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Thread: DC offset question.

  1. #31
    Join Date: Feb 2013

    Location: W Lothian

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    I'm Grant.

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    Quote Originally Posted by lilolee View Post
    Why don't you connect up the Slagle to the ARC and some speakers and connect an mp3 player/phone to the Slagle and play some music. That takes everything else out of the equation. You could also open up the cdp and check if there are caps on the output (there usually are) and then you could try that as a source.
    he sold the slagle...keep up
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  2. #32
    Join Date: Apr 2012

    Location: London

    Posts: 685
    I'm James.

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    I am horrified to read that your preamp will output 10V dc if it isn't connected to a source (I am wondering if that mightn't be load) . What if the source is connected but turned off, what if there is a blocking capacitor, what if there isn't in the power amp (as is the case here)?

    This is unstable behaviour and has no place in a purportedly high end component. If it was mine I would now remove the Truth and replace it with a buffer, pretty much any buffer, still using your passive attenuator, and enjoy the amp.

    Was it you who sold me a homebrew BB OPA627 'pre' some years ago? If so I'd be happy to post it to you if you'll return it/buy it back when you're done, no time constraints? It is neutral, runs off a 9V battery, and doesn't misbehave. If it wasn't you then it ain't a beauty but functions fine! PM me if interested?

    Sent from my GT-I9195 using Tapatalk

  3. #33
    Join Date: Feb 2010

    Location: Maidenhead, Berks

    Posts: 288
    I'm Lee.

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    Quote Originally Posted by struth View Post
    he sold the slagle...keep up
    Oops, I was just looking at his list of kit in his signature.

    Ok then direct connect your phone to the amp and play music, even simpler. That way you can test the amp.

    As Jazid says put a buffer in, or stick some nice quality DC blocking caps in line. HiFiCollective have a very nice range, or I'm sure many here could advise.
    Cheers Lee

  4. #34
    Join Date: Apr 2012

    Location: London

    Posts: 685
    I'm James.

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    Even better, and don't forget to turn the volume right down on the phone first!

    Sent from my GT-I9195 using Tapatalk

  5. #35
    Join Date: Aug 2008

    Location: Suffolk, UK

    Posts: 1,473
    I'm Paul.

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    Quote Originally Posted by Jazid View Post
    I am horrified to read that your preamp will output 10V dc if it isn't connected to a source (I am wondering if that mightn't be load) . What if the source is connected but turned off, what if there is a blocking capacitor, what if there isn't in the power amp (as is the case here)?

    This is unstable behaviour and has no place in a purportedly high end component. If it was mine I would now remove the Truth and replace it with a buffer, pretty much any buffer, still using your passive attenuator, and enjoy the amp.

    Was it you who sold me a homebrew BB OPA627 'pre' some years ago? If so I'd be happy to post it to you if you'll return it/buy it back when you're done, no time constraints? It is neutral, runs off a 9V battery, and doesn't misbehave. If it wasn't you then it ain't a beauty but functions fine! PM me if interested?

    Sent from my GT-I9195 using Tapatalk
    Yes, I’m a bit worried by this too. If the source has relay switching or muting at the outputs then a momentary activation could cause the Truth to output a large DC voltage, based on what has been said.

    Adrian, I really feel for you. You have invested a lot to have a good system and it has gone pairshaped. However, often the most seemingly dire issues can be the simplest to resolve, although they don’t seem so at the time.

    Im sure we can help, but I think we should start right at the beginning and help you work through each piece of equipment one by one methodically.

    If you’re interested can you list your system setup source to power amp and we will go step by step.
    ~Paul~

  6. #36
    Join Date: Dec 2015

    Location: Alicante. Spain.

    Posts: 1,885
    I'm Adrian.

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    SP10/Reed/Allaerts/Vida/hashimoto hm-x/Truth/ARC Ref 75/Tannoy Kensington - all interconnects VDH Integration. Speaker cables Townsend Isolda.

    It's typical that I'm in this position towards the end of the academic year when money is tight! I might just buy a very cheap passive to use for the summer and in September I can buy one of the Slagle Emias (very expensive). Just silly if in fact the truth isn't/wasnt the problem - but that doubt persists. Unhappy bunny .

    How would i fit a DC blocking cap at the outputs?
    Technics SP10 mk2
    Jan Allaerts MC 1 Boron mk1 cart
    Miyajima Shilabe cart
    Hashimoto HM-X SUT
    Siggwan (gimballed not unipivot) Cocobola 12"
    Aurorasound Vida LCR Phonostage
    The Truth linestage
    Dave Slagle Autoformer Volume Controller
    Cary 805c SET amps
    Audio Note ANe-SPX speakers
    Townshend Isolda speaker cables
    Cardas Golden Presence interconnects

  7. #37
    Join Date: Aug 2008

    Location: Suffolk, UK

    Posts: 1,473
    I'm Paul.

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    Okay. For now we can ignore the TT, cart, SUT.

    Vida- looking at the circuit I can see some relays. I rekon that two of these are for disconnecting the output of the Vida during switch on, off and possibly if there is a fault or an overload. Sometimes the relay will switch the central pin of the output phono socket to ground, but this depends on the design and sometimes the relay may just disconnect the pin of the phono socket. Effectively this will either ground the input of the Truth, or just disconnect it. Either way the input of the Truth will be disconnected at some point. Even if the relay grounds the input there will be a very short period of time when the relay is between connecting the output of the Vida and switching it to ground (0V).

