The M2 Output Stage in Class A/B, and maybe a Power WHAMMY?

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Joined 2003
How do you control the bias drift ?
Assume FETs in parallel drift the same ?

Haven't tried, might still work, as source resistor is quite large.
Will help to stabilise bias.


Patrick
 
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Joined 2018
Progress here with Toshiba and opamp rolling system with some limitations of course
First lab measurements are ok
Mixed feedback MFB
Bias 1.47 A @23,35V rails
Gain ~22dB

IMG_20231217_105905.jpg
 
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It is pointed out to me that D1 and D2 are swapped on the PCB compared to the schematics.
This has been made known to me before, but since they are identical parts (SMD 1N4148), it has no impact on the circuit.
I therefore do not see the necessity to change the Gerber files.


Cheers,
Patrick
 
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smalll update in concern to opamp rolling. (see post #297, #317 with LM329..)

For me it is worth it, because the OPA 828 beats all....really sounds fine and precise :cool:
(LT1793 is also better than OPA604 but some time I do have small shut down plop, sometimes not ??- dont know why....)
 
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If you are going to use low voltage opamps anyway, why not just use 18V rails and oncrease OPA bias to 1.7A ?
You wil never be using the M2OPS to fill swing anyway.


Patrick
 
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some days ago, I had a sound session at my place.
Please understand, that I have in some weeks up to 20 hours of listening and that for more then 30 years.. in this room for 11years, so the following impression are subjective...

gear to be tested:

Combo
1) Pre amp BA3-with Fairchild Mosfet and power amp M2OPS with Fairchild (FQA16N25/FQA9P25 self selected -B-grade ;))
2) Pre amp BA3-with Toshiba Mosfet and power amp M2OPS with the famous Toshiba (only 14,8W/4R)
3) for comparison AVM Ovation A6.3

Hifi Chain-
Audioquest Niagara 1200- Power conditioner
Source-Streamer-DAC Auralic Vega G2.1
Loudspeaker KEF R11
cabling Furutech-DIY

The audience had a lot of fun and impressions on this day
The biggest jump was to change the power amp from Fairchild to Toshiba because IMO the possibility in the Toshiba to have the OPA828 inside!! ;)

The differences between the pre amps was smaller but there. - Toshiba sounds alway more darker and had more low end especially the power amp, and again because of OPA828.
-Toshiba was more able to produce the contours of the actor clearer, but some found the mids are louder....
- Fairchild has also fine sparkling high end with more airiness and is a bit faster...

at the end we want to challenge the "man of the house"-----AVM, but all agree that the Tosiba combo makes more fun and more liveness and super details. -If you like class A you stay there ;)

I was host in my house and was not all the time especially with the acting of the AVM in the listeening area, and busy with preparing beer and food. -So I was confuse that someone shout "through away this AVM crab" in a funny way of course.

Next day I try it by my self -- and can confirm, that in some situations the Toshiba combo is clearly the better one!!! with all the benefits of smooth and very dedailed sound

PS. for me is the next step the modify the power amp with fairchild, to be able to insert the OP-amp rolling possibility. the con s are the POwer swing of the opamp is limited and so you have limited power, particulary for 8R speakers..
And adding a better PS with Cap Multiplier....
 
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Joined 2003
You can actually bootstrap 15V opamps to higher rail voltages.
Please read this carefully and understand first before trying.
If you design your own PCB with SMD, you might even fit this onto a DIP8 adaptor.


Patrick

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