CMOY Headphone amp mod questions

[aandree]

Hello, I know this topic is little bit old but I am building this device and I have several questions.

1) If I look at the last scheme from jasonsmusicgear and compare it with GGG scheme of JFET guitar buffer, there are few differences in values of capacitors and resistors. I suppose there are mixed values of the parts from two schemes - JFET and standard NPN - but maybe I am wrong So which values should I follow?

2) Unfortunatelly I cant get film caps with suggested values, only electrolytic ones. But in their case I am not 100% sure about polarity...can somebody please help to specify the right polarity? I suppose all "+" should be oriented on left but as I said, not pretty sure and dont want to destroy any other part in the circuit.

All my questions are "expressed" bellow graphically... I would be very greatful for any help.

[Eddododo]

The first schematic works, as-is.. I imagine the smaller resistor values are simply to eat up less current, and the cap values are 'kind of' non-critical.. larger caps mean a lower freq for low-end roll off that comes with using coupling caps.

the polarity would be the same for caps in both circuits

[aandree]

First of all thanks for reply Eddododo.

I have made few changes in the previous scheme - mainly I took and placed there the buffer scheme from GGG (NPN version) with all the original values.

Another thing - you said you could imagine lower resistor values in order to have less consumption...can you please specify which resistors exactly and how much can I lower the values?

And last thing - you also said that cap values are not so critical...would it all work with marked cap values without any harm? I changed all the 10uF caps to 4,7uF. Just to remind, I am going to use this device as an instrument (guitar, violin) monitor for live playing, so there is no such a high demand on sound quality, especially in low freqs. The reason of changing the values is because I want to use film caps and since it is a portable device, I want it as small as possible. And 10uF film caps are really big in comparison with 4,7uF.

[Eddododo]

Sorry for the delay

I was referring to the  differences in resistors that yOu pointed out.  Smaller bias voltage resistors will eat less current up than larger , which are thOse you pointed out. 4.7 should  be fine  for the caps.

[aandree]

Well, anyway I have already made the device according to the scheme I uploaded in my last comment. There are actually different (lower) resistors values in the buffer circuit because I used the original values for NPN buffer from GGG (as I wrote before). The device works perfect But still I want to make a few modifications.

First one which I am not sure how to resolve is changing of the two pots which are currently 100k but I want to change them for 10k. The reason is that I want to change them for smaller (dimensions) ones with integrated switch, but could get them only in 10k version. Can I just put after each of them 100k resistor in series configuration (between the pot and 1 uF cap - C3, resp. C4), or can I change the value of R6 (resp. R7) to 100k? Or something else?

Second plan is to supply the circuit by one of Tangent's "Simple Buffered Virtual Ground Circuits" http://tangentsoft.net/elec/vgrounds.html but I am not sure which one. One thing I am sure is that I cant get TLE2426. The simpliest one to make seems the Sijosae's one, but doesnt it consume too much current only for itself compared to the ones with op-amps?

[botmayank]

Hey, I'm so glad I found this thread ! I have been looking for a simple solution for modifying my CMoy amp. These are my baby steps into the world of audio circuits and I'm loving the kind of output I'm getting by implementing relatively easy Op-Amp circuits 

I used these common tutorials to make the amp, ( I used the virtual ground config using a single 9V battery)
http://tangentsoft.net/audio/cmoy/
http://www.instructables.com/id/Headphone-Amp-Chu-Moy/?ALLSTEPS

I switched out the 220uF caps at the input for 470uF, added 4.7k ohm res at the input for each channel (haven't found a stereo pot yet) and the audio is sounding great through my Sennheiser cans and its even driving smaller impedance loads like iPod headphones quite well. I would really appreciate it if somebody could help me sort a few things out. (sorry if some questions are really dumb  )

1. As per the last schematic posted, will the guitar input be split and given to both the L and R inputs as is or do I need to implement some sort of mono to stereo conversion ckt or is it simply going to go into just 1 channel (either L or R) ?

2. Does the addition of a 10uF or so decoupling cap help at the 9V battery input?

3. How can I add a simple 3 channel EQ to this circuit?

4. Most of the schematics I'd found online suggested using an LM386 based amp for a guitar headphone amp, is it sufficient to drive the guitar through such a CMoy if the intended use is just for headphones?

5. Can I implement a simple distortion effect as well using the virtual gnd circuit for my CMoy?
http://www.instructables.com/id/Make-an-easy-guitar-distortion-pedal-STEP-BY-STEP/

As in, in your opinion, will a single 9V battery last me a couple of hours if the entire ckt includes the guitar+iPod CMoy as well as a 3 channel EQ and a distortion effect ckt for the guitar input?

6. I'd swapped the 220uF caps used to make the power ckt for the CMoy for 470uF ones and it really improved the bass in the music, can I safely swap those for 1000uF or are there any drawbacks in doing so?

Thanks a lot in advance to anybody who can shed some light on these questions 

[Borbanv]

Hi Jason. I need an information.. I'm from Brazil.. I just made this cmoy headphone, but I didn't find the opa2134.. for this reason I place using TL072... The sound is nice when I turn on the device, but after some seconds the sound goes disappearing.. Any suggestion?

[PRR]

Welcome.

Are you using a battery?

Check your connections again and again. De-biasing after start-up is often a bad connection.