[Apheared]

(God only knows what the actual count is)

It's 2am, this is gonna ramble a bit.

A few people have stuck hansen's pcb in the ET version of the HML-9VB PacTec case, to fit 2 9Vs in there. That's a killer idea, but the hansen board still takes up as much "floor space" and limits what caps, jacks, and pot you can use.

I decided to make an HD600 portable amp. Not that I really like HD600s or plan on walking around with them, but hey it's a project.

To be different, instead of laying the board flat, I made it a vertical board... look at all the room. And since there's no "bottom" to the board, I can stuff both sides.

One chip I really like the sound of on HD600s is Analog's AD823. It's a beautifully designed chip, although 15mA isn't much drive for our needs. It's a true single supply opamp (although I didn't use it that way) and can swing like the dickens because of it.

I was going to buffer the output with a low power discrete stage... 2N3904/06s or BC549/559s, or BC317/337s... but ppl graciously sent me some 100mA buffers from Elantec to try, the 2001s (baby brother to the 2008s I love)

The best thing about all this: battery! The 823 is 6.5mA quiescent for both channels, the 2001s are 1.3mA each quiescent, and a TLE2426 isn't even worth mentioning. Even with a 1mA CRD per channel, the total is under 12mA! Compared to just one dual OPA132/4 and a resistor voltage divider... sweet.

Driving HD600s I doubt you can get the drain to 15mA. You can try.

An added bonus of the 100mA buffers is it will drive lower ohm phones, although say goodbye to your 9Vs pretty fast... an average rockin volume on Grados is 50mA.

I wanted a gain around 12 and the parallel of the feedback to be 300. 332 and 4k7 ohm worked close, 308 ohm parallel and gain x14. Add a 301 ohm +input resistor and the offset for both channels is under 0.8mV - It's not bipolar input and this is really overkill, but why not?

The 2426 doesn't really need the 470uF Cerafines, it's output is under 1/100th of an ohm to like 1k, and 20k is still like 0.5 ohm. For just driving HD600s, you can completely omit the reserve caps. I'm serious, try it. You can't hear the difference (but you can measure it, more on this below) The 470s/1s are for "cheater current" driving lower ohm loads. There is a 22uF stablizer cap in front of the 2426, again just because.

Since this is for HD600s that I will probably not use portable that much, I added a power jack for an external 24V filtered wallwart. Both the batteries and AC in go thru 4001s in a diode OR gate config. (only the higher voltage will get passed). To add more safety to the thing, the AC jack is switched and the battery snap ground goes here. When the plug is inserted it lifts the battery ground, so diode gate or not - nothing is flowing to/from batteries.

The silliest part - a huge Noble AP series potentiometer is in there! heh. Took over half the faceplate space. Someone recently posted pics of a cmoy he built for $20... well, this one ain't. The pot was that, alone.

One thing re: addiction... I have gotten a little obsessed with this, as most of you know.

So here I am with a scope trying to find the perfect output resistance to stop the tiny ring/overshoot. But scopes are dangerous. What looks like an insanely large overshoot on 10mV/div isn't audible. And with resistors on the opamp outputs, it adds distortion and shifts the phase. By MINISCULE amounts, but there ya go. I could visually see the tone generator's pulses looking different... from overshoot and a little ring, to mostly flat, to softened corners... depending on the resistance used. In this case with HD600s as load, the closest to perfection was 66 ohms. 61.9 went in, and that's what it's stayin at. But truthfully, I can't hear a difference. But I can measure it. Damn measurement tools.

All in all, it sounds great! It's a cooler chip, and on Grados the treble might be too agressive... but I didn't make it for Grados.

edit: duh, photos... ok so it's 2am did I say that?

 

[nick danger]

I noticed that you are using a 24V wall wart. The one that I am using is 9V. Is 24V better than 9V? and is there any mod that I need to make to use it with the CMoy/Hansen?

 

[skippy]

24v should be better, especially with cans like the hd600. just make sure your caps can handle the voltage.

 

[Apheared]

Not just HD600s, everything... the chip's specs are usually much much better if you power them from more. 24V isn't what it is, it's actually 31V. (because of the incredibly low load) DON'T get a 30V thinking you'll run +/-15V, it'll end up being 40V or more. (and most opamps don't like more than 36V ever)

 

[nick danger]

All my caps are 50wv except for for the power caps, they are rated at 25V. Should I be safe with them or should I go up to 50V? I don't care about blowing the caps or the ICs, it's the cans I'd be concerned about.

 

[thomas]

One very simple way that i use to switch between external power supply and batteries is to use a DPDT switch- batteries go to one pole, external goes to the other pole, circuit is connected to the centre....

When its wired like this, only one source will be connected to the circuit at a time...


btw, where are some good sources to get audiophile quality parts like your caps and the pots? thx

 

[Tides]

Apheared,

Another nice amp

Now my question,

Do you build these portable amps for sale ?
Because I am interest in a portable amp but dont know much about the DIY projects and parts ( I do have the tools since I mod game systems) and I dont feel like buying the TA at current TA price tag ( since I have xcanv2 already)

I am here on Long Island, and can prob drive to the City and pay you a visit ,or you can just mail it to me priority ( if you decide to sell a portable amp)

let me know
tidesofkali@hotmail.com
or PM me.

