Passive Volume Control for DACs/Sources

Discussion in 'Digital: DACs, USB converters, decrapifiers' started by Madaboutaudio, Dec 20, 2015.

  1. Thenewerguy009

    Thenewerguy009 Friend

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    Can you take a picture of the insides?

    The Goldpoint just passes the signal, it doesn't have any power cord connected to it to power it, right?
     
  2. GoodEnoughGear

    GoodEnoughGear Evil Dr. Shultz‎

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    No power cord...purely passive.
     
  3. wormcycle

    wormcycle Friend

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    As @GoodEnoughGear said it is a passive volume control, no power
    [​IMG]
    [​IMG]
    That's the picturu from Goldpoint web site. I opened my unit and the red and yellow (right input and left output wires are fried:, isolation is brown, and the chassis paint above those wires is damaged , looks like by flames.

    [​IMG]
     
    Last edited: Jun 4, 2019
  4. bilboda

    bilboda Florida boomer

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    You'l have to open it up and look for shorts and broken resistors, loose solder, etc.. The switch itself could be failing which may be hard to see but should be obvious when turning the dial. Solder touch up or resistor replacement may be the answer.
     
  5. rlow

    rlow A happy woofer

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    How long ago did you buy it? Did you get the original receipt? Could you contact the seller to see if he has it? You may be able to get warranty support from Goldpoint.
     
  6. wormcycle

    wormcycle Friend

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    The seller bought it on July 15 2018 directly from Goldpoint, I have the original order and paypal receipt. I bought from him few weeks ago and the unit was new. He is a good guy and is helping me.
    Contacted Goldpoint and waiting for response. The chassis inside looks like this thing was literally on fire for few secs. I a bit disappointed, everything is connected to pretty good power conditioner, grounded etc.. So fingers crossed..
    But I was scared like hell for a moment I did not now where the fumes were coming from. But everything else works when I connected BHA-1 as preamp in place of SA1X.
     
  7. atomicbob

    atomicbob dScope Yoda

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    The Goldpoint is a completely passive device. It has no power supply, stores no energy and is not capable of the damage described. Normal audio line level signals also do not have the energy to cause such damage. The source and output devices to which the SA1X was connected must have developed a significant potential between them for such damage to be possible. If so, this is a dangerous situation and should not be taken lightly.

    Measuring AC and DC voltages on the various pins between source and output devices would be prudent. Do this carefully as if a fault exists, risk of electrocution is possible.

    In my lab, dozens of DACs, Amps, Preamps, and other devices have been interconnected using SA1X, SA2X, SA1 and SA2 with no such damage ever occurring, no sparks, no potential differences (voltage.) No trouble hot patching either, provided downstream equipment is suitably muted or electro-acoustic drivers (headphones, speakers) disconnected.
     
  8. Thenewerguy009

    Thenewerguy009 Friend

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    I have been scouring the internet for different passives & the prices are ridiculous if you want to try something above the Sys or Khozmo/Goldpoint price points with a transformer.

    I did find two Chinese Transformer volume controlled passives, both for around $150-ish.

    https://www.ebay.com/itm/HiFi-10K-4...eamp-Permalloy-Audio-Transformer/254164032876

    https://www.aliexpress.com/item/4-w...mer-converter-passive-preamp/32994541826.html

    Anyone with a good eye on what to look for, to know if they would be decent buy or should I stay away?

    Mind you in my search, every other TVC or AVC is a minimum of $900 (except for Prometheus) & most averaging close to $2,000, all while having the internals look exactly like those two cheap Chinese preamps. Two very small transformers with wires connected to RCA inputs & outputs & a potentiometer. Some with a lot with much more sloppy wiring that the two above as well.
     
  9. Taverius

    Taverius Smells like sausages

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    Tbf that's because good transformers are f'ing expensive.

    There's a reason a SET costs so much more than an OTL, and a silver dna stellaris commands a four figure premium over the normal version.

    Not saying all those trafos are good, but good trafos are not cheap.
     
  10. Thenewerguy009

    Thenewerguy009 Friend

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    I think I saw aliexpress selling those small transformers for like $15 or something. None of these TVC/AVC preamps have massive transformers that you see in SET or power amp. They are tiny transformers that can fit in the palm of your hand & they are sold dirt cheap.

    Even the $3,000 TVC I I see, have those small trafos as well. Maybe a bit better quality, but I can't see the price of them alone being hundreds of dollars.
     
  11. Thad E Ginathom

    Thad E Ginathom Friend

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    Well, pre-amps have always been expensive. My audio antique, currently sitting in the repair man's shop while I decide if I want to spend money on its restoration) was $1,000 two decades ago. Transparent, it seems, was (and still is?) expensive.

    Want a piece of wire with gain? That's going to cost you a lot. Hmmm... looks like a piece of wire with just attenuation might cost at least as much.

