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The PPL08AC Project

post #1 of 15
Thread Starter 
I'm gonna type this in the hopes no one reads it.

ppl's portable amp design is the one amp I like Grados on more than a well-built primo Szekeres. And it's portable. (kinda) It's a biased opamp buffered with a machine gun... in the original it was 825 into 2008s, but I had a CRD fail and took the 825 to the grave. I did an 823, and you know all about that.

But I can't take it anymore. 180-250mA isn't much at home, but on the town it just eats batteries like nobody's business. I was up for it before, but now I just can't be bothered with it. Still, it's a great amp and I want to use it.

Also, I've never NEVER built an AC only amp, other than a few Szekeres. They might run off that stuff in the wall, but you could always unplug them. Even discretes... everything battery.

Red letter day. Retrofit this battery-eating beast with a power supply, utilizing the same case.


aos laughed at me when I said I had to use heatsinks on my battery amp... well, just to let ya know before I gutted it I took this shot... remember that this is with the CASE OPEN (on for 30 mins).. I don't wanna know how hot they'll get w/o sinks.

So anyway...

Sheesh, you're still reading this? you are as bored as I am...

Here's what it looks like now. I'm not gonna go off about how silent it is, how perfectly flat the noise is and immeasurable for me, how ****ing black silent it is at any volume you can't tell it's on.. no, I'm not gonna talk about that.


Talema 15V/1A xform
IR 400/6 bridge (hey it's what I have)
2x Teccor 4700uF/50V
317/337 with resistors and 10uF adj bypasses
(philips 10uF/40V if you actually care)
2x Wima 1uF/63V
4x Elna 470uF/35V
Noble 10k pot
everything else is re-utilized.

Two things for the only ones that read down this far:

Dan, you're right re: turn-on glitches/pops/whatevers. It's something to do with Cerafines. I had others in here and they change from a full pop, to just a switching glitch, to silence... and the silence is Cerafine. WELLWHADDAYAKNOWABOUTTHAT? Great discovery, I'm sure there's other things that can do this but hey...

ppl, get this... the bass is better on AC with smaller capacitance... so batteries must have much more series resistance when we stack em that hard than I ever thought. I had 48KuF per rail, and the bass is so much better on the dual 470 Cerafines. "Better" in that it's crisper/snappier, heavier impact, more detailed, just all in all BETTER. You gotta try dropping that capacitance down. I tried from none to 5600, this dual 470 is just damn gorgeous.

edit: 15V @ 1 or 30VCT @ .500, but not 15VCT @ 1. My bad.
post #2 of 15
How much/from where did you get those 470uF / 35V Cerafines? Basically what I see online (specifically www.angela.com) are 470uF / 50V Cerafines for $13 EACH!
post #3 of 15
Thread Starter 
Yea I know. What's yer point? The pot is $25 EACH too. I got em cheaper than $13 but this is "audiophile" DIY... none of it is ever cheap.
post #4 of 15
That thing is insane! How long do those batteries last?

Even though I think you're crazy I also admire you amp-frankensteins, I wish I had knowledge and skills (and money) to make such amps. (I am still very proud of my Cmoy tho).
post #5 of 15
Apheared, are 2008/2009 buffers really so much better than 2001s?
post #6 of 15
Thread Starter 
it's all relative:

Yes. Depends. No.

Close your eyes and point at the screen. That's my answer.
post #7 of 15
Hi Apheared
where is the circuit for this amp? I would like to have a look at it.
post #8 of 15
Thread Starter 
sorry wab... uhm, a few days. But they're alkalines. $7 in batteries every couple days. A couple weeks if you are not using it alot. 16 AAs.

ppl uses rechargable AAAs for +/-9.6V and this is the bare minimum I'd ever want em because the sound changes as you power them... they'll work lower, you can run em off of +/-5V... but 10V sounds better. Anyway the runtime must suck terribly, I'd be suprised if he got 6 hours out of a charge.

zapel, the circuit? Ah shi... it's been so long. A year already?! hsnam hosted it on his Apple iDisk account, anyone remember the link?