Tides

 

[ppl]

Apaheared: Glad you found a use for the EL-2001's. The Quessent Current on these are speced at 1.3 ma but most are about 0.6 MA. Moreover these are not Discontinued like the EL-2008. Insight has the EL-2001's in stock at around $4.00 Ea. last time i checked. The Typical output Current of these are 160 ma into a short.

Regarding the 60 ohm resistor you mentioned I gather from your post this resistor is Between the Opamps output and the Buffers Input? I hope that this large of a resistor is not upon the output of the Buffer. The Peaking you menttioned can be taimed by selecting an optimum value of resistor between the Opamp and Buffer. That's what i do. The HD-600's Higgh output impedance along with the Large cable capacitence would Dictate the use of an RC snubber on the Buffer's output.(see data sheet).

The EL-2001 with the AD-823 should almost be a match made in Hevan. I made a Pocket amp with a pair of 2001's and AD-744's. operating on (2) 9 volts. sounds fine. I do agree with you about Driving Grado's with this Buffer. This is because of the limited output Current. Now i know some people will object but i have found that Grado's and Most Sony's and Most Surley the MDR-V700 @ 24 ohms Need at least 3/4 of an Amp of available output Current to sound right to me.

Are you using a CRD for that 1 amp opamp Bias? The AD-823 dose not like low impedance loads at all it will load down at loads at 5K or less, so this OPA MUST BE BUFFERED. Did you use Multiloop?

Any way enough of this for now Great job.

 

[Apheared]

ppl, yea I mean opamp output resistor ie between out and buffer input. Nothing on the output of the buffer. the 2001s are a great pairing partner to this chip, more HD600 enjoyable than the 744 config... Multiloop, no. Get this... I was tryin to fit in the extra 4 resistors in the initial layout and couldn't, so decided not to... then in building it, I changed the positions and had plenty of room for them, but didn't. Heh.

Tides, sometimes. I have built on spec and have sold my frankensteins because they keep piling up (I have this problem, you see)

But if you think a TA is too pricey I can't help you. There's alot of hours in one. That amp you're looking at right here costs more than a TA just in parts... you though, it's REALLY not that hard. Even if you have nothing you can build a cmoy, including all the tools, for about $80. If you need motivation head over to the CMoy Pocket Amplifier page @ HeadWize... you can do it! DIY is not about saving money, trust me and the other mad scientists here... we're broke but entertained.

thomas, I get parts from all over the world and spend waaay too much money on stuff tracking down discontinued and ancient crap... but try Percy, Parts Connection, Angela, Antique, etc. if you want North American guys that'll sell in low quantity.

nick, you're pretty safe. While the power reserve caps will only see half the supply voltage each, usually you try to have them over the total rails... so in case something goes wrong you don't pop them too. but 25V for +/-15V is ok.

 

[ppl]

YA ICAN POST AGAIN: Sa it aint so Apaheared I bowared a Clone of my origenel amp that used one EA BUF-634 and a OPA2132. His thinking the same low supply voltage resulting in maximum output "Kids". anyway i replaced the opa2132 with the AD-823 Then compaired it with the AD746 the Dual AD-744 and YA the 823 for sure. Arent this new crop of NEW OPAMPS alot Better and Cheeper than Old so called state of the art just a few years ago. Well i gave the Amps owner the AD-823 installed since he also thought is rocks .

 

[jude]

Quote:

Originally posted by ppl YA ICAN POST AGAIN:

ppl,

That was you who wrote me an e-mail about that? I wrote you back. I tried finding the associated profile by crossreferencing the e-mail address you included in the e-mail body (you didn't list your username so this was my only way), but it appears you missed a "c" in that e-mail address which why I wasn't able to find out which user was having problems.

Anyway, I didn't make any changes to your profile because I didn't know it was you. I'm not sure what problems you were having, but if you want to describe them to me via PM, that'd be cool.

-- Jude --

 

[ppl]

Ya i compaired the Dual AD-744 to the Dual AD823 in my pocket amp using the EL-2001CN and a resounding YES the 823 sounds alot better this latest generation of opamps sure outperform their counterparts of yester-year lake the Single AD-825 just blow ayay the older OPA-627 and other prior reference oopamps.

 

[Tomo]

Hello,

I screwed up and forgotten to back up multiloop discussions we had. I never thought HeadWize would go down for a while and never thought twice about it.

Anyone kindly post the schematics again?

Thank you,

Tomo

P.S. I am looking into Elantecs too.

 

[Possum]

What do you use to mount the LED so it looks bare and neat, just sticking out of the case? I was trying to do that in a few projects, but ended up having to get some kind of panel-mount LED holder.

 

[Apheared]

Ah. they're lenses. The bomb. Not tellin you what ones, because it's my thing.

They're easy enough to find on your own though.

edit: whoops... url, img, same diff...