    Something cheap from ali-express? Try it. You might get lucky. We all love a giant killer! Or if you really think that the sum is too much for the parts, buy the parts and DIY.
     
  12. Cspirou

    Cspirou They call me Sparky

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    Smoke out of a passive preamp is really weird. Usually shorting the input of an amp is not a problem, but shorting the outputs of source gear can be an issue. However output impedance is usually high enough to where you shouldn't get smoke.

    If you really did get smoke you should have some black marks in there somewhere. Open it up and investigate.
     
  13. Thenewerguy009

    Thenewerguy009 Friend

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    Yeah, I'm going to test my luck & buy one of them. Better than spending over a grand on one of the other boutique brands that don't really seem to be built better internally.

    Anyone know which of them would be better from the spec they give? I'm clueless on this stuff. There seems to be two differences between them.

    The eBay one is 100K chip stepped potentiometer.
    The Aliexpress one has a 24-stepped potentiometer.

    The eBay one has the primary and secondary inductances of 1320H to 1380H.
    The Aliexpress one has the primary and secondary inductances of 1000H to 1600H.
     
  14. Argopo

    Argopo Facebook Friend

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    @Thenewerguy009

    Those two passive units are not TVC.

    They are 1:1 or 1:4 isolation transformers coupled to resistor-based pots using SMD resistors. The transformers isolate or provide a step-up in gain, and the resistors attenuate volume.

    TVC units and AVC units attenuate volume using the windings on the bobbins.
     
  15. Thenewerguy009

    Thenewerguy009 Friend

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    Simple if you can solder what looks to be dozens & dozens of tiny wires to small connectors.
     
  16. bazelio

    bazelio Friend

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    Yeah, probably very few folks are building their AVC with a loose autoformer as the starting point when for a couple hundred extra you can get it pre-wired to the switch decks. Then it's just a matter of wiring up inputs and outputs, and is a beginner level project at that point.

    Figure, new from Slagle, $425 for the minimalist pre-wired standard taper AVC.
     
  17. wormcycle

    wormcycle Friend

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    I know this is why it is so disturbing, although I sent the unit to Goldpoint I doubt very much they will find anything wrong with the wiring. I think the best I can hope for is that they find out what got fried and it will not cost a fortune. When I looked inside it is simple soldering as long as I get parts.
    I was testing the Bryston 2B LP power amp with SAX1, the DAC is BDP-2. The amp was working with Big Knob before, no issues. It happened when I turned on the amp. Thankfully the 2B is gone, working with no issues in my friend's home theater setup. I have no idea what went wrong and how I could have prevented it.
     
  18. ogodei

    ogodei MOT: Austin AudioWorks

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    As said above the goldpoint has no power, so if its burnt it took a surge from something else. Betting me says there was a short in the amp somehow, say you directly-coupled a speaker output or two by having the cables crossed by accident. When you turned on the amp the power ramp up combined with the short, power arched inside the amp to the input lines, then smoked the first resistor it came to.

    Would be a pretty random event but makes sense to me.
     
  19. Argopo

    Argopo Facebook Friend

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    "Say hello to my little friend..."

    [​IMG]

    So, this is my DIY autoformer. I wound the AVCs myself at Dave Slagle's place when he still had the loft in New York. This is many many years ago. Winding magnet wire onto bobbins is the most stressful form of DIY. Huge respect for guys like Dave Slagle who make these parts for us DIYers.

    Just look at that rat's nest. Complete disregard for good wiring techniques. Looping wires, un-twisted signals. Kinda of a dumb way to ground the RCA chassis connectors. Good lord what an eyesore.

    This AVC has been sitting on my shelf for years. Since I gave up on speakers for headphones, I had no need for a single-ended preamp since I needed balance for my headphone amp.

    But, in late 2018 I went back to speakers. Been using my Freya as the preamp of choice for both my headphone amp and speaker amp. Recently, because of @rlow 's experience with the Schiit SYS, I decided to swap out my Freya for the SYS for my speaker system.

    But, then for shits and grins, I decided to dust off my DIY AVC to have a listen.

    Shockingly, it actually sounded pretty good. Totally forgot how good magnetic volume control was. Also, no buzz, no hum no noise despite the nasty wiring.

    Now, because of @bazelio and @sfoclt and their DIY efforts with Dave's silver AVC, I am considering ordering Dave's current silver versions. And putting it in a nice box. But, with a cleaner approach to layout and wiring.

    Here are the side views:

    [​IMG]
    [​IMG]
     
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  20. bazelio

    bazelio Friend

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    Haha just as I say most people probably buy the pre-wired switch decks, this guy shows up with autoformers that he wound and then wired up entirely himself.

    Fun project, and impressive job!
     

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