P3A-MORE UPGRADES

[Jay]

The P3A performance is I think better with higher voltage rail. The problem is stability with difficult load. So how about increasing the supply voltage and doubling the output pairs.

Another CFP pairs can be added with the input taken from the VAS.

[sakis]

to my ears there was no sonic difference while the P3A was working at 52+52 volts ...

The test have been made at the same setup same speakers same listening levels and same sources

Also there was no change from the original circuit except ltp that was formatted with a bit higher voltage semis

Yes correct if stabilized a second pair the way you describe it will be an interesting thing to listen to, i might give it a try

Kind regards

[effebi]

As I am sure Sakis know, I was also playing a lot with P3A.
I agree that carefull choice (i.e. hfe) of the components, especially in the input stage will make a lot of difference.

I am not sure what Jay wants to say wih increased performance with high voltage, with all the due respect.
Surely if you go bejond 45V rails or you want to safely drive 4 ohms a second OP pair is desiderable.
But then, to double the drivers as well it looks to me a too radical solution. Otherwise at this point the choice is mainly how to arrange the OP Re, and we have seen different solutions and opinions about that.
All in all that will not be a P3A any more, I think.

[Jay]

Originally Posted by sakis

to my ears there was no sonic difference while the P3A was working at 52+52 volts ...

The test have been made at the same setup same speakers same listening levels and same sources

Also there was no change from the original circuit except ltp that was formatted with a bit higher voltage semis

For every fixed circuit there is optimal voltage (and bias current). It means that for different supply voltage, the design (bias current for example) must be different. For original circuit, if I'm not mistaken, 36V is best.

The benefit of a regulator is that we can arrange the voltage drop to get the optimal voltage we want for the rail (not strictly dependent on transformer secondary).

[kroto]

been trying many excluded from the process MJE series since sounded worst eventhough pretty rugged device, and realized that this process is seriously related to the choice of outputs ....For the record the best combination ever was the BD829-830 paired with 2SA1302-2SC3281...BD 139-140 with 2SA1943-2SC5200... obviously different combinations will produce different sonic signature.

have you try to change R11 R12 to 270Ω.
& bypass D1 with cap?

[sakis]

Originally Posted by effebi

As I am sure Sakis know, I was also playing a lot with P3A.
I agree that carefull choice (i.e. hfe) of the components, especially in the input stage will make a lot of difference.

I am not sure what Jay wants to say wih increased performance with high voltage, with all the due respect.
Surely if you go bejond 45V rails or you want to safely drive 4 ohms a second OP pair is desiderable.
But then, to double the drivers as well it looks to me a too radical solution. Otherwise at this point the choice is mainly how to arrange the OP Re, and we have seen different solutions and opinions about that.
All in all that will not be a P3A any more, I think.

Welcome my Italian friend

in cfp pairs it has been seen twice in the history of audio so far that when they double the outputs they also double the drivers ...The funny thing is that actually this also an Italian design the Alchemist forsetti....shame on you effebi you should have known better

the designer claims that double output and double driver provides extra punch tight sound and amazing drive abilities

worth looking at ...though i only wonder if the VAS circuit is good enough to drive that end especially if bootstrapped

To complete the idea one may think double the outs bit voltage more will be a nice achievement extra kick extra power all the benefits of bootstrap and sziklai but all this will be if stabilized without extra miller caps especially in the outputs since they are notorious sonic killers.

Yes though worth looking at .... will do in the feature and let you know ...

kind regards sakis

expecting also more ideas
thank you all so far

[Jay]

Originally Posted by sakis

It seems that after i common heatsink both of the drivers and in the middle attached the VBE transistor i ve noticed that the amp become much more stable and sound was far better and in a better "order " i have added 0.1mfd as a bias stabilizer ....

I have always thought that the problem with bipolar amps is linearity. Because any effort to increase linearity will always improve performance considerably.

1) I may try a mechanical way to trim the thermal coupling (2 heatsinks on top of each other with insulator in between).

2) Have anybody tried the thermal track device with the P3A? Somebody may say that it is not a P3A anymore, but... It will still has the goodness of P3A. I have "steal" the P3A frontend with good results. I have inverted P3A topology (become EF) and it is the best I have so far for that topology, outperform commercial design with the same topology and complex auxiliary circuit. I have also changed the output stage of P3A with darlington transistor and it is so far the best also for darlington amps.

[sakis]

sorry ... no darlingtons for me (that will include thermal track ones )

[Jay]

Originally Posted by sakis

sorry ... no darlingtons for me (that will include thermal track ones )

Yes, it was just to say how thoughtful the P3A has been designed. I collect amps with all "topology", trying to get the best for each of them, including darlington amps.

But I forgot that P3A is a CFP.

When I'm okay with a circuit, I will do a perfect implementation, including:

1. The shortest point-to-point construction (preventing bad influence of no capacitance/inductance from PCB traces)

2. On-board (near the output transistor) capacitor bypass (MKP) value is selected by ears. I also try -V to +V bypass. There is always an optimal cap.

3. Good supply cap, I prefer a multiple of 4700uF.

About bootstrap cap, I would like also to choose the value and capacitor brand/type by ears.

[sakis]

in my case instruments is before ears ...