It doesn't really matter: the zener only serves to balance the dissipations in the VAS transistors, and at such low voltage, it is small anyway. You could even remove it completely, it wouldn't alter the performance or characteristics
![DSCF3018[1].jpg](/community/data/attachments/304/304010-0f60e780e1352c20b406a36008063d99.jpg)
Good news
Hello all,
I just converted one of my channels to mosfet version just by replacing 120R with 390R and fitting IRFP250's at output..Powered up and nothing seem catastrophic. I did a quick 1khz square test and it doesn't have a overshoot issue that I observed with darlington version. Very clean.. even with absence of input filter capacitor (just a slight ringing at high levels). My modified layout was the one that I posted earlier: http://www.diyaudio.com/forums/solid-state/189599-my-little-cheap-circlophone-116.html#post3434593
I modified that pcb and altered for BC/2N and Japanese type small transistors. Hope to provide them with a understandable way according to possible builder preferences.
I also tested MN2488 from Sanken on darlington version and there is no trace of a oscillation despite their high Ft (55mhz). I cracked one of failed transistors and it seems they are genuine according to their built quality and die size (4*4mm).
Hello all,
I just converted one of my channels to mosfet version just by replacing 120R with 390R and fitting IRFP250's at output..Powered up and nothing seem catastrophic. I did a quick 1khz square test and it doesn't have a overshoot issue that I observed with darlington version. Very clean.. even with absence of input filter capacitor (just a slight ringing at high levels). My modified layout was the one that I posted earlier: http://www.diyaudio.com/forums/solid-state/189599-my-little-cheap-circlophone-116.html#post3434593
I modified that pcb and altered for BC/2N and Japanese type small transistors. Hope to provide them with a understandable way according to possible builder preferences.
I also tested MN2488 from Sanken on darlington version and there is no trace of a oscillation despite their high Ft (55mhz). I cracked one of failed transistors and it seems they are genuine according to their built quality and die size (4*4mm).
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They all seem to me genuine. If your multimeter is capable of Hfe rank measure, at least you can get an idea about them. Especially with small ones. MEV ones seem 30 years old but this is not a bad thing -if they are healthy-.
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Thanks,my multimete has hfe measuring function but it always gives false readings on ohms and voltage but not on current,never tested the hfe but ill test it now and post the results
Hi terranigma,
Did you try Lateral fet for the output? Thanks for the feedback
Regards,
Boyet
No way ~200 hfe for a BC550C. Even my BC546 ones have ~350 Hfe. BC550C's must have minimum 420 Hfe according to Philips/NXP datasheet. If you are sure about your multimeter, I suggest to find another good one. You can distinguish Philips/NXP ones with their silver color.
Same for 2n5551's.. Mine ones give ~150-200 rating. It seems you are in bad luck with these ones.
Hi terranigma,
Did you try Lateral fet for the output? Thanks for the feedback
Regards,
Boyet
If I could find a latfet for cheap I would try. But it is good to use this kind of robust device at first try. I listened them for one hour and it seemed that they deliver good, very good.. at least for my ears.
Regards.
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im pretty sure its the multimeter,my dad promised me he will buy another one for me,i need to find a good one for less that 35 $,
thanks for helping me,ill try them in the amp when i build it
I meant, If you are sure about that your MM is not faulty, then these transistors are problematic. I suggest you to find another transistors for compare. I didn't suggest you to find another MM. Hope there is no misunderstood.
Transistor is just an option. Transistor type must be similar with what used in bias servo stage. I decided to add a single 1/2W zener at rating around Vs as another option. Two zener option will be remain but my personal preference is single zener due to its simplicity.
I just made a sim by drop in replacement of IRFP with a 2sk1056 model. It works but distortion level is 10 times higher. Maybe it requires a pre driver stage. We need assist from who familiar with lateral mosfets for adapt them to this topology properly. I don't hesitate to draw a special version of pcb for latfet version. I actually made one pcb according to output device leg arrangement but it seems that is not enough.
Circuit isn't vary with or without Japanese devices. It's same circuit but supply margin can be higher with Japanese counterparts. I'm just altering layout for their different leg arrangement. If you are aware of what you're doing, you can use a single layout but within taking care of their leg arrangement.
Code:
* 2SK1056C VDMOS copyright Cordell Audio December 6, 2010
.model 2SK1056C VDMOS(nchan Vto=0.02 Kp=0.85 Lambda=0.02 Rs=0.62 Rd=0.1 Rds=1e7 Cgdmax=100p Cgdmin=5p a=0.25 Cgs=600p Cjo=1080p m=0.7 VJ=2.5 IS=4.0E-06 N=2.4)
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Hi guys, my Circlophone is now finished. I got the current draw issue sorted, it's 200mA per channel now. There was an issue with the preliminary power supply I used, I think (haven't done anything else than replace that). It was acting really strangely. I had pulled it out of some sketchy surround sound receiver from the early 00s.
I would like to add a headphone output to it. On all the amps I've looked at, it has simply been the speaker output with a 1-3W resistor in series. This value varies, but some examples are 330 and 470R. What would you guys suggest? Is this even a good approach for this?
Another thing. The thing takes forever to drain out the psu caps when I turn it off and a signal is still playing. Bad sound, of course. Could this be harmful to the speakers? I guess some sort of speaker protection circuit would be nice, here. Or add bleeder resistors to the caps, perhaps?
I would like to add a headphone output to it. On all the amps I've looked at, it has simply been the speaker output with a 1-3W resistor in series. This value varies, but some examples are 330 and 470R. What would you guys suggest? Is this even a good approach for this?
Another thing. The thing takes forever to drain out the psu caps when I turn it off and a signal is still playing. Bad sound, of course. Could this be harmful to the speakers? I guess some sort of speaker protection circuit would be nice, here. Or add bleeder resistors to the caps, perhaps?
