Thanks, with all that support, I will consider it.
Didn’t quite follow your logic there. I’m with Steve, maybe build the stock one first. You can of course roll your own thing.
If I build the stock one, then I don't need to go further 🙂
Ok, the logic was to use the parts that I have on hand, and see if it works.
Irf 9620 should work as a bottom mosfer, irf620 should work as a gain device, and another irf9620 should work as a CCS.
Lower voltage should work, altougj it might have a lower swing, but for a Mofo, it might be sufficient.
I will let you know when it gets done 😉
Yes, a voltage doubler would get you 100+ volts with your trafo. Good idea!
Those FETs should work but I recall a brightish sound with the 620.
Driving the MoFo requires quite a bit of swing. I’d shoot for at least 40V over the gain FET, same amount for the CCS, and 20V for the bottom one to keep it out of the high capacitance region. The CCS in the latest SCG (mu-follower mod) also provides input into the gain FET by adjusting the AC current based on the load. Makes quite a difference. So, keep that in mind.
Those FETs should work but I recall a brightish sound with the 620.
Driving the MoFo requires quite a bit of swing. I’d shoot for at least 40V over the gain FET, same amount for the CCS, and 20V for the bottom one to keep it out of the high capacitance region. The CCS in the latest SCG (mu-follower mod) also provides input into the gain FET by adjusting the AC current based on the load. Makes quite a difference. So, keep that in mind.
Progress. All resistors, diodes, and zeners are in.
And done, except the PS caps that arrive later this week. All told, about two hours of effort. Solder slingers like you guys will knock this out in an afternoon.
Five points for correctly guessing the identity of the red caps 🙂
Five points for correctly guessing the identity of the red caps 🙂
In anticipation I have been looking at the raw power supply. No question, the voltage needed is not a popular one!
Looks like a voltage doubler is the only way to have some leeway. I found a SIGNAL Belfuse isolation transformer with two 105 volts secondaries and not terribly expensive but it is probably better to just go with the ANTEK - though there I will need to wire the secondaries in series, which according to the God ZM is the way to do things. Figure the 24 volts x 2 version is good though one can choose from the 22, 24 and 25 volts variants.
With DUNCAN power supply tool it seems the doubler does not like a choke input so that eliminates the temptation to do that. I will use a choke after the input capacitor and it is hard to resist an additional RC stage after that.
What is the range of voltages for the input to the board? I have seen a few numbers but wondered if ra7 had come up with a value to shoot for with the new boards for all of the folks who will be using them.
Looks like a voltage doubler is the only way to have some leeway. I found a SIGNAL Belfuse isolation transformer with two 105 volts secondaries and not terribly expensive but it is probably better to just go with the ANTEK - though there I will need to wire the secondaries in series, which according to the God ZM is the way to do things. Figure the 24 volts x 2 version is good though one can choose from the 22, 24 and 25 volts variants.
With DUNCAN power supply tool it seems the doubler does not like a choke input so that eliminates the temptation to do that. I will use a choke after the input capacitor and it is hard to resist an additional RC stage after that.
What is the range of voltages for the input to the board? I have seen a few numbers but wondered if ra7 had come up with a value to shoot for with the new boards for all of the folks who will be using them.
Looking at the schematic and board, it takes AC as it has the complete power supply, including rectifiers on it. It is also dual mono so a power transformer with two secondaries would work well - one for each channel. 105V seems about right as the on-board regulator looks like it needs approximately 135Vdc minimum after the C12 capacitor.
Dual secondaries in that range are hard to come by, but the option is there. I use a single secondary and just wire the two together. I have two preamps going right now. One with a Hammond trafo (supplied by my friend Bob Flocchini) and another with an Antek donut.
Do not worry too much about dual secondaries. The PSSR is very high after the regulator. Coupling between channels is not an issue. The preamp easily shows differences between amps.
Edit: will dig up some recommendations tonight.
Do not worry too much about dual secondaries. The PSSR is very high after the regulator. Coupling between channels is not an issue. The preamp easily shows differences between amps.
Edit: will dig up some recommendations tonight.
My recommendation if you roughly need 2 x 105 Vac would be to simply use an isolation power transformer. Vin 115 or 230Vac and 2 separate 115Vac windings on the secondary side. Not sure about the VA requirements.
See attached transformer.
BR
Eric
See attached transformer.
BR
Eric
Triad makes these toroids. I use one in my preamp. They have two secondaries and I use one for each channel although their spec sheet says, "Primary and secondary windings are designed to be connected in series or parallel. Windings are not intended to be used independently." I figure since my preamp operates in Class A and the current draw from each channel is constant and equal, it should be ok.
Triad Toroid Transformers
Triad Toroid Transformers
I guess you didn’t read my post, you’re saying exactly what I said...lol
When Triad says; Windings are not intended to be used independently." It’s only intended for the primary side.
For 230V connect both primary winding in series and for 120V connect both primary winding in parallel.
When Triad says; Windings are not intended to be used independently." It’s only intended for the primary side.
For 230V connect both primary winding in series and for 120V connect both primary winding in parallel.
?
I did read your post and looked at the attached pdf. But my suggestion was for a toroid.
I was trying to help. 🙂
I did read your post and looked at the attached pdf. But my suggestion was for a toroid.
I was trying to help. 🙂
Both options from Ben and Eric should work. Here is another one:
Hammond 169QS
https://www.mouser.com/datasheet/2/177/169s-1390028.pdf
Slightly more expensive though. Of course, several single secondary ones are also available from Mouser and there is a nice toroid from Antek.
Hammond 169QS
https://www.mouser.com/datasheet/2/177/169s-1390028.pdf
Slightly more expensive though. Of course, several single secondary ones are also available from Mouser and there is a nice toroid from Antek.
Got it working! Worked straight away. LEDs are working, voltages are good, the pots work. The boards are good. Would like to run some measurements over the weekend and make a couple of tweaks to the board. And then we'll be ready to get boards for everyone.
