[CaptBubba]

My old amp was destroyed om Monday due to a fall that resulted in my getting five stitches beside my right eye. Instead of going through the dang thing and resoldering eyerything, I decided to build another amp. Being broke made me look and see what parts i could salvage from my recently departed Szekeres amp.

After a while I figured out I could build the wonderfull little amp that everyone around here seems to have: a Cmoy.

Here's the pics of what resulted, something I am modestly proud of.

The front:

The insides:

It may look pretty messy, but the signal only travels about four or five inches total.

The actual circuit:

Voltage spliter to the left actual amp to the right (as if you couldn't figure that out)

My wonderful soldering job:

Yes, I know, its nearly impossible to see, but it is a decent soldering job, no cold joints for once.

It took me about 30-45mins to build the amp itself, and about an hour to get everything into the box. It runs off of 8AA's for +/- 6V. I can use 9V batts in it but that would probably not run for long.

It draws about 24mA at idle and I estimate that it will run for about a month without changing batts (with normal use). I don't know what the normal mAh rating of Alkalines are so that is based off of 1600mAh NiMh cells.

It sounds much better than my old amp, mostly because it works at all. I only have my V6's here at home so I'll have to wait until Sunday to tell all of ya how it will drive my HD580's, I think it will work great.

Tell me what you think.

 

[andrzejpw]

It sounds BETTER than the szkeres?????

 

[CaptBubba]

Quote:

Originally posted by andrzejpw It sounds BETTER than the szkeres?????

My old amp was a peice of junk. I relised that as I was stripping it for parts. I had about five caps in the signal chain (compared to one with the cmoy), cold joints everywhere, bad layout, bacisly you name it it was wrong with it. The Cmoy seems to have more high freq. response than my old one (prob because of the caps).

A different amp is not necisarily better that another. I depends on the layout and work done on both of them. Remember when we found out about the insides of the Grado amp? It was basicly a cmoy ( a bit different, but not overwhelmingly so) and everyone was astonished because an expensive amp used the same tech we use for our cheap home built amps, but it had a good layout and design so it sounded good.

To give you an idea of how much junk I had on my old amp; I had to empty my solder sucking ball three times, and I only removed the gain stage and most of the film caps, perhaps 1/2 the amp.

Comon people, any more comments? You guys are normaly itching for pics and now that there are some you are silent?

 

[tangent]

You built the whole amp board in less than an hour? That's quick -- I still take about 2 hours to do that, and another 2 to hook up all the panel components, modify the case, etc.

24 mA running current sounds high -- are you using low-impedance headphones?

 

[CaptBubba]

3/4 of that is the LED. I couldn't find a low current one and had to get one that draws 15mA. I figure that the LED will ultimitly save me money because I won't leave the amp on and run the batterys down. I will either get a low current LED ( I already have a 5mm hole to mount it in)

I probably saved most of my time by not really stopping to test the circuit. I tested the power supply really quickly but that was it. I also built both channels at the same time, which is why they are simply mirrors of each other.

 

[aixer]

Did you not learn NEVER mix Energizer with Duracell?
Bad Bad boy..
Doh..! Duracell now owns Energizer, No more bunny.

Just having a little fun

 

[Redwoood]

Quote:

Originally posted by CaptBubba 3/4 of that is the LED. I couldn't find a low current one and had to get one that draws 15mA. [...]

But that's just the max rating, right? have you tried to feed it 1 or
2 mA ? Most LEDs are bright enough at this, low-current or not

 

[CaptBubba]

Yes, but I have 16 1600mAh NiMh AA's coming to me in a few days, so battery life will be much less a concern for me. I'm guessing that the LED actualy draws around 10mA, because that would put it more in line with what other Cmoys get as far as current draw.

Also I left all my spare parts at home, so I don't have any resistors that I could experiment with.

 

[kevin gilmore]

let me guess, the wood box is from a scale weight set???

 

[weeghel]

Quote:

Originally posted by aixer Doh..! Duracell now owns Energizer, No more bunny.

Over here, in europe duracell also advertises with a bunny (well they did, when they actually advertised. I haven't seen an ad in a long long time)

So, there is hope for you yet

 

[CaptBubba]

Quote:

Originally posted by kevin gilmore let me guess, the wood box is from a scale weight set???

Actualy it isn't. It is an old 4H electronics camp project. Basicly it was a jewelry box that had a mercury switch operated alarm on the top that would go off if you opened it without disabling it. I figured that I wouldn't be needing it for that and it was large enough to fit 8AA's, decvent looking, and had thin enough walls to mount stuff through.

I have tried it with my my Hd580s and I must say the combination is awsome. Because I don't listen at high or even medium volumes I don't have to worry about voltage swing or gain issues.

I do want to mess around with different opamps though, any suggestions?

 

[tangent]

Quote:

I do want to mess around with different opamps though, any suggestions?

Of the chips I've looked at so far, those that would work well with HD-580s and an 8-12V supply are the OPA132 and the AD823.

The former will give a small improvement in sound quality, but if you aren't noticing distortion with your current setup, it probably won't give any audible improvement, except perhaps at very low battery levels.

The AD823 is a small improvement in quality over the 132/134, IMHO, and will let you drink your batteries dry (1V or lower). I'm looking forward to a deeper investigation into this chip. So far I'm very happy with it. It could become my stock OPA2132 replacement.

I'm in the middle of evaluating the LM6172, and it also shows promise for this. The last of the distortion went away in my torture test with a 7V power supply. By the time your batteries get down to 7V, their series resistance will probably be high enough that they'll be continually starving the amp for current. But, you would have to redesign your amp to accommodate the LM6172. I've got a preliminary how-to article on the changes you have to make to the stock CMoy design to make this opamp work right. Beware that I'm not 100% happy with my LM6172 test amp, though, so that article might well be changed in the near future. I expect to sort all this out over the weekend.