Just did a repaired triple ...
Ahhh - toshiba !
https://www.mouser.com/datasheet/2/408/TTA004B_datasheet_en_20170109-1102732.pdf
TT/A and C 004b $0.44
just used these as pre-drivers for a yamaha amp.
They are cheap/fast. Very low Cob... Me thinks they would be a good
replacement for the dreaded 1381/3503 unobtanium. I think they might be
good for VAS duty as well - as long as the amp is >70V rails.
As far as drivers - go for a TO-3P Sanken pair with 60mhz Ft or even
the MJW0281/0302. An fast small output pair as the driver pair is ideal for
a huge output stage.
Bypass the predriver(s) with a 10R/100uf filter and the EF3 is golden.
OS
Ahhh - toshiba !
https://www.mouser.com/datasheet/2/408/TTA004B_datasheet_en_20170109-1102732.pdf
TT/A and C 004b $0.44
just used these as pre-drivers for a yamaha amp.
They are cheap/fast. Very low Cob... Me thinks they would be a good
replacement for the dreaded 1381/3503 unobtanium. I think they might be
good for VAS duty as well - as long as the amp is >70V rails.
As far as drivers - go for a TO-3P Sanken pair with 60mhz Ft or even
the MJW0281/0302. An fast small output pair as the driver pair is ideal for
a huge output stage.
Bypass the predriver(s) with a 10R/100uf filter and the EF3 is golden.
OS
3503/1381 is hard to beatEspecially the very low internal capacitances. TTC/TTA004 is more like KSC2690/1220. Anyway KSC3503/KSA1381 still in production...
Another good parts from Toshiba, are the TTC011/TTA006 pair, which looks like 4793/1837....
Sajti
Yeah ,TTA/C pairs are slower than the 3503/1381 pair. 3503/1381's were made
for CRT video ... we do audio. On my fastest CFA simulations , the TTa/c's
just slow down by 20-30 uV/s. I can handle 250 v/uS ...
On any VFA there is no difference.
I see Mouser has 1K of them TTC/A 006's , 011's...none till may 2021.
OS
I use 3503/1381 on both VAS, and predriver in my CFA amplifier. Using TTC/TTA004 in predriver position needs to change the compensation (slow down the amp somewhat).
Sajti
Hello Russell, I am glad to see new progress in your RK-Auto200W Amplifer.
You said: "The MJE1503x parts were limiting things. I tried substituting an NJW0281/0302 for each of them, and that helped a little."
I am very curious about this~ because I am also using NJW0281/NJW0302 as outputs, 5 of each in parallel, 200W/8Ω.
I also tried to use NJW0281/NJW0302 as drivers. In order to avoid Hfe drop and FT drop, I used 60mA drive quiescent current. I think the quiescent currents of drivers and outputs are close, and their FTs will be close. In addition, a larger quiescent current of the driver may be better to drive 5 pairs of parallel power tubes?
At present, the whole circuit works well and no oscillation occurs.
I want to know if you get detailed test results when you try to use NJW0281/NJW0302 as drivers? What are its advantages and disadvantages? Do you have suggestions for improvement?
Expect your reply
Thanks and wish all the best
You said: "The MJE1503x parts were limiting things. I tried substituting an NJW0281/0302 for each of them, and that helped a little."
I am very curious about this~ because I am also using NJW0281/NJW0302 as outputs, 5 of each in parallel, 200W/8Ω.
I also tried to use NJW0281/NJW0302 as drivers. In order to avoid Hfe drop and FT drop, I used 60mA drive quiescent current. I think the quiescent currents of drivers and outputs are close, and their FTs will be close. In addition, a larger quiescent current of the driver may be better to drive 5 pairs of parallel power tubes?
At present, the whole circuit works well and no oscillation occurs.
I want to know if you get detailed test results when you try to use NJW0281/NJW0302 as drivers? What are its advantages and disadvantages? Do you have suggestions for improvement?
