@PMI
Your post is very interesting to me and I learn a lot from you. Thank you.
@Shaan
How would you change the circuit for these higher voltages, lets say +-50V DC rails? The BC's at the input pait would need replacement? Changing the 15k resistor for a higher vaule?
I'm sorry, I don't want that, I just want to spend my money wisely.
Your post is very interesting to me and I learn a lot from you. Thank you.
@Shaan
How would you change the circuit for these higher voltages, lets say +-50V DC rails? The BC's at the input pait would need replacement? Changing the 15k resistor for a higher vaule?
Buy the most expensive 2200uF caps you can afford. That alone will be enough trust me. However, be ware of snake-oil stuffs.
Input: BC546B/BC556B.
VAS: MJE340/MJE350.
Current feeder: 27K.
I would like to correct something the transistor
2SC3503D and 2SA1381E without comp not oscillate.
but the instability in offset is due to the large difference between in hfe D and E
measuring 400 point difference with my device
Lets say 700 2sa1381E 1100 2sc3503D
What we also saw the more we matched transistors input VAS ,the ringing is less under load .
Does anyone supply us a few 2sc3503E??
2SC3503D and 2SA1381E without comp not oscillate.
but the instability in offset is due to the large difference between in hfe D and E
measuring 400 point difference with my device
Lets say 700 2sa1381E 1100 2sc3503D
What we also saw the more we matched transistors input VAS ,the ringing is less under load .
Does anyone supply us a few 2sc3503E??
Last edited:
Hi Paulo.
Use trannies tha have Vce higher than 100V. Choose the ones that give lowest distortion and have close hFE pairs available, in real world.
The sim showing lower distortion with a certain pair doesn't guarranty the same in reality.I'd say, try the MJEs. These are cheap devices, meaning you can buy some of them for little money and test them with peeceebee beside other pairs, and keep the ones that perform best.
Hi Paulo.
Use trannies tha have Vce higher than 100V. Choose the ones that give lowest distortion and have close hFE pairs available, in real world.
I'd say, try the MJEs. These are cheap devices, meaning you can buy some of them for little money and test them with peeceebee beside other pairs, and keep the ones that perform best.
MJE devices have excellent voltage rating but I found Ft for them is just 10MHz. That is the reason why you see higher gate resistor values are used on Lateral Mosfets with MJE devices (at least 330R): to slow them enough in order to alow that MJE
can be used. Otherwise you can have stability issue. But if you slow lateral mosfets that much the question is why you used fast output transistors in the first place (except for simplicity of circuit and reliability)?
If it is possible to find 2SB649A/2SD669A with their high voltage rating (160V) and speed (150MHz) and low Cob, that is excellent choice for VSSA with +/-50V supplies. Or KSA/KSC which are best choice overall, if one can find them. Also, 2SA1837/2SC4793 are excellent choice for 50V supplies.
Hi ivanlukic and Shaan,
I think I can also find the 2SA1837/2SC4793. Any changes to the circuit necessary? What about compensation?
Many thanks for your help, guys!
EDIT. can't use them because the pinout is reversed.
Can the KSA/KSC work with 50V? Otherwise I can't use 50V and have to settle with 35VDC...
This would be my first choice too but can I use them with 50V rails? They're rated 300V Vce but only 100mA Ic.
I think I can also find the 2SA1837/2SC4793. Any changes to the circuit necessary? What about compensation?
Many thanks for your help, guys!
EDIT. can't use them because the pinout is reversed.
Can the KSA/KSC work with 50V? Otherwise I can't use 50V and have to settle with 35VDC...
Last edited:
Hi ivanlukic and Shaan,
This would be my first choice too but can I use them with 50V rails? They're rated 300V Vce but only 100mA Ic.
I think I can also find the 2SA1837/2SC4793. Any changes to the circuit necessary? What about compensation?
Many thanks for your help, guys!
I think that KSA/KSC 100mA rating is no problem with 50V rails and PMI's pcb has space for small heatsinks that you should use on any VAS tranies you decide to use with 50V rails. 1837/4793 are in isolated TO220 case and have pins reversed compared with TO126 tranies and no heatsinks are required..
