Nevod Posted September 21, 2011 Report Posted September 21, 2011 If you do SRPP you end up in the same troubles as the ray samuels A10. Same sort of thing as mikhail's original disaster. Ehm, no, I wasn't talking about using tubes as the plate current source. I was about using mu-follower wired solid state plate current source, output connected to drain of the source's transistor, as luvdunhill said. Ah, it is only called SRPP is the current source is made using same tube?
jcx Posted September 21, 2011 Report Posted September 21, 2011 (edited) I think the SRPP should be viewed as a modulated CCS like Pass Aleph http://www.passdiy.c...df/zen-ver2.pdf - the 50% split of AC current seems likely to optimize efficiency of bias current/power dissapation with little danger of destabilizing gain swings that the higher modulation levels of the mu follower extreme Pass shows enhancment mode power fet with bjt regulator and AC coupled modulation - with depeltion mode power fet and tapped resistor string the circuit is a lot simpler I tried talking about these ideas in the T2 thread when the good Doctor asked/speculated about alternatives Edited September 21, 2011 by jcx
kevin gilmore Posted September 21, 2011 Report Posted September 21, 2011 Actually because the load is not a constant impedance with frequency the term SRPP does not apply anyway. It degenerates into a simple current source. And solid state seems to be a much better idea for this.
Nevod Posted September 21, 2011 Report Posted September 21, 2011 And the final mad thought.. What crossed my mind is an such remake of SRX circuit: Input stage is modified by using a mu-follower/CCS/modulated CCS. Output stage modified same way as well. Interstage coupling capacitors replaced by voltage divider connected to highly negative voltage (say, 1.5 kV). Input stage CCSes handle the DC current through that divider. It is simple and straightforward, compared to active batteries etc.. Drawbacks I see is really poor PSRR and loss of gain - though not very high. Or should I banish that thought in deep night?
Hopstretch Posted September 21, 2011 Report Posted September 21, 2011 I also added Pro bias to one of the sockets and it sounds pretty nice driving a SR-007Mk2.... To the Birgir-mobile!
DouglasQuaid Posted October 1, 2011 Report Posted October 1, 2011 To the Birgir-mobile! I'd like to think whoever made that pic was tripping balls while watching HeMan and drinking eggnog.
Antistar Posted September 29, 2012 Report Posted September 29, 2012 ^Awesome GIF, one should be warned not to drink while watching it. Actual reason for the bump though is that i'd like to know what could be causing unsatble offset and balance readings with my the KGSS, mainly the left channel keeps bumping up the offset to around 7-8V and the trimmer is already at the end if it's rotation range and is clickin. the balance is 2-3V but i'm able to adjust it easily while the offset is a lot less responsive. Also the readings fluctuate pretty wildly in a scale of 1-2V with me doing anything, No phones connected and no input signal presnt. Is that supposed to behave like this ?
spritzer Posted September 29, 2012 Author Report Posted September 29, 2012 Not supposed to happen. What are the psu voltage readings?
Antistar Posted October 1, 2012 Report Posted October 1, 2012 Hi spritzer, Aplogize for the delay, I've not had the time to do any measuremts until today. I'm getting 366V in the postive rails, 355V on the negetive rails. After some time (a few hours) another 3-4V are added on both rails. Bias is 584V. And i have 300VAC across the primaries on the trnasformer btw, It was commissioned accrding to your specs from sumR. Is there anything else i should check?
spritzer Posted October 1, 2012 Author Report Posted October 1, 2012 The voltages being off isn't a good sign. AC in is a bit high but that will only cause a bit more heat so nothing to worry about. What I'd check are the zener strings and measure each step against ground. Personally I'd just replace them to eliminate a possible cause for the voltage difference.
Antistar Posted October 1, 2012 Report Posted October 1, 2012 Well i did just that not long ago, after i got both the FETs blow up on me... Unfortunately it took off all the traces between them and the zeners so i had to adjust: No vert pretty but gets the job done, basically at least... I have tested all the zeners and they pass the diode test, but the 1N4757 at the positive rail (The beaten side:) has double the resistance, 3.9Mohm at the voltage drop vs 2Mohms of the parallel negetive rail. Reversed it's half the resistance from the other rail 12Mohms vs 24Mohms. Is that significant for the voltage pass to the mosfet?
