goldenreference low voltage power supply

[mwl168]

Built yet another GRLV for my CFP amp. 

This one set for 26VDC rails and the current draw from it is about 1.1A (for a balanced CFP amp with 220mA bias current). Empirical evidence that the GRLV can supply more than 1A current from both rails.

Don't have LT1021 on hand so using LM4040 for voltage reference for now. It's much cheaper but also much higher noise. OP07 in place of OPA134.

Those resistors standing tall and proud is my way of easily adjusting rail voltage while I am tinkering with the CFP amp. They are inserted into Mill-Max headers below.

Cannot really see from the pic but the pass transistors are bolted to a heatsink below.

EDIT: at this current draw, you need to allow for higher dropout voltage and heatsinking for the pass transistors. I would plan for solid 26vac input for 26VDC regulated rails to be safe. 

Edited November 11, 2017 by mwl168

[Pars]

Nice Michael! You seem to like those bridges...

Is this current draw for a balanced amp (4xCFP boards) or a pair?

[sorenb]

1 hour ago, mwl168 said:

Built yet another GRLV for my CFP amp. 

This one set for 26VDC rails and the current draw from it is about 1.1A. Empirical evidence that the GRLV can supply more than 1A current from both rails.

Don't have LT1021 on hand so using LM4040 for voltage reference for now. It's much cheaper but also much higher noise. OP07 in place of OPA134.

Those resistors standing tall and proud is my way of easily adjusting rail voltage while I am tinkering with the CFP amp. They are inserted into Mill-Max headers below.

Cannot really see from the pic but the pass transistors are bolted to a heatsink below.

EDIT: at this current draw, you need to allow for higher dropout voltage. I would plan for solid 26vac input for 26VDC regulated rains to be safe. 

zeners? ...really?

[congo5]

what zeners? no see um

 

[mwl168]

2 hours ago, Pars said:

Nice Michael! You seem to like those bridges...

Is this current draw for a balanced amp (4xCFP boards) or a pair?

Yes, I do like those bridges. This pair is wider than the other ones I used for the SuSy Dynalo so I had to "relocate" the 2 10 R resistors to the reverse side of the PCB. 

Current draw stated is for a balanced CFP amp - 4 boards. 

[jose]

I'm waiting for a pair of "Pars bridge's" [emoji6]

[Whitigir]

Sorry but I am a brick, why use the zeners Bridges instead ?

[Pars]

I think you meant Schottky. They supposedly have lower switching noise than std. silicon rectifier diodes.


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[Ariamella]

Hi there. If I were to go for the GRLV, where would I be able to get boards for it? I can't seem to be able to find any at the moment.

[rumina]

hi jose

i think if you want to adjuste the voltage via rv2/rv1 you don't need the resistors in r7/r8 , r9/r10. 

maybe someone can correct me if i'm wrong, i think either via r7/r8 , r9/r10 or via rv2/rv1, not both.

 

 

[kevin gilmore]

You need all the resistors if you want to adjust the voltage. Otherwise too noisy. The adjust is calculated for about .1% range

[jose]

Hi

I read all thread and I though that all resistors was necesary.

I use this GRLV with my Dynalo SS. I didn´t any adjust (I matched all resistors, leds and I adjusted trimpots on 50K before plug in). With the Dynalo SS connected to this, I can measure; -19,993 volt and +20.000 volt and between rails 40,00volt exact. With no load, same measures.... I hadn´t noises or issues.

I´m using a r-core with 25Vac@1Amp x2 

 

[kevin gilmore]

the pot and the 2 associated resistors are the optional parts. and the values of the resistors change depending on what voltages you want.

none of the 4.5 digit dvm's are accurate enough. Especially since if you reverse the leads you get different numbers. In fact 6.5 digit dvm's are just barely enough and the keithely ones in particular read different numbers if you flip the leads. The agilent ones do not.

7.5 or 8.5 digit dvm's highly recommended.

[wink]

Agilent 4401A is a good 6.5 digit meter

Agilent 3458A is just about the tops.....   8.5digit. We used to use them to calibrate the DC voltage on the Fluke 3500A and 3520A calibrators.

