasonic "FM" types, the lowest ESR, lowest inductance types they offer. (Guess I bought their spiel on them)There's five 2200uf's paralleled per polarity, and the DC runs at an op-amp freindly +/- 11V. With bleeders and a power on LED, music continues to play about 20 seconds after power is removed ! (driving one pair of cans)
The sound ??? All I can say is "OHMYGOSH", I highly recommend this circuit. I cant think of any sonic flaws, I have'nt enjoyed cans for a long time, but I sure could again, using this thing.
I paid no attention to grounding other than the center tap connects to ground at just one point, but the chassis and volume controls have all sorts of ground points -- NO matter, this is absolutely dead nuts SILENT. It is the quietest audio device I've ever DIY'ed. My guess is the real key is that it only has a voltage gain of five. The circuit instantly reveals sonic differences between cans (they are often huge), especially with the single in, you can just connect four pair and cycle through them all live. We mainly tested with Sony 7502 and 7506, niether of which have bass response solid enough for me, but the 06's are some really good phones, and they sound unbelievable behind this thing just hooked up to a walkman.
The case has been in my possesion for over twenty years, I think Dad and I picked it up from electronic surplus in Cleveland, or possibly Lafeyette or Olson's - a real wood vinyl veneered thing, in the pic its still in its cardboard protector. You'll not find anything like it now unless You fab it yourself, but I'd love to do another in a 1U rack enclosure.
Cost about 50 bucks, and I stuck with the OPA2134's, but there are some better BB units You could use that are a few bucks more per. These were about 2 dollars/IC. There are other real worthy designs, and this one wont quite get You to 120dB land before it clips, but it'll get really loud and stays perfectly clean right up until clip.
In the un-nude pic of the front, its sitting on a 1U unit that performs a similar function (a commercial device) - the user tells me my unit is noise-free and uncolored, while the commercial unit he complains is noisy and bright sounding. This of course, pleases me, and is about the ultimate DIY compliment.
I am glad to share it here, and do a little contributing instead of snipping all the time. I hope You all enjoyed - TRY ONE !!