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Old 14th December 2011, 09:08 PM   #521
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The resistor with value of 47kohm should be lower. Try with lower values 39k,33k,30k.... to voltage drop across 5W resistors are 2A=voltage drop/ resistor value. With 2A current you will have 36W/8ohm on pure class A.

The resistor's value 0.47ohm 10W is large. Try with 0.22ohm. Lower value of this resistor should improve the bass control.
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Old 17th December 2011, 03:34 PM   #522
ash is offline ash  Iran
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Hi Whitesnake
I believe those 47k resistors set the bias of the second stage driver transistors. could you please tell me how redusing their values affect the circuit here?
Thank you
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Old 19th December 2011, 07:22 PM   #523
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Don't care about first stage. It is emitter follower. The most important stage is the last stage and their current.
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Old 19th December 2011, 08:30 PM   #524
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I built a couple Hiraga Class A with different rail voltage. Never so high like 28V or 35V etc. To me that absurd! One pair power transistor can't take that much heat fully Class A bias! No way!!!
At least I don't know such a transistor was produced to audio purpose. Can be some company special design but I don't know about if it would be assailable for DIY purpose.
30W more than enough in Class A at normal listening level (home use)
To write some info the bias set up
There is two important think you must take care!
One the diode V rating!
Second the 47K resistor in your case! But think, if Dan uses the same Voltage and 47K resistor you have some other problem. The driver transistors lightly warm even under heavy load to..
Take a look these two parts how it change when you use different rail voltage.
I built the 13V diode version- I would never ever try again
I built two 20 and 22V version and bot work and sounded great.
I'll build it again with better component.
The high voltage version can't be biased in a full Class A mode but who need that risk (you newer know when the power transistor trow the towel in and take out your woofer)
I would not even try to build that!
If you need high power Class A amplifier (because your speaker power hungry) build some N Pass Aleph amplifier like 2, 4, or 5.
If you prefer transistor sound go with A40.
Again with 24V you can get 30W. That must be enough for a normal size living room to drive even 84-85db speakers!
These is the problem when someone built something different (out of the ordinary)and we try to copy that but different rail voltage.
I believe with the 35V rai voltage Dan did his home work to until everithing was set up and get out the right compromisum.
With that high voltag you must have some compromisum like not full Class A bias, change the power transistors often so on...
Please study the diode and the resistor value at different rail voltage.
13V to me worked but sounded awfull.
20 and 22 was nice.
I can't comment different voltage.
I marked the resistor responsible for the bias! But the diode to!
I hope these help!
The 19-20V is the 20W , the 24V is the 30W..
Start with low bias and increase it. Pay att. do not fry the transistor. After you set up the amp chek it with your tumb 10 second min.
At the begining check it every 5-10 minutes or so after every 30 min..

Greetings Gabor
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Last edited by gaborbela; 19th December 2011 at 08:36 PM.
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Old 20th December 2011, 07:30 AM   #525
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gabor good argumentation, i like the towel part .
just a suggestion, why not use TL431 for the zener? then you can set it like you want easily, and the performance might be better than an ordinary single zener diode.
SPU --> tube MM/RIAA; Kaneda pre; 300B SE driven by ECC35; Open Baffle PM2A, 2A9
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Old 20th December 2011, 07:58 AM   #526
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You right, probably it would be better.
But first I want to help him to set up his amp (at least to get some life or sound).
I think if He use all the same component after Dan's schematic it must be problem with some of the semiconductor(s)
Can be the power transistors, do you have any offset? Can you measure any +/- voltage on the power transistors?
Do the drivers and the signal transistors are at the right place, check their pin out to.
These amp so simple it must work!!
That is the minimum, a 12 year old boy can build these amp.
There is a mistake somewhere that is sure.
Please look up on the net all the transistor pin out E-C-B and follow the schematic not the lay out!
Please check if all PNP and NPN transistor if are at the right location.
Measure all the transistors for shortage or open to.
Greetings Gabor
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Old 20th December 2011, 03:38 PM   #527
ash is offline ash  Iran
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Hi, everybody
There is some sound actually,you know? but the output stage transistors dont get warm at all and the driver transistors run quite hot.Garbor,what transformer secondery do I need to obtain the voltage rail that you suggest? Bytheway my zeners are 22v.Is it possible to drop the volltage with other choice of zeners?
Greetings, Ashkan

Last edited by ash; 20th December 2011 at 03:51 PM.
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Old 20th December 2011, 06:32 PM   #528
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Hello ash
How much (sound) power you get?
Please use a Digital MM and measure on the power transistor DCV to the ground. Please let me know what you get on E, C, B. Disconnect your speaker when you measure or do some adjustment!
To me both the driver transistors and the power transistors are suspicious to!
Toshiba long time (15 years) does not produce 2SC5200 and it's complementary parts.
Also 10 years a go when I used those NEC driver transistors it was hard to get them.
If you have at hand MJL21193/94 or MJ0281A/3281A ON semi for power transistors or if you can use metal case please use MJ15003/04 or MJ15022/23
Honestly I had all the orig NEC orig. transistors and after I tested the MJ11022/23 for power and MJE15030/31 driver transistors I sold the orig NEC transistors on Ebay.
I get more punch, deeper and controlled bass, cleaner mid range. Over all I got a lot of improvement with the ON semi transistors in every way.
Pay att. the driver transistor in (TO220 case) has different pin out.
To get 24VDC you must use 20VAC but use min 500VA rating for a stereo (2 channel)
The 22V Zener is OK.
Pleas use solid wire to connect the power transistors! I see your power transistors not soldered direct in to the PC board.

Greetings gabor
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Old 22nd December 2011, 07:40 AM   #529
ash is offline ash  Iran
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Hello Gabor
these are the voltages that I measured;

2SA634; B 33.5, C -11.3, E 34.3 \ 2SC1096; B -33.5, C 13.8, E -24(other channel -34) \ 2SC5200; B -11.2 , C 34.5 , E 0.3 \ 2SA1943 B 13.8 , C -24.5 ( other channel + 2.2) , E 0.3

Thank you

Last edited by ash; 22nd December 2011 at 08:02 AM.
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Old 22nd December 2011, 01:28 PM   #530
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[QUOTE=ash;2830216]Hello Gabor

2SA634; B 33.5, C -11.3, E 34.3 \ 2SC1096; B -33.5, C 13.8, E -24(other channel -34) \ 2SC5200; B -11.2 , C 34.5 , E 0.3 \ 2SA1943 B 13.8 , C -24.5 ( other channel + 2.2) , E 0.3

If you use color coded resistors at first check them all if all value at the right place.
If not color coded to make 100% sure please remove one side (one pin) all resistor from the PC board where you have problem and measure all of them.
Be careful sometimes one resistor like (for example)2.2K exchanged with 22K mess up all your circuit.
After you check all of them soldered it back and change all the semiconductors from the good PC board to the one has problem.
I think (99% sure) one side (in one PC board) of your power or driver transistor or both are bad .

Also you can not have in one side -voltage other side + voltage. Is a mistake somewhere there! That mean one or more transistor is open (bad)

Greetings Gabor

Last edited by gaborbela; 22nd December 2011 at 01:30 PM.
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