I recently got hold of a pair of these monster mono block amplifiers and documented the story on Audiokarma...
I got them from a scrap dealer and as expected they didn't work. The problem appears to be that the same pcb in both amplifiers has been messed around with by someone in the past. One has had parts removed, the other has had incorrect bits added.
The problem is no schematics or circuit diagrams exit for these amps, and every tech I have contacted has said they can't help.
I have tried to contact anyone related to NRG control to no avail.
At 55kg , with 48 output transistors and a transformer larger than a brick each , I REALLY want to get them working, even if it isn't practical to use 400w class A amps everyday, one day I might just have a use for them.
The original plan of hoping a tech could figure out the problem without a diagram didn't work.
Next I thought about reverse engineering the pcb and drawing a circuit diagram from that, but it would take ages AND only give me the diagram for that particular board, there are 2 other similar sized boards + all the outputs + the power supply section which would take far too much time to draw out...
The latest idea was to build a clone of a more popular amp, like a Krell KSA 250 based around the power supply and chassis of the NRG amps....
Can anyone advise...?
I got them from a scrap dealer and as expected they didn't work. The problem appears to be that the same pcb in both amplifiers has been messed around with by someone in the past. One has had parts removed, the other has had incorrect bits added.
The problem is no schematics or circuit diagrams exit for these amps, and every tech I have contacted has said they can't help.
I have tried to contact anyone related to NRG control to no avail.
At 55kg , with 48 output transistors and a transformer larger than a brick each , I REALLY want to get them working, even if it isn't practical to use 400w class A amps everyday, one day I might just have a use for them.
The original plan of hoping a tech could figure out the problem without a diagram didn't work.
Next I thought about reverse engineering the pcb and drawing a circuit diagram from that, but it would take ages AND only give me the diagram for that particular board, there are 2 other similar sized boards + all the outputs + the power supply section which would take far too much time to draw out...
The latest idea was to build a clone of a more popular amp, like a Krell KSA 250 based around the power supply and chassis of the NRG amps....
Can anyone advise...?
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Yeah...
It's a big box.
It might not have been terribly stable, thus the "mods".
A good tech could trace the PCBs and determine the schematic, unless someone finds one online or has one.
I'd first check the condition of the output devices. If enough of them are blown, then it becomes questionable as to what to do with the chassis.
Part of the issue is the long runs to the ouput devices... this tends to make for a layout that is difficult to run at a wide bandwidth.
For all I/we know this was a clone of a Krell... 😀
You could clone one of the Krell amps, they have been discussed here, and PCBs made, iirc. Low down on my list of favorite amps, but some people love them.
Interesting find! 😀
It's a big box.
It might not have been terribly stable, thus the "mods".
A good tech could trace the PCBs and determine the schematic, unless someone finds one online or has one.
I'd first check the condition of the output devices. If enough of them are blown, then it becomes questionable as to what to do with the chassis.
Part of the issue is the long runs to the ouput devices... this tends to make for a layout that is difficult to run at a wide bandwidth.
For all I/we know this was a clone of a Krell... 😀
You could clone one of the Krell amps, they have been discussed here, and PCBs made, iirc. Low down on my list of favorite amps, but some people love them.
Interesting find! 😀
I'm in the UK, London.
I totally forgot about this thread. Anymore advice? More interested in building a clone amp around these rather than hold out for a schematic as I don't think one will ever turn up.
I totally forgot about this thread. Anymore advice? More interested in building a clone amp around these rather than hold out for a schematic as I don't think one will ever turn up.
According to Google:
"NRG A401M ClassA mono-block amplifiers are extremely rare, just a few of these units were manufactured by NRG Control."
"A mighty amp from the 1990's designed by Denton Clarke" You may want to give-a-go at contacting Mr. Denton Clarke for a schematic and suggestions.
"Ghosts in the machine"..... a warning in several SciFi movies. A ghost in a 400W amp will destroy any speaker in a few seconds. Your PCBs look full of ghosts A QUICK BLOW FUSE in series with the speaker is good insurance.
OPTIONS you probably already considered.
1) Historic restoration to add a "SELDOM USED" amplifier to your collection / trophy room.
2) Use chassis + parts to construct a ghost-free modern stereo amp with circuits you understand. High power supply voltage means two 400W, lower current amplifiers.
---what output transistors and driver transistors are used? Do the output transistors test good.
