Hello!
Since I didn't want to hijack sakis's thread about the P3A comparison I decided to open a new thread.
I'm referring to my recently build Rod Elliott P3A stereo amp, described and showed here:
http://www.diyaudio.com/forums/solid-state/96192-post-your-solid-state-pics-here-146.html
One member asked about the sound, and now the unit had about one week burn in and I discoverd a few things I would like to share / discuss with you.
First of all, the amp is build with very good parts. No fancy high-end stuff, but very solid and reliable "a-grade" insdustry stuff like Vishay/BC capacitors, Wima film caps, thomsson 1% metal film resistors, transistors (including output devices) from ON Semi (Motorola I think), Talema toroid, large Fischer (Conrad) heatsink with 0,7K/W, thick multistranded hookup wire, optimized wire placement and so on.
First I adjusted the quiscent current to 75mA (Rod's suggestion), later to 60mA.
The amps works quite nice. It is absolutely dead quiet. No humm or noise of any kind, no on/off switching noise, nothing!
The sound seems to have quite a lot potential (I will explain the reason for this expression later on). It plays a bit more on the relaxed, musical, powerful and juicy side, it has power, authority and a nice sense for small details, without being analytical. The bass is solid, the midrange fluid and open, the treble is nice and detailed without any hint of grain or harshness. Very nice so far!
But, my source is a Non-Os Philips TDA1543 dac with passive i/v conversion and a passive 20k volume pot, so no active preamp. And this is the first problem. This dac seems to be unable to drive the amp properly. There is always this feeling as if the amp really WANTS to play, but is not able to because of the weak source. This is noticeable because of the weak dynamic abilities, slighly recessed resolution and focus, a rather unprecise and rounded bottom end. I have to add that this dac has absolutely no problems to drive my Anthony Holton nxV200 amps, but perhaps these modules do have a lower input sensitivity and they actually do have a higher input impedance (33k instead of 22k for the P3A).
So, there is the need to build a active preamp :-(
And I was so happy because at the moment my setup is completely opamp-free!
Alright, then there is another problem. The amp produces a lot of heat! Even in idle with the quiscent current set to 60mA, the large heatsink gets really hot after some time. Ok, we do have a very hot period here in germany at the moment, around 37°C for quite some time now, and ok, the heatsink gets very hot, but it stays that way without getting hotter and hotter. But I think it is a bit too much heat, especially in idle mode! I really wonder if this is the normal behaviour of the P3A circuit? As said, it seems to work absolutely fine. Bias is rock solid and stable when once adjusted, dc-offset on both speaker terminals is around 5mV each, the amp is dead quiet and seems to sound great (when a stronger source or a preamp is used), so, do I really have to use a heatsink that is MUCH larger for this small 60-100W power amp?
Here are, for comparison, some pictures of my nxV-200 stereo amp with even smaller heatsinks, and this amp NEVER gets hot, even with 37°C ambient temperature and loud listening levels, and it delivers about the same power as the P3A (slightly smaller transformer but the same rail voltage).
http://www.diyaudio.com/forums/soli...ur-solid-state-pics-here-125.html#post2065323
Any thoughts are appreciated!
Thanks a lot!
Martin
Since I didn't want to hijack sakis's thread about the P3A comparison I decided to open a new thread.
I'm referring to my recently build Rod Elliott P3A stereo amp, described and showed here:
http://www.diyaudio.com/forums/solid-state/96192-post-your-solid-state-pics-here-146.html
One member asked about the sound, and now the unit had about one week burn in and I discoverd a few things I would like to share / discuss with you.
First of all, the amp is build with very good parts. No fancy high-end stuff, but very solid and reliable "a-grade" insdustry stuff like Vishay/BC capacitors, Wima film caps, thomsson 1% metal film resistors, transistors (including output devices) from ON Semi (Motorola I think), Talema toroid, large Fischer (Conrad) heatsink with 0,7K/W, thick multistranded hookup wire, optimized wire placement and so on.
First I adjusted the quiscent current to 75mA (Rod's suggestion), later to 60mA.
The amps works quite nice. It is absolutely dead quiet. No humm or noise of any kind, no on/off switching noise, nothing!
The sound seems to have quite a lot potential (I will explain the reason for this expression later on). It plays a bit more on the relaxed, musical, powerful and juicy side, it has power, authority and a nice sense for small details, without being analytical. The bass is solid, the midrange fluid and open, the treble is nice and detailed without any hint of grain or harshness. Very nice so far!
But, my source is a Non-Os Philips TDA1543 dac with passive i/v conversion and a passive 20k volume pot, so no active preamp. And this is the first problem. This dac seems to be unable to drive the amp properly. There is always this feeling as if the amp really WANTS to play, but is not able to because of the weak source. This is noticeable because of the weak dynamic abilities, slighly recessed resolution and focus, a rather unprecise and rounded bottom end. I have to add that this dac has absolutely no problems to drive my Anthony Holton nxV200 amps, but perhaps these modules do have a lower input sensitivity and they actually do have a higher input impedance (33k instead of 22k for the P3A).
