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Old 5th January 2009, 02:57 PM   #1
jman 31 is offline jman 31  United States
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Default Headphone amp issues again

Alright I'm back again. I finally built a headphone amp that I am extremely happy with. It works great except that when I run through the distortion circuit it doesn't distort! I am afraid that I have left out a key component or something. If anyone would be so kind as to look over this circuit and see if I'm missing something I would greatly appreciate it! Everything works great otherwise, so I assume it's only the distortion circuit that is giving me problems.

Thanks
Jeremy
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Old 5th January 2009, 04:29 PM   #2
Minion is offline Minion  Canada
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It should distort if you have the chip set up for enough Gain...The Diodes should start clipping when the output reaches 0.7v , the problem with this is that the output will be of really low Volume as 0.7v output is a very low Volume (Barely Line level) so a Makeup Gain section would be good to get the Volume higher...

If you put a 10uF cap between pin 1 and 8 it will set the gain to 200 which should be enough to start clipping...or put a Pot in series with the 10uF and you get adjustable gain...


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Old 5th January 2009, 05:27 PM   #3
jman 31 is offline jman 31  United States
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Thanks again minion! As always, you are very helpful! I will give that a try and report back.
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Old 5th January 2009, 05:50 PM   #4
jman 31 is offline jman 31  United States
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OK, I tried that. No dice. I even tried a 33uf cap I had laying around. Does it matter if its a polarized or non poarized cap?

it's really loud but no distortion. Even with the guitar pot volume at 1 it is really loud. do you have any ideas for a simple distortion circuit that would work better or take less gain?
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Old 5th January 2009, 06:11 PM   #5
Minion is offline Minion  Canada
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Well Try a clone of the DOD250 and put the LM386 curcuit after it with a lower gain....

http://www.generalguitargadgets.com/...ist_250_sc.pdf


it is pretty much simular 2 your curcuit but uses a regular opamp...
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Old 5th January 2009, 06:38 PM   #6
mjf is offline mjf  Austria
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hallo.
distortion should beginn at a( low) level of 0,6v .
perhaps there is something wrong with your connection of the parts(missing connection of the diodes or so.....),or the switch(you need only one switch : s2=effect on/off,s1 can be closed always........).
greetings.............
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Old 5th January 2009, 07:18 PM   #7
jman 31 is offline jman 31  United States
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Quote:
Originally posted by mjf
hallo.
distortion should beginn at a( low) level of 0,6v .
perhaps there is something wrong with your connection of the parts(missing connection of the diodes or so.....),or the switch(you need only one switch : s2=effect on/off,s1 can be closed always........).
greetings.............
I have checked all of the connections and went as far as to change the diodes to some IN914's. Everything checks out with with a meter, as far as continuity and the diode seem to read right. When I get a chance I will measure the output voltage to see if I am anywhere near the .6v required for the diodes.

The switches are in order although I understand what you are saying about one switch. I am getting good output through the distorted circuit, it just isn't distorted.

Thanks
Jman
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Old 5th January 2009, 07:30 PM   #8
mjf is offline mjf  Austria
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what kind of headphones do you use?
high impedance,600 ohm or so.
or low imp. 30 ohm...........
greetings.........
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Old 5th January 2009, 08:26 PM   #9
jman 31 is offline jman 31  United States
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All of the headphones I have are low impedence between 24 and 44 ohms.
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Old 5th January 2009, 08:37 PM   #10
jman 31 is offline jman 31  United States
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Quote:
Originally posted by Minion
Well Try a clone of the DOD250 and put the LM386 curcuit after it with a lower gain....

http://www.generalguitargadgets.com/...ist_250_sc.pdf


it is pretty much simular 2 your curcuit but uses a regular opamp...
The problem that I am trying to work around is space. I am trying to keep the circuitry as minimal as possible to fit it in a very confined little box. I have a bunch of regular components available so I am trying to avoid buying surface mounted items. And I'm using half of a premade perf board from Radio Shack
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