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PPA builders' thread - Page 3

post #31 of 646
tangent's updated his step-by-step guide!
Damn that "expedited" mail. It's been a week now (admittedly with a long weekend) and my board is still not here :~(. Should've taken the FedEx route, I'd have it finished long time ago.

It's very nice with pictures and all. Say what you will (i.e. disagree with parts of the content or the way it's presented) but I think he's pouring a lot of time and effort into these guides. These things take time and your head will hurt after a bit, trust me.
post #32 of 646
Well, this will all be very interesting to see pan out. I have a GTXP, a Phillips card, and the onboard Analog Devices Soundmax in various PCs, the soundmax has both toslink and coax digital outs which I can connect to the superdac. The superdac has balanced outputs...I have not yet really though about taking any measurements in RMAA, but perhaps it might be something to look into.

On to the section for those curious but less technically astute (no offense to anyone, as this includes me). This testbed PPA was built to spec right off the schematic, and I had an issue with hiss at first, which turned out to be my negligence in jumpering the bass-boost switchpads (who really needs a feedback loop anyway?). Thought I had in the back of my mind, but I had actually done the power switch pads, and my mind was telling me it was all squared away. Anyway, now that they are closed*, the hiss is gone, and DC is down to 2.1mV and 1.9mV, which is super, and there is no hiss, of course. .
I'm powering it off a bastardized version of a half-PS1 type PSU that is outputting a regulated 24.4v (my on-PPA caps are 25v r-t-r).

It is a 'really nice amplifier' is what I have to offer so far. I have not had the luxury of extended listening periods as of yet, but do look forward to more time soon! It is still on the bench with the HD570s and Sony DVD player. Yeah the cans are a bit sketchy, but it's what is on my workbench. I hope to get the amp upstairs shortly to hook up to my HD580 C541i rig, which is a great workable rig, though not exotic. I'm not really the reviewing type, but the PPA is a very smooth and responsive amplifier. It initially seems very powerful, yet articulate/responsive. I have the OPA627s in it for now out of convenience, but plan to mount a few more 8610s onto Browndogs so I can load a set of them. I also have two buffers per channel at the moment (burning in for the last 20 hours now), but will populate the other six locations this weekend. I'll prolly replace the six in there now first, and repeat the burn cycle, then load all twelve buffers. I have not done any subjective testing side-by-side as of yet.

*the S2 switchpads are for the bass-boost config, which I did not want to implement on this breadboard-style PCB. You thus leave out those components, but still need to jumper the pads to enable the feedback loop to function.
post #33 of 646
Thread Starter 
aren't we going OT here? this thread was for PPA building experiences to share

can the mods split the relevant posts to a new topic on testing methodology?
post #34 of 646
Thread Starter 
would the PPA be powerful enough to drive AKG K1000s?
post #35 of 646
Yes if you have a 24 volt power supply. BTW you are so Right this is a builders thred and all these apperent new concerns that people have should have been done in a timley manner in the thread located hear http://www4.head-fi.org/forums/showt...&highlight=PPA
post #36 of 646
Thread Starter 
thanks ppl. I can't wait to start on it myself.

anyway, I've asked JMT to split the posts into a new thread..hope he checks his PM soon..
post #37 of 646
cool then this can be back to Building issues.

The PPA will put slightly under 400 mW into the AKG K1000's and get about 100 dB of SLP. the K1000's require lots of voltage and that is why thay recomend driving them from a Loudspeaker amp. However if normal listening levels are used then the PPA will work
post #38 of 646
anyway, I've asked JMT to split the posts into a new thread..
I gave it my best shot. Some of the posts I left intact so the subsequent posts would make sense, so you may see some duplications.
post #39 of 646
Sorry, but I am going to have to repeat these answers since my original post was moved to the other thread. Perhaps the original thread contents and order could be restored or a second attempt to sort the threads be made, as both threads are sort of scrambled now.

Peranders: 4 buffers result in less distortion, and tighter, gutsier, more accurate bass. One buffer is not as good. If you refer back to the many threads that discuss the HA5002 and BUF634 you will see that many people have listened to them and prefer the sound of the HA5002. It is also cheaper and has no output protection, which results in lower output impedance.

Arzela: You can use your ±15V Elpac as you suggested only if you reduce the voltage or choose opamps that can handle 30V. The AD8610 should not be subjected to more than 24V.

Peranders: The current META42 still uses Elantec buffers. The reason the BUF634 was chosen for the next META42 incarnation is because the EL2001/2002 are discontinued and the BUF634 can be operated in low or medium bandwidth mode to save power. The current META42 does not have differential output, either.

(Glassman) "could someone explain me how does the 'amplified and buffered' ground work?"
(Peranders) "This is only an active voltage divider."
(Chipko) "So the groundchannel is just a fancy TLE2426 that can be omitted and bridged if you have a dualvoltage supply?"
(Peranders) "It can certainly be omitted if you have a split power supply."

Not true. I quote my description of differential output from the ppa website:
The PPA has 3 amplifier channels: left, right, and ground, which use the same output buffers and noninverting opamp topology. The ground channel sources and sinks the return current from both drivers which would otherwise have been dumped into signal ground or power supply ground. This shifts responsibility for the high current reactive load of the headphones from signal ground to the supply rails of the ground channel buffer, thus removing the primary source of signal ground contamination. The drivers have symmetrical output buffers with equal impedance and transfer characteristics on both sides, rather than an output buffer on one side and the large capacitor bank of the power supply ground on the other. This results in lower output impedance and greater linearity.

Standard headphones have 3 wires: left, right, and ground, which is tied to the negative side of both drivers. Standard headphone amplifiers have 2 channels: left and right, with signal ground or power supply ground used for the return path from the headphone ground wire. Fully balanced headphone amplifiers have 4 channels, require custom 4 wire headphones, and are typically operated in bridged mode, which doubles the output voltage and quadruples the power by using inverting and noninverting pairs, but does not offer symmetrical transfer characteristics due to the difference between inverting and noninverting modes.
As PPL says, be sure to read the various PPA websites.
post #40 of 646
Installed the other six buffers tonight. Here is an updated pic with the 24.4 volt PSU and the buffers...

No, I have not measured it yet, but when I do, it will be in the other thread.
post #41 of 646
Just finished mine. Listened only for a few minutes and with MP3's of all things. I'm gonna order some well deserved pizza now but the first impression - with just one HA3-5002 per channel - is that the bass is very powerful and well controlled.
post #42 of 646
Based on current listening do you guys think the sound resembles the meta or any other amp?
post #43 of 646
the soundstage is much bigger .. better imaging ... clearer, quicker more pronounced, snappier than the meta. ppa in a stock config is overall much better than a meta42 in a max config.
post #44 of 646
Originally posted by aos
Just finished mine. Listened only for a few minutes and with MP3's of all things.
Sorry to go partially off-topic again... IME, a better amp can actually make MP3s sound better, rather than be more revealing of flaws in this case. I believe this is because the psychoacoustic algorithms involved in lossy compression expect a theoretically "perfect" response from equipment -- part of the auditory prediction performed by lossy encoders. Something many people may not be aware of (and a welcome benefit for those of us who have our amps hooked to a sound card, and a few MP3's floating around).
post #45 of 646
Thread Starter 
Originally posted by xtreme4099
the soundstage is much bigger .. better imaging ... clearer, quicker more pronounced, snappier than the meta. ppa in a stock config is overall much better than a meta42 in a max config.
what is a ppa "stock"? ie. 12 buffers or 1 per channel?

just got my PPA boards todae
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