The AC voltages required an AC measurement standard like a Datron/Wavetek 4920  or Fluke 5790A/B as the Agilent 3458A was slightly too soggy.

[rumina]

thanks kevin, learned something new :-)

[Ariamella]

For 30VDC output, would a 25VAC or 30VAC transformer be better, out of the standard ranges? I'm pretty sure it's 30 but just wanted to make sure first.

[ruslanch]

Can I simply replace the tantalum capacitors with electrolytic capacitors? For example, the Nichicon KL series.

[Pars]

For 30VDC output, would a 25VAC or 30VAC transformer be better, out of the standard ranges? I'm pretty sure it's 30 but just wanted to make sure first.

A 2x30Vac SumR is what I am using on mine. The Antek transformers seem to work well also, and much cheaper.


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Can I simply replace the tantalum capacitors with electrolytic capacitors? For example, the Nichicon KL series.

You can do anything you want
Whether it is a good idea or not is another matter. I know I asked Kevin a number of pages ago about using ceramics here and he said he couldn’t guarantee that it would meet the noise specs that he had measured. I would suspect electrolytic would have pretty abysmal performance here. Much higher ESR and leakage I would think.


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[Ariamella]

24 minutes ago, Pars said:

A 2x30Vac SumR is what I am using on mine. The Antek transformers seem to work well also, and much cheaper.

Alright, thank you. Thinking of something like these:

https://airlinktransformers.com/product/chassis-mounting-toroidal-transformer-standard-range-cm0030230

https://www.ebay.co.uk/itm/220V-30W-R-Core-Transformer-for-Audio-AMP-Amplifier-Preamps-DAC-CD-30V-30V/232178765651

[mwl168]

8 hours ago, Ariamella said:

For 30VDC output, would a 25VAC or 30VAC transformer be better, out of the standard ranges? I'm pretty sure it's 30 but just wanted to make sure first.

I would not recommend using 25 vac trafo for 30VDC output. The drop voltage will also vary a bit depending on current draw.

[Ariamella]

37 minutes ago, mwl168 said:

I would not recommend using 25 vac trafo for 30VDC output. The drop voltage will also vary a bit depending on current draw.

Yeah, that's what I figured. 30VAC it is!

[MrSlim]

On 3/19/2017 at 4:46 PM, Kerry said:

Just got the boards back for the GR78/9xx boards.  They look good.  I'm hoping to have them built up next weekend.

Hey Kerry, 

Are you making the Gerbers available for these boards, or do you happen to have a few spares you could part with?    I'm thinking that these might make a nice little +- 15V power supply for a DAC board I have on the way.  I would also thinking about a second + supply for 3.3V, if it could be configured that low.

[masamoto]

For some reason, my transformer just died. I had a 230v/2x24v with 50VA it get's a little warm but that's it normally.

I use it to power a 20V GRLV for a Susy. was that too much for it? I was sure that would be enough.

[cspirou]

1 hour ago, masamoto said:

For some reason, my transformer just died. I had a 230v/2x24v with 50VA it get's a little warm but that's it normally.

I use it to power a 20V GRLV for a Susy. was that too much for it? I was sure that would be enough.

With 24vac you are getting 33Vdc before regulation. Thats a 13v drop and far more then you need. The problem though is for a given VA rating the current capacity goes down as the voltage goes up. You probably sourced too much current and burned out the windings.

get 2 x 18v instead 

[mwl168]

2 hours ago, masamoto said:

For some reason, my transformer just died. I had a 230v/2x24v with 50VA it get's a little warm but that's it normally.

I use it to power a 20V GRLV for a Susy. was that too much for it? I was sure that would be enough.

Agree with cspirou that 13V drop for 20V regulated output is likely excessive.

How much current does your application draw from each rails? The GRLV's dropout voltage varies with load - the higher the load the higher the dropout voltage. 

For my balanced CPA2 amp which I set it up to draw about 1A each rail, I have to use a transformer with 22v secondaries to support 22VDC regulated rails from the GRLV.