Replacing IGBTs with BJTs in Elektor IGBT design! - diyAudio
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Old 18th February 2007, 12:14 PM   #1
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Default Replacing IGBTs with BJTs in Elektor IGBT design!

Hi

I read Reviews about IGBTs, MosFETs and BJTs uses in Audio Power amplifiers.
I want to build the Elektor 50W Compact AF IGBT power amplifier. I want to replace IGBTs with BJTs.
I have two questions:

1- which components should I change?
2- What is the best BJT to use? (part Number)

P.S. I know how to replace it with MosFET. But I do not know about BJT replacement.

Here is the Original Design.
http://www.4shared.com/file/10820796...TPowerAmp.html

Here another design with BJT from the same designer. maybe it could help. (I don't know the supply Voltages)
http://www.4shared.com/file/10820833.../ne5534pa.html

ThanX
Shahriar
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Old 18th February 2007, 12:27 PM   #2
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Hi Shahriar,

Just change the collector resistors of MJE drivers from 390ohms to 68 ohms and igbt gate resistors from 22 ohms to 4.7 ohms 1W for BJT bases , Also insert 100 ohm resistors inthe bases of MJE drivers and readjust the bias for Iq=100mA for output BJT's
Also change the emitter resistors of output BJTs to 0.47ohm 5W non-inductive types
For BJTs You can use 2SC5200/2SA1943, MJ21195/MJ21196, MJ15003/MJ15004, MJ15024/MJ15025, TIP35/TIP36
Caution: These type of Geisberts designs were prone to oscillations, try to check this amp for stability also

regards,
K a n w a r
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Old 18th February 2007, 07:54 PM   #3
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Hi
ThanK you very much for your reply.

I have also found this design very close to Accuphase Power Amp.
I have attached a link which is a manual for Accuphase and another schematic which is related to some one who has tried to draw a schematic from a hardware. (it has some mistakes)

http://www.4shared.com/file/10268547...e_px-600e.html

http://www.4shared.com/file/9862517/...Accuphase.html

What if we try to put the output section as Accuphase has done. Just remove the parts after Variable Zener in Elektor design and replace them with topology in Manual block diagram (figure 2)

ThanX
Shahriar
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Old 19th February 2007, 04:30 AM   #4
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You cannot change it, because the VAS stage has lower supply rails and output supply rails are higher in elektor design, You can change it unless the supply rails are adjusted accordingly...to compensate for the adequate rail loss....
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Old 20th February 2007, 12:58 PM   #5
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Hi

ThanK you very much for your reply. you are right

but let me ask another question.
In some designs the output is connected to Power Transistors Collector and in some designed to Emitter via a resistor.

can andbody compare these two Topologies.

ThanX
Shahriar
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Old 20th February 2007, 01:28 PM   #6
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Collector Outputs give higher Impedance=less damping
Emitter Outputs give Lower impedance=higher damping

Emitter outputs are much more preferred
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Old 21st February 2007, 02:09 PM   #7
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Thnk you your reply.

But damping factor for this Elektor IGBT PA is 700 (1KHz)
For Accuphase p-650-e Model with 4 Emitter output is 270.

Shahriar
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Old 21st February 2007, 02:20 PM   #8
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Quote:
Originally posted by Shahriar
Thnk you your reply.

But damping factor for this Elektor IGBT PA is 700 (1KHz)
For Accuphase p-650-e Model with 4 Emitter output is 270.

Shahriar
These Damping Factor Figures are obtained by the virtue of amount of applied negative feedback

while I was stating in case of open loop amp or simply a buffer with out any feedback
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Old 21st February 2007, 02:55 PM   #9
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Shahriar,

may i suggest reading Rod Elliot's guidelines on amplifier design about compound output stages, found at his ESP homepage.
Something done earlier by Mr Giesberts, also sziklai/cfp output stage and prone to oscillation : here
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Old 25th March 2007, 08:52 PM   #10
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Shahriar,
been there, done that. All I can say is, don't it. Using 2SA1943/2SC5200 as output devices with the attached schematic, the sound became really dark. Although it measured fine on the bench, I frankly though that the tweeters in my Proac Studios were busted. I tweaked the design for loop gain/feedback and waited for the bjt's to break in, but the character of the sound never changed. I switched back to the igbt's and sonic happiness is here again. These high frequencies are waaaayyyyy better that they have ever been with the bjts. And no prejudice here.
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