---mounting: all N on one heatsink.... all P on the adjacent sink (N-N sinks next to P-P sinks) or ?? ... mixed N & P on each heatsink??
3) Sell it on eBay Euro in "as-is" condition.
"NRG A401M ClassA mono-block amplifiers are extremely rare, just a few of these units were manufactured by NRG Control."
"A mighty amp from the 1990's designed by Denton Clarke" You may want to give-a-go at contacting Mr. Denton Clarke for a schematic and suggestions.
"Ghosts in the machine"..... a warning in several SciFi movies. A ghost in a 400W amp will destroy any speaker in a few seconds. Your PCBs look full of ghosts A QUICK BLOW FUSE in series with the speaker is good insurance.
OPTIONS you probably already considered.
1) Historic restoration to add a "SELDOM USED" amplifier to your collection / trophy room.
2) Use chassis + parts to construct a ghost-free modern stereo amp with circuits you understand. High power supply voltage means two 400W, lower current amplifiers.
---what output transistors and driver transistors are used? Do the output transistors test good.
---mounting: all N on one heatsink.... all P on the adjacent sink (N-N sinks next to P-P sinks) or ?? ... mixed N & P on each heatsink??
3) Sell it on eBay Euro in "as-is" condition.
They look a mess - clearly attacked with a soldering iron . . .
I'd use the parts and build a modern design.
I'd use the parts and build a modern design.
Hello dazaa,
I write this from Germany, as I have the schematics you are looking for.
Plesa contact me: Herbert.Kukuk@gmx.de
Best regards
Herbert
I write this from Germany, as I have the schematics you are looking for.
Plesa contact me: Herbert.Kukuk@gmx.de
Best regards
Herbert
this are what these look like -
so,
how are this going with these?
1282
so,
how are this going with these?
1282
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That is a big chassis, but doesn't look like 400W worth of class A unfanned heatsinking to me.
Max efficiency 50% means 800W min dissipation, which should look like about a kW space heater but without anything being allowed to approach glowing or be cooled by air, so much bigger. Methinks the Class A designation was using the loose definition sometimes used (class A to maybe 80W, AB the rest of the way up). Or maybe a sliding bias scheme.
Still a nice chassis to work from. Power supply, case, and heatsinks are most of an amp's cost, anyway. Throw away the boards and transistors, and you have a great development platform for a custom amp build (along with LTSPICE of course).
Max efficiency 50% means 800W min dissipation, which should look like about a kW space heater but without anything being allowed to approach glowing or be cooled by air, so much bigger. Methinks the Class A designation was using the loose definition sometimes used (class A to maybe 80W, AB the rest of the way up). Or maybe a sliding bias scheme.
Still a nice chassis to work from. Power supply, case, and heatsinks are most of an amp's cost, anyway. Throw away the boards and transistors, and you have a great development platform for a custom amp build (along with LTSPICE of course).
Can anyone give me the contact info of Mr. Denton Clarke.
I cannot find any info nor his email adress.
I have 400 and A201s here, both are broken and noone seems to can help.
I cannot find any info nor his email adress.
I have 400 and A201s here, both are broken and noone seems to can help.
Just on the net soothing around for monos and came onto your post here Daz. Kudos to you. I must say. If it were me, I'd take them to right my wizard tech and tell him to have at'er....
He'd sort those things out...
Kudos...
He'd sort those things out...
Kudos...
After hassling around, I got a lot of infos and after talking to Mr.Denton and taking a look in the shematic I may strongly not advice going into further repair with this piece.
Mister Denton and 3 repair shops in Germany gave me the following info.
The type of Mosfets in this amp are no longer available, so generally replacing them with counterparts is also not possible as their curves are totally different and even speaking of gaining the same matching credentials in their coefficient range would require the purchase of several thausand Fets.
Mr. Denton and some of my collegues in Germany told me that it would be possible to redesign the driver stage and to drive TO-3 Mosfets directly. These are the most available Mosfets on the planet, but they do have totally different characteristics then the orginal ones used in the amp which are no longer available. The repair method for this option would require several thausand dollars up front for designing the new driver stage and again a couple of grand for matching the transistors. Their are no swapped or limit banks, so you have to match all 40 of them precisely.
In other words 3-5K for the design work and probably another 3K grand for matching transistors can make up 8.000$ for repairs if you wish to do so. The amp then does neither have the orginal characteristics any more nor the sound when you bought it new.
