Studio Reference Amplifier

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Arif Budiyanto

Member
Joined 2011
My SR200 is now having a trouble, it has 250mV dc out...Q1-2, Q5-6 are matched pairs..I put 10pf between bQ2 to cQ9,
and values for R11 8k2, R18 2k2...
I need advice to solve my problem.
Thank you so much...
Best Regards...
 

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thimios

Member
Joined 2009
sr200 studio refer.

thimios said:
Everything starts from here.
This modification is the cause of the problem.
Today early in the morning about 5.30 o'clock i examined the amplifier again.
But this time I was sure for the pcb because it passed the point to point test.
As changing transistors and matchig didn't solve the problem, having in mind that the others' amplifiers didn't have the problem,i decided to return to the original circuit.
So i put at R11 the original value 15K.and that was all!
Thanks everyone for trying to help .
Especialy thanks Mr AdrewT who advised me to stabilize the LTP without servo.
Thanks a lot to John Balli for your instant reply in mine request for measurments.
Last but not least thanks overall feedback for his atempt to help.
Thanks again Mr.Mile for this excellent amplifier.
I also attach this hopping that it will be useful
Click to expand...
Arif Budiyanto read #1337 carefully
 
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Arif Budiyanto

Member
Joined 2011
thimios said:
Arif Budiyanto read #1337 carefully
Click to expand...
Thank you dear Thimios for your suggestions.....

I put back 15k for r11, 1k for r18, using 2X10pf caps in parallel for compensation. DC offset now is 133mV..
But when I disconnect dc servo, offset raise into 2,56V!...and when I put back dc servo offset is back to 130mV...
I am sorry that my background is an accountant just doing my hobby..so I am sort kind a lack of electricity background...
Thank you...
 
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thimios

Member
Joined 2009
Junie said:
Hi Thim, amazing mid isn't? :D

I see you're making a new SR200, which version is it?

BR,
Junie
Click to expand...
Hi Junie how about your vacations?
This version is 3.2? .
Pcb by Alex mm of cource:)
3 pairs output.
MJW21195/96
 

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thimios

Member
Joined 2009
studio reference

Arif Budiyanto said:
Original schematic with 20pf cap...something wrong with my SR200 amp..still struggle with it...
Maybe I will disconnect zobel network from pcb and put it in speaker terminal...
I will up load another photos.
Thank you so much...
Click to expand...
Hi Arif .

I see that your problem is still there.
Did you have any measurements about ltp transistors?
Q1 Q2 VR11 VR12 VR13 VR16 VR17
Measurments are on the shematic, see post #1337.
Is this a previus running amplifier or a new board?
 
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thimios

Member
Joined 2009
studio reference

apexaudio said:
Add 20pF only if amp is unstable, no need to add compensation on stable amp.
Regards
Click to expand...
Hi Mr.
Tell us a simple test in order to check the stability of an amplifier.
Is the parallel capacitor to dummy load the appropriate method ,until what capacity the amplifier must be stable at full volume gain.
Regards.
 
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Arif Budiyanto

Member
Joined 2011
thimios said:
Hi Arif .

I see that your problem is still there.
Did you have any measurements about ltp transistors?
Q1 Q2 VR11 VR12 VR13 VR16 VR17
Measurments are on the shematic, see post #1337.
Is this a previus running amplifier or a new board?
Click to expand...

Ok Thim, thank you so much for your very kind attention. I will do measurement when I am fully recovered from my sickness soon. This is my 4th SR200, I have been Ok with 3 previous Sr200 amps. My friends really love these amps. And I want to build SR200 for myself. No commercial use only for hobby. I am just proud when some one likes my amp...
 
A

Arif Budiyanto

Member
Joined 2011
apexaudio said:
Add 20pF only if amp is unstable, no need to add compensation on stable amp.
Regards
Click to expand...

Dear Mr. Mile S...
thank you so much for your kind advise as always...
I will check my amp again...before it is fine only zobel network was hot when playing couple songs...
Strange behavior is, when first turn on, the dc offset is high, 300mv and more, and getting down after more or less 10 minutes up to 14 mV...
the sound is Ok...really like this amp...
 
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