jwzhan Posted October 2, 2012 Report Posted October 2, 2012 damn that looks nasty must've been a pretty scary explosion if it took out that many traces... not commenting on anything else, but I think the jumpers could have been done better.. and if the diodes are in circuit, you are probably not measuring the diode, but measuring everything around them. I don't know how useful this is, I checked a few points on my kgsshv psu, in ohm test, the negative and the positive rail at the same component gave me near identical readings (just poked some random ones.)
jdkJake Posted October 2, 2012 Report Posted October 2, 2012 Well i did just that not long ago, after i got both the FETs blow up on me... Unfortunately it took off all the traces between them and the zeners so i had to adjust: No vert pretty but gets the job done, basically at least... I have tested all the zeners and they pass the diode test, but the 1N4757 at the positive rail (The beaten side:) has double the resistance, 3.9Mohm at the voltage drop vs 2Mohms of the parallel negetive rail. Reversed it's half the resistance from the other rail 12Mohms vs 24Mohms. Is that significant for the voltage pass to the mosfet? Just a suggestion. You might want to consider nylon washers under those mounting screw/washer combos that overlap the board traces. Solder mask is quite thin and easily subject to tears/penetration. Very easy to create unseen shorts just by torquing down the screws a bit too tightly.
spritzer Posted October 2, 2012 Author Report Posted October 2, 2012 I would install nylon washers on those screws as that is just an accident waiting to happen. The 1N4757 could be the culprit as the uneven PSU voltages could be causing your problems. The caps might also be damaged from the time it all went arcy sparky...
pagan Posted November 25, 2012 Report Posted November 25, 2012 Since you're back onto the KGSS, I do have a question if I may. I've just put together a KGSS using Justin's pcb's, (I think they were his last from a while ago). How hot do the 50 mm heatsinks, on the amp pcb, normally get? I'm measuring 62 to 70 degree C after a approx 30 min's warm up. PSU sits at 361 and 362 +/- vdc, and the +/- 15 vdc are stable and ok. Offset and balance vary a fair bit on warm up, approx 20 to 30 Volts Just seems too hot and maybe the offset/balance shows something is not quiet right, The psu heatsinks run at approx 40 Deg C Boards not cased yet, in open test rig. Allan
spritzer Posted November 25, 2012 Author Report Posted November 25, 2012 I just measured mine through the top panel and got 62-70°C. This is after about 30 minutes in chassis which is not the best in terms of cooling. Large drifts in offset and balance could be tied to how the output devices are attached to the heatsinks. What interface did you use?
pagan Posted November 25, 2012 Report Posted November 25, 2012 I just measured mine through the top panel and got 62-70°C. This is after about 30 minutes in chassis which is not the best in terms of cooling. Large drifts in offset and balance could be tied to how the output devices are attached to the heatsinks. What interface did you use? Hi I'm using sil pads at present, was thinking of mica and goop. Still, it does seem a bit hot,,,, The devices will be even hotter. Does the offset/balance vary much while it's getting up to temp? Allan Just a thought I could drill same vent holes just under the heatsinks
spritzer Posted November 25, 2012 Author Report Posted November 25, 2012 The went holes will help but it is also a good idea to lift the sinks off the board a bit.
pagan Posted November 25, 2012 Report Posted November 25, 2012 I already have the nylon spacers under the heatsinks
pagan Posted November 25, 2012 Report Posted November 25, 2012 Might get the taller ones.. AAVID THERMALLOY - 530002B02500G - HEAT SINK HEAT SINK Packages Cooled: TO-220 Thermal Resistance: 2.6°C/W External Height - Imperial: 2.5" External Height - Metric: 63.5mm External Width - Imperial: 1.65" External Width - Metric: 41.91mm External Length - Imperial: 1" Same dimensions just taller
spritzer Posted November 25, 2012 Author Report Posted November 25, 2012 That's what I've been using for years now. Runs a bit cooler.
pagan Posted November 25, 2012 Report Posted November 25, 2012 But on the build at the start it recommends the 50 mm ones. I'll try the 63.5 mm one's too.. And maybe perforate the pcb, while have the heatsinks off, and use mica and goop
spritzer Posted November 25, 2012 Author Report Posted November 25, 2012 The sinks are not grounded so you can just use the shoulder bits for the screw and plenty of goop.
pagan Posted November 26, 2012 Report Posted November 26, 2012 but then the heatsinks would be live. Voltage is a bit high to have live heatsinks.
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