just found back a quick drawn schematic of my amp - diyAudio
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Old 14th March 2003, 02:32 PM   #1
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Default just found back a quick drawn schematic of my amp

I've designed this amp some months ago, it worked well. The sound was good, but I still haven't finished the whole case (a little bit out of time and money).
Attention! one transistor (T17) in the protection circuit is placed incorrect!! The pcb is correct! I've used other output transistors than shown in the schematic!! (BDV 66 - BDV67 I think) I've also experimented with the amount of bias diodes, the value of R28 and the adjustable CCS to get the right quiescent current.
Any comments are welcome.

best regards,

HB.
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Old 14th March 2003, 02:34 PM   #2
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the pcb:
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Old 14th March 2003, 02:38 PM   #3
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this was the first version of the pcb; this is incorrect! but it might be a good guideline to place the components.
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Old 14th March 2003, 06:51 PM   #4
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Nice circuit.
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Old 15th March 2003, 09:53 AM   #5
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Maybe pot R23 could have a zener from top to bottom so the voltage across it's length, and consequently the setting of ccs T14 won't vary with supply rail variations. The resistor below the pot that goes to 0v (can't see the schematic while replying!) may need to be lowered a bit.
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Old 15th March 2003, 11:33 AM   #6
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Default My sugestions...

Hi hugobross!!!


Here is my sugestions:

-Change the Zener to two small sinal diodes (aka 1N4148) ...less noise!...as the LTP current is 2,5mA , R17 must be changed to 240 Ohm!

-Delete R 23 (pot) and conecte directely.the base of T14 to the diodes and the base of T13...then choose R 20 for 0'6 volts across it, with a current that you want for the Vas stage...after that, R1 must have a value to put +- 2 mA across the 4148 diodes...
The base of a CCS transistor like to see a stif voltage source at the base and the pot(R23) was kiling this!

- Put a 4'7 k resistor betwen the colector of T13 and the point of union of R7/R8...it will isolate the LTP from the nonlinear output capacitance of T13...

-Put a 100 Ohms resistor betwen the emitors of the drivers..

Tell me what you think!

Ps:some degeneration in the emitor of the lower Vas transistor (BD241 C) will be also a good idea..but R4 must be recalculated!

One more point...What is it for R 29 (22K)?
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Old 18th March 2003, 04:28 PM   #7
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Thanks,

Circlotron, good point! What about placing a pot over the excisting zener??

Tube dude, I don't know if normal diodes have better noise figures than zeners; but I guess you're right! It's no big deal to change that!
I like this adjustable current source, and I'm not sure about deleting the pot.
A 100 ohm resistor between the driver emitters is a good idea
Quote:
- Put a 4'7 k resistor betwen the colector of T13 and the point of union of R7/R8...it will isolate the LTP from the nonlinear output capacitance of T13...
In which way do you mean non-lineair?? I don't know if this non-lineair capacitance will affect the working of the LTP. The current through T13 is constant, right?

R29 is for bridging two of this amps, didn't use it by now.

Quote:
Ps:some degeneration in the emitor of the lower Vas transistor (BD241 C) will be also a good idea..but R4 must be recalculated!
euh, what do you mean with this one?? my english isn't that good I guess.

thanks,

HB.
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Old 18th March 2003, 09:06 PM   #8
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Default To Hugo...

Quote:
Tube dude, I don't know if normal diodes have better noise figures than zeners
zeners produce "white noise"...zeners are one of the elecronics components that produce more broadband noise...
Quote:
In which way do you mean non-lineair?? I don't know if this non-lineair capacitance will affect the working of the LTP. The current through T13 is constant, right?
The efect is even greater then when you take out the muting transistors in a CD player...the logical is about the same...and in a CD player the impedance is lower...the efect in the LTP is greater!!
Quote:
euh, what do you mean with this one??
To put a emiter resistor in this transistor(BD241C)....
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Old 19th March 2003, 10:33 PM   #9
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Looks good

Assuming you can't (or don't want to redesign the PCB ....
Don't you need a cut in the "ground loop" around the perimeter of the pcb?

Maybe I should rephrase that: I'd make a cut through that ring around the circuit.


Quote:
Originally posted by hugobross
this was the first version of the pcb; this is incorrect! but it might be a good guideline to place the components.
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Old 22nd May 2003, 05:40 PM   #10
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still didn't finished the amp completely
no time, no money

best regards,

HB.
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