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Old 17th January 2019, 06:22 AM   #1281
tsmith1315 is offline tsmith1315  United States
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Location: Doerun, GA
About 254mm x 54mm
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Old 17th January 2019, 02:41 PM   #1282
ckwong99 is offline ckwong99  Hong Kong
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Thank you Sir
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Old 19th January 2019, 10:45 AM   #1283
cubicincher is offline cubicincher  Germany
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Default AUSTIN boards - Why Zetex 696B/795A?

Hello diyaudio-memebers,


I am building an M2X like you do.



At the moment I am working on the Austin inputboards. I am matching
the ZETEX devices.
Why are devices used with different hFE from NPN to PNP side?
Zetex 696B (HFE around 600-800)
Zetex 795A (HFE around 300-400).
Sorry for this stupid question - I am not an electronic engineer!


Does the different HFE-factor shift something more to the NPN - side?
Short answer is enough.



Have a nice day!
Dirk
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File Type: jpg M2X Austin Zetex matching.jpg (102.9 KB, 279 views)
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Old 19th January 2019, 12:04 PM   #1284
cubicincher is offline cubicincher  Germany
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The ZETEX devices seem to be like a follower (complementary devices).
Shouldn't they have a similar HFE?



KSA992 and KSC1845 (Q1/Q2 at the input) seem to be the first stage. (looks like a diamond configuration)



The second pair of KSA992 and KSC1845 (Q3/Q4) seem to be a ccs (together with the LM4040 + R3/R6.


My brain is working....


Greets

Dirk
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Old 19th January 2019, 12:29 PM   #1285
Zen Mod is offline Zen Mod  Serbia
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practically ..... no need to match anything
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Old 19th January 2019, 02:23 PM   #1286
Mark Johnson is offline Mark Johnson  United States
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The diyAudio First Watt M2x
By all means, please feel free to substitute different transistor part numbers when building your Austin boards. To make this a little bit easier, I put recommendations on the Austin schematic itself (upper right), and I included additional remarks in the Notes For Builders (post #4 in this thread), quoted here

Quote:
Originally Posted by Mark Johnson View Post
2. Transistor Orientation. I expect that many builders will substitute different bipolar transistors in their Austin boards, either to use what they’ve already got, or to “improve” the Austin circuit, or to avoid ordering a new transistor type they’ve never used before, with a goofy sound prefix (KSA/KSC?? c’mon, really?).

So I’ve used a PCB footprint that is circular and symmetric.
It will accommodate Japanese transistors with ECB pinout,
it will accommodate European transistors with CBE pinout,
it will accommodate American transistors with EBC pinout.
In my opinion, the (hFE / current gain / beta) of Austin's output transistors Q5 and Q6, need not be matched. As long as (hFE / current gain / beta) is large, greater than 100, the circuit will work well and sound great.

Of course, the circuit will not perform worse if you do select Q5 and Q6 to have matched (hFE / current gain / beta). So, please feel free to do so if you wish. Buy 20 or 30 of each part#, measure them carefully, and find two pairs with good matching.

However, if you want to choose different devices, I recommend that you ONLY consider transistors in the Super E-Line package, made by Zetex, because that package has superior thermal resistance. This is an important requirement for the Austin output stage transistors.

Please notice that the 220 uF output coupling capacitor "C1" is not optional on Austin (unlike Ishikawa). Any DC offset present at the junction of R9 and R10, is prevented from entering the Edcor transformer primary; C1 blocks the offset. If you are worried about DC offset, rest easy, it's been taken care of.

If you're contemplating a complete redesign of Austin, including a new PCB layout, then you could change the PCB footprints of Q5 and Q6 to accommodate either Super E-Line transistors OR medium power transistors in the hefty TO-126 package. This would give you a significantly larger set of possible transistors, from which to choose your Q5 and Q6. Beware, the board layout is pretty tight already, and this modification would make it tighter still.

I've attached the datasheets of the ZTX696B and ZTX795A, below. I downloaded them from Diodes Inc's website this morning.
Attached Images
File Type: png sch_Austin.png (84.8 KB, 265 views)
File Type: png betas.png (18.9 KB, 260 views)
Attached Files
File Type: pdf ZTX696B.pdf (58.5 KB, 8 views)
File Type: pdf ZTX795A.pdf (66.4 KB, 7 views)
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Old 19th January 2019, 03:15 PM   #1287
cubicincher is offline cubicincher  Germany
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Default Big thank you!

Hello Mark Johnson,
Hello ZenMod,


thanks for your explanations! I have the parts from Zetex and I am looking
for some good matches.
I am relaxed. And I am learning from you.


I understand that the decoupling cap will solve the problem with any offset
at the output of Austin to the edcor.


Have a nice weekend!


Dirk
Gimme that wrench and let me build those transistors in
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Old 19th January 2019, 08:28 PM   #1288
JSA1971 is online now JSA1971  Canada
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Finally had time to finish off and install the front panel of my M2-X (and put a selector switch on my B1) and get it properly installed into my audio rack. Decided to just go with a plain 3mm aluminum sheet. In the meantime I’ve been listening to it daily and it sounds fantastic! Thanks again to Nelson Pass for creating the M2 and Mark and Jim (6L6) for bringing the M2-X to the DiyAudio Store.
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Old 20th January 2019, 10:57 PM   #1289
stablgr is offline stablgr
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Just as I've managed to get all the parts I need to build my M2x, my circumstances have somewhat changed. We're moving to a new house and SWMBO (she who must be obeyed) has expressed a very strong desire for a wireless sound system throughout So I now find myself heading in the direction of needing a really nice headphone amp so I can retire into my own little musical world without disturbing anyone else.

As a total novice in this area I think I have a relatively simple question. After having spent the time, effort and money on buying all the parts for the M2x, rather than hooking up a pair of loudspeakers to it can I use it to drive a pair of headphones directly if I add a volume pot to the input of the amp? Please don't shoot me down too harshly if this is a really stupid idea. I guess my other option would be to build a Whammy, but it would be a shame not to put all the M2x parts to good use.

Many thanks,
Gary
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Old 21st January 2019, 02:10 AM   #1290
dBel84 is offline dBel84  United States
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Quote:
Originally Posted by stablgr View Post
can I use it to drive a pair of headphones directly
Hi Gary

coming from the headphone world, there are many folk who use power amps , first watt amps in particular, to drive headphones directly

It does somewhat depend on your headphones, if you have a pair of high efficiency in ear monitors, then clearly no. But if you have planar magnetic or some of the older headphones form Beyerdynamic or Sennheiser, it could work out well for you.

a few things to consider - noise floor in power amps is often higher than dedicated headphone amps - power up transients can be much higher than typically seen in headphone amps : my M2X can spike up to a volt which on a speaker is nothing but headphones will not like this, so it will be important not to have headphones plugged in with power up and this brings in the next problem - a standard TRS jack will short the signal to ground as you plug it in - this is not something the amp will like , most people who use headphones and power amps use a 4-pin XLR which mitigates the risk for a short but does mean that your headphones will need a balanced cable.

Happy to discuss further if you want to take it to PM
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