So, there is the need to build a active preamp :-(
And I was so happy because at the moment my setup is completely opamp-free!
Alright, then there is another problem. The amp produces a lot of heat! Even in idle with the quiscent current set to 60mA, the large heatsink gets really hot after some time. Ok, we do have a very hot period here in germany at the moment, around 37°C for quite some time now, and ok, the heatsink gets very hot, but it stays that way without getting hotter and hotter. But I think it is a bit too much heat, especially in idle mode! I really wonder if this is the normal behaviour of the P3A circuit? As said, it seems to work absolutely fine. Bias is rock solid and stable when once adjusted, dc-offset on both speaker terminals is around 5mV each, the amp is dead quiet and seems to sound great (when a stronger source or a preamp is used), so, do I really have to use a heatsink that is MUCH larger for this small 60-100W power amp?
Here are, for comparison, some pictures of my nxV-200 stereo amp with even smaller heatsinks, and this amp NEVER gets hot, even with 37°C ambient temperature and loud listening levels, and it delivers about the same power as the P3A (slightly smaller transformer but the same rail voltage).
http://www.diyaudio.com/forums/soli...ur-solid-state-pics-here-125.html#post2065323
Any thoughts are appreciated!
Thanks a lot!
Martin
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Heatsink should NOT get very hot at only 60-75 mA current.
Might be that there is some high frequency oscillation going on.
That is the amp is maybe not STABLE.
If looking at schema 60-80W Power Amplifier
there are some important components for stability:
C4 100pF ... you may try increase to 150pF, 220pF to see if this makes anything better
C6 100pF ... probably should be same value as C4
At output:
R15 10 Ohm + C7 100nF ... make sure they are attached alright
Of course best is to contact and ask Rod Elliott.
He has probably had other people who have had hot heatsinks in P3A.
Might be that there is some high frequency oscillation going on.
That is the amp is maybe not STABLE.
If looking at schema 60-80W Power Amplifier
there are some important components for stability:
C4 100pF ... you may try increase to 150pF, 220pF to see if this makes anything better
C6 100pF ... probably should be same value as C4
At output:
R15 10 Ohm + C7 100nF ... make sure they are attached alright
Of course best is to contact and ask Rod Elliott.
He has probably had other people who have had hot heatsinks in P3A.
-----you have been sugested to change the ceramics you used ....
-----then again none of these projects is really complete unless you look at it with a scope signal generator and some resistive and reactive load
------ many things happen i hoonestly have no intention to insult you but is there a chance that you misscaculated the idle ??? or used a wrong method ???
often if you use an A meter to seee the idle there is a chnace that something wis not proper ...best way is to do both ...check with A meter but also check voltage drop on colector resistors
( what is your rail voltage ??? what is your collector resistors ??? what is the voltage reading across them ??? what outputs ??? what drivers ??? is there any chance that any of them is fake ??? )
i run my P3A one version at 120ma some other at 60 it gets a bit warm but nothing to worie about ...then again my heat sinks are by far smaller ....so something from all is wrong
the suggestion from line up i wouldnt go for.... 220pf in the vas stage will kill many of the nice sonics of the particular amp
post your info and measure and will compaire it with mine and leto you know
kind regards sakis
-----then again none of these projects is really complete unless you look at it with a scope signal generator and some resistive and reactive load
------ many things happen i hoonestly have no intention to insult you but is there a chance that you misscaculated the idle ??? or used a wrong method ???
often if you use an A meter to seee the idle there is a chnace that something wis not proper ...best way is to do both ...check with A meter but also check voltage drop on colector resistors
( what is your rail voltage ??? what is your collector resistors ??? what is the voltage reading across them ??? what outputs ??? what drivers ??? is there any chance that any of them is fake ??? )
i run my P3A one version at 120ma some other at 60 it gets a bit warm but nothing to worie about ...then again my heat sinks are by far smaller ....so something from all is wrong
the suggestion from line up i wouldnt go for.... 220pf in the vas stage will kill many of the nice sonics of the particular amp
post your info and measure and will compaire it with mine and leto you know
kind regards sakis
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This might not be a very helpful suggestion but looking at the pictures of your amplifier that you have posted elsewhere on the forum I can't see any ventilation holes in the bottom of your case, only on the top cover.
If this is the case then you will not be getting proper air flow over the heatsink cooling fins and this will quite easily cause everything to get very hot very quickly. Typicaly if you want to mount a heatsink insode of a case it is a very sensible idea to make sure there are a lot of ventialtion holes both above and below the heatsink fins to alow enough air to flow over the heatsink and to cary away the heat.
