[ablaze]

hey guys,
anybody started on their PPA yet? Do share your experiences on this thread.

me, I'm waiting for my PPA boards to arrive from tangent before I start trying to figure the whole thing out

[edit] Per Ablaze's request, the original thread was split and the applicable posts were moved here.[/edit]

JMT
Moderator
Head-fi.org

 

[morsel]

I just updated the PPA website at http://elvencraft.com/ppa/ with a small section on wiring considerations:

Signal ground is input ground, not output ground. Output ground is the output of the ground channel. It exists solely to drive headphones. It is not a true ground. Do not connect signal ground to output ground. This defeats the purpose of differential output and may cause amplifier instability. Do not use the headphone output as a line level output as this may short signal ground to output ground. Use signal ground instead of output ground for line level outputs.

Do not connect V+ or V- to the case. This may cause damage to the amp or other components.

Connect the case and pot housing to signal ground. This will shield the amp from hum and noise.

Do not connect AC ground to signal ground or the case. This may cause ground loop problems.

 

[Voodoochile]

The four locations on the board are effectively 'stacked', so hard to imagine ever wanting more than four per channel.

Anyone else under way yet?

 

[morsel]

My, that was quick work, and nice pictures too, Voodoo! Be careful about using caps with a WV rating too close to your PS voltage. You don't need much capacitance, 1000-2000uF is plenty. Room for 8 caps exists so 220uF 35WV Silmics or Cerafines can be used.

 

[peranders]

Question to Morsel or the other "guys". Why using fictive ground and not just +- supply?

Why using four buffers? Isn't one quite enough?

Why not BUF634 which can handle a little bit more power in TO220 case.

 

[xtreme4099]

honestly the buf634 doesnt sound good on the ppa compared to the current ha5002 as the prefered buffer ... sound good is the key phrase, thats what an amp supposed to do to your music.

 

[Glassman]

could someone explain me how does the 'amplified and buffered' ground work? I know that symetricaly driven headphones sounds better, but I don't understand the PPA ground circuit..

 

[Arzela]

I have an Elpac wm071 wall wart. It's a +15, -15 volt supply. Could I use this to power the PPA? I'd just connect the + and - leads from the wart and leave its ground unconnected.

 

[peranders]

But you mean BUF634 is OK at a meta42 pcb with same opamp and the same multiloop feedback? I don't the think the difference is that dramatic.

 

[peranders]

Quote:

Originally posted by Glassman could someone explain me how does the 'amplified and buffered' ground work? I know that symetricaly driven headphones sounds better, but I don't understand the PPA ground circuit..

This is only a active voltage divider. If you have done this with two resistors it would have been rather thirsty. This is an electronic way to create a low impedance node with too much current consumption.

I personally don't understand the benefit of this if you have no trouble to get +- voltage.

 

[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.

 

[Glassman]

I meant something else, not that TLE2426 rail splitter, I know how this works but there are 3 channels each with AD8610 and HA-5002s, one for left channel, one for right and the third is for ground and I don't understand this.. is that something like active current sink or what??

 

[peranders]

The ground channel serves as a power buffer for the rail splitter. It may seems to be a little bit odd but this is the designers priviledge to whatever he/she wants.

 

[ppl]

Ok! Once again I find I must explain the operation of the Ground channel. Not that this information is unavailable, several well Known PPA related web sites have this information. I refer you to either Tangent’s PPA site or the official PPA site. Binary_digit’s. LaRocco Audio web site also has complete Info on the Ground Channel in technical documents area.. These PPA Site’s have complete explanations of the ground channel operation as well as The LaRocco Audio site. So I would see any of the below links for this info.

In short the Ground channel allows for symmetrically driven headphones as Glassman noticed. If one were to just use a conventional rail splitter, Virtual Ground Driver such as a Buffer or even the Normal ground connection on a AC +/- Bipolar supply The Headphones will not be symmetrically Driven. This Balanced drive is an integral part of the PPA and if omitted You could no longer call the Amp A PPA because you removed one third of the circuit. If you wish for a lower cost then another alternative like the META42 or the META42 V. 2.2 would be a better option for you

From tangents site I quote "differential drive means the qualities of the rail capacitor bank don't affect the sound of the amp as much as in other topologies. "


From Binary Digit's site I also quote the Following "One of the Principle advantages of Differential output drive operation are reduced audio frequency modulation of the power supply Voltages and enhanced common-mode rejection of residual Power supply noise. This Topology also results in Cancellation of even order distortion products by virtue of the true symmetry employed in the output stage. Reduced voltage induced distortion in gain stages is the direct result of not dumping large current spikes from the load into the Amplifiers ground and thus causing subsequent Application by the Voltage gain stages. Remember that ground is the return for the input signal and it is wise to also avoid returning the output load Current to this same location in the signal path that also handles small low current input signals. Designers have devised a myriad of methods to substantially reduce the amount of signal the input ground is presented with. Such methods include but are not limited to star grounding and multiple grounds in a design. The pollution of the ground by high current pulses is a real problem in Digital circuits also and again plenty of techniques are available to reduce the negative effect on the sensitive Analog ground. "


Links>
http://elvencraft.com/ppa/ See Discription on Page
http://laroccoaudio.com/home.html See Technology Center
http://tangentsoft.net/audio/ppa/amp/