It's interesting that there are MPQ-6600's on a MOSFET Forte . I wonder if Julius found a source for a good supply of these ? After I was no longer in the audio biz -I ran into a couple of Audire amps that had substituted pairs of transistors glued back to back to a common heatsink -these were substituted for the MPQ-6600. But I assume the MOSFET amps are quit a bit newer than the units I was working on ?
Audire Audio Components
- Thread starter Bostown
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Zarathustra
Active Member
As you can see in my picture of the Forte the Philips large can capacitors have a datecode 9116 meaning week 16 of year 1991 I believe.
They were made I read somewhere from 1982 till 1993 so the ones from Sungear and me are probably last incarnations of the Forte.
Out of curiosity -just ran a search for Motorola MPQ-6600 and two places claim to have them in fair quantity - unfortunately the min. quantity was 40 pieces - might be time for some of ya'll who own these to do a group buy? A guess would be -that over a more than 10 year period -about 10% of the Audire power amps we sold required a MPQ-6600 to be replaced -usually after years of use. the last time i did a search for these parts (years ago) -no one had them in stock.
Zarathustra
Active Member
Great idea count me in!
Zarathustra
Active Member
Just got my Audire Forte.
The Motorola MPQ-6600 are replaced in my Forte with two pairs MSP 8099/8599 NPN - PNP thermally coupled on each side of course.
These are of course available in abundance I reckon
Unit looks really great inside and is pretty heavy for such a small chassis.
The Motorola MPQ-6600 are replaced in my Forte with two pairs MSP 8099/8599 NPN - PNP thermally coupled on each side of course.
These are of course available in abundance I reckon
Unit looks really great inside and is pretty heavy for such a small chassis.
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Zarathustra
Active Member
Forte sounds great on my second office room set with a Conrad Johnson PV12 tube-pre-amp and KEF C60 loudspeakers.
Much better than the Accuphase E-206 integrated. This is a preliminary verdict based after 5 minutes listening
Power MOSFETS are indeed the IRF130 & 9130 as Sungear already clarified.
Much better than the Accuphase E-206 integrated. This is a preliminary verdict based after 5 minutes listening
Power MOSFETS are indeed the IRF130 & 9130 as Sungear already clarified.
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Zarathustra
Active Member
Unit keeps relatively (too cold IMO) cold. Does anybody what the correct bias (idling current) must be for the Forte.
I can use a MM over the .33 emitter resistors and measure it in mV's or remove one of the railfuses and measure the Amps directly.
Any suggestions?
I can use a MM over the .33 emitter resistors and measure it in mV's or remove one of the railfuses and measure the Amps directly.
Any suggestions?
I think it is safer to measure the voltage across the emitter (or source, in the case of MOSFET?) resistors, as you mentioned.
Not sure what the idle current should be set to from the factory, but I can post some measurements from mine for you to use for comparison in a day or two.
Zarathustra
Active Member
That would be great!
The switches
The switches are also 4 amp circuit breakers. I haven't had much luck finding a suitable replacement, but maybe someone else has.Good info here.
Have a Forte here. Never hooked mine up, part of a collection I saved from the dump.
Would like to replace the two switches for cosmetic reasons.
Zarathustra
Active Member
These are E-T-A 41-10-P10 4 Amps circuitbreakers.
You could contact E-T-A they still exist:
https://www.e-t-a.com/home/?forceCountry=US
Maybe a partsupplier still has them but I think their obsolete.
Success!
Zarathustra
Active Member
Measured the bias over several of the .33 Ohm resistors and got values around 1.5 mV.
Unit kept cold also.
Connected a MM over one of the fuseholders (fuse removed of course) and adjusted the bias to 0.4 A per channel about 1.3 Watts of Class A at 8 Ohms.
Those one turn trimmers should be banned for adjusting the bias!
DC Offset is 35 mV and 9 mV respectively. The 35 mV is too high and maybe if I swap the lytics on both boards (they're all 27 years old now) it will getting better.
Unit gets properly warm, moderate not too hot to touch but comfortably.
Nelson Pass recommends 50 Degrees Celcius just too hot to touch but I'm content to have that First Watt in Class A!
Any thoughts?
Unit kept cold also.
Connected a MM over one of the fuseholders (fuse removed of course) and adjusted the bias to 0.4 A per channel about 1.3 Watts of Class A at 8 Ohms.
Those one turn trimmers should be banned for adjusting the bias!
