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GB for DC coupled B1 buffer with shunt PSUs

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#1,984
AndrewT said:
we have been here before, discussing VA requirement.

A 3.6VA 15-0-15Vac transformer has a maximum continuous AC current of 120mAac.

When fed into a capacitor input filter the maximum continuous DC current rating becomes 60mAdc after applying the voltage and de-rating factor.
Taking 60mAdc from the 3.6VA transformer will make it run as hot as taking 120mAac from it.
If the relay draws some extra current and the LED draws some extra current and the CCS control draws some extra current then the 60mAdc of the shunt regulator will overload a 3.6VA transformer.

Many builders suggest and I support that body of opinion that the transformer should be rated so that continuous DC load is ~50% of the maximum rated DC current.

This would require a 9VA 15-0-15 transformer for a 60mA CCS Shunt regulator.

This is quite different from most transformer duty.
In amplifiers and such equipment the transformer runs much of the time at <10% of it's rating and copes admirably with short term peak currents that are upto and even in excess of it's maximum rating. That does not apply with a CCS+Shunt regulator.
Click to expand...

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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#1,985
wushuliu said:
As much as I enjoy this forum I really freakin' wish you could modify posts and easily create stickies with all the pertinent information for a project in one place. Having to slog through *multiple* threads with >100 pages just to get up to speed on a project is a nightmare...
Click to expand...

My blog has some information.
Once the new PCB is close, I will update it with pertinent info.

Salas said:
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.😀
Click to expand...

Nude. Cool.
 

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#1,992
jean-paul said:
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.
Click to expand...

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?
 
#1,993
jean-paul said:
Hi, I use a 7VA 2 x 12V 0.292A small toroid without any issues.
Click to expand...
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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#1,995
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.
 
#1,999
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.
 
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