Bonsai said:
I decided not to fiddle with the LTP cct.
The amp gives out a good none distorted signal now and the DC offset is 0V3 so that is good enough.
Its built on Verobaord that is getting pretty full now.
I can pass on everything I have learned to the next build when it comes.
VAS is an interesting subject on its own.
After letting the amp settle down for a while I found 5V9 bias gets rid of any distortion. But the MOSFET gate voltage required depends on the load so setting the bias at a low input signal seems alomost pointless. In the end I set the signal to around half V+ and tuned out the crossover distortion.
To be honest even when there was bags of cross over distortion I couldnt hear the difference. I am a little worried about using a pot in the bias chain because if this goes o/c for some reason by the amp getting knocked it will wipe out 6 MOSFETS !!
. . . . I'd fix it and end up with a reasonably performing amp (given the topology you are using).
If you read Self, you will quickly see that under the current LTP conditions you have, you will have loads of distortion (maybe not visible, but I can assure its there). It will sound better as well.
Dont get fooled into thinking having a high LTP load resistor (12k) and no LTP emitter degeneration will give you better performance because you have higher loop gain - under dynamic conditions (music) you will be getting loads of distortion and all sorts of other artifacts.
If you read Self, you will quickly see that under the current LTP conditions you have, you will have loads of distortion (maybe not visible, but I can assure its there). It will sound better as well.
Dont get fooled into thinking having a high LTP load resistor (12k) and no LTP emitter degeneration will give you better performance because you have higher loop gain - under dynamic conditions (music) you will be getting loads of distortion and all sorts of other artifacts.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.