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Dual CMOY Amplifier Idea, will it work?

post #1 of 27
10/7/09 at 6:36pm
Thread Starter 
Hello everybody, I'm considering producing an amplifier that's a slight modification on Chu Moy's design. The way I understand it, it should work (but keep in mind I understand very little).

I had a thread I was writing in but it's deteriorated into an argument between other people so I'm starting a new thread so I can get my question answered.

My primary headphones are ATH-AD700's, and I want to have a good solid amplifier to support it, and eventually a dac (either y2, or dac) to support and complement it.

As for the amp, here's what I got. Per tangent's site, the resistor divide on the cmoy can be replaced with a TLE2426, and if you give it a buffer, it can greatly improve thoroughput and the amount of power it can provide the amp. I'm chosing to use the TEL2426, because what I understand of it (again very little) it handles uneven loads better. Since I'm not going to be using both sides of the operational amplifier equally (at least that I understand, maybe I am) this seemed like a good step in the right direction. Also, I'm opting to go with a stronger capacitor, though I may increase the capacity even further since I'll have plenty of room to budge.

Anyway, here's the amplifier circuitry that I'm considering building, if there are errors in how it'll work, I'd like to know. Each side of the amplifier (there will be two fully populated CMOY boards, functioning as a pre-amp and then the final amplifier). My hopes, is that it will reduce the noise produced after amplification. As it stands my current CMOY is gets noisy after about 7 o' clock. it's almost inaudible until 8 o' clock.

If there's anything I should change or questions I can answer, please ask. This is basically two cmoy's sitting side by side, but acting as single channel amplifiers and pre-amplifiers for the amplifier side. If you were to look down on it'd look like 2 regular CMOY's but with the wire going from output of one side to input of the other, and then to the headphone jack.


Worst case scenario I'll just end up building more than 1 CMOY if the idea is just novelty to me (and doesn't sound good). But, my main concern is if the power supply shown is a direct replacement for the one shown as the default power supply for the CMOY on tangent's site, shown here:

http://tangentsoft.net/audio/cmoy-tu...angent-sch.pdf

The way I understand it, it'll work fine. Also, can a single TREAD power multiple boards, or would I be required to setup two TREAD's? I'd like to pick up a single treads and power both of these boards. (also, what kind of parts should I put between the treads and the DC jack or will it even work)?

Anyway, here's the schematic, tell me what I'm doing wrong, etc.

Another question, is there any merit to connecting the two virtual grounds together?

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post #2 of 27
10/7/09 at 7:10pm
You are solving the problem the wrong way.

Find the source of the noise and eliminate it. It shouldn't be making noise.

Doing the same thing twice as hard will likely just make it twice as noisy.
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post #3 of 27
10/7/09 at 7:19pm
Thread Starter 
Quote:
Originally Posted by ericj View Post
You are solving the problem the wrong way.

Find the source of the noise and eliminate it. It shouldn't be making noise.

Doing the same thing twice as hard will likely just make it twice as noisy.
If I understand it correctly, I'm cutting the gain in half.

I understand the idea isn't very practical, but I'm more so concerned with whether or not it'll work. I understand how to determine the gain, with 10k for r3 and 10k for r4, we're at a gain of 2 for the "pre amp". For the "power amp" section, we're looking at a gain of 3. If It's multiplied, it's a total gain of 6.25, if it's added, it's a total gain of 5.25, so it's not a huge difference (again if I understand it correctly).

This is more or less an exercising in figuring out how to handle wallpower.
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post #4 of 27
10/7/09 at 7:21pm
You could cut the gain in half by changing two resistors on one cmoy.

It would work. There are commercial products that do the same thing (such as the Hippohifi 'bloat' dac/amp).

It's just the wrong solution to the problem at hand.

Edit: One tread is overkill for two cmoys. You don't need two. Also, there needs to be just one virtual ground.
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post #5 of 27
10/7/09 at 7:26pm
Thread Starter 
Quote:
Originally Posted by ericj View Post
You could cut the gain in half by changing two resistors on one cmoy.
I could.

I'm simply asking if this will work based on what's on the image. Do you see any glaring errors that would prevent it from working? I plan on utilizing sockets for R3 so I can tweak this section or alternatively switch it back to 2 CMOY's, and also I plan on utilizing those clips that grab wires (not sure what you'd call them) for the connections between the different boards, etc.
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post #6 of 27
10/7/09 at 7:29pm
You don't need the second input section, if the second opamp is jfet-input.

Have you taken a look at the 'A47' amplifier? It's basically the same thing, with different objectives.
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post #7 of 27
10/7/09 at 7:37pm
Agreed. The second section is unnecessary.

Also, unless you plan on using a single 9 volt battery, there's also no need for the rail splitter power supply. Just feed it from a proper split supply in the first place.

se

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post #8 of 27
10/7/09 at 8:19pm
Thread Starter 
Well I guess I may end up scratching this idea then. *sigh*

Thought I had at least somethign figured out, I know this won't be all that great sounding, perhaps better than a stock CMOY, but potentially had the benefit of mixing op-amps for unique sounds.
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post #9 of 27
10/7/09 at 8:47pm
Quote:
Originally Posted by ericj View Post
You don't need the second input section, if the second opamp is jfet-input.

