http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?Ref=168852&Row=63834&Site=US
5.70 at 1 qty. 🙂
You should also be able to use OPA1632. I will be trying that chip out tonight.
Cheers!
Russ
5.70 at 1 qty. 🙂
You should also be able to use OPA1632. I will be trying that chip out tonight.
Cheers!
Russ
FIXED PDFs
Had a couple traces too close together. Here are the Fixed PCB PDFs.
Please discard older PDFs.
Corrected PDFs
Had a couple traces too close together. Here are the Fixed PCB PDFs.
Please discard older PDFs.
Corrected PDFs
Your latest version looks really good, Russ. I don't see anything that I would suggest tweaking. Great effort!
Thanks so much for looking it over Terry! 🙂
Cool. 😎
It seems to be handling very well. No stability issues at all. That 22K resistor in the feedback loop had me worried, but it is working fine. One could change it to 10K if they lowered R1 and R2 to 1K, but that seems like a very low input impedance to me.
Cheers!
Russ
Cool. 😎
It seems to be handling very well. No stability issues at all. That 22K resistor in the feedback loop had me worried, but it is working fine. One could change it to 10K if they lowered R1 and R2 to 1K, but that seems like a very low input impedance to me.
Cheers!
Russ
Great work Russ!
You should definitely try opa1632 - it's basicaly the BurrBrown version (THS4131 - Texas Instruments) of the same circuit, with impressive datasheet (http://www-s.ti.com/sc/ds/opa1632.pdf) characteristics, lower price and better availability (at least in Europe). To make it work at its' best try R5, R6=470 ohms and R3, R4=2K2. It'll run a bit cooler and THD/IMD will improve somewhat. Now, with R5, R6=221 ohm and R3,R4=1K you are loading it down a bit (not that it can't take it). Keep up the good work!
Cheers!
You should definitely try opa1632 - it's basicaly the BurrBrown version (THS4131 - Texas Instruments) of the same circuit, with impressive datasheet (http://www-s.ti.com/sc/ds/opa1632.pdf) characteristics, lower price and better availability (at least in Europe). To make it work at its' best try R5, R6=470 ohms and R3, R4=2K2. It'll run a bit cooler and THD/IMD will improve somewhat. Now, with R5, R6=221 ohm and R3,R4=1K you are loading it down a bit (not that it can't take it). Keep up the good work!
Cheers!
Russ White said:
Hi, Russ. Why not try an original BOSOZ to drive it. Current sources dig low load impedances like voltage sources dig high load impedances.
eLarson said:
I have been alternating between my XBOSOZ and my Twisted Sibling preamp. 🙂 They both are doing the trick just fine. 🙂 The 2.2K and 22K combo seems to be working fine. So I will not change that for now.
juma said:
Hi Juma,
I had also thought along those same lines, but what I was hoping was that by making the opamp work harder it would make it less likely to get itself into trouble.(idle hands) 🙂 I have swaped the 1K(R3/4) for 2.2K and the 221R(R5/6) for 390R. That seems to be a good combo so far.
Also the OPA1623 is in a running. Seems to be no issues at all using either chip, which is what I suspected.
Cheers!
Russ
I think it's time to bring this one one step further.
Remember this nice idea from NP: http://www.passlabs.com/np/GC-OUTPUT-BIAS-1a.pdf
Add two CCS from the outputs to negative rail, bias it to perhaps 0,5 Amps (2 Watts on 8 Ohms), then you have the chip equivalent of what Pass Labs would call an X30.5 or X50.5 (depending on the rails).
Power CCS shouldn't be a problem, boosting an LM317 with a power transistor should be fine.
Remember this nice idea from NP: http://www.passlabs.com/np/GC-OUTPUT-BIAS-1a.pdf
Add two CCS from the outputs to negative rail, bias it to perhaps 0,5 Amps (2 Watts on 8 Ohms), then you have the chip equivalent of what Pass Labs would call an X30.5 or X50.5 (depending on the rails).
Power CCS shouldn't be a problem, boosting an LM317 with a power transistor should be fine.
Update...
