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Old 1st September 2013, 04:15 AM   #1
Gost22 is offline Gost22  Bolivia
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Default 100W audio amplifier with Ne5534

Hi guys!
Will I create this amplifier under this schematics. Seeking your opinions on this audio amplifier. What can change of the schematics to improve its features?
Otherwise, instead of 2sc2921/2sa1215 want to use mj15003/mj15004 ate possible to do it without making any changes to the schematic?
What OP for IC1d in this schematics is best used?
Thank you for your cooperation and help!
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Last edited by Gost22; 1st September 2013 at 04:20 AM.
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Old 1st September 2013, 07:37 AM   #2
PetruV is offline PetruV  Romania
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seems to lack an vas stage.....,voltage swing will be the maximum ic1 can put out.If you use ne5534 you will get 30v peak to peak and that wont get even near 100w at 4r,maybe 25watts max
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Old 1st September 2013, 10:22 AM   #3
ilimzn is offline ilimzn  Croatia
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Originally Posted by PetruV View Post
seems to lack an vas stage.....,voltage swing will be the maximum ic1 can put out.If you use ne5534 you will get 30v peak to peak and that wont get even near 100w at 4r,maybe 25watts max
Look at it again - the CFP output stage does not have a gain of 1. However, this amp can be a problem to stabilize as this sort of output stage does like to oscillate sometimes. Then there is the problem of thermal stability which is only marginally addressed in the design. A different combination of driver and output transsistors may not be thermally stable. In particular, MJ15003/4 will not only be thermally unstable but also may prove marginally driven due to a much lower current gain and lower ability to keep this gain at higher currents. They are also slower than the 2SA/2SC parts by a factor of 6-10, so the output will have the classical problem of driving slow devices with fast ones, and the actual bandwidth will be yet lower because the output stage has gain - expect instability.
There is also an obvious error in the schematic, a resistor is labelled 5.6 ohm instead of 5.6k.

Last edited by ilimzn; 1st September 2013 at 10:27 AM.
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Old 1st September 2013, 04:07 PM   #4
Gost22 is offline Gost22  Bolivia
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So for Ucc for IC1d (Ne5534 or TL071) should be: Ucc = + /-15V. For broadcasters, the output transistors should be placed 0.15 R/5W.
See the new schematics.
Thank you!
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Last edited by Gost22; 1st September 2013 at 04:36 PM.
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Old 1st September 2013, 09:54 PM   #5
ilimzn is offline ilimzn  Croatia
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Originally Posted by Gost22 View Post
So for Ucc for IC1d (Ne5534 or TL071) should be: Ucc = + /-15V. For broadcasters, the output transistors should be placed 0.15 R/5W.
See the new schematics.
Thank you!
You will accomplish nothing with 0.15 ohm resistors in the collectors, they have to go into the emitter side (between power supply line and emitter). It may require a higher value (0.22-0.33 ohms).
The voltage drop resistors can't be 0.5W if they dissipate 0.53W, resistor power dissipation is the absi=olute maximum assuming low resistor case temperature. Under normal circumstances calculate dissipation, and use resistor at least 2x and preferably 3x that - in your case 2W resistors.
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Old 2nd September 2013, 03:37 AM   #6
Gost22 is offline Gost22  Bolivia
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Ilimzn, so this should be the schematics:
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Last edited by Gost22; 2nd September 2013 at 03:49 AM.
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Old 3rd September 2013, 08:59 PM   #7
jaycee is offline jaycee  United Kingdom
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I tried a few similar circuits early on as I liked the idea of using an opamp for the small signal stage. Unfortunately it just doesn't work reliably - with gain in the output stage it is a nightmare to get it stable.

I also wouldn't use BD139/BD140 as drivers. MJE243/253 would work better.
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Old 4th September 2013, 05:20 PM   #8
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If you use a high voltage opamp such as the OPA452 or OPA453 (supply up to +40V for both) you don't need the feedback resistors in the output stage or the Zeners e.a. for the opamp.

For my adventures with opamps in a power amplifier, look at this thread:

Very simple class B amplifier
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Old 4th September 2013, 06:00 PM   #9
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Here is a version of my circuit using a +40V supply, an OPA551 opamp and discrete pre-drivers and drivers transistors. Unfortunately, the output cannot be driven to the rail voltages which means that 100W is no longer doable. It gives out 75W into 8 ohms, a loss(!) of about 1.2dB. However, THD is predicted to be 0.0019% at 1kHz and 0.035% at 20kHz. I doubt that an NE5534 can match that.
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Old 4th September 2013, 06:21 PM   #10
jaycee is offline jaycee  United Kingdom
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Such opamps are usually expensive and limited - there is not really any point in using them for this task, you may as well just use a few more transistors and make a completely discrete amp.

Or if you really want something like this, use a device made for the job such as LM4702.
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