So assuming that the PSU voltage could be switched by putting the transformer(s) in series or parallel, and having caps rated for the higher voltage, how much more would have to be switchable to be able to change from a high power to a half power configuration? Not necessarily instantly but in a few minutes with the cover off if that would be required.
R4, and R7/R8 - these resistors control Iq. You may also need to adjust the trimmer that is in series with R4. You may be able to fine tune R4 for each voltage while keeping the same trimmer setting for both voltages.
Trimmer for SIT also needs to be set for each voltage (to set SIT Vds).
Trimmer for SIT also needs to be set for each voltage (to set SIT Vds).
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Thanks! That’s kinda what one would expect I guess. Not hard, but not a matter of a couple of switches!
I can understand and sympathize with Ben finding it so darned tempting to use a device that can handle big power to it’s max, when VFETs, SITs, SETs, etc, often are best in low power circuits….
Might be more practical to just have a second board installed for each channel with all trimmers trimmed, and the correct resistors, with jumpers that one can move to share the expensive and/or rare active devices, and to change the PSU wiring…
More expensive, but a lot less than 2 amps. In fact for hobbyists that want to compare various amp types, installing two sets of amp boards, sharing one chassis and power supply, with jumpers to select between them would be a ton cheaper. Especially for First Watt projects which tend to have the same PSU’s and cooling requirements.
Now let’s see if I get even one SIT amp finished!
I can understand and sympathize with Ben finding it so darned tempting to use a device that can handle big power to it’s max, when VFETs, SITs, SETs, etc, often are best in low power circuits….
Might be more practical to just have a second board installed for each channel with all trimmers trimmed, and the correct resistors, with jumpers that one can move to share the expensive and/or rare active devices, and to change the PSU wiring…
More expensive, but a lot less than 2 amps. In fact for hobbyists that want to compare various amp types, installing two sets of amp boards, sharing one chassis and power supply, with jumpers to select between them would be a ton cheaper. Especially for First Watt projects which tend to have the same PSU’s and cooling requirements.
Now let’s see if I get even one SIT amp finished!
It can be done with switches. At each power supply voltage and each channel, determine the trimmer resistances for each channel (for the CCS trimmer include the resistor value that is in series with the trimmer). That means for each power supply voltage the Iq and SIT Vds need to be chosen and then the trimmers adjusted to suit. Once the resistances are determined the trimmers, and in the case of the CCS trimmer plus series resistor, can be replaced with resistors of equivalent resistance. These resistors can be placed in the circuit with switches.
The same can be done with the series resistor string in series between the mosfet and SIT. This series resistance in conjunction with the CCS trimmer set Iq. A resistor will likely need to be added for one of the power supply voltages.
My thoughts on the Tokin SITs is that they are capable of high power dissipation so why not take advantage of that property. It also allows owners of lower sensitivity speakers to try SIT amplifiers.
I also believe high sensitivity speakers benefit from more amplifier power, especially if the bass drivers are large. More power is better.🤓
The same can be done with the series resistor string in series between the mosfet and SIT. This series resistance in conjunction with the CCS trimmer set Iq. A resistor will likely need to be added for one of the power supply voltages.
My thoughts on the Tokin SITs is that they are capable of high power dissipation so why not take advantage of that property. It also allows owners of lower sensitivity speakers to try SIT amplifiers.
I also believe high sensitivity speakers benefit from more amplifier power, especially if the bass drivers are large. More power is better.🤓
Yeah that was the original idea, but thanks for the specifics, and as I mentioned I completely understand the appeal of a single transistor clapping out enough power to try speakers that weren’t possible before. And yeah, all my woofers are 15”
I’m getting fired up! I have the SITs here in Costa Rica but need to pick up the other parts next time I’m in the US.
I’m getting fired up! I have the SITs here in Costa Rica but need to pick up the other parts next time I’m in the US.
I get that. I'm trying to follow in Ben's footsteps here and figured out if I erred. The top PCB is mine. The bottom is his.
Regards,
Dan
Regards,
Dan
Long thread. I may have mistakenly posted one of Ben's PCBs that was still being revised. I'm having trouble getting the correct Iq on the CCS so I'm investigating.
Regards,
Dan
Regards,
Dan
What are trying to do? Increase or decrease Iq?
And what resistor values are you using right now at R4 and between the mosfet and SIT? And what Iq range are you getting?
If you reduce R4 you will increase Iq.
And what resistor values are you using right now at R4 and between the mosfet and SIT? And what Iq range are you getting?
If you reduce R4 you will increase Iq.
Increased R7 and R8 to 0.15. R4 is 16K. RV2 is 10K. Iq is around 1.9A with no discernible adjustment.
Regards,
Dan
Regards,
Dan
I just checked with LTSpice and yes, there is not much change to Iq, just a bit more than 0.1A.
1.9A and 44VDC power supply is a good operating point though, and is a good fit for a First Watt amplifier sized chassis.
If you want more adjustability, change R4 to 5k, and change two of R9, R10, R11 to 0.15R 3W (KiCad and PCB designations). That should allow a range of 1.75A to 2.3A. If the trimmer is changed from 10k to 20k, the range would increase to 1.6A to 2.3A, all according to LTSpice simulations. Note that parts in my LTSpice simulation have different designations than the ones in my KiCad schematic and PCB. There are other possible combinations too.
Unlimited current range is not feasible. 🙂
1.9A and 44VDC power supply is a good operating point though, and is a good fit for a First Watt amplifier sized chassis.
If you want more adjustability, change R4 to 5k, and change two of R9, R10, R11 to 0.15R 3W (KiCad and PCB designations). That should allow a range of 1.75A to 2.3A. If the trimmer is changed from 10k to 20k, the range would increase to 1.6A to 2.3A, all according to LTSpice simulations. Note that parts in my LTSpice simulation have different designations than the ones in my KiCad schematic and PCB. There are other possible combinations too.
Unlimited current range is not feasible. 🙂
When I posted my 44VDC power supply version, the goal was to be able to build it using my pcb and with a minimum number of changes to parts. And 1.9A was a reasonable Iq in conjunction with 44VDC. 🤓
