Most of that discussion was due to questioning the need for more power in the first place. Of course the basic idea of the P3A is almost infinitely scaleable - BUT what you end up with is a different amplifier. The more you go off the rez, the more different it becomes, the more the sound you’re fond of changes, and the more design challenges you run into. Project 117 is one potential result. It will work, but won’t sound anything like a P3. And you take your life into your hands when you plug it in. A similar “accident“ with a P3A will only result in one pair of dead transistors and you won’t need to call the fire department.
Just adding output transistors usually changes how things sound. Some like it better others hate it, for the technical reasons I outlined above. Depending on your own expectations, you may not even notice a difference. Cranking the supply voltage requires tweaking. The increase in VAS standing current alone will UNbalance the input diff pair. You can fix that but the open loop gain increases, so the compensation will not behave the same. Go far enough and that dreaded square wave overshoot becomes oscillation. Use a 600 watt transformer and 50,000 uF of cap and now it won’t tolerate even momentarily brushing the + and - speaker wires against one another. All of this can be mitigated, but you have a design problem on your hands. And before you go off and think you can just simulate your way out of it, be WARNED that CFPs are notorious for not behaving like the simulation, if you get your models from the usual places.
If you like the amp you have, keep it as is and make another to experiment on. You will need to build actual hardware to get it right. Do this and you will actually be able to compare the original with a mod.
Just adding output transistors usually changes how things sound. Some like it better others hate it, for the technical reasons I outlined above. Depending on your own expectations, you may not even notice a difference. Cranking the supply voltage requires tweaking. The increase in VAS standing current alone will UNbalance the input diff pair. You can fix that but the open loop gain increases, so the compensation will not behave the same. Go far enough and that dreaded square wave overshoot becomes oscillation. Use a 600 watt transformer and 50,000 uF of cap and now it won’t tolerate even momentarily brushing the + and - speaker wires against one another. All of this can be mitigated, but you have a design problem on your hands. And before you go off and think you can just simulate your way out of it, be WARNED that CFPs are notorious for not behaving like the simulation, if you get your models from the usual places.
If you like the amp you have, keep it as is and make another to experiment on. You will need to build actual hardware to get it right. Do this and you will actually be able to compare the original with a mod.
That's why I've mentioned several times about adhering to 'simplicity' for purity in music.
A single set of outputs.
Because the less silicon junctions that the music has to go through, the less it's prone to distortion/change.
Any particular sound qualities you can hear from an electronic amplifier can actually be simulated by another, even one of a quite different topology and type, to the degree of being completely indistinguishable from it.
Maybe we could all learn something about recreating particular amplifier sound quality from the amazing Bob Carver - if only we knew what the design of his "nulling pots" electronics were: https://www.bobcarvercorp.com/carver-challenge.
Maybe we could all learn something about recreating particular amplifier sound quality from the amazing Bob Carver - if only we knew what the design of his "nulling pots" electronics were: https://www.bobcarvercorp.com/carver-challenge.
At a normal listening volume, both my Technics 60w/ch solid state receiver and my home-made/designed 17w/ch EL84 PP amp are indistinguishable from one another.
Volume levels are matched within 0.2DB.
Yet, my self-proclaimed newbe audiophile neighbor with self-proclaimed Golden Ears thinks they sound different in an A/B comparison.
I proved him wrong, told him it's his 'perception' kicking in, not reality.
Flipping a fake A/B switch that he thought changed amps was all I needed to know.
So when people on here and other sites try to argue with me about this sort of thing, I'm amused.
DBT is a cruel b*tch 😛 😛 😛
Absolutely HATED by "Golden ears" 😉
Absolutely HATED by "Golden ears" 😉
It's such a shame, isn't it?
I think maybe it's merely another universe, another planet, like a drug, which rears its elusive head at certain times.
It takes you into....... The Twilight Zone.
One would think if a design paramater is "4", you're stuck. Increase the rail voltage and everything changes. Bridge the amp with a second, identicle unit and things change too...
I took an old dusty amp board that I had laying around in my junk drawer for decades to play with.
I felt sorry for the poor thing, and thought I could give it a new life.
It's really nothing special, low powered receiver's amp board - from a Harman Kardon 330A receiver, circa 1972ish.
Interestingly, that receiver is coveted and adored by some even today.
I wasn't expecting much in the end, I keep my feet on the ground about things, I like living in a real world, not contrived or fad-based - I'm not one to 'follow the crowd'.
So.. I changed up some of the board's components - heavier outputs and drivers, and newer bias control transistors, new pots, caps, etc.
I used my extensive technician's experience and went slowly into the project, again, not expecting much.
I designed a new power supply for the board too.... relatively basic, yet robust.
A second winding on the transformer allowed me to power the preamp section seperately, and regulated.
Upon firing up the board, voltages measured ok (55V B+), I set the center Volts, and then the output bias a bit higher than stock since the outputs (MJL21194's) can handle 16 amps anyway. (the originals were 3 amp TO220's)
Well, the thing amazed me on the bench!
