I recently purchased a broken P3000 for cheap.
The following link contains a schematic of the amp.
http://www.hafler.com/techsupport/pdf/MAN1461C_P1500_P3000_man.pdf
Diagnosis revealed that one of the N-channel output MosFets was shorted source to drain. No other failure was found on initial diagnosis. The AC fuse was correct and still intact!
Removing the bad MosFet from circuit resulted in the amplifier becoming functional again with near 0 VDC offset, and somewhat reduced positive current output on the affected channel.
There are two N and two P MosFets per channel.
After replacing all four of the output MosFets on the afflicted channel with matched devices; the amplifier appeared to operate normally.
On to the next phase, modifications.
1. Parallel the existing 6800uf main filter caps with an additional 10,000uf and 4.7uf film capacitor each.
2. Install CPU cooler type heat sinks on the bridge rectifier modules as the bridges ran uncomfortably warm during extended high power testing.
3. Replace the original DC block electrolytic caps C21,C22 in the servo loop with film types. A single 4.7Uf was used in each channel.
After these mods the amp was placed in service in my home stereo system.
I was pleased with my work and the sound that the amp delivered.
-------------------------------------------------------------------
Now the original problem rears it's ugly head:
After basking in my apparent success for a few days the amp decides it is time to humble me.
Snap, crackle, pop sounds now emit from the channel that I had just repaired!!! This likely was causal in the initial failure.
With the amp on dummy load and 'scope with incandescent lamp in place of fuse:
Tapping the cascode transistors on the problem channel greatly aggravated the unwanted noise waveform.
Looking at the original cascode transistors specs (MPSA06/MPSA56).
I calculated that they were being operated uncomfortably near their maximum dissipation in this particular amplifier.
Looking for superior transistors suitable for cascode led me to the Sanyo 2SA1403/2SC3597 pairs.
Next phase, Repair/Mods MkII.
1. Replace original MPSA06/MPSA56 pairs with 2SA1403/2SC3597. Small ferrite are placed on each emitter lead in deference to the 800Mhz Ft of the new cascode transistors.
2. Parallel C116 with 47UF electrolytic. This forces the idle current to rise and fall slowly on turn on/turn off.
The main filter caps are almost completely discharged now each time the amp is turned off.
This can prevent screwdriver damage and other unpleasantness.
Don't ask how I know
Now three plus weeks later, all is well with the repaired/modified amp.
I won't resort to glowing tales of "air" "space" "mosfet mist" etc.
I will only say that I like the results!!!!
Looking at amplifier input on the 1 channel and amplifier output on the 2 channel of my Tek 2213 'scope, then nulling the two signals reveals an indicated residual noise+distortion of about .006 V P-P for 110 V P-P output into 8 ohms with a 20 Khz sine wave input.
Admittedly my measuring technique could be improved with additional equipment.
I set the total idle current to 300 Ma per channel prior to measurements. (yes,yes I know what the book says)....trying for closer to "Class A".
All initial "smoke testing" was done with a 100W light bulb in place of the AC fuse.
No parasitic or other anomalous waveforms were detected during final testing on dummy loads or speakers.
Comments? Critique?
Thanks.
Rickey.
The following link contains a schematic of the amp.
http://www.hafler.com/techsupport/pdf/MAN1461C_P1500_P3000_man.pdf
Diagnosis revealed that one of the N-channel output MosFets was shorted source to drain. No other failure was found on initial diagnosis. The AC fuse was correct and still intact!
Removing the bad MosFet from circuit resulted in the amplifier becoming functional again with near 0 VDC offset, and somewhat reduced positive current output on the affected channel.
There are two N and two P MosFets per channel.
After replacing all four of the output MosFets on the afflicted channel with matched devices; the amplifier appeared to operate normally.
On to the next phase, modifications.
1. Parallel the existing 6800uf main filter caps with an additional 10,000uf and 4.7uf film capacitor each.
2. Install CPU cooler type heat sinks on the bridge rectifier modules as the bridges ran uncomfortably warm during extended high power testing.
3. Replace the original DC block electrolytic caps C21,C22 in the servo loop with film types. A single 4.7Uf was used in each channel.
After these mods the amp was placed in service in my home stereo system.
I was pleased with my work and the sound that the amp delivered.
-------------------------------------------------------------------
Now the original problem rears it's ugly head:
After basking in my apparent success for a few days the amp decides it is time to humble me.
Snap, crackle, pop sounds now emit from the channel that I had just repaired!!! This likely was causal in the initial failure.
With the amp on dummy load and 'scope with incandescent lamp in place of fuse:
Tapping the cascode transistors on the problem channel greatly aggravated the unwanted noise waveform.
Looking at the original cascode transistors specs (MPSA06/MPSA56).
I calculated that they were being operated uncomfortably near their maximum dissipation in this particular amplifier.
Looking for superior transistors suitable for cascode led me to the Sanyo 2SA1403/2SC3597 pairs.
Next phase, Repair/Mods MkII.
1. Replace original MPSA06/MPSA56 pairs with 2SA1403/2SC3597. Small ferrite are placed on each emitter lead in deference to the 800Mhz Ft of the new cascode transistors.
2. Parallel C116 with 47UF electrolytic. This forces the idle current to rise and fall slowly on turn on/turn off.
The main filter caps are almost completely discharged now each time the amp is turned off.
This can prevent screwdriver damage and other unpleasantness.
