Got objective data which shed light on the inner workings of the schematic in the above post; which is also reproduced here. Here are key details of the test:
- Balanced input signals to the diff amp were offered via the secondary windings of a toroid step-down [120V to 12v] transformer.
- Sine test signal at 130 Hz.
- AC multimeter measured voltages at the selected nodes in the circuit of the attached schematic.
- Note switches Sl and Sr at the power output of the amp. When open [Case 1], the resulting balanced amp operated in the open loop mode [no SuSy]. By contrast, SuSy was enabled when the switches were closed [Case 2].
- The voltage gain of the diff amp is ~10
- The open loop voltage gain is ~240
- Note the close matching of the two channels in S/150; a needed property to enable perfect SuSy
- The voltage gain of the diff amp is ~1.3
- Closed loop gain of the banlanced-SuSy amp is ~33
- Voltage gain invested in negative feedback = 17 dB; to mostly correct for error in diff amp; because the performance of S/150 is pristine by design.
Attachments
The thread had gone stale for 2+ years. It is possible that the builders of ssgc had already unsubscribed. Maybe a PM to metalman [owns post 439] will help.Question to the ssgc builder´s
is the schematic in post 439 still the last one?
and anyone tried with fet input stage (there have been some comments that bipolar is better there but i don´t know why)
thanks
Thank you for the info.We made boards for this a long time ago, but have since moved on. They used the ZTX bipolar front end.
Gono, I congratulate you on successfully completed project. It's a nice amp you built - I happen to like point2point too
I took another shot at this idea (like in post #672) with inverting OPA549 and OPA1632:
SuSy amp sa inv. OPA549 - DIY Audio Forum
(it's our local, Serbian, forum but pics and schematics are self-explanatory).
With LM3886 you have to get rid of too much gain for my likings so I chose OPA549 and improvements in sound are noticeable. I listen to this amp two months already and I still enjoy it (I usually get bored by AB class amps after week or two).
Here is the final schematics:
Cheers!
any cheaper alternative than OPA549?
Burr-Brown ICs are expensive compared to TI
What I use today (LM4780), for bass drivers only :
F5X -- the EUVL Approach - The Build Thread
Patrick
F5X -- the EUVL Approach - The Build Thread
Patrick
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