[mr man]

I'm looking at either the basic cmoy or the cha47. This will be my first amp so I want it to be easy. I've read that the cha47 works well for grados but those phones are 32 ohms while the ksc-35s are 60 ohms. Can anyone compare the two amps?

p.s. I just discovered the a47. how does this amp differ (in terms of sound) from the cha47?

 

[rickcr42]

The original Chu Moy Pocket Amp is fine for most heaphone listening , a good sounding basic amp.Also a good first project.

http://headwize.com/projects/showpro...=cmoy2_prj.htm

The Hansen amp is a Chu Moy amp with a crossfeed circuit on a printed circut board for easy assembly.

The Apheared 47 amp is a Chu Amp with doubled op-amps for higher current output into low inpedence cans,a nore dynamic sound with Grados.

The CHA 47 is a combination of ALL the above amps
C = Chu Moy Pocket Amp
H = Hansen circuit board with crossfeed
A47 = current doubling opamps

 

[eric343]

Grr! It's *not* an A47! It's a levallois with Meier crossfeed!

"CHA47" is one of my pet peeves... it's a CHL.

 

[rickcr42]

yes the hansen board was based on Jazz's layout , but the "47" stands for the current doubled (two op-amp) version on the hansen pcb.As shown in the pocket amp project addendum and apheareds project scrapbook

 

[CaptBubba]

Well, actually the 47 stands for the value of the resistor that is there to keep the dual opamps from frying cans with the output current.

 

[rickcr42]

ALL the parts were a value factor of 47 , hence the "47 Amp" designation

 

[eric343]

Yes, but how many parts in a Hansen board have resistors of value 47ohms? In an A47? See my point?

 

[rickcr42]

point made , and the CHA47 designation has caused MAJOR confusion and probably should be dropped from the Head-Fi dictionary (or explained in a DIY forum FAQ)
I have even seen it in reference to PPL's amps

But the above description by me pretty much explains each amp type though not all the possible variants which REALLY confuse the newbies to no end.

My advice for first timers is to build the basic Chu Moy Pocket Amp , gain match it to the application and THEN consider something more advanced , such as raising the current output of the amp.
And that could be easily implemented by either-----------
A-paralleling a second op-amp "piggybacked" for more current (with load resistors added to the output of EVERY op-amp)
B-adding a buffer to the output , either by just "hanging " it on the output or using the multiloop feed back configuration.Also easily added without modification the the basic amp

 

[eric343]

Agreed.

 

[mr man]

I will go with the standard cmoy then do the a47 mod.

Thanks for the clarification.

 

[millerdog]

Did I read right or did you guys say that the CHA47 is just the CMOY amp with 47 ohm resistors on the audio outs? I mean Tangents design with the dual opamp..and placing 47ohm resistors in place of the jumpers?
I don't believe there is crossfeed in my CHA47 that I bought used.
What the flerck? Is there a CHA47 schematic online?
md

 

[rickcr42]

Apheared was looking to get the most out of his Grado headphones and was always experimenting.This is what he came up with

he used a dual op-amp PER CHANNEL in a current doubling configuration.The "47" designation came from the use of passive parts with a vlue factor of 47

the original idea is from this data sheet-
http://www.burr-brown.com/download/ABs/AB-051.pdf

I have used a variation on this for years which also gives good performance and can be simply added to ANY op-amp based amp.That is by piggybacking an identical op-amp on top of the first but you must use some resistors on the output (47 ohms or so) or the amps will fight each other

this is the original chu moy pocket amp ,a basic single stage amplifier that is really very good at driving just about any headphone

Jan meiers natural bass crossfeed

The Levallois layout

and finally the hansen pc boards using that layout

all this can be found at the headwize project library

http://headwize.com/projects/showpro...heared_prj.htm

http://headwize.com/projects/showpro...=cmoy2_prj.htm

http://headwize.com/projects/showpro...meier2_prj.htm

 

[rickcr42]

Apheared was no fan of crossfeed circuits so he was always screwing around with the hansen board ,trying for more current

notice there is no crossfeed but there IS two dual op-amps

this is mikes volume pot wiring mod

and finally this scary monster

build it at your own risk

 

[slindeman]

I don't see what's confusing about the CHA47. It can only mean one thing: an (A)pheared "47" amp, which is based on (C)moy's pocket amp, and built on a (H)ansen board. It has to be called a "47" amp because it is still the exact same circuit whether it's on the Hansen board or not, and "47" is what Apheared named the circuit. The CHA is just the tribute to the three persons involved in the evolution of the end product.

Quote:

Grr! It's *not* an A47! It's a levallois with Meier crossfeed! "CHA47" is one of my pet peeves... it's a CHL.

Grr! It *is* an A47 if you build it that way. The Hansen board can be either one. Perhaps that is the source of the confusion. You can wire the Hansed board as either the Levallois (cmoy front end + meier crossfeed + unity gain opamp) or the standard Apheared "47" (47-based resistors + current boosting parallel opamps + no crossfeed). You can probably wire it up as the standard cmoy with some jumpers, though you would be wasting the other half of your dual opamps due to the board design.

 

[millerdog]

Damn! No wonder there are so many holes in the board on my CHA47. The on board components are the same as the cmoy..except for the dual opamps.
Sheesh!
Now I gotta bother JMT again!
Thanks,
md