Expect your reply
Thanks and wish all the best
Hi zergxia,
I am still very much in the development phase of just the schematics right now. I am several months away from building anything. All I have are simulations right now. Sims are showing crazy low THD
Ultimately, I wanted the driver and predriver to be quite a lot faster than the outputs, and not just the same speed. As it was, the MJE1503x drivers were much slower. When I tried the NJW0281/0302 as drivers, I did much the same as you--I biased them at the same quiescent current as the outputs. They were the same Ft. I prefer not to have all the poles of the output stage stack up on top of each other, but spread out a bit. Not easy. They want to stack up.
Ultimately, Bespav gave very good advice: externally slow down either the outputs or the drivers. My outputs are now bypassed with strong zoebels to effectively make the OPS a double-EF as it approaches 1 MHz. My amp's overall loop gain crosses 0dB at 3MHz, which is lower than I wanted, but this seems to be the most stable OPS I've ever designed with discrete transistors (at least in simulations). About 1dB of peaking at 10 MHz.
I ended up using the following:
When I finally build it, I will detail everything over in the Auto200W Amplifier thread.
I am still very much in the development phase of just the schematics right now. I am several months away from building anything. All I have are simulations right now. Sims are showing crazy low THD
Ultimately, I wanted the driver and predriver to be quite a lot faster than the outputs, and not just the same speed. As it was, the MJE1503x drivers were much slower. When I tried the NJW0281/0302 as drivers, I did much the same as you--I biased them at the same quiescent current as the outputs. They were the same Ft. I prefer not to have all the poles of the output stage stack up on top of each other, but spread out a bit. Not easy. They want to stack up.
Ultimately, Bespav gave very good advice: externally slow down either the outputs or the drivers. My outputs are now bypassed with strong zoebels to effectively make the OPS a double-EF as it approaches 1 MHz. My amp's overall loop gain crosses 0dB at 3MHz, which is lower than I wanted, but this seems to be the most stable OPS I've ever designed with discrete transistors (at least in simulations). About 1dB of peaking at 10 MHz.
I ended up using the following:
Predrivers: KSA1381/KSC3503 in a diamond configuration
Drivers: KSA1220/KSC2690
Outputs: NJW0302/NJW0281 x4
Drivers: KSA1220/KSC2690
Outputs: NJW0302/NJW0281 x4
When I finally build it, I will detail everything over in the Auto200W Amplifier thread.
Look to the old 1970 Japanese EF3's.
They decoupled and used a BC bootstrap on the predrivers.
They "aced" this EF3 thing in '75. I have repaired and recapped
40 year old EF3's.
The fastest drivers I've used is some of the Sanken TO-3p devices.
Don't be scared of EF3. I was for a decade , I am ashamed.
OS
They decoupled and used a BC bootstrap on the predrivers.
They "aced" this EF3 thing in '75. I have repaired and recapped
40 year old EF3's.
The fastest drivers I've used is some of the Sanken TO-3p devices.
Don't be scared of EF3. I was for a decade , I am ashamed.
OS
Don't be scared, yes, i fully agree!
Just design EF3 with proper understanding like this one:
The YAP Output Stage
Sadly such an analysis aren't usual here at Diyaudio.
This is what I’m using in my EF3’s, followed by 15033/33 then NJW’s (6 pairs). The VAS uses the usual 3503 and 1381
Here Ovation High Fidelity - Model 1721
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Dear friend, thank you for your valuable sharing.
Many medium power tubes have a higher FT than high power tubes. When the driver stage uses a high-power tube, it is slower than the frequently used medium-power tube.
I thought before that the speed of the driver stage should be fast enough to avoid becoming a bottleneck. So I tried to increase the quiescent current of the driver stage to make the speed of drives and outputs as same as possible. But the reality seems to be different~
It seems that I should connect a small capacitor in parallel between the B/C of the drive to appropriately limit the speed.
Will this cause a decrease in usable gain and deterioration of distortion performance?
Thanks again：p
You are welcome!
Hmmm...
You meant vacuum tube? Or base-collector junction of bipolar transistor?
Ok
Any medium power stage will be an order or two faster than audio amplifier need. So it will not become a bottleneck.
Yes and no simultaneosly.
No - slowering will not nor decrease gain, nor add distortion.
Yes - slowering (based on speed of the last output transistors) will limit effective bandwidth of the output stage. Because of this you will be limited in unity gain frequency and feedback depth at higher audio frequencies, say 10-20 kHz, without complicated high-order frequency correction methods.
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