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Bonzoro

WTB, M1.0t (Non Inv)

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On 12/1/2019 at 11:43 PM, Bonzoro said:

Noticed right off the bat these opt2 amps run out of gas WAY before a WOPL.  If  (And I mean IF), these will push 400 WPC, they don't do it for long.  Something to do with not having a real transformer.   They sound excellent but have no legs. But, they are cheaper so that must be why they are popular.  Guess I could try them out as Mono's, one on each channel.  Don't know if it was a cost cutting thing or not why they used a gadget instead of a true transformer.  I even returned my Gain Jumper on my C-1 to the normal position due to lower sensitivity (Lower than the White Oak Mod on a Phase Linear 700 Series II).  I'm running a series of tests on my Audio Precision P1P Access, and I'll run both modded M-1.0t's along with 2 WOPL's and see if anything pops out at me.  The THD=N numbers are not as good either.  One amp got new RCA's and 5 ways, the other has not (as of yet) and I'm waiting on the Thump fix FET's for the second amp since it scared the hell out of the dogs AND ME......

 

I have ready made thump-fix boards for the non-inverting if you're interested. In fact, I have all kinds of resources for that mod.

 

The THD is not going to be ultra impressive on them - they are transfer function modified so the goal was not to make a transparent amplifier but an amp with a 'voice'. However, the THD should stay below 0.2% over the power bandwidth, improving to 0.05% near max power. If you A-weight the SNR it should easily get above 100dB, and this is what I found to be the best measure of those amps when working properly.

 

Also, ensure your commutators are working correctly and switching as they should. If the commutators are not switching, the amp will still work fine until you reach high power where it will start clipping prematurely.

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On 12/1/2019 at 9:43 PM, Bonzoro said:

Noticed right off the bat these opt2 amps run out of gas WAY before a WOPL.  If  (And I mean IF), these will push 400 WPC, they don't do it for long.  Something to do with not having a real transformer.   They sound excellent but have no legs. But, they are cheaper so that must be why they are popular.  Guess I could try them out as Mono's, one on each channel.  Don't know if it was a cost cutting thing or not why they used a gadget instead of a true transformer.  I even returned my Gain Jumper on my C-1 to the normal position due to lower sensitivity (Lower than the White Oak Mod on a Phase Linear 700 Series II).  I'm running a series of tests on my Audio Precision P1P Access, and I'll run both modded M-1.0t's along with 2 WOPL's and see if anything pops out at me.  The THD=N numbers are not as good either.  One amp got new RCA's and 5 ways, the other has not (as of yet) and I'm waiting on the Thump fix FET's for the second amp since it scared the hell out of the dogs AND ME......

 

Sorry to hear of your problems.  I've done a number of M-1.0t mk II opt 2 upgrades.  I found a lot of ways to screw them up, but once working properly, they all produced rated power until the dummy load resistors started to melt.  And if the thump problem is bad enough to scare you and your dog, consider it a symptom of some other problem, not your normal annoying (but fixable) M-1.0t thump.  Here are a few suggestions.

 

1.  If its running out of gas at high power levels, there is likely a problem in the commutator circuits.  Note that the high rail commutators are triggered by a single set of components.  So a failure there will cause both channels to loose the benefits of the high rail commutator.  Suggest you put a scope on emitter of Q139.  (I'll use examples from the positive leg of the left channel, but you might want to look at both legs of both channels.). At idle the emitter should be at the middle rail voltage.  As you apply an input signal you should see some gradual switching to the high rail.  Use two channels of your scope.  Trigger off the output of the amp.  Use the second channel to watch the emitter.  No need for a load at this point, the commutators will work without it.  Its also educational to look at the collector of Q127.  It should sit at the low rail voltage, rising as the signal requirements dictate.

 

2.  Check switching diodes.  Shorts/open/backward diodes cause all sorts of confusing symptoms.  D125 thru D132.  

 

3.  You didn't mention if the loss of power was in one or both channels.  That's an important clue.  Loss of power in both channels is a strong indicator of a problem in the high rail switching since the control circuits are shared between channels.

 

4.  Horrific thumps.  Put a scope on the positive and negative side of each rail of the power supply.  One at a time is OK.  Turn the amp on and back off.  Observe the decay time.  If one drops like a rock while the other just drift down, it's a strong indicator of a short somewhere.  Asymmetric decay of the supply voltages is the primary cause of thumps.  Look at the 12v supply while you are at it.  They too should drift down together.

