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PPA v2 construction discussion - Page 2

post #16 of 1082
I would strongly advice you stick with the 2N5088 and 2N5087. Electrically the BC550C and BC560 will work but require rotation 180 to match pin out of the 2N devices. The 2SA1015 and its complement less suited electrically however have the base and emitter interchanged from the 2N types. See Below links to the data sheets.
2AS1015> http://www.alldatasheet.co.kr/datash...A/2SA1015.html
2SC1815> http://www.alldatasheet.co.kr/datash...A/2SC1815.html
2N5087 > http://www.alldatasheet.co.kr/datash...MI/2N5087.html
2N5088 > http://www.alldatasheet.co.kr/datash...MI/2N5088.html
BC550C> http://www.alldatasheet.co.kr/datash...LA/BC550B.html
BC560C> http://www.alldatasheet.co.kr/datash...LA/BC560C.html
BC337> http://www.alldatasheet.co.kr/datash...OLA/BC337.html
BC327> http://www.alldatasheet.co.kr/datash...OLA/BC327.html
MPS8099> http://www.alldatasheet.co.kr/datash...A/MPS8099.html

The selection of the 2N5087&2N5088 transistors was primarily based upon creating the ideal devices for use in the current Mirrors; however the high bandwidth and extremely high Gain at very low collector currents proved to provide a more stable buffer when operated at low quiescent currents, Moreover the low noise figure of These transistors have been used in the past in High gain Microphone and Magnetic phono preamps in both high end Equipment such as Mc-Intosh Preamplifiers and power amplifiers in addition to Mark Levenson. The low noise figure of 2-3 dB typical for the 2N5087&2N5088 are one of the primary reasons for there use in high gain low noise Audio circuits. Anyone that thinks these devices are not suitable for audio use or popular should perhaps look into this further

The PN4392-PN4393 as well as the MPF4392-MPF4393 will interchange just fine. The Bias adjustment makes some tolerance on this transistor possible as long as the device you select has a min Idss of 30mA and your not looking at setting the output bias at 40 or so mA then things will be ok. Matching transistors are not mandatory however lower DC offset and perhaps better sound with slight measurable Right mark performance will be obtained with matched devices. The output transistors should all be matched in all three channels because of the symmetry created by the ground channel with respect to the right and left channel.

The output transistors allow some considerable flexibility. The default MJE243/253 provide the best solution for low impedance headphones as thay are of considerably higher current than the BD139 and BD140. However the BD139/140 pair have higher bandwidth with an ft of 190 typical vs 40 typical for the MJE243/253 at high currents the Hfe falls quicker on the 139/140 pair than the Mje’s so for low impedance headphones the Mje243 and 253 provide greater high frequency because the Hfe hold up better because of the higher current capacity of the devices. This is the paradox of BJT output transistor selection more power less fast devices. This is accounted for by providing driver transistors that have bandwidths of over 300 MHz at the currents they are operated at in the PPA v 2.0. However for you speed demons I might suggest the flowing transistors as output devices mind you the maximum short circuit current of these faster devices will be about 1 amp for a few seconds.
BD139/140> http://www.alldatasheet.co.kr/datash...IPS/BD139.html
KSA1220> http://www.alldatasheet.co.kr/datash...D/KSA1220.html
KSC2690> http://www.alldatasheet.co.kr/datash...D/KSC2690.html
2SC3421> http://www.alldatasheet.co.kr/datash...A/2SC3421.html
2SA1358> http://www.alldatasheet.co.kr/datash...A/2SA1358.html

The BD787/788 and the MJE 243/253 provide the best all around performance with load impedances lower than 50 ohms at bias currents above 20 mA throught the output transistors emitter resistor. Lower bias currents and or higher load impedances generally favor the lower current higher speed devices.
BD787/788> http://www.alldatasheet.co.kr/datash...OLA/BD788.html
MJE243/253> http://www.alldatasheet.co.kr/datash...LA/MJE243.html
post #17 of 1082
Thanks a lot for that very detailed post ppl. Decided to get some 2N5087/2N5088's shipped over with someone else's Digi-Key order in the end.

Would they benefit from hfe matching?
post #18 of 1082
Thanks for that informative explanation, ppl. Trying to source everything from one vendor (Mouser) but wasn't sure of the alternatives.
post #19 of 1082
Originally Posted by individual6891
Would [the driver transistors] benefit from hfe matching?