    Here I suggest that this could be an incompatibility with the Vida and the Truth. However, we should still check the Vida with a multimeter (DMM from now on) and a oscilloscope if possible, this will be the next stage.

    Before we move on can anyone add anything else, or see any technical issue with what I have said?
    ~Paul~

  8. #38
    Join Date: Dec 2015

    Location: Alicante. Spain.

    Posts: 1,885
    I'm Adrian.

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    Quote Originally Posted by Primalsea View Post
    Okay. For now we can ignore the TT, cart, SUT.

    Vida- looking at the circuit I can see some relays. I rekon that two of these are for disconnecting the output of the Vida during switch on, off and possibly if there is a fault or an overload. Sometimes the relay will switch the central pin of the output phono socket to ground, but this depends on the design and sometimes the relay may just disconnect the pin of the phono socket. Effectively this will either ground the input of the Truth, or just disconnect it. Either way the input of the Truth will be disconnected at some point. Even if the relay grounds the input there will be a very short period of time when the relay is between connecting the output of the Vida and switching it to ground (0V).

    Here I suggest that this could be an incompatibility with the Vida and the Truth. However, we should still check the Vida with a multimeter (DMM from now on) and a oscilloscope if possible, this will be the next stage.

    Before we move on can anyone add anything else, or see any technical issue with what I have said?
    I think the relays are part of the power supply to the Vida, they click Street switch on. I will clarify with the maker if a source that is switched off has an effect - though I can't believe it would, that is crazy. The amp is never on unless everything else is powered up.

    I haven't measured the truth with the Vida switched on, connected yes. I will check it later and see if that has any effect on readings.
    Technics SP10 mk2
    Jan Allaerts MC 1 Boron mk1 cart
    Miyajima Shilabe cart
    Hashimoto HM-X SUT
    Siggwan (gimballed not unipivot) Cocobola 12"
    Aurorasound Vida LCR Phonostage
    The Truth linestage
    Dave Slagle Autoformer Volume Controller
    Cary 805c SET amps
    Audio Note ANe-SPX speakers
    Townshend Isolda speaker cables
    Cardas Golden Presence interconnects

  9. #39
    Join Date: Apr 2012

    Location: London

    Posts: 685
    I'm James.

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    Quote Originally Posted by farflungstar View Post
    SP10/Reed/Allaerts/Vida/hashimoto hm-x/Truth/ARC Ref 75/Tannoy Kensington - all interconnects VDH Integration. Speaker cables Townsend Isolda.

    It's typical that I'm in this position towards the end of the academic year when money is tight! I might just buy a very cheap passive to use for the summer and in September I can buy one of the Slagle Emias (very expensive). Just silly if in fact the truth isn't/wasnt the problem - but that doubt persists. Unhappy bunny .

    How would i fit a DC blocking cap at the outputs?
    Quote Originally Posted by Primalsea View Post
    Okay. For now we can ignore the TT, cart, SUT.

    Vida- looking at the circuit I can see some relays. I rekon that two of these are for disconnecting the output of the Vida during switch on, off and possibly if there is a fault or an overload. Sometimes the relay will switch the central pin of the output phono socket to ground, but this depends on the design and sometimes the relay may just disconnect the pin of the phono socket. Effectively this will either ground the input of the Truth, or just disconnect it. Either way the input of the Truth will be disconnected at some point. Even if the relay grounds the input there will be a very short period of time when the relay is between connecting the output of the Vida and switching it to ground (0V).

    Here I suggest that this could be an incompatibility with the Vida and the Truth. However, we should still check the Vida with a multimeter (DMM from now on) and a oscilloscope if possible, this will be the next stage.

    Before we move on can anyone add anything else, or see any technical issue with what I have said?
    You've got a lovely kit list, its not a disaster, just a compatibility problem. Once again I suggest that you get the Truth out of the system for now. It can come back once you have made sure everything else is happy if you can bring yourself to do so. An element that is not unconditionally stable could/will make a mockery of any help given irrespective of whether it has amazing sonic attributes when behaving... The rest of the kit is available on the open market so shouldn't suffer such issues.
    So saying - for safety and to tick it off the list - do as Primalsea suggests and check the output from the VIDA for DC using your multimeter on the 200mV setting and report back. Using your SUT will block the dc but using a SUT as a dc blocker is wrong in many ways. If you can get access to an oscilloscope it would help strike off potential issues but if not no stress.

    I'd also try the phone straight into the power amp, it's overwhelmingly likely to work straight away, costs you just a cheap cable (I have old phones that provided them in the box), and will give you some music while you work

  10. #40
    lordmortlock Guest

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    Quote Originally Posted by farflungstar View Post
    This is my worry. I really can't say for absolutely sure what caused it (the techie said it was DC at the input) - but what other equipment did it? The problem came up (or was very apparent) when I bought that ill fated CDP and connected it direct to the amp using its inbuilt volume. That was returned but I cannot be 100% sure it was the cause.
    As I read through this I can't help but feel sorry for the seller of the Resolution audio Opus 21 CD player, as it sounds like his unit may not have been the cause of the problem after all.

    He got a bit of a kicking on here iirc, and in light of this thread does that not seem rather unfair?

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