[Earwax]

Well, here she is, your bog standard CMOY.

inside:

 

[Jaypetermen]

Quote:

Originally Posted by Earwax First, did you build it according to standard specs for gain and cap values? Do you hear anything at all from the PDA, noise or dead silence? What headphones? The standard CMOY seems to match well for portables, I'd start off looking for other problems, such as intermittent connections, before trying to tweak the amp.

I used all of the parts specified on the Tangentsoft page. Well except I did add two 1000uf caps power supply in parallel with the 220ufs.

There is no unwanted noise or dead silence then the volume control is turned up. The amp sounds sweet from silence to eye bleeding volumes on my Sennheisser PX-100 portable headphones.

Actually the amp performs flawlessly when a PC or portable Walkman tape player is used as the source. I believe that the PDA output is the culprit.

 

[Earwax]

I made two changes which have really improved this amp.

First, I put in a OPA2227PA, I love it! Bassheads probably won't like it as much as the standard OPA2132, but the midrange and treble clarity is really improved.

Second, I changed the gain from 5.5 to 4, this is a better value for the 28 to 64 ohm headphones I'm using with this amp, giving more precise volume control.

This little baby is sounding really sweet right now!

One more note: with the OPA2227 I was able to run the battery down to just about 4 volts before getting noticable distortion.

 

[Madcat05]

Nice work. How does it sound with the R50?

 

[brschmid]

double post

 

[brschmid]

Quote:

Originally Posted by Earwax Mounting in the tin is harder than I thought it would be. How do some of you ever get 2 x 9v into a mint tin?

my CMOY is ugly, but it works and 2 batteries fit really well.

my mint is much prettier

 

[drewd]

Here's mine - I guess it's a cross between a Cmoy and a MINT. The outputs are buffered and I threw in a buffer after the TLE. I like the battery name, too...AGRESSOR. What were they thinking?

-Drew

 

[Earwax]

Drewd, you etched the PCB yourself? That is very cool.

How much do the additional buffers affect battery life?

 

[drewd]

Quote:

Originally Posted by Earwax Drewd, you etched the PCB yourself? That is very cool.

I'm not quite that good! I had ExpressPCB make the board, then cut it out on a bandsaw.

-Drew

 

[nkd]

What does buffering the outputs actually achieve, and how is it done? I've only seen buffered power supplies on these amps before... and i'm not even sure what that does

 

[drewd]

Quote:

Originally Posted by nkd What does buffering the outputs actually achieve, and how is it done? I've only seen buffered power supplies on these amps before... and i'm not even sure what that does

Buffering the outputs provides the same benefit that buffering the power supply gives - more available current. For the outputs, the specific benefit is that the buffers can provide more dynamic current than the opamp itself can provide, especially if the headphone impedance is a little low.

There's a drawback though - decreased battery life. The current has to come from somewhere...there ain't no such thing as a free lunch. The amount of current draw is adjustable to a degree by varying the bandwidth control resistor (I'm referring to the Burr Brown BUF-634 here). The buffers have a somewhat high quiescent current draw so the battery doesn't last as long as with just a vanilla CMoy with a single opamp and resistor divider. But I feel that the buffers improve the sound, especially on dynamic events and the decrease in battery life isn't a huge amount - maybe 10% on one of my CMoys with a total of three buffers, so to me it's worth it.

Poke around Tangent's web site (http://www.tangentsoft.net/audio) and you'll find some nice tidbits about buffers, especially in his notes on the PPA and Pimeta projects.

-Drew