ExtremA, class-A strikes back?

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pinnocchio

pinnocchio

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Joined 2010
quebecdiy.forumactif.com/
Hehehe! You are right! Too bad!! It is a good sounding amplifier.

Jacco answered me on the "post your solid state pictures" thread.

Here's his answer

http://www.diyaudio.com/forums/solid-state/96192-post-your-solid-state-pics-here-429.html#post4440223

So this makes sense to me. I will however have my friend Fab check for oscillation just in case. This thing does get REALLY hot! it heats up the room and it is a 12' x 26' room!

Let's check all this and see, next will be an amplifier replacement if it oscillates.

I'll keep you posted.

Thanks
Do
 
sonnya

sonnya

Member
Joined 2001
mirand-audio.dk/?post_type=product
pinnocchio said:
Hi Fredlock,

Sorry for the late reply, just came back froma business trip.

No, I have not solved my issue yet, seems to be an oscillation at high frequency since my emitor resistors on the Sanken are reaching 80+ Celcius and it should not be the case at all with 4x 3 watts resistors in parallel...

I know now due to Jacco and my friend Fab that trying to divide this amp in a Class A and AB mode will not be pleasant due to the topology of the amplifier and that it should stay at all time in Class A...

I'm hoping PMA and Jacco (which seems to have studied the design) could help me and others here. If I had seen Bruno's warning to not build the amplifier before I did, I would have chosen a different amp to play with... Now after having spent tons of money, it almost look that I might have to put everything in the garbage... I don't have a scope, thus cannot now where the oscillation is coming from, for all I know it could just be a type a capacitor that could be responsible.

Also, I've built the amplifier from the start using the latest part change below that are supposed to give an improvement in slew-rate, step response and overall stability

C1/C2 = 68pF - COG or NPO - 5mm pitch (Vishay NP0 ceramic)
C4/C9 = 220pF - film capacitor, polypropylene or polyester - 5mm pitch (WIMA FKP2)

But I don't know if they could be responsible for the oscillation that I have encountered?? Have you tried to build the amplifier with the parts prior to these recommendations?

If anyone need a list of parts I can provide no problem.

In my previous post I have supplied the voltages that the amp is working on.

Thanks
Do
Click to expand...

I have been looking on it. Bias current is ~5A giving 130Watt to dissipate in every sanken transistor. What where they thinking of!???? :confused:

By shorting D11 and D12 it comes down to ~3.5A

By changing D5 and D8 to a schottky type (BAT42) it comes down to ~2.5A.

But Maybe R32,R33,R47 and R48 should be reduced to 470R when using BAT42 + shorting D11 and D12. But leave the 1K in the circuit for a start.

Bias current will drift all over the place as it the change with a rate of 2.3mV/K per diode/transistor...

So in original configuration it will start out at 5A and when the inside of the case reaches 50 degrees Celcius the bias will be reduced to ~4A.

Something that would boost an change in sound signature over time... :confused:
 
pinnocchio

pinnocchio

Member
Joined 2010
quebecdiy.forumactif.com/
sonnya said:
I have been looking on it. Bias current is ~5A giving 130Watt to dissipate in every sanken transistor. What where they thinking of!???? :confused:

By shorting D11 and D12 it comes down to ~3.5A

By changing D5 and D8 to a schottky type (BAT42) it comes down to ~2.5A.

But Maybe R32,R33,R47 and R48 should be reduced to 470R when using BAT42 + shorting D11 and D12. But leave the 1K in the circuit for a start.

Bias current will drift all over the place as it the change with a rate of 2.3mV/K per diode/transistor...

So in original configuration it will start out at 5A and when the inside of the case reaches 50 degrees Celcius the bias will be reduced to ~4A.

Something that would boost an change in sound signature over time... :confused:
Click to expand...

Thanks Sonny,

I will look into this asap

Thanks
Do
 
sonnya

sonnya

Member
Joined 2001
mirand-audio.dk/?post_type=product
pinnocchio said:
Hi Sonny,

There's two bat42 versions but I don't know which one to buy

BAT42 STMicroelectronics | 497-2495-1-ND | DigiKey

BAT42-TR Vishay Semiconductor Diodes Division | BAT42CT-ND | DigiKey

It's only the Voltage Forward (Vf) (Max) @ If that changes. One is 650mV @ 50mA and the other 1V @ 200mA. Which one should I buy?

Thanks
Do
Click to expand...




Please look at the current where it is measured. The current is 4 times higher and that is why Vf is higher. They are identical.

Whe also run them at a lower current than 50mA so Vf is a lot lower.


Sent from my iPhone using Tapatalk
 
F

fredlock

Member
Joined 2008
pinnocchio said:
Hi Fredlock,

Sorry for the late reply, just came back froma business trip.

No, I have not solved my issue yet, seems to be an oscillation at high frequency since my emitor resistors on the Sanken are reaching 80+ Celcius and it should not be the case at all with 4x 3 watts resistors in parallel...

I know now due to Jacco and my friend Fab that trying to divide this amp in a Class A and AB mode will not be pleasant due to the topology of the amplifier and that it should stay at all time in Class A...

I'm hoping PMA and Jacco (which seems to have studied the design) could help me and others here. If I had seen Bruno's warning to not build the amplifier before I did, I would have chosen a different amp to play with... Now after having spent tons of money, it almost look that I might have to put everything in the garbage... I don't have a scope, thus cannot now where the oscillation is coming from, for all I know it could just be a type a capacitor that could be responsible.

