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Old 1st August 2011, 10:10 PM   #1
tade is offline tade  United States
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Default Tade's new CMoy amplifier

So I heard you can make these things point to point...

I was bored on sunday, and wanted to do something artsy, and also to check out the beautifully simple Chu Moy amplifier. The following, impossible to package, skeletal amp was the result. lol

It sounds great, but I think it may be a little too low voltage for my headphones which i think are like 65 ohms. AKG K702 Any other explanation for clipping?

Tade
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Old 1st August 2011, 10:16 PM   #2
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There aren't many (any?) DIP opamps that will drive a 65 ohm load. Without a schematic or other pertinent information, I can't really say much else.

Mike
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Old 2nd August 2011, 04:16 AM   #3
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what opamp are you using? you will need something like AD8397 or few JRC4580 (paralleled) to drive K702...
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Old 2nd August 2011, 07:16 AM   #4
qusp is offline qusp  Australia
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its a cmoy, do you really need the schematic? actually opamps to drive a 65r load are not unheard of, with buffer would be better of course, but any decent rail to rail I/O opa will do the job. like lme49710/20 for example

a schematic isnt really needed, but can you say what the supply voltage and opamp you are using is?
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Old 2nd August 2011, 12:18 PM   #5
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qusp, maybe you should post a schematic of what OP built since you appearently know. Seriously, the reason I asked for a schematic was I don't know what exactly what was built, and OP was complaining about clipping. And I will stand by my oiginal statement, not many opamps will perform optimally into a 65 ohm load even at reduced supply voltages and low drive levels.

Mike
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Old 2nd August 2011, 02:35 PM   #6
qusp is offline qusp  Australia
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its a cmoy, you havent seen the cmoy schematic? seriously? a cmoy if traditional is basically nothing more than the opamp with a pot at the input and VERY basic gain network, power supply (usually 2 batteries, or 1 and a splitter formed by a capacitor bank, or resistor divider) and decoupling.

Click the image to open in full size.

linked to Kevin Gilmore's old site and originally by Dr Chu moy, the design is so simple

reducing supply voltages for most opas, worsens the problem into a low impedance, not improves, generally it means because they dont swing as close to the rails into lowZ there becomes very little swing left. but ermm, we are talking about a cmoy, you can find an opamp that maybe performs better than whatever hes using, but basically if you add anything at all to the circuit its not a cmoy anymore. sure its not driving the headphones optimally, but its a cmoy, thats never going to happen and its not in the brief.

however i also stand by my statement, some opamps do a pretty decent job of it and 65r is actually a pretty kind load as headphones go these days, where some multidriver in ears present less than 10r at some frequencies

Last edited by qusp; 2nd August 2011 at 02:51 PM.
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Old 2nd August 2011, 03:56 PM   #7
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My point was, how do you know what was actually built, there are a million variations on these things.
Tade, if you could post what you put together and what opamp was used, it would help.
By the way, I've been building opamp circuits since the uA709 days, so I do know a little bit about how to use them.

Mike

Last edited by Michael Bean; 2nd August 2011 at 04:06 PM.
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Old 10th August 2011, 07:49 PM   #8
tade is offline tade  United States
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lol I need to setup a proper email adress to post replies.

That might explain the clipping... But it really sounds good. I forgot to buy 1K resistors, so i used 4.7 for a gain of only 2. But otherwise the above posted schematic is exactly right, but I build the non inverting version. Yeah, i guess there are a bunch of varieties.

Honestly, this was an afternoon boredom inspired project. I mainly just wanted to share the construction, but the help is great because I am currently bored and am gonna do the parallel suggestion. I am going to use a protoboard this time... I have some NF535N opamps that are dual packaged JFET inputs. I am going to configure them in parallel. It's a shame I haven't biwired my headphones yet because I would like to run them bridged, but I reckon I'll just build another amp.

I will repost pics when i get this built. Thanks for all the advice!
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Old 11th August 2011, 12:16 AM   #9
tade is offline tade  United States
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Just got done building this design:
http://i54.photobucket.com/albums/g1...rt/aph_47b.gif

I'm not proud of the back, but maybe I suck at proto boards. N535n dual opamp chips.

Check out the super audiophile approved ultra filtered 9V battery power supply. Those old computer parts needed to be used sometime.

It sounds punchy!
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Old 11th August 2011, 12:20 AM   #10
tade is offline tade  United States
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Forgot the PS lol
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