Don't ask how I know
Now three plus weeks later, all is well with the repaired/modified amp.
I won't resort to glowing tales of "air" "space" "mosfet mist" etc.
I will only say that I like the results!!!!
Looking at amplifier input on the 1 channel and amplifier output on the 2 channel of my Tek 2213 'scope, then nulling the two signals reveals an indicated residual noise+distortion of about .006 V P-P for 110 V P-P output into 8 ohms with a 20 Khz sine wave input.
Admittedly my measuring technique could be improved with additional equipment.
I set the total idle current to 300 Ma per channel prior to measurements. (yes,yes I know what the book says)....trying for closer to "Class A".
All initial "smoke testing" was done with a 100W light bulb in place of the AC fuse.
No parasitic or other anomalous waveforms were detected during final testing on dummy loads or speakers.
Comments? Critique?
Thanks.
Rickey.
Last edited:
Thanks for the correction Sir.
I see the title has a typo in it too.
Multitasking is a challenge for me sometimes.
It's fixed now.
Regrettably,
I took no pictures at the time of repair/modification.
Lets just say some are 10,000 Uf caps are oriented vertical and some are horizontal, and no air vents were blocked.
An appropriate amount of RTV silicone rubber was used.
I plan to have it apart again for some front end mods.
I aim to eliminate the IC op amps, the DC servo loops, replace the diff inputs with matched devices, and put a DC balance adjust in the diff amp.
Maybe a little more bypassing on the low rails.
Ferrite beads on the input signal path etc.
I will take some pics then.
This may take awhile as I have a full time career chasing me! HeHe.
Stay tuned..........
Rickey.
Mono Config Improvements?
Good read here, I have had 2 of these amps for a few years now and really like them. Been using them in mono configuration on a couple of AE TD15M drivers. Will be looking into your suggested modifications.
Any idea floating around on improving their mono configuration/sound?
Is it a "no no" to try & drive them in 4 ohm loads in mono?
Is 1/2" enough "stacking" room enough between the two amps?
Driving them with the Hafler 945.
Pound for pound at the rated 400 watt output, the best amps I have had in a long time!
Thanx
DC
Good read here, I have had 2 of these amps for a few years now and really like them. Been using them in mono configuration on a couple of AE TD15M drivers. Will be looking into your suggested modifications.
Any idea floating around on improving their mono configuration/sound?
Is it a "no no" to try & drive them in 4 ohm loads in mono?
Is 1/2" enough "stacking" room enough between the two amps?
Driving them with the Hafler 945.
Pound for pound at the rated 400 watt output, the best amps I have had in a long time!
Thanx
DC
What loads you put on an amp has to do with what the spec is obviously. If you are the daring type and have to power some neat 4 ohm load, I would put in marginal fast blow fuses for sure but maybe use a variac to bring up the power slowly to half to see what cooks or not. I don't recommend that you really do that unless your amps are expendable.
As far and clearance room between amps, .5" is too close for that kind of wattage. It also depends what else is around the amps and the humidity and temp of the room. I have used little 120mm computer fans to draw heat when amps are in an enclosed cab run at half power. The rule of thumb is if you can't hold your hand on the chassis of the amp, they are too hot and need cooling.
The basic rec for amps that you think need to sound better is to get better sounding amps rather than modify them unless you really know what you are doing. If you have to ask, I wouldn't mess with it. Having said that with an assumption that the amp is the source of poor sound, the real item to look at is the speakers and the room acoutics. Sound is all about having a reference to compare with meaning anything going into or out of an amp will be influenced by what feeds it and what it powers. If those are confirmed to be perfect then ....
Last advice is don't take any one source as the perfect audio guru. Get an average of talk and see what seems to be redundantly said. Doesn't matter if they just listen or tinker.
dB
As far and clearance room between amps, .5" is too close for that kind of wattage. It also depends what else is around the amps and the humidity and temp of the room. I have used little 120mm computer fans to draw heat when amps are in an enclosed cab run at half power. The rule of thumb is if you can't hold your hand on the chassis of the amp, they are too hot and need cooling.
The basic rec for amps that you think need to sound better is to get better sounding amps rather than modify them unless you really know what you are doing. If you have to ask, I wouldn't mess with it. Having said that with an assumption that the amp is the source of poor sound, the real item to look at is the speakers and the room acoutics. Sound is all about having a reference to compare with meaning anything going into or out of an amp will be influenced by what feeds it and what it powers. If those are confirmed to be perfect then ....
Last advice is don't take any one source as the perfect audio guru. Get an average of talk and see what seems to be redundantly said. Doesn't matter if they just listen or tinker.
dB
Matching
To xmitterengineer:
Did you hafta match the 2SA1403/2SC3597 pairs? And...
My interest in your project is MPSA06/MPSA56* replace what my repair project uses for the dual dif front end. That said I can't help but wonder if 2SA1403/2SC3597 is a worthwhile upgrade to same*.
I'll post the DIYAudio link on my next visit.
Thanks for your input, tony
To xmitterengineer:
Did you hafta match the 2SA1403/2SC3597 pairs? And...
My interest in your project is MPSA06/MPSA56* replace what my repair project uses for the dual dif front end. That said I can't help but wonder if 2SA1403/2SC3597 is a worthwhile upgrade to same*.
I'll post the DIYAudio link on my next visit.
Thanks for your input, tony
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