So I built a nice enclosure for it so that it looks presentable - I'm retired now so I like the enjoyment of hand-crafting stuff.
But what really amazed me was taking that amp next door to my neighbor's and hooking it up to his power-hungry AR LST speakers which are fantastic performers.
Now mind you, the amp's not a powerhouse design (cap coupled), I measured clean unclipped scope readings up to around the 30 watt level.
That amp, cranked up to "9"ish spit out window-rattling crystal clear music from a CD!
Those LST's were amazing too.
And that amp's heatsink never got beyond mildy warm.
Closing argument ....
To remind you :
the amplifier that i am willing to outperform in the first place is BTL topology that to begin with means in a few words that you have 2 amplifiers 150w each summed on the speaker, and with 180 degrees diference they produce 300W
Given fact when you have 2 amplifiers summed like that BTL, you have double the LTP, double the suport: current sources current mirrors, double the VAS double the drivers , double the safety measures, double everything
Only thing that is half is the capacitance of the output stage which is now shared between the 2 amplifiers per ch.
So the P3a A will outperfrom the big amplifier in terms of sound any way you slice it due to far lower part count
i take this as a fact
let us say that 150 W of power will be more than enough to outperform the beast with the given speakers .
so the original question is how you produce 150 W of power but without loosing all the sweet features of a P3A
there is a chance that the answer is: " you dont"
this is what i am willing to learn
The event was an audio show on the extreme side where a DAC was tagged at 42k euro , preamp 20K amplifier 30K proarc speakers 30K in total with cables something about 130k euro ....
at the first day of the event i noticed that the system of 130 K had poor response in the low freq .
i asked the owners of the stand and they said to me that they also noticed the problem and had to do with the room reflections and they been trying diferent placement of the speakers for 2 days before to select the best placing for the audience .... The room was actually inside a hotel which they had the 1/3 of a ballroom separated with panels ...indeed the location was terrible add to it that a huge metallic ventillation ch was running across the room ....
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------
Listening though and compairing to what i know allready from years of measuring and listening my gut and my ears said that indeed the amp and possible the preamp had poor low end .... I was trying to explain that inside my mind and given some expirience from pro audio indeed you Cannot have a 300W@8R amplifier absolutely free in the lowend and the high end . If so any abuse will blow speakers within a split of a second ....
So the second day was even more busy and they have been playing kinda loud and it appears that the big beast was overheated there was a noticable change in the allrady poor performance of the system
so i erge them to hook up the P3a combo on the system .... they grab the bate and the p3A is now hooked up....allowed some 20 min warm up
Classic recipy main amp with all the known goodies configured as dual mono 300VA trafos per ch, 60k uf total , 1302-3281 engine , 200 mhz drivers and VAS ,160V styroflex miller caps, MKS input caps, decoupling , bleed resitors , speed up capacitors and dual fast rectifiers
configured as integrated amplifier with DOZ preamp times 6 , shunt relay input selector , supplied by ultra low noise salas philosophy but sakis designed ,beefy 10k uf , seperated PSU and trafo matched transistors and groovy capacitors ....
----------------------------------------------------------------------------------------------------------------------------------------------------------------------
tara !!!!!!! here comes the missing bass, here come the high , here comes the wide stage and image , here comes astronomical speed !!!!
The beast was outperformed by all means except power and drive ability ....Even though power was clearly not enough to drive the Proarc in a decent level for a noisy crowd of 15 people at the time and some others walking arround in total the sound was clearly much better and left the owners of the stand with jaws dropped and breathless
Amplifier stayed there for a couple of hours obviously warm but with absolutely no signs of stress ...
the problem occured when visitors that allrady visit the first day and come back again the second day noticed the diference and started to ask which is the amplifier that is palying today .
at this point my amplifier had to be remooved from the rack with a very fasttrack procedure .... there was question of prestige after all....
---------------------------------------------------------------------------------------------------------------------------------------------------------------------
Boulder 1100 Pre Amp,
1160 Power Amp
Proac K6 Signature
busted !!!!!!!
To remind you :
the amplifier that i am willing to outperform in the first place is BTL topology that to begin with means in a few words that you have 2 amplifiers 150w each summed on the speaker, and with 180 degrees diference they produce 300W
Given fact when you have 2 amplifiers summed like that BTL, you have double the LTP, double the suport: current sources current mirrors, double the VAS double the drivers , double the safety measures, double everything
Only thing that is half is the capacitance of the output stage which is now shared between the 2 amplifiers per ch.
