| danville |
In the old days, I used 2N3440 & 2N5415 transistors. Obviously, these are not a particularly contemporary choice.
I haven't seen a lot of discussion on transistor choices for anything but the output and driver transistors.
I like the availabilty (at least in the US) of the ON Semi parts and I can be confident that they are "real"
What are some favorite complementary pairs? |
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| vynuhl.addict |
A fast and low cob part is most ideal. I personally love to use either the
800mw 2sc2705/a1145 parts or the 5w 2sc3423/a1360 for the vas 1.8pf for the npn/2.5pf for the pnp. These are 200mhz 50ma devices with an average Y-beta of about 200.. I see most designs using 1amp parts but these are emtremely unneccesary not to mention have an average collector capacitance anywhere from 10-30pf..
Colin |
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| jcx |
| quote: | Originally posted by danville
In the old days, I used 2N3440 & 2N5415 transistors. Obviously, these are not a particularly contemporary choice.
I haven't seen a lot of discussion on transistor choices for anything but the output and driver transistors.
I like the availabilty (at least in the US) of the ON Semi parts and I can be confident that they are "real"
What are some favorite complementary pairs? |
but did you do any searching?
like for instance "vas" + "search in tiltle"?
maybe you would have picked up on:
http://www.diyaudio.com/forums/show...&threadid=66234
(admitedly I cheated, rather than look thorough all 82 threads I also know to look for AKSA as poster)
(which also brings up the apparent issue that "search in title" currently seems to pick up on more than just Thread Titles - should it do this?) |
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| danville |
Yeh, I searched VAS but I missed the earlier thread. Too many irrelevant hits.....
I've looked at many of the suggestions and they look good but most are thru hole parts. I plan to build my VAS stage with SMT parts. This really restricts the recommendations and most of the parts don't seem to have SMT equivalents.
I haven't seen a selector guide from either Sanyo or Toshiba. This might make it a little easier to search. |
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| danville |
| quote: | A fast and low cob part is most ideal. I personally love to use either the
800mw 2sc2705/a1145 parts or the 5w 2sc3423/a1360 for the vas 1.8pf for the npn/2.5pf for the pnp. These are 200mhz 50ma devices with an average Y-beta of about 200.. I see most designs using 1amp parts but these are emtremely unneccesary not to mention have an average collector capacitance anywhere from 10-30pf..
Colin
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I have looked at a lot of transistors since last night and the Toshibas that Colin mentioned would be excellent for my purposes. I haven't found anything better on paper than the 2SA1145/2sc2705 pair.
The only catch I see is that there doesn't seem to be SMT equivalents. I have looked at Sanyo, Zetex, Toshiba, ON-Semi & Fairchild so far for similar performance. This seems a bit odd since high volume today is in SMT.
Any new suggestions? |
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| jacco vermeulen |
Here's a picture of a doubled 2SC2705 in the Vas stage of an expensive buggar from the 90s.
A single 2SC3955(+2SA1540) only costs 10 cents more. |
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| sajti |
Try 2SC2911/2SA1209! High voltage, TO-126 for cooling, linear hfe, and very low capacitances.
sajti |
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| Dejak |
| I would suggest 2SA1538/2SC3953 as a VAS stage transistors. fT 400Mhz, Cre 1.7pF. They are cheaper than 2N5415/2N3440, at least in Finland :) |
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| AndrewT |
Hi,
if 1360 is not good enough consider
1370,
1380,
1406.
I never put 1209 or 1145 on my list of suitable VAS devices due to superior specs available and/or cheaper prices from the above.
I have not looked for equivalents in SMT, sorry. |
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| LineSource |
| Consider adding a large copper DIY heatsink to the popular TO-92 packaged signal transistors to extend their power handling. The BC850C / BC860C have good hfe up to 40ma, and the On-Semi specs show 625mW at 25C ambient with no heatsink. |
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| danville |
I want to thank everyone we has replied so far. I thought this would be an easier process:
Here is an update of some of the issues I have looked at. These may apply to many other designs.