Ah! here it is:
Click on "PPL designs" then on "ppl portable amp.doc"
post #9 of 15
Well funny, I was just thinking this morning about using discrete shunt regulator for the portable DAC (just like I use in stationary one) and then remembered that both the regulating transistor and the resistor are heatsinked... Even though they really got just midly warm to the touch. But the battery drain would likely be unacceptable. Apheared's "craziness" is infecting us all .
post #10 of 15
Apheared: I get about 10 Hours out of one Charge. The Amp Draws 48MA @ Min Volume and maintains that at what would be Considered Normal Listening Level. My Implimentation of This Amp is EL-2008 as outPut Buffers, Buf-634P X3 as Virtual Ground Driver. AD-825 as the gain stage and a 1 Ma CRD on the Output of Each AD-825. and 2 Ma for the Blue LED.

Since your now using AC for this amp Get a pair of AD-843's and allow for a DC offset Pot as showen on the AD-843 Data sheet. This will make you Verry Happy.

aos: I went through tthe same Delema when i designed this amp How to Isolate the Opamps afordind an Inproved Power Supply Rejection Ratio for the gain stage without Drawing more Power and the Circuit i used on My Portable amp is what i used and works great and uses the Curent Drawen by the Opamp so no additional current is required. Now true you dont get any Voltage reg. but you get all the Other Advantages of separate regulation like Low power supply impedance, and Power supply isolation.
post #11 of 15
ppl: I need voltage regulation in this case since I need to drive reference voltage to DAC chip . But I am most likely going to use different batteries for analog and digital...
post #12 of 15

Man I'm really glad this amp is up and running. Folks, this has been a long time coming and a LOT of work on Apheared's clock as well as the design clock and extreme knowledge of PPL.
This might just be the ultimate portable amp!
Yes Apheared, The Cerafines are incredible, no pops. Isn't it amazing. Where can I get more of these! I've got enough for one more portable plus the set for the Szekeres.
Speaking of the Szekeres, I finally got one page up on my website for DIY amps.


This is my final Szekeres board. I etched the traces nice and thick. I have changed the output caps since the photo and the power supply bypasses. This amp has CMF 60 resistors throughout except for the Vishay Aluminum power resistors (Black). I like the big heatsinks which keep the Mosfets really cool. This amp will be housed in a round enclosure with perforated metal all around. The power supplies are external. Sometimes a Lambda 3 1/2 amp and sometimes a 3 amp switcher from a Toshiba computer! It is actually very quiet.
The other photos are other amps and the tiny mini amp which now has an aluminum enclosure covered with Brazilian Rosewood. 1 1/4" X 1 1/4" ! this amp runs on one 15V remote battery for four hours. Just to make it small. I may redo it, but heck, it was just for fun. A standard RCA to the right shows the size of this amp. I now has a 2134 instead of the 2228 in the photo.
post #13 of 15
Thread Starter 
Uh, damn DP I know you have a tendancy to just disappear but this has been my daily carry amp for months... it exploded a constant current diode once and sunk much more than 2mA into a rail (which led to the #42 AD823 experiments) repaired, and still it was my daily carry. but even buying AAs in 288 packs, this amp is for people that are only gonna use it intermittently not 10-24 hours a day... you're afraid to get up and walk away with it running, if you forget.. dead cells.

So this is the retrofit to make it non-portable. Me. ME. An AC-only amp that could be portable, that was portable. That should tell you something about how I think it sounds.

Woah... those "big" heatsinks actually keep that thing from melting down? And the source resistor right on the board!? YEOW. That's nuts. What's the bias current, less than 300mA/ch? I know you've built more than a few Szekeres and this doesn't have a gainstage but sheesh. Can you touch either heatsink or resistor case without pulling your hand away in pain?
post #14 of 15
The heatsinks are almost 2" high and never get hot on an amp without a gain stage. I think you run into heat with a gain stage added. The one I built for my brother has the same heatsink but only an inch high and it too never gets hot even with his 5 amp Lambda.
This is just the standard Szekeres with all the stock values. The source resistors probably get hotter than the Mosfets.
I reduced the heatsinks on my brother's amp as I thought they were too big! Even when I drive it with a preamp it doesn't get very hot at all. Nothing near hot actually.
These heatsinks are good as they seem to suck the heat away. I even heated them with a torch and it took some time to really warm up. The Aluminum resistors dissipate very well too. This amp never even approaches the heat potential of the Mosfets.
It sounds great.
My first Szekeres used the little RS heatsinks I see you have with no problem either.
post #15 of 15
Hi Apheared
thanks for the link to see the schematic but I can't see it, my stupid computer tries to convert things to m/sft word.
Is there another way I can view it? What value is the vol pot?
Do you ever have problems with instability on your layouts? and finally as the EL2001 has a large current output is it possible to use this chip on its own to drive sr60's
Thanks for your help
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