So the P3a A will outperfrom the big amplifier in terms of sound any way you slice it due to far lower part count
i take this as a fact
let us say that 150 W of power will be more than enough to outperform the beast with the given speakers .
so the original question is how you produce 150 W of power but without loosing all the sweet features of a P3A
there is a chance that the answer is: " you dont"
this is what i am willing to learn
The event was an audio show on the extreme side where a DAC was tagged at 42k euro , preamp 20K amplifier 30K proarc speakers 30K in total with cables something about 130k euro ....
at the first day of the event i noticed that the system of 130 K had poor response in the low freq .
i asked the owners of the stand and they said to me that they also noticed the problem and had to do with the room reflections and they been trying diferent placement of the speakers for 2 days before to select the best placing for the audience .... The room was actually inside a hotel which they had the 1/3 of a ballroom separated with panels ...indeed the location was terrible add to it that a huge metallic ventillation ch was running across the room ....
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------
Listening though and compairing to what i know allready from years of measuring and listening my gut and my ears said that indeed the amp and possible the preamp had poor low end .... I was trying to explain that inside my mind and given some expirience from pro audio indeed you Cannot have a 300W@8R amplifier absolutely free in the lowend and the high end . If so any abuse will blow speakers within a split of a second ....
So the second day was even more busy and they have been playing kinda loud and it appears that the big beast was overheated there was a noticable change in the allrady poor performance of the system
so i erge them to hook up the P3a combo on the system .... they grab the bate and the p3A is now hooked up....allowed some 20 min warm up
Classic recipy main amp with all the known goodies configured as dual mono 300VA trafos per ch, 60k uf total , 1302-3281 engine , 200 mhz drivers and VAS ,160V styroflex miller caps, MKS input caps, decoupling , bleed resitors , speed up capacitors and dual fast rectifiers
configured as integrated amplifier with DOZ preamp times 6 , shunt relay input selector , supplied by ultra low noise salas philosophy but sakis designed ,beefy 10k uf , seperated PSU and trafo matched transistors and groovy capacitors ....
----------------------------------------------------------------------------------------------------------------------------------------------------------------------
tara !!!!!!! here comes the missing bass, here come the high , here comes the wide stage and image , here comes astronomical speed !!!!
The beast was outperformed by all means except power and drive ability ....Even though power was clearly not enough to drive the Proarc in a decent level for a noisy crowd of 15 people at the time and some others walking arround in total the sound was clearly much better and left the owners of the stand with jaws dropped and breathless
Amplifier stayed there for a couple of hours obviously warm but with absolutely no signs of stress ...
the problem occured when visitors that allrady visit the first day and come back again the second day noticed the diference and started to ask which is the amplifier that is palying today .
at this point my amplifier had to be remooved from the rack with a very fasttrack procedure .... there was question of prestige after all....
---------------------------------------------------------------------------------------------------------------------------------------------------------------------
Boulder 1100 Pre Amp,
1160 Power Amp
Proac K6 Signature
busted !!!!!!!
Last edited:
The first time I saw a compound output was 35 years ago, when I had just got my degree in electronics.
It was in a National Semiconductor application for LM391.
Around 1992 I decided to mod this amp, and try to make it more stable, in terms of idle current, and of course more powerful.
For those familiar with that chip, the bias transistor was inside the 16 pin chip, so there was no thermal connection with the temperature of the heatsink.
I used an external transistor (BC183 if I remember correctly) mounted on the heatsink so that idle decreased when the heat was up.
Being young and fresh I converted the output to emitter follower and then the LM391N100 would drive A968/C2238 and 3 pairs of A1943/C5200. At 4Ω loads the amp could make over 250Wrms.
However I am not sure about the benefits of the compound output and I decided to modify my amplifier which used a triple darlington output.
So I studied the p3a schematic and made a test board to support one pair of output transistors.
Rod Elliot says maximum rail voltage should not exceed +/-42VDC
After adjusting the Vbe multiplier, I fed the amp with +/42V and tested for oscillations above 50 KHz.
It looked ok so I raised the voltage to +/-64V. Same here, it looked quite stable.
I need to make another channel and have listening tests in comparison to my amp.
This will go a bit slow but I can post the results here.
It was in a National Semiconductor application for LM391.
Around 1992 I decided to mod this amp, and try to make it more stable, in terms of idle current, and of course more powerful.
For those familiar with that chip, the bias transistor was inside the 16 pin chip, so there was no thermal connection with the temperature of the heatsink.
I used an external transistor (BC183 if I remember correctly) mounted on the heatsink so that idle decreased when the heat was up.
Being young and fresh I converted the output to emitter follower and then the LM391N100 would drive A968/C2238 and 3 pairs of A1943/C5200. At 4Ω loads the amp could make over 250Wrms.
However I am not sure about the benefits of the compound output and I decided to modify my amplifier which used a triple darlington output.
So I studied the p3a schematic and made a test board to support one pair of output transistors.
Rod Elliot says maximum rail voltage should not exceed +/-42VDC
After adjusting the Vbe multiplier, I fed the amp with +/42V and tested for oscillations above 50 KHz.
It looked ok so I raised the voltage to +/-64V. Same here, it looked quite stable.
I need to make another channel and have listening tests in comparison to my amp.
This will go a bit slow but I can post the results here.