Hi Terry ,MJL2119..isn't a good choice for slewmaster.
I already have some MJW 21195 burned devices, but i pushed them hard.
Now i use 2sc3264 ,a1295 ,i can't destroy them,even if i push them hard😀
The compensation cap/s is/are in the IPS in general. When you use different IPSs with the same OPS you have to compensate each IPS to that OPS. If you start to change OPS and use it with the IPS compensated for other OPS you play with fire. That is one of the reason I don't like idea of interchange different IPS with different OPS. Other is long connection in between and you lose possibility to get an optimum from the amp. It is OK in the design and testing phase but final is better to be on the same PCB.
I'm afraid you'll have to find-it by yourself with an oscilloscope.
Take the dadod advice in consideration too. The two PCBs contiguous with shortest wires between them as possible (straps).
Last edited:
Only when the OPS is undersized, you're not blowing out 3000 watts of BJT with a 1000VA transformer on a short term short. Protection circuits are an issue for me, IMO, they tend to kill dynamics and sound quality. A necessity in under built amps, so , yes, i do understand, unfortunately more red flag than safety blanket for me.
Can't find it myself. I wouldn't even know where to start. I can certainly use very short wires once it is in an amp. Just testing right now. I have to decide which IPS will be best. On my other boards, csa/csb are not used and no problem with oscillation with any of the IPS I have built including the new Symasui I just finished. This is makeing me wonder if these transistors are my problem it the LTT4 I hav been struggling with.
Blessings, Terry
OMG Terry, now you are on your own, God bless you.
Thanks for the blessing. I know you have not built one of these. Nor have Esperado nor Dado. I suppose it doesn't hurt to theorize but I was looking for actual help, not to be told to find it on my own. I'm not a designer nor engineer, just a builder and tester as I have been told several times. Unfortunately I have to rely on the knowledge of others for technical matters and OS is still moving and getting settled. Again, thanks for the blessing.
Terry, don't misunderstood, tweak with the values of the compensation caps is the only way, and we can not do-it for you.
Or build your parts, following exactly the same components than the original designer.
We all remember that feeling of loneliness, when we were very young beginners and something was going wrong, building of our first kits.
And the smell of the smoke.
Or build your parts, following exactly the same components than the original designer.
We all remember that feeling of loneliness, when we were very young beginners and something was going wrong, building of our first kits.
And the smell of the smoke.
Last edited:
Terry it looks dramatic, well but it's not. All you have to do is to properly compensate amp at HF, find enough phase margin, meaning the amp would not get too close to positive feedback and started to oscillate.
It's simple, use your bulb tester, leave current compensating caps installed, just add parallel trimm caps 10-60 pF to all compensating caps, usually ceramic low pF value in the input stage and few in the OPS.
Short the input, connect the scope, power on and voila fun starts. Trimm slowly and observe the scope to set trimm caps to sweet spot in between oscillations (higher/lower freq) or lowest by the level. Finally you'll find sweet spot where none oscillation will be present at any circumstances.
Voila again.
It's simple, use your bulb tester, leave current compensating caps installed, just add parallel trimm caps 10-60 pF to all compensating caps, usually ceramic low pF value in the input stage and few in the OPS.
Short the input, connect the scope, power on and voila fun starts. Trimm slowly and observe the scope to set trimm caps to sweet spot in between oscillations (higher/lower freq) or lowest by the level. Finally you'll find sweet spot where none oscillation will be present at any circumstances.
Voila again.
And the law of the first power-on is: Oscillators never start, amplifiers always oscillate.
Last edited:
a cap in parallel with the feedback resistor to cancel the 4mhz pole of the mj21193/94 should help i think...
the thing is not to ask the slow output device to have gains outside of its fT...
protection
Hi AJT
greetings just give me few days i will design the pcb for the short circuit protection here my pcb for protection dc protect temprature cutoff clip overload
i use resettable circuit breaker here MONO AB class amps locals use them till
1 ohm load so protection very important
Warm regards
Andrew😉
Hi AJT
greetings just give me few days i will design the pcb for the short circuit protection here my pcb for protection dc protect temprature cutoff clip overload
i use resettable circuit breaker here MONO AB class amps locals use them till
1 ohm load so protection very important
Warm regards
Andrew😉
Attachments
Wolverine 1.2-C
Phase distortion.
Ch.1 (yellow)is output signal
Ch.2 (blue)is input signal.
Phase distortion.
Ch.1 (yellow)is output signal
Ch.2 (blue)is input signal.
Attachments
Last edited:
OPS compensation
Ok, let's go back to OPS stability with different output devices for a minute.
I did some simulations, actually confirming what's been said above.
Analyzed circuit is my tube-hybrid IPS together with SlewMonster OPS.
OPS creates additional pole on overall frequency response curve.
Picture 1 - with faster NJW3281/1302 transistors this pole is around 4.6 MHz and 5.5 db below the unity gain level. Acceptable - we cross unity gain with 20 db/decade slope.
Picture 2 - with slower MJL21193/21194 the pole is located at 3.2 MHz and actually lays on the edge - roughly at the unity gain. This is a problem - frequency response slope changes from 20 db/decade to 40 db/decade here and we don't want 40 db/decade to be located at the unity gain level.
Picture 3 - this is how we can solve it - increase the value of C107, C109 (pre-drivers shunts) from 33pF to, let say, 150pF. The pole stays at 3.2 MHz, but moves down to -6 db - and we are fine again.
Anyway, the faster devices are the better. SC2922/SA1216 Sankens would be a good choice here as well, with Ft = 50 MHz and Cob = 250 pF (half of any of the above).
Hope this helps.
Cheers,
Valery
Ok, let's go back to OPS stability with different output devices for a minute.
I did some simulations, actually confirming what's been said above.
Analyzed circuit is my tube-hybrid IPS together with SlewMonster OPS.
OPS creates additional pole on overall frequency response curve.
Picture 1 - with faster NJW3281/1302 transistors this pole is around 4.6 MHz and 5.5 db below the unity gain level. Acceptable - we cross unity gain with 20 db/decade slope.
Picture 2 - with slower MJL21193/21194 the pole is located at 3.2 MHz and actually lays on the edge - roughly at the unity gain. This is a problem - frequency response slope changes from 20 db/decade to 40 db/decade here and we don't want 40 db/decade to be located at the unity gain level.
Picture 3 - this is how we can solve it - increase the value of C107, C109 (pre-drivers shunts) from 33pF to, let say, 150pF. The pole stays at 3.2 MHz, but moves down to -6 db - and we are fine again.
Anyway, the faster devices are the better. SC2922/SA1216 Sankens would be a good choice here as well, with Ft = 50 MHz and Cob = 250 pF (half of any of the above).
Hope this helps.
Cheers,
Valery
Attachments
Personally, i have nothing against this idea, just Mr Harry Nyquist don't agree ;-)
(Nice one, Valery, you probably saved still4given)
Last edited: