Don’t feed the chip’s input directly, use the resistor of a few tens, maybe 100 kOhm. Don’t forget that the diodes will be low impedance points.Sheldon said:
Its cut frequency can not be too low, but HF properties of bigger caps can be too bad…
Thus you don’t know it does that.sek said:
Thump is solely buffer related problem. Talking about solid state buffers, at least discrete buffers I tried in GC, the problems finish in about or in less than a half of the second.sek said:
Pedja
Pedja said:
Thanks Pedja, I think I might give it a try. I can use a bit larger cap and bypass it with a smaller one (sounds like I know what I'm talking about here, but don't be fooled - I'm just guessing).
As for the buffer thump, I found something that may be interesting. As you might remember, I rigged the selector switch so that one position shorts the buffer output to ground. In this position, when I turn on the amp I get the very slightest click on output. No noise at all when I then switch the buffer to the "normal" position. This with a ss cd player. However, when I use my tube based pre for the source, I get a fairly loud pop if I switch between "short" and "normal" for the 30 seconds or so when the pre is warming up or shutting down. No pop when the pre is fully on or off.
Sheldon
Thanks Nuuk,
Normally I am careful about that. I discovered this one accidentally. Lulled into complacency by the fact that the pre-amp is very well behaved. Even if I turn it on or off with the usual power amps on (not recommended, I know), I get no noise at all. We are sometimes a bit spoiled by all the fail-safe features added to most commercial gear. Many here believe that some of those features have a sound quality cost, and should be left out. May be true, but then we have to remember to be a bit more careful.
Sheldon
Normally I am careful about that. I discovered this one accidentally. Lulled into complacency by the fact that the pre-amp is very well behaved. Even if I turn it on or off with the usual power amps on (not recommended, I know), I get no noise at all. We are sometimes a bit spoiled by all the fail-safe features added to most commercial gear. Many here believe that some of those features have a sound quality cost, and should be left out. May be true, but then we have to remember to be a bit more careful.
Sheldon
Re: Dc Offset
After getting some good suggestions from Malichi and Pedja, I gave it a try. The +25v feed went to a pair of 11k resistors in series, followed by a diode to ground and to one side of a 500ohm multiturn pot. Between the 11k resistors, I connected a 3uf electrolytic and a 0.1uf film capacitor, in parallel, to ground. The other side of the pot was connected to a duplicate circuit for the -25v (with electrolytic and diode in reversed orientation, of course). The center lead of the pot went, via a 90k resistor, to the signal in for the chip amp board.
I was able get appropriate voltage output from the trimmer circuit (very low mv) , but it was not very stable when all hooked up. After taking some measurments with my digital multimeter, I'm guessing (Pedja?) the low impedence of the discreete regulator created a current path between sections of my divider circuit. Sooo--, since my original DC offset was negative in both channels, I completely disconnected the negative half of the divider and connected that side of the trim pot to ground instead. That way I could inject from zero to positive, to trim the neg. offset. Works fine (keeping in mind that this is all probably unnecessary overkill, as I couldn't hear any bad effects from even 100mv of DC offset from the amp). I can trim to within a millivolt or two at the amp output, and the total offset seems as stable as without the trim circuit. No loss of sound quality, as far as I can tell. No channel cross talk. In fact, this little amp sounds pretty darn good, and runs quite cool. If I push it hard, the regulator output transistor sinks get hot to the touch, but that's it. I might improve the sinking if I want to drive something other than my 90db efficient z-Horns, but with those, no problem. Actually, I've used it on some bigger 87db three way speakers (Raven ribbon, 4" and 8" Seas Excell) and it sounds very nice. Drives them no problem too, but might need more sinking for the reg. transistors for heavy duty on those.
I checked out this DIY site to learn something about speakers. Ended up doing a complete amp with some discreete circuits, and even this little extra experiment. Thanks to Brian GT for the initial inspiration (made it easy with his board and component group buy), PD for a chassis that would go on megabuck commercial gear, Pedja for circuits and explanations so clear, that a complete novice (me) was willing to take a shot, and all the others to give freely to the DIY community.
Sheldon
Sheldon said:
After getting some good suggestions from Malichi and Pedja, I gave it a try. The +25v feed went to a pair of 11k resistors in series, followed by a diode to ground and to one side of a 500ohm multiturn pot. Between the 11k resistors, I connected a 3uf electrolytic and a 0.1uf film capacitor, in parallel, to ground. The other side of the pot was connected to a duplicate circuit for the -25v (with electrolytic and diode in reversed orientation, of course). The center lead of the pot went, via a 90k resistor, to the signal in for the chip amp board.
I was able get appropriate voltage output from the trimmer circuit (very low mv) , but it was not very stable when all hooked up. After taking some measurments with my digital multimeter, I'm guessing (Pedja?) the low impedence of the discreete regulator created a current path between sections of my divider circuit. Sooo--, since my original DC offset was negative in both channels, I completely disconnected the negative half of the divider and connected that side of the trim pot to ground instead. That way I could inject from zero to positive, to trim the neg. offset. Works fine (keeping in mind that this is all probably unnecessary overkill, as I couldn't hear any bad effects from even 100mv of DC offset from the amp). I can trim to within a millivolt or two at the amp output, and the total offset seems as stable as without the trim circuit. No loss of sound quality, as far as I can tell. No channel cross talk. In fact, this little amp sounds pretty darn good, and runs quite cool. If I push it hard, the regulator output transistor sinks get hot to the touch, but that's it. I might improve the sinking if I want to drive something other than my 90db efficient z-Horns, but with those, no problem. Actually, I've used it on some bigger 87db three way speakers (Raven ribbon, 4" and 8" Seas Excell) and it sounds very nice. Drives them no problem too, but might need more sinking for the reg. transistors for heavy duty on those.
I checked out this DIY site to learn something about speakers. Ended up doing a complete amp with some discreete circuits, and even this little extra experiment. Thanks to Brian GT for the initial inspiration (made it easy with his board and component group buy), PD for a chassis that would go on megabuck commercial gear, Pedja for circuits and explanations so clear, that a complete novice (me) was willing to take a shot, and all the others to give freely to the DIY community.
Sheldon
Amazing
Sheldon:
Congratulations on your efforts! Is this project now in a state where you can share your end result with others? I am in the process of constructing four of BrianGT's GainClones and would be very interested in joining in on a group buy to add active buffer input circuits to the passive preamp portions of my project.
Regards,
Scott
Sheldon:
Congratulations on your efforts! Is this project now in a state where you can share your end result with others? I am in the process of constructing four of BrianGT's GainClones and would be very interested in joining in on a group buy to add active buffer input circuits to the passive preamp portions of my project.
Regards,
Scott
heh. I wasn't suggesting anyone was being impatient. 
Except my wife, who is using up most of my free time having me paint and install hardwood (bamboo actually) floor.
The good news is, it looks like a matching set of these boards will all sidle up to each-other on a single PCB quite nicely. That's power, both amp boards, both buffers.
C
Except my wife, who is using up most of my free time having me paint and install hardwood (bamboo actually) floor. The good news is, it looks like a matching set of these boards will all sidle up to each-other on a single PCB quite nicely. That's power, both amp boards, both buffers.
C
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.