He should consider redesigning the whole thing....
No pun intended against Rod, but as a minimum,
an output LR filter is mandatory.
hello wahab why you say that ??? in the P3A C+R filter exists
my friend wahab here i will not agree ....as stated befor i have P3A amplifiers working in an italian dinner wired with simple flat cable tops 2x1mm in lenght some 10 or 15 or 20 or even more driving weird loads and some of them driving piezos ...all this is done in a terrible env. that include dimmers transformers of any kind power and signal cables mixed all together and working perfectly for more than 2years now only with an cR that exists in the circuit and no inductor
the P3A is a perfectly working amp as is and to my understanding the fault lays only in the choise of parts and probably some mistake in tuning ...lets wait of what the OP has to say and we will take it from there ...
other than that is good to talk to you again and hope that you are doing well
wise to think will be that performance versus cost and simplicityis superior
kind regards sakis
my friend wahab here i will not agree ....as stated befor i have P3A amplifiers working in an italian dinner wired with simple flat cable tops 2x1mm in lenght some 10 or 15 or 20 or even more driving weird loads and some of them driving piezos ...all this is done in a terrible env. that include dimmers transformers of any kind power and signal cables mixed all together and working perfectly for more than 2years now only with an cR that exists in the circuit and no inductor
the P3A is a perfectly working amp as is and to my understanding the fault lays only in the choise of parts and probably some mistake in tuning ...lets wait of what the OP has to say and we will take it from there ...
other than that is good to talk to you again and hope that you are doing well
wise to think will be that performance versus cost and simplicityis superior
kind regards sakis
Hey you guys,
thank you all VERY MUCH for your advices and suggestions!
@ lineup
Since this board I purchased from Rod actually is a revision of an earlier version, I guess Rod had a reason to make these values 100pF. He might have checked all this with a scope and considered it as right and stable. I do not own a scope, so changing any component values to others than the originals might lead to completely unpredictable results. That's why I hesitate to do that.
R15 and C7 are installed correctly.
@ sakis
Well, I know you don't like ceramics that much... ;-)
But it's Rod himself who suggests ceramics in these positions, and while we can always discuss the sound of ceramics, I'm pretty sure he suggests these caps because he knows that they work for the intended purpose. I'm thinking about changing these to silver micas or Wima FKP's, but I doubt that these ceramics do cause oscillation, only because of the fact that they are ceramics...
The method I used for biasing the quiescent current is exactly the method Rod describes in his article, the voltage drop across the two resistors R13 & R14.
Concerning the B1 Buffer: I thought about that, too. But the problem here is not only the slightly recessed dynamics, but also a noticeably lower output level with the P3A in comparison to the nxV200 with my dac as source. So I think a little bit of gain might be helpful here to increase dynamic headroom.
Rail voltage is +/-35V (2x25V transformer secondaries). Collector resistors are 0R33, voltage across them was 50mV (for around 75mA quiescent current) and is now 40mV (for around 60mA). All parts are purchased from Conrad Elektronik, Germany. A very good shop, not cheap, but all the parts are really good. No comparison to other german suppliers like Reichelt, fo example......... cheap, but really many fakes and bad parts!
@ richie00boy
Actually, in this revision the 100nF caps in the supply rails is paralleled to 100uF caps. 100nF is Wima MKS2 63V, 100uF is Vishay/BC 63V (non low esr).
The nxV200 and the P3A are two projects I started simultaneously. I purchased the board for the P3A months ago and parallel decided to build the nxV200, simply out of curiosity, and to have something to compare against each other. In fact, these two amps do have quite a different sound signature. They do things different, but I like both for the way they deliver music. In the end I will have to make a decision between those two, mainly because of monetary reasons :-(
This is going to be difficult...
@ jaycee
He already did! But I hesitate to attach the current schematic because of copyright reasons. You can always have a look at his web page.
@ Andrew.Thompson
Yes, you're right! But on page 147 of the solid state picture thread I explained why this is supposed to work as well. But beside this, even without the top plate of the case the heatsink temperature rises to a quite high level, even with no music playing. I mean, it is not THAT hot, but I have the idea that it is just a bit too hot for an amplifier that is just turned on with no signal on the input and no speakers connected (but anyway, there is no difference with speakers connected and without).
@ wahab & sakis
I can't say anything about the need of a LR filter instead of a CR filter because this is above my level of knowledge. The CR filter from output to ground in this revision is C=100nF, R=10R.
Well, I will send Rod a message, perhaps he is willing to have a look at this thread. We'll see!
Thank you all!
Martin
thank you all VERY MUCH for your advices and suggestions!