My VAS uses cascode circuits and also wilson mirrors. The wilson mirrors are configured to have some gain (about 2.5). This means several things:
1. The only transistors that have a large Vce requirement are one of the transistors (the non-matched one) of each wilson mirror.
The wilson mirrors drive the bias voltage source as typical in most designs. This means that the high voltage transistors have the highest current requirement as well. Maybe a TO-92L might be OK but I would prefer an SOT-89 or larger.
2. The remaining transistors have relaxed requirements. None of the transistors will need high Vce (60-80V would be OK). I think that an SOT-23 might be OK even though they can dissipate about 300mW. The Ft of the input transistors are also less critical since the cascode configuration helps in this regard.
3. The Toshibas parts are less desirable in my case since I would probably have to buy a whole reel if SMT. Fairchild & ONSemi are good choices for Americans since Mouser and DigiKey carry these lines.
On a different note, I am considering the NJL3281/1302 for outputs since the internal diode would be convenient for bias tracking. I used to clamp the bias transistor to a TO-3 case in the past. This is much better than mounting on a heatsink, but not as good as being on the same die as the transistor. |
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| danville |
I have finally decided on a set of VAS transistors
I was looking for SMT packages that are easy to procur (at least in the US)
Here are the results:
BC850C - BC860C (Fairchild). These are SOT23 versions of the popular BC550/560. They can't handle the same current however. I am using these for 2/3 of a wilson mirror and the bias circuit (assuming I don't use a BC560 glued to the output Q). I think I will use the embedded diode in a NJL1302.
BCP56-16/BCP53-16 (ON Semi). These are not as fast as some of the TO-92 suggestions but handle more power. They are in SOT-223 packages. I have cascode circuits which allow the 80V Vce to be adequate.
KSA1381/KSC3503 (Fairchild). I gave up finding an SMT part that was good enough. These are 200-300V parts that have an Ft of 150MHz. You can buy F versions with high beta. They come in a TO-126 package. The only SMT part I found was the MJD340/MJD350 (ON-Semi). These are SMT variants on the MJE340/350. The high frequency characteristics seem to be a secret with these parts, which suggests they are not too special. The beta was not real high either.
I am thinking of building a VAS module that I can use with a variety of output stages. My VAS design should be good for half bridge amplifiers as large as 250 - 300 Watts (75 - 80V rails) |
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| LineSource |
| quote: | Originally posted by danville
I am considering the NJL3281/1302 for outputs since the internal diode would be convenient for bias tracking. I used to clamp the bias transistor to a TO-3 case in the past. This is much better than mounting on a heatsink, but not as good as being on the same die as the transistor. |
danville,
What Thermaltrak bias circuit will you use? The OnSemi application note shows a simple string of several of the diodes, while Leach suggests a Vbe multiplier transistor on the main PCB plus thermal diodes from the heatsink in its C-B bias leg. Leach feels the RC in this leg provides more stability than using long wires to the Vbe multiplier transistor.
I've been debating using ThermalTrak with the Leach circuit, but the specs on the Sanken 1215/2921 specs look attractive for my low voltage application, unfortunately... much more expensive. |
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| danville |
I've never done it with an external diode. My thought was to add a single diode in series with the emitter. The BE junction of the transistor will be fairly constant if it is not near the heatsink. The variation will then be caused by the diode.
I use a two transistor circuit. The second Q just lowers the impedance.
I can tell you that you can control bias quite well when the tracking transistor is mounted directly on an output Q (not on the heatsink). The diode should be better.
I don't like the whole string of diodes method. This doesn't give you flexibility in setting the bias point in a fairly arbitrary way. |
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| Leolabs |
| 2SB647(A)/2SD667(A). |
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| thanh |
Thank all !
I'm using D669/B649. I don't know whether they still on producing.
How can I do to know whether a tst is on producing ?
Thank! |
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| fab |
| quote: | Originally posted by thanh
Thank all !
I'm using D669/B649. I don't know whether they still on producing.
How can I do to know whether a tst is on producing ?
Thank! |
Hi Thanh
The D669/B649 pair has 27 pf Cob ! :hot:
I would rather use the bjts mentioned in other previous posts for VAS. ;) |
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| thanh |
Thanks Fab!
