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Old 17th August 2010, 02:28 PM   #21
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I'm not using KSE340 but BD139. Any advice for better transistor for that purpose?
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Old 18th August 2010, 03:11 AM   #22
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Quote:
Originally Posted by astankov View Post
I'm not using KSE340 but BD139. Any advice for better transistor for that purpose?
2sc3503.. or 2sc2690 (best)
OS
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Old 18th August 2010, 06:45 AM   #23
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Quote:
Originally Posted by ostripper View Post
2sc3503.. or 2sc2690 (best)
OS
Is this also the best for driver, compare to MJE 340/350 gold pin, or BD 193/140?

thx,

Ervin L
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Old 18th August 2010, 07:14 AM   #24
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Is this also the best for driver, compare to MJE 340/350 gold pin, or BD 193/140?

thx,

Ervin L
for 1 pair mosfet those would do. For more pairs or just better performance , mje15032/33 or 2sc4793/2sa1837 (super fast). BD's are low voltage , no good to me.

Some idiot designs run the mosfets direct off the voltage amp with "hot" MJE's, no drivers!!
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Old 18th August 2010, 11:09 AM   #25
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Quote:
Originally Posted by ostripper View Post
2sc3503.. or 2sc2690 (best)
OS
Nopes, Id say something like 2sd1508 or any other low to medium voltage darlington or super beta transistor. One super beta I have used is 2sc3964 which is specifically made for this purpose but the darlington solution does perform better though. This way there is no need for the resistor you and Andrew are contemplating. Note this is for the temp compensation only, not in the case of drivers.
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Old 18th August 2010, 11:31 AM   #26
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Originally Posted by homemodder View Post
Nopes, Id say something like 2sd1508 or any other low to medium voltage darlington or super beta transistor. One super beta I have used is 2sc3964 which is specifically made for this purpose but the darlington solution does perform better though. This way there is no need for the resistor you and Andrew are contemplating. Note this is for the temp compensation only, not in the case of drivers.
Just looked at the 2sd1508 .. gain of 4K ! I did notice an improvement going from the BDxxx/mje low gain to the 200hfe 2sc3503.So you say use a darlington?
At least the 1508 is to-126 ..
Would that not be overkill ? I have seen them used to Tcomp triples but that is it.
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Old 18th August 2010, 12:39 PM   #27
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Default Update made!

Well guys I make some changes to the amp.

1. Added Zobel and removed output coil.
2. Increased gate resistors to 470R
3. Corrected Bootstrap resistors to 1.5k and 2.2k
4 Added 100nF cap in parallel of the bootstrap 47uF cap.

There is some sound improvement - bass is deeper and tighter , trebles more clear and pleasant. Overall sound is better. I like it.

Thanks very much again guys for your good advices.

There is the new schematic.
Attached Images
File Type: png amp.png (35.5 KB, 278 views)

Last edited by astankov; 18th August 2010 at 12:42 PM.
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Old 18th August 2010, 04:03 PM   #28
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Quote:
Originally Posted by ostripper View Post
Just looked at the 2sd1508 .. gain of 4K ! I did notice an improvement going from the BDxxx/mje low gain to the 200hfe 2sc3503.So you say use a darlington?
At least the 1508 is to-126 ..
Would that not be overkill ? I have seen them used to Tcomp triples but that is it.
OS
Its mostly used on triples because here tcomp is more critical but it will have the same effect with EFs, one just has to decide if its worth the extra cost of the darlington. Well it can save on that resistor and less pcboard complexity. The 2sc3964 works pretty good and I would go this route for normal EFs, If I remember correctly they are 30v 500hfe minimum trannies.
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Old 18th August 2010, 05:17 PM   #29
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Look at the left transistor in the current mirror. How much Vcb does this have? I would reduce the emitter resistors to 100R to give it higher Vcb and avoid saturation on volume peaks.

Also try increasing the 47uF cap to 470uF or higher. Just try a larger cap and see how it sounds, this will decrease bass distortion.

Connect the 22pF cap across both the 470n cap and 51k resistor. I like to avoid putting caps in series when possible.

- keantoken
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Old 18th August 2010, 06:14 PM   #30
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Quote:
Originally Posted by keantoken View Post
Look at the left transistor in the current mirror. How much Vcb does this have? I would reduce the emitter resistors to 100R to give it higher Vcb and avoid saturation on volume peaks.
Can you explain that better to me because I dont unedrstand what you want to tell me. I'm not that good at electronics so I will need additional info for this.

Thanks.
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