DC Offset is 35 mV and 9 mV respectively. The 35 mV is too high and maybe if I swap the lytics on both boards (they're all 27 years old now) it will getting better.
Unit gets properly warm, moderate not too hot to touch but comfortably.
Nelson Pass recommends 50 Degrees Celcius just too hot to touch but I'm content to have that First Watt in Class A!
Any thoughts?
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Zarathustra
Active Member
Got a tip from a other Dutch guy on Audiofreaks.nl that a good substitute for the Motorola MQP6600 would be:
a pair of Analog Devices SSM2212 en SSM2220 (SOIC8 package) to replace one MQP6600.
Sounds good to me!
Only you need a SOIC->DIP converter...
a pair of Analog Devices SSM2212 en SSM2220 (SOIC8 package) to replace one MQP6600.
Sounds good to me!
Only you need a SOIC->DIP converter...
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Zarathustra
Active Member
Just discovered that at first sight I thought there where four Philips 12.000uF 75V filtercaps per channel.
That's all I could see with the hood removed that 12.000uF cap rating
But when I removed the aluminum fold-over I saw that these where the smaller and shorter ones.
Opposite of every 12.000uF cap there's a longer 26.000uF cap so the whole filtercapacitor section is better supported than would be the case when you took 8 caps of the same length.
Total cap rating per channel is a whopping 76.000uF that's with a railvoltage of approx. 53 Volts 212 Joules of stored energy.
That's pretty substantial for such a small amp and even more storage than a Otez has, well the one at the beginning of this thread (week 44 1986 datcodes) at least. Maybe later Otez's got the same eight 26.000uF filtercaps as the Parlando and the bigger amps got probably a higher railvoltage.
I think I will opt for an original MPQ 6600 but there are three versions:
6600, 6600A and 6600A1
The A1 is probably the latest incarnation.
Can I use all?
That's all I could see with the hood removed that 12.000uF cap rating
But when I removed the aluminum fold-over I saw that these where the smaller and shorter ones.
Opposite of every 12.000uF cap there's a longer 26.000uF cap so the whole filtercapacitor section is better supported than would be the case when you took 8 caps of the same length.
Total cap rating per channel is a whopping 76.000uF that's with a railvoltage of approx. 53 Volts 212 Joules of stored energy.
That's pretty substantial for such a small amp and even more storage than a Otez has, well the one at the beginning of this thread (week 44 1986 datcodes) at least. Maybe later Otez's got the same eight 26.000uF filtercaps as the Parlando and the bigger amps got probably a higher railvoltage.
I think I will opt for an original MPQ 6600 but there are three versions:
6600, 6600A and 6600A1
The A1 is probably the latest incarnation.
Can I use all?
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I bought some 6600A and 6600 parts a few years ago but I have never tried the 6600A parts. They might not work well, or they might actually sound better than the 6600 parts. I might try the 6600A parts on my next Crescendo or Forte project. Practically everything I buy nowadays has the MPS8099/MPS8599 pairs in place of the MPQ6600 parts.
Zarathustra
Active Member
So the two pairs of MPS8099/MPS8599 pairs I found also in my Forte are standard from factory?
I purchased the model One in 1976 to drive Magneplanar MG-IIs. At the time, I used a Frank Van Alstine modified Dyna preamp called the FET-5. I took a page from his "Double Dyna" approach and upped the bridge to a 30A model and built an external case with an additional 60,000 uF of capacitance bringing it to 80,000 uF.
It improved transparency and dynamic punch big time. Once unplugged, it would play on for a good thirty seconds.
Zarathustra
Active Member
Hi E-Stat is the avatar you have from Beveridge?I purchased the model One in 1976 to drive Magneplanar MG-IIs. At the time, I used a Frank Van Alstine modified Dyna preamp called the FET-5. I took a page from his "Double Dyna" approach and upped the bridge to a 30A model and built an external case with an additional 60,000 uF of capacitance bringing it to 80,000 uF.
It improved transparency and dynamic punch big time. Once unplugged, it would play on for a good thirty seconds.
I believe that PS Audio they believes in big powersupplies for pre-amps also.
I once had a Krell KRS-2 with four transformers in a separating housing and lots of capacitance and four bridge-rectifiers in a another separate housing and the main unit.
Totally overkill for a pre-amp but typically the Krell V8 approach.
Did sound quite good, on par with a Levinson ML-7a.
