Hi
About two years ago I bought a set THF-51 like so many others on this forum (I think we all know who to blame…).
To start with I needed to figure out what to build wit them. Single ended class A was a given, and based on Ben’s excellent builds I decided to make a common drain choke loaded amp. This out put stage does of course not offer any voltage gain but Rahul’s SCG could be used as a front end for the THF-51 out put stage. But I would also need some way to bias the THF-51 and I would like a low impedance bias supply (seen from the THF-51) to prevent any (high) gate current from messing with the set points. I achieved this by inverting the SCG.
I have not done any simulations on this circuit other than ohms law on a calculator. And measurements are limited to DC work points only. So, you have to make due with a hand drawn schematic. The reason is that I have been on a tight schedule to finish the amplifiers for a DIY loudspeaker event yesterday in Viborg Denmark.
The bias is adjusted by a small DC voltage applied at the bottom end of the 1M input resistor.
And here is a photo of the two amplifiers ready for yesterdays DIY event:
Best regards
Simon
About two years ago I bought a set THF-51 like so many others on this forum (I think we all know who to blame…).
To start with I needed to figure out what to build wit them. Single ended class A was a given, and based on Ben’s excellent builds I decided to make a common drain choke loaded amp. This out put stage does of course not offer any voltage gain but Rahul’s SCG could be used as a front end for the THF-51 out put stage. But I would also need some way to bias the THF-51 and I would like a low impedance bias supply (seen from the THF-51) to prevent any (high) gate current from messing with the set points. I achieved this by inverting the SCG.
I have not done any simulations on this circuit other than ohms law on a calculator. And measurements are limited to DC work points only. So, you have to make due with a hand drawn schematic. The reason is that I have been on a tight schedule to finish the amplifiers for a DIY loudspeaker event yesterday in Viborg Denmark.
The bias is adjusted by a small DC voltage applied at the bottom end of the 1M input resistor.
And here is a photo of the two amplifiers ready for yesterdays DIY event:
Best regards
Simon
It is a lot more stable than I expected. When temperature settles 10-15 minutes after turn on, then the Iq is stable. It varies a few % but the drift is close to zero.
I was a bit concerned that variations in the mains voltage would have a direct impact on the SIT's Vgs. But it has proven to be a minor problem so fare.
I was a bit concerned that variations in the mains voltage would have a direct impact on the SIT's Vgs. But it has proven to be a minor problem so fare.
few % is nothing to worry about
and, without active biasing mechanism, if it slides with rail value, no fret ......
and, without active biasing mechanism, if it slides with rail value, no fret ......
I auditioned the mono blocks at the event (as I was the host). They sound very smooth and you can't avoid having a BIG smile listening to them. In fact I'm already smiling having the M2 clone as standard power amp, but smndao's monoblocks are a step up.
We played with the bias, but at least with my speakers which are easy 4 Ohms it didn't make that big a difference. Well done smndao
We played with the bias, but at least with my speakers which are easy 4 Ohms it didn't make that big a difference. Well done smndao