Sorry this one will be kinda long ....
Most of you know that i work with the P3A more than 5 years now i end up changing minor things that had quiet serious effects on it .Meaning of the post is that i am looking for more suggestions for the best but without changing the original concept of the P3A .
Dear Friend Wahab suggested to remove the bootstrap and make it a ccs but this will alter the character of the P3A and on the other side i like the bootstrap so this type of changes is not my go .
bellow i will summarize and comment the changes ive made in categories and wait for your comments and suggestions .
LTP
for the LTP all my PCB feature thermal junction that is better for stability and offset,then always semis are chosen for high hfe over 400 and closely matched improved and made the bass more tight and generally improved the all amplifier by far . also tried to choose semis from a trusted manufacturer and also use semis that have lower voltage than BC 546 to force them work on the edge . Also played with LTP current +- a few ma with good results .
FILTER-MILLER CAPS
for filter and miller caps i try to use best of quality styroflex for the input and silvermica 500V 2% for VAS and driver depending on the choice of VAS semi i have lowered the values low as 68 pf with no obvious stability issues but with some sonic difference for the best. install a DC input and skip input cap when its possible to do .
VBE multiplier
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 ....
VAS /DRIVERS
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.
These are in a nut shell the small changes i ve made and most of my P3A run at no more than 40+40 volts and with 60.000 mfd for 2ch amplifier as about the bias always depending on the choice of semis an optimum 70-120ma is the best while tests ive made to 250ma didn't improve much and actually i think made the amp worst .
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As many know i am in the repair business so many of my costumers often take a P3A amplifier as a replacement amplifier from my shop while their amplifier is under repair ...At 99% of the cases the costumer will call the office in order to know more about the amp since he is thrilled with sound and even express the intention to buy one .
For the record i will state the type/brand of amplifiers that the P3A kicked *** off at least according to the costumer
---Plenty of Musical Fidelity
---Plenty of AUDIOLAB
---Few Goldmund
---Plenty Of QUAD
---One ADCOM
---2 NVA amplifiers
---Few Rotels
---Few Hardman Cardon
Changes that produced bad results
---High bias 250ma i think made the amp stiff and slow
---High rail voltage 52+52 volts produced more power and heat, some stability issues But no sonic improvement ...
---been thinking to make the all thing run from a regulated power supply but i am not sure if this will change anything for the best
---Been thinking to separate output from drive circuit in order to supply input circuits from other regulated voltage probably higher but never done that yet
---Been trying very fast drivers with relatively slow outputs with bad results
---Been trying the opposite like normal drivers but with very fast outputs
now suggestions please ppl !!!
kind regards
sakis
(Thanks for your time )
Most of you know that i work with the P3A more than 5 years now i end up changing minor things that had quiet serious effects on it .Meaning of the post is that i am looking for more suggestions for the best but without changing the original concept of the P3A .
Dear Friend Wahab suggested to remove the bootstrap and make it a ccs but this will alter the character of the P3A and on the other side i like the bootstrap so this type of changes is not my go .
bellow i will summarize and comment the changes ive made in categories and wait for your comments and suggestions .
LTP
for the LTP all my PCB feature thermal junction that is better for stability and offset,then always semis are chosen for high hfe over 400 and closely matched improved and made the bass more tight and generally improved the all amplifier by far . also tried to choose semis from a trusted manufacturer and also use semis that have lower voltage than BC 546 to force them work on the edge . Also played with LTP current +- a few ma with good results .
FILTER-MILLER CAPS
for filter and miller caps i try to use best of quality styroflex for the input and silvermica 500V 2% for VAS and driver depending on the choice of VAS semi i have lowered the values low as 68 pf with no obvious stability issues but with some sonic difference for the best. install a DC input and skip input cap when its possible to do .
VBE multiplier
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 ....
VAS /DRIVERS
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.
These are in a nut shell the small changes i ve made and most of my P3A run at no more than 40+40 volts and with 60.000 mfd for 2ch amplifier as about the bias always depending on the choice of semis an optimum 70-120ma is the best while tests ive made to 250ma didn't improve much and actually i think made the amp worst .
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------
As many know i am in the repair business so many of my costumers often take a P3A amplifier as a replacement amplifier from my shop while their amplifier is under repair ...At 99% of the cases the costumer will call the office in order to know more about the amp since he is thrilled with sound and even express the intention to buy one .
For the record i will state the type/brand of amplifiers that the P3A kicked *** off at least according to the costumer
---Plenty of Musical Fidelity
---Plenty of AUDIOLAB
---Few Goldmund
---Plenty Of QUAD
---One ADCOM
---2 NVA amplifiers
---Few Rotels
---Few Hardman Cardon
Changes that produced bad results
---High bias 250ma i think made the amp stiff and slow
---High rail voltage 52+52 volts produced more power and heat, some stability issues But no sonic improvement ...
---been thinking to make the all thing run from a regulated power supply but i am not sure if this will change anything for the best
---Been thinking to separate output from drive circuit in order to supply input circuits from other regulated voltage probably higher but never done that yet
---Been trying very fast drivers with relatively slow outputs with bad results
---Been trying the opposite like normal drivers but with very fast outputs
now suggestions please ppl !!!
kind regards
sakis
(Thanks for your time )
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There is also something else to notice especially in the part that costumers take a P3A as a replacement amplifier ....
The amplifier and PCB i make are well made with order and proper wiring and cable rooting and with good and rugged material so obviously this will make any amplifier better than a commercial amplifier difference is that often commercial amplifier have a quite pricy tag on them .....
The amplifier and PCB i make are well made with order and proper wiring and cable rooting and with good and rugged material so obviously this will make any amplifier better than a commercial amplifier difference is that often commercial amplifier have a quite pricy tag on them .....
D
Deleted member 148505
p3a
Hi sakis i allways find your posts interesting. I have built 3 p3a amps the current one is using a jlh regulated supply(see ETI international 1983) of +-35v. i was wondering since you like to modify have you tried different method of compensation,i.e cap from vas collector to ltp base? thanks and good luck
Hi sakis i allways find your posts interesting. I have built 3 p3a amps the current one is using a jlh regulated supply(see ETI international 1983) of +-35v. i was wondering since you like to modify have you tried different method of compensation,i.e cap from vas collector to ltp base? thanks and good luck
If nothing is modded in the amp topology itself the best it can gain from
would be to add filtering to the front end since this amp has not
basicaly good supply noises rejection.
100R + 470uF in each side would already improve supply rejection
quite efficently considering the simplicity but it wont be as good , by far ,
as adding also cap multipliers consisting of BD139/140 with a 4.7K resistor
and a 100uF cap.
would be to add filtering to the front end since this amp has not
basicaly good supply noises rejection.
100R + 470uF in each side would already improve supply rejection
quite efficently considering the simplicity but it wont be as good , by far ,
as adding also cap multipliers consisting of BD139/140 with a 4.7K resistor
and a 100uF cap.
Attachments
The question is: have you tried it? The reason for the question is:
1) The CFP has "good" character, and is difficult to design. But Rod has made a very good work here. What I mean is, it should be a good design whether using bootstrap or not.
2) The P3A has been "dominated" by odd order distortion anyway, may be the usual perception about a bootstrap (e.g. its effect on vocal) not so dominant here?
EDIT: what i mean with "dominated by odd order is..."...
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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
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
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.
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.
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).
http://sound.westhost.com/p3a-f1.gif[/
have you try to change R11 R12 to 270Ω.
& bypass D1 with cap?
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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
Thermaltrack
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.
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.
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.