[Porksoda]

Hey guys. I graduated, and got a good deal of $$ in presents

I've already bought an Audigy 2 ZS and some other small computer stuff I needed. Next order of business is an amp, mini-to-mini interconnect, mini-to-rca interconnect, and some SR-225s.

So, I have about $120 for amps and interconnects, but I already have some parts. I already have the ICs, and CAT-5 for the interconnects. I also have a lab where I go to school from which I might be able to salvage housings, transformers, and maybe some jacks.

The two amps I want to build is a home PPA and some sort of "largish" portable with two 9V NiMH in paralell. I figure since the portable will be driving SR-225s they won't need the 18V, and as long as I use a suitable op-amp it should be fine. For the PPA, I plan to use the Class-A discrete component buffer off of Headwise, seen here.

So, one of my big questions is what kind of coupling caps to use on the PPA? I can't afford anything top of the line, but seeing as grados are low impedence I don't want to risk DC offset killing them.

Also, if I have this smaller amp running on 9V, what is a good buffer to use? I was thinking about the Class AB buffer on headwise might be a good choice, seen here.

I'm using the Audigy2 and an imp-350 as sources, btw. (for now

)

Thanks for any suggestions you can offer!

 

[was ist los?]

Well you can't build a PPA for $100, considering you'll use $20 for the interconnects' plugs. Look more at a Pimeta at that range.
As for coupling caps, you probably wouldn't really need them unless your sources have high DC offset. I use my PPA based portable with no input caps and use it with SR-60s and iMP-350.
You can also look into a "clone", but it works much better off real sources rather than portables.
BTW, if you were willing to shell out so much for a Audigy 2 ZS, you should have just bought an M-audio Revolution and modded it or Audiophile 24/96, but that's just me.

 

[Porksoda]

Quote:

Originally Posted by was ist los? Well you can't build a PPA for $100, considering you'll use $20 for the interconnects' plugs. Look more at a Pimeta at that range. As for coupling caps, you probably wouldn't really need them unless your sources have high DC offset. I use my PPA based portable with no input caps and use it with SR-60s and iMP-350. You can also look into a "clone", but it works much better off real sources rather than portables. BTW, if you were willing to shell out so much for a Audigy 2 ZS, you should have just bought an M-audio Revolution and modded it or Audiophile 24/96, but that's just me.

Well, I have my own protoboard to use, and all the soldering equipment and a multimeter. The way I see it, getting the blue velvet pot for the ppa, and the caps are the only major expenses. Resistors for BOTH amps shouldn't ammount to more than $15 even with VD 1%.

 

[Pappucho]

Depending on what opamps and buffers you decide on, these could easily exceed 100. I spent 100 just on the buffers alone, but that was for EL2009's...

 

[Porksoda]

Quote:

Originally Posted by Pappucho Depending on what opamps and buffers you decide on, these could easily exceed 100. I spent 100 just on the buffers alone, but that was for EL2009's...

Well I was planning on making my own discrete component class a buffers for the PPA, and discrete component class ab buffers for the portable. Each class a buffer is just 2 transistors and a regulator, and each ab buffer is 2 transistors and a couple diodes.

See the links in my original post.

 

[taylor]

It would be a good idea to parallel the op-amps, as reccomended in this Headwize project,

Quote:

I live in Manhattan on the Lower East Side. Manhattanites are the perfect headphone canidates. It's all you get to listen to. We don't HAVE cars. We walk or subway or cab ($$) everywhere. I listen to headphones 4-10 hours everyday. I built the Jasmin Levallois' version of the pocket amp using the OPA4134 (the quad version of the Burr Brown OPA134), but it got distorted very quickly and had no stomp, even for Grado SR-80s. It just didn't have enough juice. I fixed that by rebuilding the amp and paralleling the opamps suggested by Skippy and the circuit found in Burr-Brown's AB-051 application note: Double The Output Current To A Load With The OPA2604 Audio Opamp. If you use Grados, build this. It is, by far, the best sounding OPA variant I've built (I've built many, many times many). It is so much better than just a single output stage. It has full, deep, effortless sound and worth that extra chip, believe me. It's not just for blasting; it changes the sound dramatically for the better at all volume levels. If you want a crossfeed section, add it yourself - after exaustive testing I do not like any of them, at all. It only has a gain of 3. What? Apheared building something with only x3 gain? Yes. It's intended only for Grados with a line-level source. MAYBE low ohm earbuds, and MAYBE up to 60 ohm, efficient cans. That's it.

 

[Porksoda]

Quote:

Originally Posted by taylor It would be a good idea to parallel the op-amps, as reccomended in this Headwize project,

Hmm... actually that would be an interesting idea for a portable amp, since you wouldn't need a buffer at all...

Only problem is that first of all you need a unity gain stable op-amp, and it worries me that the output of one amp is the input of the second amp. This means each op-amp is running off of different sources, so you would get a mix of two different sounds. If I had the extra ICs, it would be interesting to play around with though. If I could get a 4 op-amp IC, it wouldn't take up any more space than a regular CMOY.

Does anyone know if it is possible to stack 2 op-amps like you would buffers?

EDIT: It occurs to me that if the op-amps have different offsets one might start sinking current into the other, unless you put a resistor in front of each. Also, I would think it would be hard if you wanted to class a bias the amps...

 

[guzzler]

the reason it's called the A47 is because Apheared used 47R load sharing resistors (like you mentioned) when making it. Search on the HeadWize DIY forum for A47 by sijosae, that's using a 4 channel opamp and you won't get it smaller than he does it!

Seriously though, the A47 was a bit of an oddity, although a lot of people ver much like the sound of it. It combines the pure opamp and opamp-buffer topologies (sort of, well not really), and it is only really a quick fix. As said before, a design like the PIMETA, or even the "old" META42 would suit you, although an A47 is much cheaper to build

edit: you can't stack buffers directly, you need the load sharing resistors

g

 

[ch1nkster]

If you want a better source, I suggest that you sell your Audigy 2 zs and get either a EMU 1212M or an Audiophile 24/96. Like was ist los said, try building a nicer Pimeta. I'm still working on my cmoy, but I have calculated the price for a nice Pimeta to around $150.

 

[Porksoda]

Quote:

Originally Posted by ch1nkster If you want a better source, I suggest that you sell your Audigy 2 zs and get either a EMU 1212M or an Audiophile 24/96. Like was ist los said, try building a nicer Pimeta. I'm still working on my cmoy, but I have calculated the price for a nice Pimeta to around $150.

First off, I just bought the A2 ZS. I play a lot of games and I need a card that is a little more well-rounded than most audiophile cards. Besides, while the imp-350 is not the IDEAL source, it is good enough.

As for the amp, since I am using my own protoboard and I have a bit of classroom experience with electronics, I may end up doing some hybrid of the two designs.

 

[Edwood]

Quote:

Originally Posted by Porksoda First off, I just bought the A2 ZS. I play a lot of games and I need a card that is a little more well-rounded than most audiophile cards. Besides, while the imp-350 is not the IDEAL source, it is good enough. As for the amp, since I am using my own protoboard and I have a bit of classroom experience with electronics, I may end up doing some hybrid of the two designs.

Even though the E-MU 1212M is a Creative product (their pro line), it does not play nice with others like the Audigy 2's driver. It's a shame since it offers such a great value.

-Ed

 

[Porksoda]

I want to add input coupling caps. What are good caps to use? I was just gonna use Panasonic PPS caps, or perhaps black gates...