Originally Posted by ppl
Matching transistors are not mandatory however lower DC offset and perhaps better sound with slight measurable Right mark performance will be obtained with matched devices.
post #20 of 1082
What size of case do you recommend for board and steps? Which one from group buy?
post #21 of 1082
Option A can't fit a power supply with it.
post #22 of 1082
Originally Posted by Vladco
What size of case do you recommend for board and steps? Which one from group buy?
If you mean the MMM case group buy, I wouldn't use any of them. 2.5" is unnecessarily tall for a PPA. The standard 2" PAR Metals case that is otherwise spec'd the same as option B will work nicely. The "Tangent PPA" pics that I and others have linked to in that thread are of the 2" case with a custom FPE panel.
post #23 of 1082
Will PPA v2 work well in the Hammond 1455N160X cases that was often used for v1? Is a ventilated case needed for v2?
post #24 of 1082
Yes. No.
post #25 of 1082
Thread Starter 
Has anyone completed their PPA v2 yet? We would love to hear from you.
post #26 of 1082
Um, since the first ones went out on Friday, I'd be surprised to find that the first ones had even arrived before today. Patience, Morsel.
post #27 of 1082
Originally Posted by morsel
Has anyone completed their PPA v2 yet? We would love to hear from you.
Just got the boards yesterday and I am still getting a parts order ready for PPA V.2....there was another project distracting us ya know...

Let me just say that the boards look great and wow..they are packed.

Hopefully, I'll have one up and running in the next week.
post #28 of 1082
pcbs arrived today, much earlier than I expected

unfortunately I'm still waiting for an order with a few missing parts, so I'm not able to complete the build atm. I'll fetch the missing parts on Friday from a local shop, although prices are much higher there, because I don't want to wait another week. You can expect my first impressions next weekend.
post #29 of 1082
Anyone notice that Newark lists the Elpac WM080-1950-760 as follows?

Newark Part # 16F126
Power Supplies; Power Supply Type: External Power Supply; Terminal Type: 5 Pin DIN Connector; Size/Dimensions: 81.28 X 55.88 X 48.26 mm

To confirm anything as basic as the output voltage, one needs to consult the datasheet. The datasheet describes the outputs for this family as follows:
Output connector: 5 pin DIN or barrel type (5.5 x 2.5 x 9.5mm)

I believe that the subtext here is: "You're supposed to know that if the output only requires 2 wires, we'll use the barrel type. Otherwise, we'll use the DIN. Do you think we'd say which is which in the datasheet? Don't you think that if that was our disposition, we'd work with vendors who will type the correct connector into their part description, and will give you some idea of shipping costs before submitting an order?"

Just wondering, before ordering. This comes with a barrel connector, right? Anyone know an alternate vendor you'd rather have me support?
post #30 of 1082
Tangent writes about Choosing an Output Jack:

If the amp is putting out a significant voltage, Ohm's law tells us that current becomes infinite. Since the PPA's output buffers don't have output protection, this momentary short will likely fry the buffers.
and goes on to not recommend 1/8" output jacks at all.

I remember this point being a debate for PPAv1. I hoped/thought the debate would now be dead, but I take this issue seriously, as I've found that when an amp gets knocked around while traveling, an 1/8" output plug can get jostled part way out.

My Etymotic 4p canalphones come with a 1/4" adapter, but it's not screw-on, so who's kidding who? We're in serious "penny-in-the-fusebox" territory here. Should the PPAv2 be described as not suitable for any headphones terminated with 1/8" jacks?

I was thinking of equipping my PPAv2 with a locking 1/4" output jack and a good 1/8" output jack such as the Tangent-recommended CUI SJ-43502PM (Digi-Key CP-43502PM), but with 50 or 75 ohms output resistance on the 1/8" jack.

This accomplishes Ety 4p to 4s conversion and provides output protection.

What is the minimum value that would provide adequate protection for the buffers? I understand all the "purity of sound" arguments against such a resistor, but the fact is that pretty much any headphones terminated in a 1/8" plug have reduced impedance to make them practical for the portable market, and sound better with some output resistance. Certainly every 1/8" plug headphones I've tested.
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