First Watt balanced gainclone idea

[mikelm]

Gosh - what would unfriendly advise be like...

gengcard

If you are still inspired to try this the CCS transistor has to be a power transistor and on a heatsink aswell as the chip amp.

mike

[gengcard]

Thanks for advice. I will change it to power transistor or MOSFET soon.

Could you suggest me which transistor should be instead of MPSA18? In Thai semiconductor market has many power transistor and MOSFET. It's hard to choose one.

[carlosfm]

Originally posted by gengcard
Could you suggest me which transistor should be instead of MPSA18?

2n3055.
You can find them everywhere, and they are cheap.

[gengcard]

2n3055.

Thank you Carlos for your advice. I'll find it one.

[Archwn]

How about using LM337 as a CCS to bias 0.5A to 1.5A current.

In this case the resistor wattage could be only 1 - 2 Watt.

This could also be replaced with LM317 or LT1085 with few adjustments.

This one has been tested with around 0.5A bias current with hours of music with no significant dc offset changes from normal operation mode. It comes with switch between class AB and A for quick comparision listening test.

http://www.htg2.net/index.php?topic=20586

I can confirm that it changed how LM3875 in normal operation sound. With low volume, few mins of burning in, not so complex music, it is more obvious, I was stunned. The sound is more smooth, more focus, more depth in soundstage but some how narrower. The sound is more like real performance to me which I like but I also notice that the details is some how dropped which I tried to improve. (I'm a newbie in electronics by the way.)

One thing I suspect is the capacitor used in CCS part. this might damp the sound so the detail is not good. I would try to take them off and do the listening test again.

Every comments on how to improve this impliment are at most welcome as this one is just a conceptual study on biasing power chip amp into class A.

[Archwn]

the board.

[vizion]

Hello Guys,


i just wanted to revisit this thread. How did Class A experimentation go with chip amps ?

[vizion]

Does the balanced gainclone idea leave Class A when amp is turned up past the wattage the bias point is set for ?

[mikelm]

I was just reminded by someone that this thread, which I began many moons ago, existed and having just moved back from the USA after five years I found in my stored possessions in the UK the same 1/2 built amps which I referred to here so it may be I will check out this idea.

Having just re-read the thread I am not surprised that carlos's resistor biased amps lost their "live", dynamic sound, the amps o/p circuits would have to have to work to switch the current to drive those resistors. The active current sources should be "invisible" to the signal so I would expect the circuit implemented this way to sound different and hopefully more effortless & dynamic.

Of course after the 1st watt or so the amps will go into AB but 1 watt is quite loud so any switching noise should be virtually imperceptible.

mike