Have you taken a look at the 'A47' amplifier? It's basically the same thing, with different objectives.
x2 - The a47 is a nice upgrade from the cMoy. It basically parallels two opamps to increase current output. Your design looks like it's trying to accomplish something similar--only with actually more parts then you really need. Here's some links:

HeadWize - Project: Apheared's Project Scrapbook by Michael Shelton

How to build the Apheared 47 Headphone amplifier for Grado Headphones

I built a balanced version of one of these using the TLE2426/BUF634 rail splitter, and it sounds surprisingly good. The design should work well with your low-impedance cans.

I didn't want to do as much jumpering as Ben did on his design, so I altered the layout slightly. You can see some real bad cameraphone pictures of it here:

http://www.head-fi.org/forums/f6/pow...ed-a47-444429/

In addition to the rail-splitter, you'd only need one of these boards (they use dual opamps), unless you wanted to go down the dark path I did and go balanced--which means balanced source, balanced amp, and of course having to mod your 'phones.
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post #10 of 27
10/7/09 at 10:55pm
Thread Starter 
Okay, how does one go about making a balanced version of any given amplifier? I'd be interested in trying this, and is it easy to make an adapter from balanced to a 6.3mm or 3.5mm? I'd be interested in trying the balanced idea for next to nithing, and the A47 looks like it could pull that off. It looks really interesting in a ghetto-fi way.

I'm imaging that you just splice both grounds from the XLR femal to the 6.3mm male connector? This would be practical since I despise the idea of dual XLR and I'd use a single 4 pin XLR.

Can anybody link me to some good information for making balanced setups?
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post #11 of 27
10/7/09 at 11:10pm
Quote:
Originally Posted by Aynjell View Post
I'm imaging that you just splice both grounds from the XLR femal to the 6.3mm male connector? This would be practical since I despise the idea of dual XLR and I'd use a single 4 pin XLR.
If you go "balanced" by way of bridging two channels together, you can't tie the "grounds" together. You'll end up with one channel driving the output of the other channel.

You'd need to either use some sort of four conductor connector on your headphones, or transformer couple the amp's output which would allow you to tie the "grounds" together.

se

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post #12 of 27
10/7/09 at 11:31pm
Thread Starter 
Quote:
Originally Posted by Koyaan I. Sqatsi View Post
If you go "balanced" by way of bridging two channels together, you can't tie the "grounds" together. You'll end up with one channel driving the output of the other channel.

You'd need to either use some sort of four conductor connector on your headphones, or transformer couple the amp's output which would allow you to tie the "grounds" together.

se
No, I think I either phrased it wrong, or you read it wrong. When I asked if you could bridge the 2 grounds, I meant can you bridge them in a 4pin XLR FEMALE to 6.3mm MALE headphone jack connector for when you want to return to a 6.3mm or 3.5mm for that matter jack. THe headphones should already be setup in such a way, since the TRS connector only supports 1 ground.
(this would only be used if I wanted to use my balanced modded headphones in a standard jack)
Am I wrong on this?
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post #13 of 27
10/7/09 at 11:41pm
Quote:
Originally Posted by Aynjell View Post
No, I think I either phrased it wrong, or you read it wrong. When I asked if you could bridge the 2 grounds, I meant can you bridge them in a 4pin XLR FEMALE to 6.3mm MALE headphone jack connector for when you want to return to a 6.3mm or 3.5mm for that matter jack. THe headphones should already be setup in such a way, since the TRS connector only supports 1 ground.
(this would only be used if I wanted to use my balanced modded headphones in a standard jack)
Am I wrong on this?
Ok, so you're saying you'll mod your headphones to use a 4 pin XLR, but you also want to be able to use them with an unbalanced amp with a 6.3mm jack? Is that what you're wanting to do?

se

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post #14 of 27
10/7/09 at 11:46pm
Thread Starter 
Quote:
Originally Posted by Koyaan I. Sqatsi View Post
Ok, so you're saying you'll mod your headphones to use a 4 pin XLR, but you also want to be able to use them with an unbalanced amp with a 6.3mm jack? Is that what you're wanting to do?

se
Yes. I'd want to have an adapter handy so I can switch back in times of need.

The way I'd understand it is you'd connect both grounds to the same ground pinout on the 6.3mm jack. This wouldn't work for a balanced setup, but that's when you pull off the dongle and plug in your XLR jack. :P
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post #15 of 27
10/8/09 at 12:16am
Quote:
Originally Posted by Aynjell View Post
Yes. I'd want to have an adapter handy so I can switch back in times of need.

The way I'd understand it is you'd connect both grounds to the same ground pinout on the 6.3mm jack. This wouldn't work for a balanced setup, but that's when you pull off the dongle and plug in your XLR jack. :P
Ah, yeah. That'd work. Your dongle would have a four pin female XLR on one end and a 6.3mm TRS on the other and if you stuck with the ipso facto four pin "standard," then pins 2 and 4 get tied to the ground sleeve of the 6.3mm TRS.

se

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