I intend to increase bias current of VAS so I'm looking for a medium power transistor |
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| AndrewT |
Hi,
b649/c669 is great as an output driver.
There are FAR BETTER devices for VAS and pre-driver.
try a1360/c3423 |
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| Bonsai |
| If you are using the plastic TO3P style output devices, another technique for bias tracking is to use an SMD device and mount this close to the collector lead of one of the power devices on the PCB. The collector lead is part of the transistor heatsink tab and is in very good thermal contact with the die inside the package so the temperature of the collector lead closely tracks the die temp - and the thermal response is quick. If you use an SMD device it has a small thermal mass so it is quickly follows the die temp. I use this on my Ovation amp - works very well. You need to be pretty adept at soldering small devices, but its not insurmountable and quite easy to get a good solder joint. BTW, most suppliers will sell small qty's of SMD devices (SOT23) so you don't have to buy a whole reel. |
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| AndrewT |
Hi Bonsai,
do you attach the sot23 face down onto the collector lead or face up?
How do you attach leads to the pins? Pic?
What do you glue it on with? |
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| Bonsai |
Andrew,
photo attached. Search for the 'Ovation' amp on this site for pictures of final result. I use this technique in that amp (I'm listening to it now over my B&W 703's - heatsinks at approx 50C and nice and stable with Iq set at circa 500mA total across 5 pairs 21193/4, solid class AAB. Forgive the diversion, I've had a bottle of Shiraz to myself . . . warm and fuzzy vs the stuff from S.A. which is way older and heavier . . . )
I've been recently working on refining the overall design so the temp sensor has been moved slightly away from the power transistor to aid in assembly.
Re the Q about where the device is located. The main power devices sit between the PCB and the h/sink. The Vbe sensor transistor therefore sits underneath the PCB - i.e. between the PCB and the h/sink.
I used to design industrial instrumentation and one of the challenges was thermocouple cold junction compensation - this is where I got the idea from.
Hope this answers your question. |
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| taj |
Would all this advice apply to a Leach amp VAS section? I'm just learning this stuff and in the process of building a Leach amp from the Prof's own PCB's. But I'd really like to replace any devices that would be better handled by something more modern -- especially in the case of those tophat packages.
I see Jens @ Delta used MJE340/350 pair, but it doesn't seem to offer any advantages that I can see other than the package type itself. And its datasheet doesn't list its FT or COB. TIP47 or MJF47 seem very similar; FT is 10 MHz but no COB is listed.
What are the volts/amps at work in the Leach VAS that I should be cognizant of when substituting? (I'm a little ohm's-law challenged still).
Any advice? Thanks.
...Todd |
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| AndrewT |
Hi,
for VAS and pre-driver the following are extracted from Leach v4.5 min spec.
Vce0>[+Vrail to -Vrail]
P>1W
Ic>50mA
hFE>50 @ 1mA to 10mA
fT>30MHz
Cob<10pF @10V
2sa1360/c3423 exceeds all these specs by a considerable margin.
All the small signal devices can be replaced with bc550c/560c
The drivers can be MJE15034/5 or 15032/3 or 2sb649/D669
The output devices can be replaced with any of the 200W+ devices from MJ21193/4 through to MJL4281/4302 |
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| taj |
Great information. Thanks Andrew!
...Todd |
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| lineup |
| quote: | Originally posted by sajti
Try 2SC2911/2SA1209! High voltage, TO-126 for cooling, linear hfe, and very low capacitances.
sajti |
Those 2SA1209 / 2SC2911 from Sanyo looks great .. for VAS/predrivers!
Anybody happen to have a Spice Model made for them?
If so, post here right away :)
Thanks.
| quote: | 2SA1209/2SC2911 - PNP+NPN
160V/140mA High-Voltage Switching and AF 100W Predriver Applications
Features
· Adoption of FBET process.
· High breakdown voltage.
· Good linearity of hFE and small Cob.
