That might be a good SS relay destruction test. I've still got a Kypton-C tuned to oscillate. I think I'll build up a two pair board with a single MT2OO pair and load it up at 63V.
This is an interesting observation. In fact, TubSuMo has got much better PSRR just by topology. However, it's got much more chances to pick up some induced interference. Also, it may be something related to grounding scheme. Sometimes I get some hum when I connect the amp to my PC-based measurement system (50Hz-based products, visible on spectrum graphs).
I will try to experiment on my test bench with regards to this.
I was wondering if it had something to do with the 47k resistor to ground on the input. Possibly lower resistance might help? I'm going to build a proper chassis and ground it better first. The odd thing I noticed was hum on my test bench. The table top is grounded stainless steel. I've never had anything hum on it before.
This might be an interesting test to compare to FetSoMo or BipSoMo inputs. Maybe the couple mA draw of the input transistors might quiet it.
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I will get some very faint hum if I return a left speaker ground return to the right OPS G1 ,
or some other out of the way, purposeful error .
The speaker grounds right to main chassis star and G1/G2 on the ops also
right to the main chassis is really silent. I also ground the heatsinks to the same
main star.
"21'st century protection" will also have a dedicated ground return.
I'm going to have fun and wind a common mode choke + caps for a nice EMI/RFI
right above my AC power input.
OS
or some other out of the way, purposeful error .
The speaker grounds right to main chassis star and G1/G2 on the ops also
right to the main chassis is really silent. I also ground the heatsinks to the same
main star.
"21'st century protection" will also have a dedicated ground return.
I'm going to have fun and wind a common mode choke + caps for a nice EMI/RFI
right above my AC power input.
OS
I'm running at 63V rails now. Everything is working excellent except for one problem. I'm getting 11.8V to the front end with 3.9K resistors for R18 and R19. I've tried dropping those values. Voltage is around 12 with 2.7K resistors but the resistors are hot. 1.3W if I'm doing the math correctly. I'm using 1.3W (BZX85B12-TAP) zeners. Would I be better to drop down to 1/2W zeners to get the voltage up?
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My tubsumo and slewmasters are silent. I did have to bypass the ground lift in the cfa xh board to get rid of hum. I'm sure there is something wrong somewhere else in the chain but it's quiet....
So far I have been living dangerous...no protection. I have the nice boards and info Jeff sent my but I'm painfully slow getting stuff together....There just isn't enough time in the day or if there is time there is no money....
Anyway these are GREAT sounding amps. Thanks to all.
Evan
So far I have been living dangerous...no protection. I have the nice boards and info Jeff sent my but I'm painfully slow getting stuff together....There just isn't enough time in the day or if there is time there is no money....
Anyway these are GREAT sounding amps. Thanks to all.
Evan
Hi Jeff, you've got 13mA with original 3.9K values, which is good (they dissipate close to 0.7W in these conditions). Some 10mA out of those 13 go via zeners. Giving them more will be just "heating the zeners".
Using lower power zeners may slightly increase the voltage, but in fact, 11.8V sounds enough to me - just leave it.
OS - do you agree?
They are working well at 11.8V. I remember OS mentioning they should come up to a full 12.2V quickly when we were messing with the Symasui boards. I changed the zeners to 1N4742 (1W). Now I have 12V on the negative rail and 12.3 on the positive rail. I liked it better when they were the same.
Control board is very useful. I just had another live test, related to power noise / blackout today. The amp was playing, when all of a sudden the power went off-on-off-on-off... The board has shut down the amp immediately at the first "off" and stayed there, indicating AC Failure. After 15-20 seconds after the power disappeared completely, the board also went off. As soon as the power came back (in 3 minutes), the board just executed the normal soft-start and the amp got up and running again. Perfect!
Yeah... zeners have got some tolerance, even with the same current, flowing through them )
Control board is very useful. I just had another live test, related to power noise / blackout today. The amp was playing, when all of a sudden the power went off-on-off-on-off... The board has shut down the amp immediately at the first "off" and stayed there, indicating AC Failure. After 15-20 seconds after the power disappeared completely, the board also went off. As soon as the power came back (in 3 minutes), the board just executed the normal soft-start and the amp got up and running again. Perfect!
The only glitch I've encountered so far with the control board is if the temp sensors aren't bolted to a heat sink they will randomly trigger. Everything else has worked flawlessly after initial setup. I'm very happy with the results of exploding an amp into the SS relays too. It would have been neat to record that with a scope but I just replaced my last one and didn't want to cook another one.
They probably catch some induced interference or something. I will think about adding a couple of caps to slow them down a bit.
And I'm going to switch to your layout and SS relays as well - next board will go this way.
I've always been too busy checking out everything else but I assumed the MJE340 were just warming up a bit with the current flowing through them. I haven't done much testing on the temp side of things.
vzaichenko,
Will you make any of those boards available for those of us to lame to make our own? It may be awhile before I assemble them but at least I would have them.
Will you make any of those boards available for those of us to lame to make our own? It may be awhile before I assemble them but at least I would have them.
These boards are still evolving. Valery won't like my choice of connectors. OS doesn't like where I put the screw holes. The next version will have the SS relays right on the board so there won't be daughter cards standing up. I'm going to change capacitors slightly to lower the overall height of the board too.
Hi Kindhornman, sure - I share the board design with everybody interested.
Drop me your e-mail address - I will send you all the docs, including firmware.
With regards to the boards - it's rather problematic to export something from where I am
p), so normally there are two ways of getting them - either people order them themselves, based on gerbers, or they use the kind help of Jeff (who is actually an author of the new layout, more compact one, than mine, plus SS relays), or Terry (he ordered a bunch of my initial-design PCBs, but I think, now he ran out of them).So... either way is fine with me.
Cheers,
Valery
Jeff, for the board - I'm ok with your connectors
Well, so far we can share the earlier versions - they work fine, all the rest is a matter of optimizations... more or less...
On my test bench, I still use the very first one-channel prototype, that does a great job, saving the circuits during some dangerous experiments
I've run into my next glitch with my Slewmonsters. Bias seems to be dropping too much as temperature rises. I set bias at 60mA at startup. I ran it for half an hour and warmed up the whole heat sink. The devices were at 155F Bias had dropped to 25mA. I readjusted bias to 60mA and let it play under lighter load. Bias was 105mA by the time the output devices were at 110F. Once warmed up the drivers seem to be staying around 115F. I'm using BD139 for Q103 and Q104. Should I switch them to MJE340 or is there another device that will work better with the MT200s?
vzaichenko,
Thank you. I guess I'm probably on some NSA list now for asking you! I wasn't thinking about your location. Grandpa is probably rolling over in his grave right now as he was from Odessa, left as an infant to come to America. Hope all is well with you, why we can't all just get along is beyond me. Have a nice Sunday.
Thank you. I guess I'm probably on some NSA list now for asking you! I wasn't thinking about your location. Grandpa is probably rolling over in his grave right now as he was from Odessa, left as an infant to come to America. Hope all is well with you, why we can't all just get along is beyond me. Have a nice Sunday.