Hello there. I'm planing to build the RJM-Sapphire 4 and conflicted about what VA rating transformer to get. Ill be using the dual mono setup with the X-reg board but the dual 25VA transformer seems excessive.
You have to state the bias that you want to choose or headphone loads you want to use.
That determines how low you can go with your VA-rating.
Usually, with class-A, you want something like VA-rating="used DC-power" x2 at least.
I had one of these superb amps (4.1 I believe).
Still have the excel-sheet for version 4.2.
It suggests for a "high-power build" to bias it at 75mA.
Assuming that at 2x12VAC you have max. +-18VDC that would mean a DC-power of 2.7W.
I would guess you can easily get away with 10VA per side or a single 16VA for both channels
without the transformer heating up excessively. If you want to be safe(r) and have more headroom choose 16VA for dual-mono or 25VA for stereo.
If you want to save some money and/or space I´d say go for a single transformer (16 or 25VA)
With separate regulators for each board I dare say that you won´t gain much vs. a dual mono approach.
That determines how low you can go with your VA-rating.
Usually, with class-A, you want something like VA-rating="used DC-power" x2 at least.
I had one of these superb amps (4.1 I believe).
Still have the excel-sheet for version 4.2.
It suggests for a "high-power build" to bias it at 75mA.
Assuming that at 2x12VAC you have max. +-18VDC that would mean a DC-power of 2.7W.
I would guess you can easily get away with 10VA per side or a single 16VA for both channels
without the transformer heating up excessively. If you want to be safe(r) and have more headroom choose 16VA for dual-mono or 25VA for stereo.
If you want to save some money and/or space I´d say go for a single transformer (16 or 25VA)
With separate regulators for each board I dare say that you won´t gain much vs. a dual mono approach.
;-)
NO "dual mono"!
Use only ONE secondary coil/winding! For both amps!
You could use a 2 x 12 V trafo: put the windings in series.
NO "dual mono"!
Use only ONE secondary coil/winding! For both amps!
You could use a 2 x 12 V trafo: put the windings in series.
For starters i'm gonna go with the base power build 35.7mA since i don't have any low impedance hp's. 2*10VA transformer would be the best but after browsing ebay a single 50VA(Toroid(not chinese)) is cheaper 😵. With this knowledge i'm tempted to build the preamp version too so the transformers have slightly more load. Thx for the info and help.
Found out that 50VA trafo's are cheaper than 2 10VA's. I'm planning to use one transformer for all. Spent way too much time drawing this.
Attachments
I see extra boards in front of the sapphire.
Are these pre-regulators?
Be sure to calculate the drop they have so that the sapphire´s on-board regulator still works as intended.
Are these pre-regulators?
Be sure to calculate the drop they have so that the sapphire´s on-board regulator still works as intended.