Hi, I use a 7VA 2 x 12V 0.292A small toroid without any issues. Very small, light, convenient, not expensive, no overvoltage and no excess heat. It stays relatively cool after hours of use. So I would suggest this one is up to the job, it is a Talema or Nuvotem 60032.
Nuvotem Talema Toroidal Power Transformers - Standard Mini Series - 60000
Nuvotem | Transformers | Transformers | Toroid Transformers | Toroidal Mini Open Style 115-230Vac Primary 1.6VA to 7VA |60032
This toroid is used for a Mezmerize with standard config ( no hotrod, I like my power bill to be low and my conscience to be clean
). IMO there is no need for a bulky 50 VA transformer when using the standard setup. It should not be too light either but this one is just right. I managed to squeeze everything in a 240 x 135 mm case. After years of useless over-dimensioning everything I finally learnt to choose parts in the right balance.
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My blog has some information.
Once the new PCB is close, I will update it with pertinent info.
The reason is we made it shooting for very good subjective quality. A 50VA isn't that expensive, its a typically much available rating and gave it space to play with higher CCS also. This is constant draw bias and cores sweat much easier. So we chose big. I would run it from 2 300VA R-Core even with 2A per side CCS, and nude Z foil signal path resistors if it was my fixation. Tight point to point air dielectric construction with solid silver hook up wire, monoblock 1.2 remote sensed regs, LSPD pot. But I am not that fixed.
Nude. Cool.
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That's good to know. It's more what I had in mind in the first place. The benefits of using a small tranny is def worth it. Just so you can use a standard external AC adapter. That way, no mains voltage to deal with, smaller & cheaper casework, no ground loop worries (considering this is unbalanced gear too), class II PSU too. So I am a big fan of this.
Just remembered you can easily find external PSU off the shelf that is 12V AC unregulated at 3A. Sometimes advertised as CCTV power supply. Like this one... Rapid Electronics - 12v 3A AC adapter. It would be enough current for the B1.
My idea is if the new boards could accept single AC input for power, then they could work with external AC adapters as well as internal transformers. It is just a slightly different arrangement of diodes, maybe it could be an optional component if there is space? All is needed is a volt doubler like this... Power Supply for Preamps. What do you think?
Exactly JP.
Using the correctly rated transformer gives good reliable performance.
Anything more than that is for apparent sound quality reasons alone.
Your 7VA 12+12Vac transformer can supply ~73mAdc continuously for ever.
What more do you need for a 60mA CCS shunt reg? That's 13mA or so to spare to hold in two 12V relays and control current to the CCS.
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and we are discussing/offering experiences and advice on whether a 3.6VA or 7VA or 9VA can do the PSU job successfully or not.
The same principles apply if you want to "hotrod" the original B1, or "hotrod" the original DCB1, or design for a "hotrodded replacement" for the DCB1.
You must first understand the needs and then the design can progress. It is not guesswork.
The same principles apply if you want to "hotrod" the original B1, or "hotrod" the original DCB1, or design for a "hotrodded replacement" for the DCB1.
You must first understand the needs and then the design can progress. It is not guesswork.
7VA 12+12Vac is adequate for the original DCB1 that had a 60mA CCS current.
9VA 15+15Vac is also adequate for a 60mA DCB1.
Change to 250mA CCS and for a rough guide to the VA rating of the transformer
use the formula
250/60 * 9VA = ~38VA 15+15Vac. The arithmetic is easy.
There is no advantage in guessing.
9VA 15+15Vac is also adequate for a 60mA DCB1.
Change to 250mA CCS and for a rough guide to the VA rating of the transformer
use the formula
250/60 * 9VA = ~38VA 15+15Vac. The arithmetic is easy.
There is no advantage in guessing.