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Old 30th April 2001, 01:30 PM   #1
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Join Date: Apr 2001
Location: Connecticut
I am looking to get my feet wet and build a simple A/B amp with a couple of OP amps and some bi-polar outputs? Where can I find some plans for this type of unit? I have switching power supplies ranging from +/-20v to +/-40v DC from some "scrap" car amps. In the least 6 months I have been reading lots of articles and books on how amplifier circuits function and I have a 'scope and have been able to repair about a half a dozen car amps (although I have created a couple of "lightning strikes" and one small mushroom cloud) Anyways I want to build some quality stuff soon, but first I would like to try some less expensive just in case I end up picking mosfets out of my teeth again

Thanks in advance

Bill
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Old 30th April 2001, 01:57 PM   #2
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Join Date: Dec 2000
Location: Önnarp, Söderslätt
Wellcome more_power.

You can always look for a project at:
http://www.sound.au.com/
an interesting source of project and inspiration.
__________________
Regards
Hoffmeyer ;0)
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Old 30th April 2001, 02:14 PM   #3
Geoff is offline Geoff  United Kingdom
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Join Date: Apr 2001
Location: UK
Have a look at this page:

http://space.tin.it/scienza/fladelle/Page1.htm

It is one of the better 'ic + output pair' circuits that I have seen on the Web, though it uses a less than common ic. However, this could be substituted with an OPA604 or even an NE5534 (with the NE5534 I would suggest restricting the supply rail voltage to +/-20V to allow for mains fluctuations, or use a regulated supply).

Geoff

ps I have just seen Hoffmeyer's posting which came in whilst I was writing my reply. By all means check out the ESP Audio Pages, there are some excellent projects there, but do not be tempted to try Project 96 ('ic + output pair' which is what you are looking for). This project is seriously flawed in my opinion and is not up to the usual high standards of the site (it is a contributed project which may explain it.)

[Edited by Geoff on 04-30-2001 at 09:21 AM]
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Old 30th April 2001, 09:03 PM   #4
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Join Date: Mar 2001
Location: Brazil
Geoff,


I think you are talking of Project #76, not #96.

What would you have against it? My guess (nothing more than that) is that Elliot wouldn't put it there if he didn't think it would work.

The bias arrangement is little weird though.

The Italian site project certainly looks much more elegant, and using a better chip would probably improve on it.


Carlos
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Old 30th April 2001, 09:34 PM   #5
Geoff is offline Geoff  United Kingdom
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Join Date: Apr 2001
Location: UK
Carlos

Thanks for the correction. Finger error I'm afraid, Yes it should have read Project 76.

There are many reasons why I consider this project to be seriously flawed. As the de facto editor of the ESP Audio Pages, I have had to provide many corrections to the original article and to the recent update, over and above the alterations and editorial comment that Rod Elliott had already made.

Some of my continuing concerns are that the power supply is a mess, the performance does not justify the cost (far more power, and improved performance, can be obtained with a better optimised circuit such as the one I recommended), the lack of an ac by-pass capacitor on the output biasing diodes, the lack of a current return path for the output biasing diodes (presumably he is relying on the driver/output transistor pair for this), the absence of any measures to control the loading on the second ic output, and the fact that, from the write-up, the circuit is obviously prone to oscillation.

Geoff

[Edited by Geoff on 04-30-2001 at 05:15 PM]
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Old 1st May 2001, 04:43 AM   #6
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Join Date: May 2001
Location: Tasmania, Australia
Hi
Try http://www.aussieamplifiers.com

regards

Anthony Holton

Quote:
Originally posted by more_power
I am looking to get my feet wet and build a simple A/B amp with a couple of OP amps and some bi-polar outputs? Where can I find some plans for this type of unit? I have switching power supplies ranging from +/-20v to +/-40v DC from some "scrap" car amps. In the least 6 months I have been reading lots of articles and books on how amplifier circuits function and I have a 'scope and have been able to repair about a half a dozen car amps (although I have created a couple of "lightning strikes" and one small mushroom cloud) Anyways I want to build some quality stuff soon, but first I would like to try some less expensive just in case I end up picking mosfets out of my teeth again

Thanks in advance

Bill
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Old 1st May 2001, 12:25 PM   #7
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Join Date: Apr 2001
Location: Connecticut
Thanks for the warm welcome!! These are some great leads. Actually I was looking at the Project 76 but maybe I will put that one one the shelf for now. The aussieamplifiers site looks awesome, but I'm not quite ready for that yet I have been into car audio for about a dozen years or so and have been using mostly PPI amps and I have a pair of 2350DM's which utilize an all discrete signal path but I have heard some really nice OP-amp based designs. Does anybody know where I might find schems for commercially produced amps such as the PPI's? I called the company and they have it locked up tighter that the Colonel's secret recipe!!
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Old 2nd May 2001, 05:44 PM   #8
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Join Date: Apr 2001
Location: Connecticut
Default oops.....

I logged onto TI's web site and found the TLE2141C and was able to request a sample. I got it the next day, but I accidentally ordered the surface mount version and wow is it small!! -- just thought I'd share a funny story. My solderin' skills (and tools) aren't ready for surface mount yet. Where is a good source for power transformers? I throw away a lot of computers and computer parts. Is the transformer in the PC power supply any good or maybe in the monitors?
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Old 3rd May 2001, 12:10 AM   #9
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Join Date: May 2001
Location: Tasmania, Australia
Smile design error in opamp design

Hi

I have had a quick look at the site shown below and I believe the amplifier has a design error in the driver/output stage. There should be load resistors connected off the Collectors of Q1 and Q2 to the supply rails. I would suggest a value of between 100 and 220 ohms would work well. If these resistors are not used the driver/output stage will not be properly biased. It is after all a Complementry feedback pair design.

I hope this helps

regards

Anthony Holton
http://www.aussieamplifiers.com

Quote:
Originally posted by Geoff
Have a look at this page:

http://space.tin.it/scienza/fladelle/Page1.htm

It is one of the better 'ic + output pair' circuits that I have seen on the Web, though it uses a less than common ic. However, this could be substituted with an OPA604 or even an NE5534 (with the NE5534 I would suggest restricting the supply rail voltage to +/-20V to allow for mains fluctuations, or use a regulated supply).

Geoff

ps I have just seen Hoffmeyer's posting which came in whilst I was writing my reply. By all means check out the ESP Audio Pages, there are some excellent projects there, but do not be tempted to try Project 96 ('ic + output pair' which is what you are looking for). This project is seriously flawed in my opinion and is not up to the usual high standards of the site (it is a contributed project which may explain it.)

[Edited by Geoff on 04-30-2001 at 09:21 AM]
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