[Paul Blythe]

Hi all, I posted this quickly in the build thread but have a few questions i wanted to ask about the cmoy...
 
This is my first diy electronics build ever ... ok I've fitted a new engine & wiring into an old Honda VFR400 NC21, fitted auxiliary lighting to other bikes I've owned & built PC's etc, but thats all mainly plug & play stuff...
 
I wanted a desktop sized amp rather than a pocket amp so selected a suitable enclosure based on that (and making wiring easier), apart from that everything is as Tangentsoft outlined for the standard build...
 
Re-build with larger 1uF input capacitors & OPA2227, first build used 0.22uF caps & OPA2132.
 


 
first time round it took 8 hours to build the circuit and wire it up, second time round, everthing took 3 hours including removing the first board from the case.

 
All encased and in use...

 

[tangent]

It is a beautiful build, Paul!
 
Next, something worthy of the HD-650s I hope?

 

[Paul Blythe]

Thank you

  the build was done in the first instance to see how good/bad the headphone stage on my Denon 2310 AV amp is ... As money is always a concideration, I wasn't sure if spending £500 on a dedicated head'amp would bring much improvement. The CMoy amp with opa2227 fitted, has proved to be the equal, maybe slightly better than the Denon, just how much better are the Burson or Beta 22 amps?
 
-
 
Controling volume - first time round I set the gain to 3 [10kOhm pot] but could only use the fist 15% on the pot before it got to loud  to listen to [for me]. On the second board I've dropped to a gain of 1 but am only able to use the first 25% before things get to loud again...
 
Should I be thinking of swapping pots from the 10K to a 50K, or can I drop in a resistor [47k] between the pot and input caps?
 
 
I've enjoyed building the CMoy and have read through most of the extras on Tangent's site about improving the v.ground and class-a bias for the opamp's... is it worth building an up-rated version of the cmoy next or trying a two channel Beta 22 [more expenssive]? Or foget the building and buy a Burson HA-160?
 
Thanks,
 
Paul

 

[tangent]

Changing the pot value won't affect overall volume range. (Well, maybe by 1%.) It only affects the loading on the output stage of the source.
 
Inserting a series resistor will have the effect you want. It's best to put it between the input jack and pot, and it should be on the order of the resistance of the pot. For your 10K pot, that means somewhere around 10K. Exactly 10K with your G=1 will give an overall gain of 0.5. Going to 20K will give G=0.33.

 

[Paul Blythe]

Fantastic, just the info I needed, thanks.
 
With the basic CMoy design in mind, is it feasible to expect an increase in audio quility if it is modified using the better virtual ground design, buffers & class-A biasing [JFET Cascode design] as discused on the site?
 
Was thinking of a two board layout using single channel Opamps, each board built as a mono version of the CMoy amp [plus mod's]... worth the experiment?

 

[tangent]

The articles you reference can be read as a travelogue of my path towards the PIMETA v2.
 
Do you want to take the same trip, or do you just want to end up at the same destination?

 

[Paul Blythe]

Good analogy and a very good question to ask...
 
In building and hearing the CMoy I acheived my main goal of proving to myself that a dedicated amp is worth getting.
 
Taking the trip would be nice, ultimately though, it's the final destination that's of greater intrest. It's just that I'm not yet 100% sure on the destination!

 

[i_djoel2000]

i wanna ask something which might be related to cmoy building
 
i'm planning to make a digital volume control for my portable amp, anybody knows where i can get the switch similar to the one used in ibasso T3D (momentary rocker switch)? i already have the chip and only need to find the suitable switch
 
this is the switch i'm looking for:

 
the one on the left, the black switch for controlling volume

 

[Paul Blythe]

Going to have one more go at building a better CMoy amp before moving onto a Betta 22, 2 channel build....
 
Tangent - your site has been a massive inspiration, helping me learn and understand the basics of a subject I knew nothing off 4 weeks ago ...  Thank you!

 

[nikongod]

 
Quote:

Going to have one more go at building a better CMoy amp before moving onto a Betta 22, 2 channel build....
 

Branch out to a pimeta, M3, ppa, or something like that. 

 

[Paul Blythe]

Spot on ... going to try scratch building something close to the pimeta on Radio Shack's protoboard. If that doesn't work out I'll order the pimeta v2 board and do it properly )
 
Currently using the ad823 opamp with the CMoy & Senn hd650's, slightly to forward (aggressive) sounding but preferable to the opa2312 & opa2227 (this one's good with Led Zeppelin). Have the ad8620 & 8610 on order ...

 

[epithet]

Paul,
 
Where did you get those big red capacitors?  I just made my first headphone amp (cmoy) and tried to get some big ones like that but ended up with small ones.  Story of my life, actually.
 
grant
 

 

[Paul Blythe]

Hi Grant ... they're Panasonic 1uF 250V caps from RS components (uk store) - http://uk.rs-online.com/web/p/products/727-0017/ . Think these are the highest rating that are recommended for the cmoy, iirc.
 
Paul

 

[fortney]

Hi,
 
I removed the input capacitors and replaced them with  1K resistors. Now there is no DC protection, but the sound quality  improved.
 
F

 

[Penpal]

can i ask where you got the instructions/parts to make this amp?