Heh.
So I finally get back working on my project(s) and find you're playing with the "modular" approach I had out there ages ago. Glad someone else sees the sense in it! I'll be running some commercial monoblocks off the X-BOSOZ/JT probably by next weekend, but still want to get my own amp stages running.
I have a passing interest in the amp stage(s) you're outlining here as well as I'm continuing to have difficulty with mine (parts should be here Wednesday for more thorough troubleshooting) - or maybe just your "bridge" portion. Still think I would like to keep the X-BOSOZ up front, JT after that, with monoblocks at my speaker(s). I think the actual chip-amp package(s) I have work properly and it's the bridge I'm having trouble with, so I may be curious to try just that - possible?
Would have pinged you on your support site about this but never got e-mails from the forum software (either a failure to send or a failure at my e-mail host and overzealous spam filtering, the latter being my primary suspect - why it thinks I need a bigger ... and yet don't need my twisted support is beyond me.
)
C
So I finally get back working on my project(s) and find you're playing with the "modular" approach I had out there ages ago. Glad someone else sees the sense in it! I'll be running some commercial monoblocks off the X-BOSOZ/JT probably by next weekend, but still want to get my own amp stages running.
I have a passing interest in the amp stage(s) you're outlining here as well as I'm continuing to have difficulty with mine (parts should be here Wednesday for more thorough troubleshooting) - or maybe just your "bridge" portion. Still think I would like to keep the X-BOSOZ up front, JT after that, with monoblocks at my speaker(s). I think the actual chip-amp package(s) I have work properly and it's the bridge I'm having trouble with, so I may be curious to try just that - possible?
Would have pinged you on your support site about this but never got e-mails from the forum software (either a failure to send or a failure at my e-mail host and overzealous spam filtering, the latter being my primary suspect - why it thinks I need a bigger ... and yet don't need my twisted support is beyond me.
)C
Boards arrived yesterday
Found a small package from Brian in the mail. It held the boards to build a Twisted Driver, power supply, and Power modules.
Guess it is time to print out the BOM and start gathering parts. The modular approach is different. Plus all the nice featues of this.
Hope to see pics soon of these. Mine is waiting on me.
George
Found a small package from Brian in the mail. It held the boards to build a Twisted Driver, power supply, and Power modules.
Guess it is time to print out the BOM and start gathering parts. The modular approach is different. Plus all the nice featues of this.
Hope to see pics soon of these. Mine is waiting on me.
George
Here are my monoblocks. I made them symmetrical (get it? ). These are actually using the protoype boards, except for the PS. That's a 400VA 20v+20v Antek trafo. So, waiting on a fuse holder for one of them (the one pictured open). I also used two bridges instead of one, but just cause I have a bunch. the heatsink doesn't get even warm, so probably overkill.
). These are actually using the protoype boards, except for the PS. That's a 400VA 20v+20v Antek trafo. So, waiting on a fuse holder for one of them (the one pictured open). I also used two bridges instead of one, but just cause I have a bunch. the heatsink doesn't get even warm, so probably overkill.An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
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Russ:
I have some questions about TXO and TXD.
also waiting for BOM and Manual for TXO.
1. What is the IC for current balancing in 3886 schematic ?
I have a few 3886, 3875, 4780 amps from chipamp, I thought to add the circuit to them.
2. You state that the TXD could be set up with gain of less than one, if so would it not be feasible to do so and then run the 3886 at higher gain for increase stability? After all, it is the final overall gain that is important
3. I was considering to build Aleph p1.7 preamp but with TXD
but it seems to be redundant to do so if I build TXO-2. So a passive preamp with Vol control and input selector seems to be
all that is needed.
All the sources are single ended but having balanced at the 3886
seems very desireable.
I will be building Pearl phono as well with a seperate PS chassis
which will be inthe preamp chassis.
Sheldon
I have some questions about TXO and TXD.
also waiting for BOM and Manual for TXO.
1. What is the IC for current balancing in 3886 schematic ?
I have a few 3886, 3875, 4780 amps from chipamp, I thought to add the circuit to them.
2. You state that the TXD could be set up with gain of less than one, if so would it not be feasible to do so and then run the 3886 at higher gain for increase stability? After all, it is the final overall gain that is important
3. I was considering to build Aleph p1.7 preamp but with TXD
but it seems to be redundant to do so if I build TXO-2. So a passive preamp with Vol control and input selector seems to be
all that is needed.
All the sources are single ended but having balanced at the 3886
seems very desireable.
I will be building Pearl phono as well with a seperate PS chassis
which will be inthe preamp chassis.
Sheldon
SheldonD said:
Hi Sheldon,
Good questions, here are some quick answers.
1) LF411 is used for the servo.
2) Certainly something one could try, but my experience was that best stability was achieved when I increased the bandwidth of the power stage (the LM3886 or similar) but lowering its gain so that the power bandwidth of each opamp (THS4131 and the LM3886) was closer together. This resulted in nice low values for the compensation caps(C7 and C8). This is especially true for parts like the OPA549 which I have used with only 6db gain.
3) Passive attenuation into the TXO is indeed excellent. the input impedance is 100K so a 10K pot or equivalent attenuator is fine. Also the Joshua Tree suits it very well with it constant output impedance of 750R. This is my current favorite scheme Opus --> JT ---> TXO.
Brian and I are working on the documentation, and as always we will be happy to answer questions.
Cheers!
Russ
Sheldon,
Your welcome. Glad to do it.
Yes, the faster the power stage can react to the input from the global feedback loop the less distortion you get. This is actually one of the things I simulated over and over trying to find a good balance.
The OPA549 is actually an excellent power opamp, but not at high gain. keep it < 4 X and it is really great. Above that and its GBWP goes to crap. OPA549 actually suites this topology very well. The LM3886 is also excellent(and less expensive), and I don't think I would put one over the other. I use the Lm3886 at 10X gain which is the lowest the data sheet recommends.
The TXO as designed is very stable. So much so that neither Brian nor I have ever been able to coax it to oscillate. It also runs very very cool. Cooler then we expected for a bridged design. The servo helps in that regard a lot.
Cheers!
Russ
Your welcome. Glad to do it.
Yes, the faster the power stage can react to the input from the global feedback loop the less distortion you get.
This is actually one of the things I simulated over and over trying to find a good balance.The OPA549 is actually an excellent power opamp, but not at high gain. keep it < 4 X and it is really great. Above that and its GBWP goes to crap. OPA549 actually suites this topology very well. The LM3886 is also excellent(and less expensive), and I don't think I would put one over the other. I use the Lm3886 at 10X gain which is the lowest the data sheet recommends.
The TXO as designed is very stable. So much so that neither Brian nor I have ever been able to coax it to oscillate. It also runs very very cool. Cooler then we expected for a bridged design. The servo helps in that regard a lot.
Cheers!
Russ
These regulators, they power the power amps? The heat sinks seem way too small...
How does the balanced opamp as an input buffer improve performance? I imagine it can improve the S/N ratio but does it do more to improve sound quality? Perhaps it colors the sound in a pleasing way? (nothing wrong with that for hi-fi)
edit: i think i just got the point of it, it keeps the whole amp in a balanced (differential?) topology?
An externally hosted image should be here but it was not working when we last tested it.
How does the balanced opamp as an input buffer improve performance? I imagine it can improve the S/N ratio but does it do more to improve sound quality? Perhaps it colors the sound in a pleasing way? (nothing wrong with that for hi-fi)
edit: i think i just got the point of it, it keeps the whole amp in a balanced (differential?) topology?
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