Been there done that, good luck with fixing it. The possible issue I see is that you have a glass of water near the amp when we should see a beer or some nice scotch 😀I think I’ve used up all my FAB karma. My latest MoFo experiment immediately produced the distinct aroma of burning resistors.No more late night amp building for me.
Cooler heads prevail. I tried again and everything is working as expected. Both channels are playing well with my test speakers. Stable, quiet operation at minimal bias. Then operating well with higher bias. The sinks are at about 50C with fans underneath. I think I’ll build a minimal chassis for this MoFo. 
One question: is it normal operation for the DC voltage measured at the inductor (and presumably the bias) to fluctuate by 10 mV or so?
One question: is it normal operation for the DC voltage measured at the inductor (and presumably the bias) to fluctuate by 10 mV or so?
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Here is my quick test build using theslowdiyer's PCB design and 193t inductors. I run it at 12 volts and 1.7A bias. Compared to the SymAsym, it has more open and lively sound with polite character, which makes my horns easier to listen to. The amp is completely silent with 113dB/W compression drivers and has no turn on or off thump. Very promising impression.
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Very nice! This is quite an impressive little amp - my scope showed clean square waves all of the way out to 300kHz and I like how it renders bass with those giant transformers. I'm thinking my next experiment is to put my MoFo between my 300B amps and my power hungry Calpamos speakers. I'd love to learn about the details on those beautiful looking OB speakers...
Those speakers are still work in progress, here shown in daylight and properly pulled out from wall. I'm using Faital 15PR400 woofers and 18Sound XT1464 horns with BMS 4554 drivers, crossed actively with MiniDSP. The baffles are made from 35mm birch plywood, not too sturdy but enough for light apartment use. There are some issues with imaging when mixing dipole and monopole radiator, damping rear wave with some front wall treatment would probably be beneficial. Nevertheless they are my best speakers so far.
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Planning to build a MoFo very soon.
Have a couple of questions:
Did anyone compare Mosfet with Compound Feedback Pair ( Sziklai pair ) output device ?
Did anyone compare Choke vs CCS ?
Interested in sound quality rather than technical improvements
Thanks
Have a couple of questions:
Did anyone compare Mosfet with Compound Feedback Pair ( Sziklai pair ) output device ?
Did anyone compare Choke vs CCS ?
Interested in sound quality rather than technical improvements
Thanks
It wouldn’t be a MoFo if it had a CCS… the choke is rather the point, really.
As for Sziklai device, I don’t recall anybody trying that. May be worth a go.
As for Sziklai device, I don’t recall anybody trying that. May be worth a go.
Well, I hear what your saying but with a choke or a CCS, they are both still technically "MoFo"s 🙂
This article shows both versions - but does not get into how they compare subjectively.
https://www.audiodesignguide.com/Inpol/index2.html
I will probably build a choke version sometime soon but right now I have a nice 25V + 25V supply in a case and all the parts I need to build a CCS version.
I will try both single mosfets & BJT Sziklai pair followers to see how they compare.
This is the BJT CFP version:
Am currently experiemnting in spice to BJT / Vertical MF Compound FB pairs - at first look they could be a better & cheaper option.
The CFP versions clearly have lower distortion but I need to establish if they actually sound good.
This article shows both versions - but does not get into how they compare subjectively.
https://www.audiodesignguide.com/Inpol/index2.html
I will probably build a choke version sometime soon but right now I have a nice 25V + 25V supply in a case and all the parts I need to build a CCS version.
I will try both single mosfets & BJT Sziklai pair followers to see how they compare.
This is the BJT CFP version:
Am currently experiemnting in spice to BJT / Vertical MF Compound FB pairs - at first look they could be a better & cheaper option.
The CFP versions clearly have lower distortion but I need to establish if they actually sound good.
