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Dear Twisted Pear,
I want to replace the switch mode supply in my studio mixer (opamp based design with THREE phono channels). I measured the stock supply outputs: +/-17.5Vdc from switch mode supply. The back of mixer indicates that it uses 37va.
My goal is to put together a linear PS of the highest quality so I can max out the sound of this mixer. Now some questions:
1. Which of the Twisted Pear supplies would be the most appropriate? Why?
2. Is it a good idea to put the Twisted Pear supply externally (lets say at the floor) and run a 3-4 foot power wire to to the mixer? Does it make a difference, and anything I need to be cautious with?
3. I have an R core transformer with a pair 18v secondaries and it's rated 30va. Can I use this one or should I get a more appropriate transf for my application?
Thank you,
Herman
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Does the mixer consume 37ma? VA is not normally used to measure consumption. Edited by user Thursday, December 11, 2014 12:15:35 AM(UTC)
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If it is consuming < 500ma I would say that the Placid-HD/BP is perfect for your application. Super low noise - and superb load regulation. That transformer should work fine up to 17V rails especially if your load is < 100ma.
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Originally Posted by: Russ White  Does the mixer consume 37ma? VA is not normally used to measure consumption. Hello Russ, I confirmed with the manufacturer. The required supply is: +17.5V and -17.5V (0.5 A every one) They never must exceed 18V. I need the above power. regards, Herman edit: I believe 0.5 (per rail) A is a bit overkill for preamp but this is what the manufacturer recommends. I am guessing that 0.4 A per rail would be ok. Edited by user Thursday, December 11, 2014 3:40:52 AM(UTC)
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Either the LCBPS or Placid BP HD would work fine for this.
The LCDPS will generate less heat. The Placid will be quieter.
I am assuming your mixer uses opamps for mixing duties, so it is likely the PSRR is high, so you can probably get away just fine with the LCBPS.
I would not mount the supply in a different chassis with long cables if you do not have to. It will just invite noise into the power lines, and reduce the supply's ability to sense/react to load.
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Dear Brian,
What voltage and Va rating transformers would you recommend to get +/-17 Vdc out of either LCBPS or Placid BP HD @ 0.5A per rail?
I am NOT sure I can fit both transformer and one of your boards inside my mixer chassis. If I make an external box, with about 4 feet of umbilical cord, do you recommend:
1. mount transformer and your board
or
2. try fit the board only in the mixer and keep transformer in the external box
Comparing Placid BP HD to other regulators such as Jung superreg, or Teddy, are they in the same league in terms of clean power output?
thanks,
Herman
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Hi,
since no response, I will assume that to get +/-17 (17.5)v I will need an 18v transformer with two secondaries. I want to get the most out of the Placid so please correct me if I am wrong. Also, if I understand correctly, the Placid boards need to be as close as possible to the load, meaning I should install them inside my mixer enclosure. I have enough space in there.
Now the essential thing is I need to have a good grounding plan so that I do not get any buzz/hum. Because this is a Phono mixer, it has a ground terminal for the turntable. How to I run the grounding if I am using an external case for the transformer?
Will I need to run a separate ground from the mixer ground terminal to the Placid board, to transformer housing, and then to the outlet ground. Am I picturing this incorrectly?
thank,
Herman
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Please clarify the above so I know for sure the Placid can provide +/-17.5 @ 0.5A per rail. Also recommended voltage transformer?
thank you,
Herman
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Yes, it can provide +/-17.5V @ 0.5A. The 18V (dual secondaries) would be a good voltage, at 50VA or more.
As for the grounding, it is hard to say, and will depend mainly on the grounding scheme of the mixer.
You should start by tying the mains ground to the transformer chassis. Be sure to use a fuse on the mains lines as well. Since you are running the transformer output to another enclosure, you should also fuse the transformer outputs in the transformer enclosure to protect against shorts.
As for grounding the Placid output, you should follow the example of the current power supply. The easiest thing to do would be to tie the Placid's GND output to the ground point of the supply you are replacing.
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Thanks!
Do you have the transformer in question by chance? If so please add to my Placid HD order.
regards,
Herman
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I do not currently carry 18v transformers, sorry.
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Got my Placid and assembled it. Everything looks correct and now it is time to test/adjust.
What is the purpose of CCS current adjustment?
I will need +/-17.5v and the ability to have 0.5A on each rail.
I understand about adjusting voltage to slightly below my needs. How do I determine the setting of CCS?
thanks,
Herman
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There are a couple of ways to do it. The recommended way would be to create a dummy load for about 500ma and adjust until the shunted current is about 50ma. Or, if your load is alright being underpowered (most are when used in isolation - meaning nothing else is connected to it) you can just adjust the current until the voltage gets back to 17.5V. Then add a bit until you get 50ma or so overhead (depending on your needs) Edited by user Tuesday, December 30, 2014 12:34:30 AM(UTC)
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Hi Russ,
got my Placid working. I understand your instructions, however one basic question: what is the purpose of the adjusting current? I though the load (studio mixer in this case) will draw whatever current it needs and the more there is available, the better for sound quality? Does adjusting the current mean limiting the current?
Clarification: i understand the reason to adjust the output voltage, but not output current.
thanks,
Herman
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Hello,
I recently built my bipolar Placid HD, adjusted it per user guide, and did a comparison with the stock SMPS. Some interesting observations and questions. Placid is used with a 30watt 18v transformer, output voltage set to +/-17v, current 460mA per rail.
Sound quality comparison -- used with a studio mixer that has many op-amp stages (10 per channel)
Pros:
The Placid HD is much more detailed and smoother in the highs, with a bigger soundstage, and a sense of space. More delicate, and distinct decays of each note. Just overall better resolution.
Cons:
softened attack of each note, compared to the switch mode PS. "Lazier", less dynamic and less focused than SMPS in the bass, and midrange. As a result, "slower" sounding.
So I am trying to figure out, what could be the cause of the softened, slower sound, of Placid?
Do I need to add a big bank of low ESR capacitors on the outputs? Bigger transformer? What gives the SMPS an edge in dynamics/attack/better timing?
regards,
Herman
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 1 user thanked noviygera for this useful post.
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Originally Posted by: noviygera So I am trying to figure out, what could be the cause of the softened, slower sound, of Placid?
Do I need to add a big bank of low ESR capacitors on the outputs? Bigger transformer? What gives the SMPS an edge in dynamics/attack/better timing? Interesting observations! I suggest you try bigger transformer - since i moved from older TPA stock 30VA trafo to 100VA i could easily hear improvements in dynamic and especially in bass - it got firm/punchier/shorter. I actually came back to 30VA a few times to check if it wasn't placebo but difference was all too obvious every time.Could be related to trafo quality though... I also changed electrolytic caps on both Placid HD 2.1 and Legato decoupling to find that (possibly) higher ESR caps make sound less dynamic... Edited by user Thursday, January 8, 2015 10:07:53 AM(UTC)
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Why not adjust the voltage to 17.5VDC, like the SMPS? Also, how much current are you shunting?
Also, if the SMPS consumed 37VA, you will need a larger (VA) transformer, as the Placid is far less efficient than an SMPS. I think I recommended 50VA.
You do not have to replace any components in the Placid.
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Current being shunted is 0.17 and 0.12 v for the channels. Although the Vout and CCS are matched to be identical. Heat sinks are only slightly warm.
If the PlacidHD is half the efficiency of the SMPS, then I would need at least 70vA, correct?
As far as transformers, is it the case where bigger is better? I can easily fit Triad torroid of 100vA or 160vA...
I will get one that you recommend and further post my findings.
Herman
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