Also, I've built the amplifier from the start using the latest part change below that are supposed to give an improvement in slew-rate, step response and overall stability

C1/C2 = 68pF - COG or NPO - 5mm pitch (Vishay NP0 ceramic)
C4/C9 = 220pF - film capacitor, polypropylene or polyester - 5mm pitch (WIMA FKP2)

But I don't know if they could be responsible for the oscillation that I have encountered?? Have you tried to build the amplifier with the parts prior to these recommendations?

If anyone need a list of parts I can provide no problem.

In my previous post I have supplied the voltages that the amp is working on.

Thanks
Do
Click to expand...

The reason why I ask is because I have the board for long time. I bought the board on 2008. I didn't have time to put it together, until I green posted his build here at DIYaudio. I saw his postings and encountered a lot of issues. That's where I hesitated to continue with this project. Then you also tried to build this amazing amp but also encountered issues on your build. Therefore, it means to say that I have to dump this $100 worth Extreme A board. I'm busy at work and don't have time to play around with it. :(
 
pinnocchio

pinnocchio

Member
Joined 2010
quebecdiy.forumactif.com/
Hi Fredlock,

Actually my only issue was this and it seems it is not related to oscillation but rather too deep in Class A so Sonny and my friend Fab gave me a few solutions which I will implement. I'm trying the BAT42 diode mod which should be perfect for my needs.

BTW, you should look at two amps from these guys
Sonny's TSSA V2, V4 and V8 (I have the V1.7 modded and it is really good amplifier)
http://www.diyaudio.com/forums/vendors-bazaar/275212-mirand-tssa-v4-v8-lateral-mosfet-amp.html

Fab's USSA
Amplificateur USSA 15W

In the meantime I'm finishing this build than move on to these ones

Ciao!
Do
 
pinnocchio

pinnocchio

Member
Joined 2010
quebecdiy.forumactif.com/
So here's a quick rundown of what I've tried so far...

1- I've jumpered D11, D12 keeping 1N4148 on D5, D8
2- I've installed Bat42 on D11, D12 keeping 1N4148 on D5, D8
3- I've installed Bat42 on D11, D12, D5 and D8

So far all have given me the same voltage across the emitter resistors, which is 0.672Vdc. This should drop as the bias drops? No matter which change I do, I always get ~0.672Vdc across Sanken BJTs emitter resistors (four 1R 3watts in parallel). Those resistors also always stay really hot (80+ Celcius) and they should never get hotter than ~50 Celcius with the current going through them?

My most current mod is the first one on top (#1). This should roughly give me 62 watts class A, right? Still getting same voltage across emitter resistors and emitter resistors are still getting extremely hot. The heat also creates other cascading effects since it overheat some local BCs as well from the radiated heat.

Now since the bias current does not seem to drop regardless of what I do (according to voltage read across BJT emitter resistors), should I change the 1K resistors (R32, R33, R47, R48) to 470R or do you suspect an oscillation at this point?

I am willing to try a few more things but the diode pads are starting to give up, two of the 8 solder pads have gone but I managed to grab the center or bottom layer. I'm pretty sure they won't survive another desoldering. I've done everything from the top layer since I did not wanted to change the thermal pads every time and to make things go a little faster.

Thanks for all the help you can give me!

Do
 
Last edited:
pinnocchio

pinnocchio

Member
Joined 2010
quebecdiy.forumactif.com/
Just as a very wild guess here...

Sander recently recommended to change the following based solely on simulations

***Update 01-12-2014: parts value change***

With a simple parts value change the ExtremA amplifier sees an improvement in slew-rate, step response and overall stability, so it is recommended making these changes. There's four capacitors that need to be changed:

C1/C2 = 68pF - COG or NPO - 5mm pitch (Vishay NP0 ceramic)
C4/C9 = 220pF - film capacitor, polypropylene or polyester - 5mm pitch (WIMA FKP2)

I never tried the original values, only the updated ones...

Could these changes actually create issues? Higher slew rate could cause instability?

C1, C2 were originally 33pF - COG or NPO
C4, C9 were originally 1nF PP - film capacitor, polypropylene or polyester

Thanks
Do
 
pinnocchio

pinnocchio

Member
Joined 2010
quebecdiy.forumactif.com/
Thanks guys,

I have a friend that will look into it and then I will put in a bounty for anyone to fix it and I'll abandon after if not fixed. I do understand that leaving it alone and moving to something else would be a better choice but I've put so much time and efforts onto it that I feel wrong in just quitting.

I need an oscilloscope anyways... So while we're in the subject, I was wondering if those would be great for audio purposes

More Info Page

More Information Page

Or better to go new like this one (I know these are probably crap if you compare them to HP or Tek but for hobby purposes??):

http://www.amazon.ca/Rigol-DS1054Z-DS-1054Z/dp/B012938E76/ref=sr_1_6?s=hi&ie=UTF8&qid=1442939690&sr=1-6&keywords=rigol

http://www.amazon.ca/Rigol-DS1102E-Oscilloscope-Channels-Sampling/dp/B001VKCJ0M

http://www.amazon.ca/Siglent-SDS1052DL-Oscilloscope-Channels-100-240V/dp/B00GQNN70A/ref=sr_1_1?s=hi&ie=UTF8&qid=1442939357&sr=1-1&keywords=rigol+oscilloscope

Thanks
Do
 
S

scanspeakman

Member
Joined 2008
Would be a pity if you have to abandon. I have build an ExtremA as well and it works great and sounds awesome. I followed the original BOM and haven't been able to do the "update"/correction. Had some problems when powering up the amp but that was solved with a small modification (that I posted here on diyaudio). Not able to do measurements for you since I am stationed abroad for a few years and did not bring my audio equipment.

Scanspeakman
 
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