I can recommend one who would work on this and ship wordwide, but I cannot give a guarantee if repair work will be sucessful.
If your interessted, drop me a message and I will provide his address.
The cost were an estimate up front and they can be higher or not as high. There is no guarantee the technican would be sucuessful with its repair job, so do this at your own wish and risk.
I would look at the new AM250 Monos. Parts should be available for those.
It is such a beautiful amplifier that it seems a shame :-(
Mister Denton and 3 repair shops in Germany gave me the following info.
The type of Mosfets in this amp are no longer available, so generally replacing them with counterparts is also not possible as their curves are totally different and even speaking of gaining the same matching credentials in their coefficient range would require the purchase of several thausand Fets.
Mr. Denton and some of my collegues in Germany told me that it would be possible to redesign the driver stage and to drive TO-3 Mosfets directly. These are the most available Mosfets on the planet, but they do have totally different characteristics then the orginal ones used in the amp which are no longer available. The repair method for this option would require several thausand dollars up front for designing the new driver stage and again a couple of grand for matching the transistors. Their are no swapped or limit banks, so you have to match all 40 of them precisely.
In other words 3-5K for the design work and probably another 3K grand for matching transistors can make up 8.000$ for repairs if you wish to do so. The amp then does neither have the orginal characteristics any more nor the sound when you bought it new.
I can recommend one who would work on this and ship wordwide, but I cannot give a guarantee if repair work will be sucessful.
If your interessted, drop me a message and I will provide his address.
The cost were an estimate up front and they can be higher or not as high. There is no guarantee the technican would be sucuessful with its repair job, so do this at your own wish and risk.
I would look at the new AM250 Monos. Parts should be available for those.
It is such a beautiful amplifier that it seems a shame :-(
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I have wondered if Dazaa had ever gotten those big beauties restored. I hope he did. My tech - a military tech that does all sorts of high end gear on the side - probably could sort out these issues and make them right as rain. He once rebuilt a vintage big class A Threshold amplifier which was so good the audio manufacturer, and dealer, of high end gear in the area selected it to run a pair of $30k Stats marketing them in a major audio show and won the entire show beating out $100k+ systems. The guy is an absolute wizard when it comes to anything electric/audio.
Hope Dazaa did end up getting these beauties back to gold again...
Hope Dazaa did end up getting these beauties back to gold again...
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I took a closer look at the 1600 series with bipolar outputs.
Parts are available, but the eletronic parts for the driver stage such as eltronic protection ciriuts and POS has essientially dried up.
None of them are available from any source.
I am not really sure if its worth working on them, too many unknown variables and problems.
Thresholds are easy to repair and their bipolars are easy in matching and at least they do not require exact matching.
Parts are available, but the eletronic parts for the driver stage such as eltronic protection ciriuts and POS has essientially dried up.
None of them are available from any source.
I am not really sure if its worth working on them, too many unknown variables and problems.
Thresholds are easy to repair and their bipolars are easy in matching and at least they do not require exact matching.
Oh... Okay. You're most likely right. You know far more than I do. This kid can do amazing things on various gear from various ages from '30s tube amps, Modern SS. He's rebuilt a number of vintage amps, pres etc. for me and is one of those wiz-kid sorts that loves problem solving and fixing anything when it comes to anything audio... Cheers and best. SirJer
Just stumbled back on this thread. To cut a long story short, nothing has really changed on these over the last few years, I left them with someone who thought he could repair then but did nothing. Yes the mosfets are NLA, but they can be found, not easy or cheap, but the chances of all 48 being blown is pretty slim. Even the NLA transistors on the low level boards (which were missing on mine) can be found from very specialist suppliers. I'll be dropping them to an ex certified Mcintosh tech soon for a proper appraisal.
Did you ever get those schematics ? Maybe post them and the part number of the mosfets and there are people here who might be able to help - if help is what you're after !
Yes I got the schematics, will need to dig out and upload. The mosfets are IRF9230, 6 are missing from my amps following the last persons attempt to repair. I don't think the monoblocks are an issue, I've got a lead on the matching preamp which is also faulty. BUT, no schematics exist, Denton Clarke said to pass on it unless it's super cheap...4 years of looking and this is the only one i've found, not sure whether i'll regret not buying it.