... As long are they are not burned in short circuit !
Hopefully not 😀
Sometimes fuses saves the day 😉
Well I practice this kind of solution for more than 10 years and there's no way to go back to output relay anymore. The same with voltage feedback. 😀
BTW 2000 posts were written in this thread.


LC.
Great looking chassis and layout , a couple questions , what is the 4 pin locking connector for ? Any issues with the transformers being so close ?
4-pin connector conducts 12 V remote trigger input/output signals if connected, so an amp can be turned on by multichannel preamp or similar and at the same time when on sends the on trigger signal to another amp etc. Trigger input is galvanicaly isolated from any amp's potential, even earth connection, to prevent any interference currents inside the system (HT, stereo, etc.). 😎
So far no issue regarding transformers position. Some DIY-ers even stuck toroids without any issue. Because on non-ferrite material of the AL-heatsinks there is none magnetic short connection between transformers. 😉
Did-you make the screw driver test at 1, 10, 100 watts ? (Big sparkles)Sometimes fuses saves the day
Well, i must agree that, since i managed a big PA system, i'm pretty paranoid.
I must admit that your solution is enough for a domestic use. But it would be better with my way to detect abnormal situations, witch is instant, comparing to your.
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LC, Is there any good substitute for 2sa1209/2sc2911 ? it seems had stop production, and almost all places out of stocked. (those have stock seems suspicious website) Had find for long time but not much result I have here.
LC, is it possible to use MJE15032/33/34/35 for cascode BC550C/560C VAS ? OR MJL3281/1302 (seems wasting)
If I abandon the Thermaltraks and go with Nico's FET version, are these values OK? Retain 2SA/SC drivers, or use BC550/60? Leave or remove the driver emitter resistors?
I assume the drivers are run at lower current levels than for the BJT version. Am also assuming this version will be easier to stabilize for temp drift.
Sheldon
550/560 are much OK for input, but avoid for drivers, they may die during bias drifts in test phase many times, Vceo not enough for full swing also. Emitter resistors on drivers did not play a key stabilization role, those were BD139/140 I had experience with though, maybe doing better for your 2SA1360/2SC3423.
Yes they can run <5mA and the amp still be fast. You may need other than 330R to turn the drivers on at the current you want. Don't assume that is too easy to stabilize VS BJT OPT though. That 330R between the output Mosfet gates need be something more elaborate IMHO, there it was a pain to keep bias in mine. Maybe a Vbe multiplier, but have your own test go to see also.
Thank you, Salas. 🙂
Is this circuit stable? I tried to simulate it and I get huge distortion unless I set VR1 to less than 300 ohm, that is, more than 3 A bias.
Thanks.
Is this circuit stable? I tried to simulate it and I get huge distortion unless I set VR1 to less than 300 ohm, that is, more than 3 A bias.
Thanks.
Here's my simulation files. Maybe it's problem with the models, I don't know.
Thanks.
Wanna share your modifications?Me I modified it a lot.
Thanks.
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550/560 are much OK for input, but avoid for drivers, they may die during bias drifts in test phase many times, Vceo not enough for full swing also. Emitter resistors on drivers did not play a key stabilization role, those were BD139/140 I had experience with though, maybe doing better for your 2SA1360/2SC3423.
Thanks Salas. Yes, bias stability is tricky. If I understand correctly, both the input devices and drivers increase conduction with temperature rise, which amplifies the affect.
Yes they can run <5mA and the amp still be fast. You may need other than 330R to turn the drivers on at the current you want. Don't assume that is too easy to stabilize VS BJT OPT though. That 330R between the output Mosfet gates need be something more elaborate IMHO, there it was a pain to keep bias in mine. Maybe a Vbe multiplier, but have your own test go to see also.
The Thermaltrak output devices are pretty well compensated by the internal diodes. They seem to be fairly stable to temperature changes, if I correct for the driver current. It's the driver current that is difficult to stabilize, so I guess that you are probably correct that a VBE multiplier would be needed to stabilize the FET version. In that case the output devices are self stabilizing, but the VBE multiplier would compensate for the driver drift. However, that means that the current through the drivers is still allowed to vary a lot - which could affect distortion. So how do we get the drivers to quickly stabilize to a desired current? It seems like that is the issue. Is LC's latest scheme the only way?
I used a JFET CCS under the upper driver and fixed their bias, some argued that goes against full symmetry, others argued its gonna effect it only near clip. To me the most important aspect is not to force too much base current to the upper driver, its going to suck it up from the respective input BJTs and be exhausting the drive ability non symmetrically with swing then.
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As I mentioned before, I considered the NTC in the early days of designing the TM5 to 'fix' the bias current stability. The place I found worked best was in place of the resistor that feeds current from the zener diodes to the feedback node. I found suitable thermistors at digikey with the right coefficient to hold it stable. But I didn't use them in the end, I don't think they are necessary - and they are expensive. Perhaps for the big higher power amps it becomes necessary again.
LC - I like the way your build is coming along, nice mechanical layout. Did you orient the power trafo's so that their magnetic flux leakage cancels out ? (I saw that done in a Goldmund amp I think).
LC - I like the way your build is coming along, nice mechanical layout. Did you orient the power trafo's so that their magnetic flux leakage cancels out ? (I saw that done in a Goldmund amp I think).
I used a JFET CCS under the upper driver and fixed their bias, some argued that goes against full symmetry, others argued its gonna effect it only near clip. To me the most important aspect is not to force too much base current to the upper driver, its going to suck it up from the respective input BJTs and be exhausting the drive ability non symmetrically with swing then.
Will this work with BJT outputs?
Sheldon
Don't know, I only did it in the Latfet amp. Not difficult you give it a try though.
Will do. But might be a couple of weeks before I can get to it.
Sheldon
Can anyone please look at my simulation files on post #2011 and tell me what I'm doing wrong? 😕Thank you.
Can anyone please look at my simulation files on post #2011 and tell me what I'm doing wrong? 😕Thank you.
R6
LC, because I can't find any good transistor to replace BCs 550/560C at VAS (Cascode makes high output impedance, not good for BJT OPS) So I decide to limit the rail voltage, is it wise to do so ?
My plan is to use 20V zener regulation for whole input and VAS (exclude Output). Buy Zener Diode,Zener,BZX85C20 Magnatec BZX85C20V online from RS for next day delivery.
its datasheet : http://docs-asia.electrocomponents.c...6b800297e6.pdf
My plan is to use 20V zener regulation for whole input and VAS (exclude Output). Buy Zener Diode,Zener,BZX85C20 Magnatec BZX85C20V online from RS for next day delivery.
its datasheet : http://docs-asia.electrocomponents.c...6b800297e6.pdf
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