@ lineup
Since this board I purchased from Rod actually is a revision of an earlier version, I guess Rod had a reason to make these values 100pF. He might have checked all this with a scope and considered it as right and stable. I do not own a scope, so changing any component values to others than the originals might lead to completely unpredictable results. That's why I hesitate to do that.
R15 and C7 are installed correctly.
@ sakis
Well, I know you don't like ceramics that much... ;-)
But it's Rod himself who suggests ceramics in these positions, and while we can always discuss the sound of ceramics, I'm pretty sure he suggests these caps because he knows that they work for the intended purpose. I'm thinking about changing these to silver micas or Wima FKP's, but I doubt that these ceramics do cause oscillation, only because of the fact that they are ceramics...
The method I used for biasing the quiescent current is exactly the method Rod describes in his article, the voltage drop across the two resistors R13 & R14.
Concerning the B1 Buffer: I thought about that, too. But the problem here is not only the slightly recessed dynamics, but also a noticeably lower output level with the P3A in comparison to the nxV200 with my dac as source. So I think a little bit of gain might be helpful here to increase dynamic headroom.
Rail voltage is +/-35V (2x25V transformer secondaries). Collector resistors are 0R33, voltage across them was 50mV (for around 75mA quiescent current) and is now 40mV (for around 60mA). All parts are purchased from Conrad Elektronik, Germany. A very good shop, not cheap, but all the parts are really good. No comparison to other german suppliers like Reichelt, fo example......... cheap, but really many fakes and bad parts!
@ richie00boy
Actually, in this revision the 100nF caps in the supply rails is paralleled to 100uF caps. 100nF is Wima MKS2 63V, 100uF is Vishay/BC 63V (non low esr).
The nxV200 and the P3A are two projects I started simultaneously. I purchased the board for the P3A months ago and parallel decided to build the nxV200, simply out of curiosity, and to have something to compare against each other. In fact, these two amps do have quite a different sound signature. They do things different, but I like both for the way they deliver music. In the end I will have to make a decision between those two, mainly because of monetary reasons :-(
This is going to be difficult...
@ jaycee
He already did! But I hesitate to attach the current schematic because of copyright reasons. You can always have a look at his web page.
@ Andrew.Thompson
Yes, you're right! But on page 147 of the solid state picture thread I explained why this is supposed to work as well. But beside this, even without the top plate of the case the heatsink temperature rises to a quite high level, even with no music playing. I mean, it is not THAT hot, but I have the idea that it is just a bit too hot for an amplifier that is just turned on with no signal on the input and no speakers connected (but anyway, there is no difference with speakers connected and without).
@ wahab & sakis
I can't say anything about the need of a LR filter instead of a CR filter because this is above my level of knowledge. The CR filter from output to ground in this revision is C=100nF, R=10R.
Well, I will send Rod a message, perhaps he is willing to have a look at this thread. We'll see!
Thank you all!
Martin
Last edited:
Hi , sakis
Well, if there s an output filter, all is good then.
Must aknowledge that it would be difficult to have less
parts for such a design, so no doubt that the cost/complexity/perfs
ratio is of first order...
Thank you for your kinds words, i hope that all
is well for you as well in these strange times we are
all currently living in since a few years...
Well, if there s an output filter, all is good then.
Must aknowledge that it would be difficult to have less
parts for such a design, so no doubt that the cost/complexity/perfs
ratio is of first order...
Thank you for your kinds words, i hope that all
is well for you as well in these strange times we are
all currently living in since a few years...
You can slightly increase the gain of the amp to
match your DAC output level.
Just increase R5 to 27K.
R2 should also be increased in that case to 24.8K
in theory, but a 27K should do it perfectly.
I had the same problem with one of my P3A.
It was defenetely self-oscillating, due probably to the fast transistors I used.
Fixed raising the CB capacitor on the low side driver to 220pF. Did not touch Cdom. No audible difference, highs still crystal clear, 100Khz square wave still satisfactory.
But then heat sink (0.5 C/W x 2 channels) pretty cool at idle, after 10'. After a doublle live LP of AC/DC played at the onset of clipping (from CD, not the ugly compressed stuff) just warm, but defenetely not very hot, something like 60 C.
BTW bias at 45 mA, just a little bit over the crossover disappearing from my scope, I liked the sound more that way.
It was defenetely self-oscillating, due probably to the fast transistors I used.
Fixed raising the CB capacitor on the low side driver to 220pF. Did not touch Cdom. No audible difference, highs still crystal clear, 100Khz square wave still satisfactory.
But then heat sink (0.5 C/W x 2 channels) pretty cool at idle, after 10'. After a doublle live LP of AC/DC played at the onset of clipping (from CD, not the ugly compressed stuff) just warm, but defenetely not very hot, something like 60 C.
BTW bias at 45 mA, just a little bit over the crossover disappearing from my scope, I liked the sound more that way.
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