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Curious about 3 channel amps...

post #1 of 64
10/4/09 at 2:43pm
Thread Starter 
Hey everybody, I've made a CMOY but I'm not 100% ready to make the jump to a fully balanced setup as I'd have to modify my headphones to utilize such a setup (at least that's the way I understand it). 3 Channel amps, if I understand it correctly have 3 amp boards, 2 driving left and right, and 1 pulling the ground (like if I made a 3 channel b22, I'd have to construct power supply, case, and 3 beta 22 boards, if I understand it correctly)... Gross sort of explained it to me at the meet, and the way I understand it if you wanna stick with a normal TRS connector it's the way to go.

At this point I know my weakest link isn't my amp, but in order to move upwards to a higher quality can set (I'm leaning towards grado's with GS/PS1000 pads), I'm probably going to have to replace my lowly CMOY with something a bit more serious.

The building and skill part isn't much of cocern, my girlfriend is more than willing to help me with the build and with her experience almsot any amp design should be easy. She was pretty confident that a beta 22 would be easy, so if that's any usefulness to you...

It seems that a 3 channel beta 22 would be great, but the footprint of such an amp would really take a toll on my desk space. Can any of you reccomend something that would be a good step from a CMOY between it and a beta22?
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post #2 of 64
10/4/09 at 4:24pm
M3?
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post #3 of 64
10/4/09 at 4:41pm
My opinion is that dual supply "3 channel" amps are wasting power and electronics when good layout with star gnd can reduce the "errors" that 3-channel amps are supposedly fixing to way below audibility

dual supply "passive" gnd is fine - with Class A output there is even less nonlinear distortion in the "passive" gnd amp's output than in a 3 channel implementation

the only reason I can see for a active gnd "channel" is that the desire to use single supply "wall warts" or single 9V battery means some sort of supply splitter circuit will be needed - an active gnd for a single supply amp can benefit from star gnd layout and shouldn't separate output from signal and feedback gnd - which is different from the locally fashionable "3 channel" amp connection

if you feel the need for extreme measures a few sq ft of 16 or 20 oz Cu roof flashing for ultra low R "technical gnd" between 2 boards is a lot cheaper than a 3rd B22 amp board

if you really want to improve the crosstalk # the 3 channel advocates tout at the headphone (ie, where it really matters) there is really no choice but to reterminate the headphone cable to a lower contact resistance pin/socket type with separate R/L gnd connections - TRS connector have too high contact R in the common R/L gnd connection
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post #4 of 64
10/4/09 at 4:51pm
Thread Starter 
Quote:
Originally Posted by PJPro View Post
M3?
Excellent idea, I'm going to look into the M3 as a nice step between my CMOY and something bigger and badder. Thanks!
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post #5 of 64
10/4/09 at 5:07pm
CK²III ? Also found on Amb's website.
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post #6 of 64
10/4/09 at 5:19pm
Quote:
Originally Posted by jcx View Post
if you feel the need for extreme measures a few sq ft of 16 or 20 oz Cu roof flashing for ultra low R "technical gnd" between 2 boards is a lot cheaper than a 3rd B22 amp board
Why not just use the case?
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post #7 of 64
10/4/09 at 6:49pm
Quote:
Originally Posted by rds View Post
Why not just use the case?
I did say extreme..

for battery power amps case gnd should be fine - although Cu can be soldered while electrical contact to Al relies on mechanical pressure and piercing the Anodized or spontaneously formed Oxide layer

when AC power is involved case gnd can have power line noise from EMI filter caps/xfmr pri-sec C - really sensitive instrumentation often uses a Faraday cage inner box connected to the case at just one point

a heavy conductive Cu technical gnd basically is trying to have a low R star gnd "point" while connecting to physically separated circuits like R/L channel boards in a B22
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post #8 of 64
10/4/09 at 6:53pm
Thread Starter 
This is going to be wallpowered. I want something that works consistently and I don't have to come up with batteries all the time, also I imagine wallpower can give higher results if you build an amp that's good for it. I'm tired of being bound to batteries, basically.
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post #9 of 64
10/5/09 at 6:36pm
Thread Starter 
Going in a slightly different direction, could anybody recommend for or against a wall-powered variation of the RA-1 clone? Also, what's our thought on using the ELPAC WM080-1950-760 for the wallpower? I imagine I could toss one together for all of 100$ (I hear 30$ for the hardware, 30$ for the case I'd want, and 30$ or so for the elpac)... and at that price I could afford to make 2, 1 for me and 1 for the misses since both of us will be rocking grado's.