· Fast switching speed. |
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| mlloyd1 |
i like the 2SA1209/2SC2911. these are nice parts that don't get mentioned a lot. borbely introduced me to them when i bought my servo 50 kit years ago.
sorry, i've never seen a spice model for them.
mlloyd1
| quote: | Originally posted by lineup
Those 2SA1209 / 2SC2911 from Sanyo looks great .. for VAS/predrivers!
Anybody happen to have a Spice Model made for them?
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| lineup |
| quote: | Originally posted by mlloyd1
i like the 2SA1209/2SC2911.
these are nice parts that don't get mentioned a lot.
borbely introduced me to them
when i bought my servo 50 kit years ago.
sorry, i've never seen a spice model for them.
mlloyd1 |
thanks mlloyd
I have never made a transistor spice model of my own.
I have just copied and pasted others.
Maybe time I study the howto of making models from curves ....
The 2SA1209/2SC2911 datasheet from Sanyo is very good.
With curves for most anything valid!
Download from my PDF web folder and have a look:
http://lineupaudio.freehostia.com/pdf/contents.php
Login. Exclusively for www.diyaudio.com members
Current Password: diyaudio
( notice, this password may I decide to change at any time,
like when I see those not not authorized by myself are downloading/copycat-ing my stuff )
Lineup |
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| fotios |
| quote: | Originally posted by danville
The Toshibas parts are less desirable in my case since I would probably have to buy a whole reel if SMT. Fairchild & ONSemi are good choices for Americans since Mouser and DigiKey carry these lines. |
Have you looked the MJD44H11 - MJD45H11 of ONsemi? |
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| lineup |
thanks, fotios
I look into it. I be back.
Lineup, regars
===================
edit:
The spice models for Onsemi MJD44H11 (npn) and also for MJD45H11 (pnp)
can be downloaded from this page:
http://www.onsemi.com/PowerSolution...ls&category=796
( .sp3 is the Level 3 .. sometimes not different from Level 1 )
thanks again |
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| fotios |
| quote: | Originally posted by lineup
thanks, fotios
I look into it. I be back.
Lineup, regars
===================
edit:
The spice models for Onsemi MJD44H11 (npn) and also for MJD45H11 (pnp)
can be downloaded from this page:
http://www.onsemi.com/PowerSolution...ls&category=796
( .sp3 is the Level 3 .. sometimes not different from Level 1 )
thanks again |
Hi Lineup, glad to meet you again after long time
These devices offered from ONsemi in two versions: MJD44-45H11 in D-Pack (in reel as prefer danville) and D44-D45H11 in TO-220 package. They are great devices with Vce=80V, Ic=8Amax, Pd=20W, ft=50MHz, hFE=250-350 for Ic=1A, the only drawback??? it is the Cob=130-230pF. I have implemented and checked those in two of my projects and their behaviour proved excellent.
The most important it is that we can obtain either of the two versions very easy. For Europe from Farnell and for USA from Digikey, in very low prices.
Regards
Fotios |
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| lineup |
| quote: | Originally posted by fotios
Hi Lineup, glad to meet you again after long time
These devices offered from ONsemi in two versions: MJD44-45H11 in D-Pack (in reel as prefer danville) and D44-D45H11 in TO-220 package. They are great devices with Vce=80V, Ic=8Amax, Pd=20W, ft=50MHz, hFE=250-350 for Ic=1A, the only drawback??? it is the Cob=130-230pF. I have implemented and checked those in two of my projects and their behaviour proved excellent.
The most important it is that we can obtain either of the two versions very easy. For Europe from Farnell and for USA from Digikey, in very low prices.
Regards
Fotios |
yes.
absolutely.
BD139/140 are also 80 Volt devices.
Here we have a very good alternative to try.
I guess with a great deal of performance improvements.
As far I I can see, from a quick look at the curves in datasheet.
Lineup - from Sweden
--------------------------
PS.
Did you know, my friend,
that under the Junta military occupation of your country, Hellas
while sweden in the regime of Olof Palme
Mikis Theodorakis & Melina Mercoury often visited Sweden with musical conserts, under exile form home country,
for the support of renewal Democracy in Greece.
Finally was a success, after many & much sufferings from Ellas brave activists.
Today, Grekland is a better land, with fair elections to Governments
DS. |
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