Hey folks, I would not go build an amp with the PDFs I posted earlier yet. I just finnished a new one and it seems prone to oscillate. I think I need to add a compensation cap or a low pass filter at some point... Any ideas?
Hey folks, I would not go build an amp with the PDFs I posted earlier yet. I just finnished a new one and it seems prone to oscillate. I think I need to add a compensation cap or a low pass filter at some point... Any ideas?
any idea what causes the osscilation? is it inherent in your design or is it unexpected?
a (quick & dirty) small cap across the + and - chip inputs might do the trick.
a (quick & dirty) small cap across the + and - chip inputs might do the trick.
At this point I am not sure what the problem is. I will keep you guys updated. The only major differnce between this circuit and what was working is that I was running on 15V rails before and did not use the VREGS. So I am a bit puzzled, but I am glad I found it now and not later.
Packaging
I really dislike working with SM chips. Cannot see the minscule leads very well anymore.
Are you using the MSOP-8 or SOIC package for this amplifier? The MSOP-8 lloks like it handles heat and power a little better.
George
I really dislike working with SM chips. Cannot see the minscule leads very well anymore.
Are you using the MSOP-8 or SOIC package for this amplifier? The MSOP-8 lloks like it handles heat and power a little better.
George
My circuit has serious issues. Don't use it yet. 🙂
Hey guys... I am so busy getting my house ready to sell that I hardly have time to do more testing, but I can say my single loop circuit as it is, is not working right at all. It is very prone to oscillate.
The circuit I had working earlier had closed loops for both chips. I did not realize that I still had the extra resistor in place for this(I was reusing ols circuit). That is the only reason it was stable.
I am sure there is a way to safely and successfully implement global feedback with the THS4131 but I don't have it working yet. If anyone has any ideas on changes to make I would appreaciate it.
Adding a 330pf resistor betwen the inputs on the THS4131 did help a littlebit, but its still not stable. Not even close. 🙁
But the good news is Terry's circuit is very stable and sounds fabulous, so I will just very happily listen to that for a while. It is a seriously incredible power amp. 😀 I never really thought mine would be an improvement, just different, and maybe smaller/simpler.
Sorry for any confusion I may have created testing out this theory of mine.
Cheers!
Russ
Hey guys... I am so busy getting my house ready to sell that I hardly have time to do more testing, but I can say my single loop circuit as it is, is not working right at all. It is very prone to oscillate.
The circuit I had working earlier had closed loops for both chips. I did not realize that I still had the extra resistor in place for this(I was reusing ols circuit). That is the only reason it was stable.
I am sure there is a way to safely and successfully implement global feedback with the THS4131 but I don't have it working yet. If anyone has any ideas on changes to make I would appreaciate it.
Adding a 330pf resistor betwen the inputs on the THS4131 did help a littlebit, but its still not stable. Not even close. 🙁
But the good news is Terry's circuit is very stable and sounds fabulous, so I will just very happily listen to that for a while. It is a seriously incredible power amp. 😀 I never really thought mine would be an improvement, just different, and maybe smaller/simpler.
Sorry for any confusion I may have created testing out this theory of mine.
Cheers!
Russ
That's why the Twisted Pear amp's sound so good. They have access to parts that are unavailable to the rest of the world 😀
Regards
Regards
This amp is a hi speed device. Slowing it down might be the right idea, but with a cap between the inputs you just decrease the signal amplitude on the inputs, not gain.
I assume you will have to fit two caps: +in to -out and vice versa.
How would I choose a value for the caps that bypass the feedback loop?
And would it be directly connected between IN+/OUT- of the THS4131 or from IN+/then the oposite phase LM3886 output?
My guess is directly from the THS4131 out, and that would make a closed loop at high frequencies which would be unity gain, correct?
Is 330pf a good value to start with? Or higher/lower. Any formula I could use to figure out this cap size?
Thanks! 🙂
Russ
And would it be directly connected between IN+/OUT- of the THS4131 or from IN+/then the oposite phase LM3886 output?
My guess is directly from the THS4131 out, and that would make a closed loop at high frequencies which would be unity gain, correct?
Is 330pf a good value to start with? Or higher/lower. Any formula I could use to figure out this cap size?
Thanks! 🙂
Russ