That's good news!
No heatsink required means I can solder them to the pcb without space problems. But I can still use the KSA/KSC - no problem with 50VDC. Do I understand correctly?That's good news!
Yes, I would use KSA/KSC (with small U shaped heatsinks) and 50V rails. I used 15pF NP0 compensation caps on my VSSA/layout by PMI boards with KSA/KSC VAS tranies. I am waiting for Panasonic FR 2200uF/10V to complete the boards, all other components are installed. I shall post pics when the boards are complete.
@Paulo: If the U-shaped heatsinks do not fit your choice of transistor, you could try a flat strip of copper or aluminum, especially with TO-220 package.
It is a little more complicated, because you have to use an insulator, and you probably need a grounding jumper for the heatsink. If you look carefully, there is an unused drill hole and pad in the center of the board to use as an anchor point for a common flat heatsink.
I thought about using one even with the smaller package, but it did not turn out to be necessary.
It is a little more complicated, because you have to use an insulator, and you probably need a grounding jumper for the heatsink. If you look carefully, there is an unused drill hole and pad in the center of the board to use as an anchor point for a common flat heatsink.
I thought about using one even with the smaller package, but it did not turn out to be necessary.
Attachments
I bought some examples of KSA1220AY / KSC2960AY and 2SA1507S / 2SC3902S transistors that I thought might be good for VAS duty. Initial testing suggests that the KSA1220AY / KSC2960AY may be a good bet.
I'm planning on etching another set of boards to see how these sound.
The KSA1220AY and KSC2690AY had average gains of 258 (KSA) and 243 (KSC) with enough overlap in the 240-290 range to get devices matched up. The 2SA1507S / 2SC3902S had average gains of 219 (2SA) and 220 (2SC), but the 2SC were all very consistent where the 2SA varied quite a bit. Despite there being a very close average Hfe there are fewer devices that are really good matches to one another.
Here's hoping to find a good transistor for VAS duty that is readily available in well matched compliments.
I'm planning on etching another set of boards to see how these sound.
The KSA1220AY and KSC2690AY had average gains of 258 (KSA) and 243 (KSC) with enough overlap in the 240-290 range to get devices matched up. The 2SA1507S / 2SC3902S had average gains of 219 (2SA) and 220 (2SC), but the 2SC were all very consistent where the 2SA varied quite a bit. Despite there being a very close average Hfe there are fewer devices that are really good matches to one another.
Here's hoping to find a good transistor for VAS duty that is readily available in well matched compliments.
Good work. Do you know how close a match we should have here?
Or, perhaps a better q should be, has anyone simulated the effect of unmatched VAS transistors?
@PMI:
Hi Pete,
I think I'm going to order these heatsinks from Mouser:
577102B00000G Aavid Thermalloy | Mouser
They have to be small enough to fit into the PCB but wide enough to allow the comp camps to be fitted. They are 13.208 mm in width and the silver micas are 9.4 mm, so all seems to fit. They're rated 25.9 C/W. Are these good? Yours look a lot better - where did you get them?
Hi Pete,
I think I'm going to order these heatsinks from Mouser:
577102B00000G Aavid Thermalloy | Mouser
They have to be small enough to fit into the PCB but wide enough to allow the comp camps to be fitted. They are 13.208 mm in width and the silver micas are 9.4 mm, so all seems to fit. They're rated 25.9 C/W. Are these good? Yours look a lot better - where did you get them?
I did not want to use up too much board space for heatsinks, because you do not need much - at 35V supply, anyway. I bought mine on ebay, after I saw them used on another board here on diy.
they are sold online at various suppliers, not just ebay.
example:
To 220 Aluminum Heatsink Heat Sink 20 X*15 x 10mm M3 x 10 PC | eBay
Are you still planning on a higher supply voltage? If you are, you should probably recalculate the heat dissipation with the expected bias current, at the expected supply voltage.
edit: those at Mouser look fine.