[mlchang]

Quote:

Originally posted by Czilla9000 Feedback loop and buffer - what are thoughs?

If you look at the schematics of the pocket headphone amp (or any of the other designs based on op-amps) you will see a line from the output of the op-amp back to the negative input of the op-amp. Usually has a few resistors in between (which set the gain). This is the local feedback loop.

A buffer is another kind of IC like an op-amp but it doesn't provide any gain. It's just there for current purposes, to provide drive for the headphones, but not actually amplify. It gets its input from the op-amp.

So you can place buffers outside the local feedback loop, meaning the output of the buffer doesn't feedback to the op-amp, inside the local feedback loop meaning the output of the opamp goes to the buffer (without feeding back on itself first) and the output of the buffer feedsback to the op-amp (aka global feedback), or you can do a multiloop where the output of the op-amp feeds on itself, AND the output of the buffer feedsback to the op-amp. The multiloop design is like the circuit on the META42 printed circuit board. It is supposed to minimize errors from the input and output side of the op-amp.

Again, please correct if this is wrong.

 

[Czilla9000]

So why are newbies suggested to build Cmoys from protoboard...when in actuallity it would be easier to build a META because there is PCB for it?


As far as I can see protoboard is only good for experiementing with new designs.

 

[mlchang]

I think it is because there are a lot less parts with a lot less soldering to do. Also, there used to be a PCB for CMOYs, but I guess JMT is not going to be selling them anymore.

 

[andrzejpw]

Quote:

Originally posted by Czilla9000 So why are newbies suggested to build Cmoys from protoboard...when in actuallity it would be easier to build a META because there is PCB for it? As far as I can see protoboard is only good for experiementing with new designs.

Also, the Meta42 uses a few transistors, small smd parts(well, it does if you use the 8610. Soldering that thing to a browndog was scary.

) It's much easier to screw up a diode/transistor by overheating it than screwing up a resistor. Basically, there's less to screw up on with the cmoy.

 

[Czilla9000]

What about the CHA...the CHA does not seem that different from the Cmoy...are there PCBs for that?


Couldn't I just enter the schematic for the Cmoy at ExpressPCB.com and wall-ha?

 

[skippy]

i don't know how it started, but this is the only forum where i've seen the word "protoboard" used for "perfboard." almost everywhere else i've seen protoboard to mean breadboard. it really confuses me, and it may confuse newbs.

CHA usually refers to the apheared's 47 amp built on hansen's pcb. this is the same pcb that JMT was selling. as far as i know, the pcb was made for a cmoy amp with crossfeed and an opamp to buffer the output. although, you could build the basic cmoy, the CHA47, or one of the various permutations of the circuit on the board.

i think people recommend cmoy's amp because the circuit is easier to understand, and it's easier to assemble without a pcb.

 

[eric343]

Quote:

Originally posted by mlchang Originally in the ETA42 the buffers (for current) were outside the local feedback loop for the op-amp I believe.

Just a very minor nitpick - there was an option to configure the ETA42 with buffer-outside-feedback, but it was never used in either of them that I built (I believe they're the only ETA42s ever made, unless someone ordered themselves some boards from ExpressPCB and didn't tell me).

 

[Czilla9000]

So couldn't I just enter a design (such as the META42, Cmoy, or CHA) using ExpressPCB design software...and walla...just add ap-amp?


Really...building is not my passion...designing is.

 

[mlchang]

Quote:

Originally posted by eric343 Just a very minor nitpick - there was an option to configure the ETA42 with buffer-outside-feedback, but it was never used in either of them that I built (I believe they're the only ETA42s ever made, unless someone ordered themselves some boards from ExpressPCB and didn't tell me).

Thanks for the correction. I knew I would get something wrong somewhere, and I'm sure there's more around. And Czilla, I think you mean "Voila!" not "walla."

 

[eric343]

Czilla - yes, though it's not "just add OP-amp"... it's "just add "OP-amp, resistors, capacitors, wires, volume pot, jacks, switches, case, LED..."

 

[mlchang]

Okay, so since eric343 is following this thread a bit and we've got a "real-live expert..."
Over on headwize you talk about Olimex...
So if I were to use the ExpressPCB beta and send a design to Olimex they could whip together a PCB for me? Or more likely, the ExpressPCB software only works for ExpressPCB.

I will probably have to use the free version of eagle instead right?

 

[eric343]

Heh, I'm definitely not an expert. Just a motivated newbie with a bit of experience

But no, you can't send an ExpressPCB file to Olimex; you'll need to use Cadsoft's Eagle. (www.cadsoftusa.com) It's a free download and supports boards up to 100x80mm; the 'standard' (which lets you use the full Olimex PCB size of 100x160; otherwise you have Olimex panelize them and get two PCBs for the price) non-profit version is $125 and the 'standard' version if you plan to make money off it is $600. The price goes up from there, each version giving more layer capability and bigger possible PCB sizes and more features for really advanced stuff.

 

[Czilla9000]

Quote:

Originally posted by eric343 Czilla - yes, though it's not "just add OP-amp"... it's "just add "OP-amp, resistors, capacitors, wires, volume pot, jacks, switches, case, LED..."

I don't understand...in the software they have caps and resistors to choose from?

 

[mlchang]

Quote:

Originally posted by Czilla9000 I don't understand...in the software they have caps and resistors to choose from?

I think what eric is trying to say is that it's not as simple as adding an op-amp, but that there is a lot more involved...like adding caps, resistors, etc when you are building up the amp.

Thanks for the info eric...do you think it would be worth it for a newb like me to get PCBs made for some early amps, or is it just as fun to do this on perfboard. Money isn't that huge of a deal. Of course perfboard is cheaper, but if a PCB is that much easier, then it would be worth it I guess. I might as well throw in another newb question for whoever is available, but what do people use for the skinny uninsulated wire to do a lot of the connections? I see the hookup wire for the longer runs from one point to another, but what do you use for the holes that are only like 4 apart, too far for a glob of solder, but too close for hookup wire?

Thanks in advance...I hope I'm not threadjacking with this question.

 

[Dreamslacker]

Quote:

Originally posted by mlchang I might as well throw in another newb question for whoever is available, but what do people use for the skinny uninsulated wire to do a lot of the connections? I see the hookup wire for the longer runs from one point to another, but what do you use for the holes that are only like 4 apart, too far for a glob of solder, but too close for hookup wire? Thanks in advance...I hope I'm not threadjacking with this question.

You place a short length of uninsulated wire across the 4 holes and flux it a little. Then solder across the wire.

edit: Place the wire across the solder pad side.