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.
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