After that I could probably graduate to a o11+m^3 setup and then maybe a o22+3 channel b22?

I really want to go with something simple and focus on what I'd have to do to make a clean sounding but simple amplifier with a nice sleek look.

A quick question on using a Wm080, I can wire it up straight to the amplifier much like I would a pair of 9v batteries, straight to the power in posts? Or is there an extra step like a steps psu or something like that required? The way I understand it is the steps would improve the psu's power quality to the amp circuitry, but isn't required for it to run. Is this correct?

An extra 34$ for a pair of treads (since I'll be building 2 of these) isn't too much to add to the project cost...
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post #10 of 64
10/5/09 at 8:50pm
For $100 you could build a pimeta, which is three-channeled, buffered, and can be run class A. RA1 and cmoy are largely the same.
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post #11 of 64
10/5/09 at 8:53pm
I would recommend against the RA-1 clone. Not because it isn't a good amp for grados, but because it is a commercial design that you don't have the rights to use. For some reason, maybe because the design is so simple or because it is so cheap to build, people think that it is fine to build an RA-1 clone in a way they would never think about another amp. What kind of reception do you think someone would get for cracking a Zana Deux open, copying the circuit and sticking plans and BOMs on the internet?

Anyway, I would also recommend the CK2III. It is about $200 all together and a great little amp. It is very compact, as well.

The m^3 would be a good option as well. Regarding the channel question, I would go 3 channel even if the benefit is questionable because I think that you would have an easier time selling the 3 channel version if you ever wanted to move in another direction. I just think that most people in the used market are looking for 3 channel m^3s and betas because those are the most discussed variations.
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post #12 of 64
10/5/09 at 9:19pm
Quote:
Originally Posted by tintin47 View Post
I would recommend against the RA-1 clone. Not because it isn't a good amp for grados, but because it is a commercial design that you don't have the rights to use.
Sure he does. There's no protected intellectual property in the RA-1.

se
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post #13 of 64
10/5/09 at 9:57pm
Maybe not, but it is pretty plainly dishonest and disrespectful considering the fact that Grado has spoken out specifically against RA-1 Clones, and that Grado was the company who took the time to find the specific opamp that makes the RA-1 sound so much better than other C-Moys and C-Moy variants.

Either way, I don't want to start another argument about this or highjack the thread so lets drop it.
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post #14 of 64
10/5/09 at 10:04pm
Thread Starter 
Quote:
Originally Posted by tintin47 View Post
Maybe not, but it is pretty plainly dishonest and disrespectful considering the fact that Grado has spoken out specifically against RA-1 Clones, and that Grado was the company who took the time to find the specific opamp that makes the RA-1 sound so much better than other C-Moys and C-Moy variants.

Either way, I don't want to start another argument about this or highjack the thread so lets drop it.
If somebody can prove to me that it's against any kind of law then I won't build the RA-1, otherwise, please let me know if my plan is invalid for other reasons. Personally I can't ever justify buying something for 350$ that I can make in my spare time. Maybe grado spoke out against them but if they didn't have a patent for such a simple amp which I doubt they could have gotten then it's fair game.

Thanks,
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post #15 of 64
10/5/09 at 10:22pm
What grado had in the Ra-1 was a trade secret. It has been reverse engineered and now is available to anyone not only to build for themselves but to sell if they like. The only caveat being you can't sell it as a grado ra-1.
Even under seriously draconian ip laws this would not qualify as infringement.
...and I have to say why shouldn't someone be free to make any amplifier they choose for their own personal use? I can't even begin to understand the thinking there.

If anything, grado should be paying gratuities to Chu Moy
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