 

Note that the high rail switching transistors (Q139 - Q142) used in the mk II upgrade have been known to be counterfeited.  They fail at the slightest provocation.  Also, you must use the TIP35C/TIP36C.  Not the TIP35/TIP36.  

 

Based on my experience the use of a mag coil instead of a real transformer is not the root of the problem.  

 

Please don't be offended by my suggestions that upgrade errors may be the source of the problems.  I've done a lot of mk II upgrades and about the time I felt I could do no wrong was when I committed the most bone headed errors.

 

Oh, and I think you are in Southern Arizona somewhere.  I'm in Scottsdale.  If these suggestions don't work out, I would be happy to take a look at the amp.  Either ship it to me or stop by when you find yourself in Scottsdale.

 

Good luck.

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On 12/5/2019 at 7:40 AM, wrf said:

 

Sorry to hear of your problems.  I've done a number of M-1.0t mk II opt 2 upgrades.  I found a lot of ways to screw them up, but once working properly, they all produced rated power until the dummy load resistors started to melt.  And if the thump problem is bad enough to scare you and your dog, consider it a symptom of some other problem, not your normal annoying (but fixable) M-1.0t thump.  Here are a few suggestions.

 

1.  If its running out of gas at high power levels, there is likely a problem in the commutator circuits.  Note that the high rail commutators are triggered by a single set of components.  So a failure there will cause both channels to loose the benefits of the high rail commutator.  Suggest you put a scope on emitter of Q139.  (I'll use examples from the positive leg of the left channel, but you might want to look at both legs of both channels.). At idle the emitter should be at the middle rail voltage.  As you apply an input signal you should see some gradual switching to the high rail.  Use two channels of your scope.  Trigger off the output of the amp.  Use the second channel to watch the emitter.  No need for a load at this point, the commutators will work without it.  Its also educational to look at the collector of Q127.  It should sit at the low rail voltage, rising as the signal requirements dictate.

 

2.  Check switching diodes.  Shorts/open/backward diodes cause all sorts of confusing symptoms.  D125 thru D132.  

 

3.  You didn't mention if the loss of power was in one or both channels.  That's an important clue.  Loss of power in both channels is a strong indicator of a problem in the high rail switching since the control circuits are shared between channels.

 

4.  Horrific thumps.  Put a scope on the positive and negative side of each rail of the power supply.  One at a time is OK.  Turn the amp on and back off.  Observe the decay time.  If one drops like a rock while the other just drift down, it's a strong indicator of a short somewhere.  Asymmetric decay of the supply voltages is the primary cause of thumps.  Look at the 12v supply while you are at it.  They too should drift down together.

 

Note that the high rail switching transistors (Q139 - Q142) used in the mk II upgrade have been known to be counterfeited.  They fail at the slightest provocation.  Also, you must use the TIP35C/TIP36C.  Not the TIP35/TIP36.  

 

Based on my experience the use of a mag coil instead of a real transformer is not the root of the problem.  

 

Please don't be offended by my suggestions that upgrade errors may be the source of the problems.  I've done a lot of mk II upgrades and about the time I felt I could do no wrong was when I committed the most bone headed errors.

 

Oh, and I think you are in Southern Arizona somewhere.  I'm in Scottsdale.  If these suggestions don't work out, I would be happy to take a look at the amp.  Either ship it to me or stop by when you find yourself in Scottsdale.

 

Good luck.

 

 

No offense taken. I found one of the issues and that was causing some crazy test results.  I reset up my test station and brought both amps back out to the bench and the WOPL. Anyway, the numbers were good on the one M-1.0t but the other was all over the place. Since I was waiting on the FET's for the Thump fix, I put the other input board into the wacky amp (by the way, it had 30 watt difference from one channel to the other). Turns out, there are issues with the one input board on the right channel as those issues went away with the swap of the input board. I want to rebuild them both but I see that the are a bunch of obsolete parts on them.  But, that's where the big issue was, so I am off to look for subs. I appreciate the offer for assistance. I may take you up on it. I get up that way often since Hereford is in the middle of nowhere.  Even with the swapped input board I was able to get some very decent results in testing. I'll post some later when I get this fingered out. Gotta send Nahash5150 a message. He got me on the right track. I appreciate the input from all!!!

 

Perry

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