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
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
Attachments
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
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
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
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.
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.
Attachments
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
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
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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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
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
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
..dB
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
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
trade your M2 hardware , go buy Whammy thingie and build it
or even better - go buy Whammy thingie and build it , leave M2 parts in closet for better times ......
If the wireless system is B&O with Beolab 90 as the main speakers in the system then maybe the price level may let your wife change position!
Wireless...….ok......for the living room…...but it should be possible for the man in the house to get a room in the celler or another place in the house where he can "play"!
Wireless...….ok......for the living room…...but it should be possible for the man in the house to get a room in the celler or another place in the house where he can "play"!
Man up and start here.
Was in a similar position a few years ago for space of my own in the house. Wife resisted my initial suggestions, so I came on with "Look, baby, I know the house is primarily the woman's domain, but I live here too."
Now she still has most of the house, but I do have an area for my stereo and listening to it.
B&O prices are indeed impressive, even frightening. However instead of being heavy handed, may I suggest she get hers in the living room.
She lives there, too.
ZM's advice for Plan B.
As ZM said - no. A lot more output device dissipation with the M2x (and more power output). To my eyes looks to be 4U (minimum) or 5U chassis - the more heatsink the better!
And not to mention the size of the PCB and power supply components wouldn't fit inside the ACA chassis.
And really, $339USD for the Deluxe 4U chassis is a bargain considering the quality and pre-drilled holes. That's the route I'll be going when I get the M2x bug; enjoying the Alpha J too much right now.
Here is the eBay chassis that I used for an M2x build. Price was $141.55 for the chassis plus $59 for shipping to California, USA. Total $201.55.
I had to drill and tap 9 holes in each heatsink: 7 holes to mount the PCB on the heatsink, plus 2 holes to bolt the output transistors to the heatsink. This drilling and tapping gave me an excuse to purchase a drill press which I had been coveting for quite some time. I also had to make a rectangular cutout on the rear panel, to accommodate the IEC mains inlet module. Drilling & hand-filing took care of that in a couple hours.
It appears the eBay chassis prices have risen, perhaps due to Trade War tarriffs or perhaps some other reason. So the money you save by purchasing a Chinese chassis and doing all the drilling and tapping yourself, compared to buying a pre drilled chassis from the diyAudio Store, is less than it used to be. On the other hand, doing it yourself is fun! And you have my permission to purchase a bunch of new tools, if you think you want/need them. BTW a tapping kit for M3 holes only costs about $25. And a can of Tap Magic is another $7 or so.
_
I had to drill and tap 9 holes in each heatsink: 7 holes to mount the PCB on the heatsink, plus 2 holes to bolt the output transistors to the heatsink. This drilling and tapping gave me an excuse to purchase a drill press which I had been coveting for quite some time. I also had to make a rectangular cutout on the rear panel, to accommodate the IEC mains inlet module. Drilling & hand-filing took care of that in a couple hours.
It appears the eBay chassis prices have risen, perhaps due to Trade War tarriffs or perhaps some other reason. So the money you save by purchasing a Chinese chassis and doing all the drilling and tapping yourself, compared to buying a pre drilled chassis from the diyAudio Store, is less than it used to be. On the other hand, doing it yourself is fun! And you have my permission to purchase a bunch of new tools, if you think you want/need them. BTW a tapping kit for M3 holes only costs about $25. And a can of Tap Magic is another $7 or so.
_
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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
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
I know one has to pick your battles, but a full house wireless system is not incompatible with having a nice listening area. If SWMBO won't tolerate speakers in the living room, then... well...there are options
In the end, my wife and I divided up the house, I got the inside, she got the outside. Now all the spare bedrooms, the office, and basement are all my domain. Was kind of expensive but worth it in the end...
All that said, I agree with the others about getting a Whammy, and storing the M2x