DC offset question.

[Barry]

Although an unfortunate experience for both parties, it is "all water under the bridge", and so not really helpful to bring it up now.

[farflungstar]

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?

Jake - I can't say what caused the damage, the damage became apparent only when the Opus was directly connected to the amp. Before that point all had seemed well. It was only after that that I thought it best to get the amp checked. The Opus may have been coincidence, the truth may be blameless, the Vida likewise, it may even have been a previous fault - I don't know, but I did try the Opus with both the Hiraga amp and the system at school and it was definitely faulty.

[lordmortlock]

Fair enough Adey. Given your last sentence perhaps the two issues (Arc and Opus) were unrelated.

[Jazid]

Checking the Vida is just prudence.

Quite possibly the Opus could have had a drying capacitor when sold but any dc was stopped by the sellers kit (which is the whole point of input PLUS output caps), clearly not so in Adrian's kit, and anyway might have become rapidly worse in its new home. Or it could be the Truth going unstable. Or a dodgy valve running away in the power amp and the techie just slightly deflecting the cause away from ARC?

We may never know, just trying to make sure Adrian's kit works without issue in future.

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[farflungstar]

Checking the Vida is just prudence.

Quite possibly the Opus could have had a drying capacitor when sold but any dc was stopped by the sellers kit (which is the whole point of input PLUS output caps), clearly not so in Adrian's kit, and anyway might have become rapidly worse in its new home. Or it could be the Truth going unstable. Or a dodgy valve running away in the power amp and the techie just slightly deflecting the cause away from ARC?

We may never know, just trying to make sure Adrian's kit works without issue in future.

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I'm driving myself to distraction over this because of the many variables. I've put in all new tubes into the ARC. I'm going to measure the Vida for DC, remeasure the truth for DC. But even if all is 0 because I dont know the cause of the fault I just don't know if I should power up. They only other option is to buy something to replace the truth and wait till it arrives, then it's a question of buy cheap but get the best in a few months or try to get something excellent at a decent price now. It's so frustrating having already v waited 3 months for the amp to be sorted.

[Primalsea]

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.

Adrian,

From looking at a photo of the Vida circuitboard there seems to be 4 relays. I suspect that two of these are to isolate the output until the powersupply has stabilised. These are to stop load thumps at power on. The relays will engage shortly after the power button has been pressed. This is quite common in source components.

Next would be to modify a set of interconnects so you can ground the inputs of the Vida. You can do this by stuffing some alu foil inbetween the pin and the outer ring on the phonoplugs at one end of the interconnects. Do this to both left and right and so that the foil contacts both the outer ring and the pin of the RCA phono plug. When you plug the other end of the interconnects into the input of the Vida this will ground the inputs. You do this so that you measure the circuit in isolation and not any noise that is being picked up and amplified by the Vida.

If you can do this and take DC and AC voltage measurements at the outputs of both channels of the Vida, using the smallest range on the DMM, and post a photo of the DMM for each of the 4 measurements (DC left/right, AC left/right) we can see what is happening with the Vida and hopefully discount it.

I strongly recomend that you work through each bit of kit separately in a methodical manner rather than just performing shotgun tests.

[Primalsea]

I'm driving myself to distraction over this because of the many variables. I've put in all new tubes into the ARC. I'm going to measure the Vida for DC, remeasure the truth for DC. But even if all is 0 because I dont know the cause of the fault I just don't know if I should power up. They only other option is to buy something to replace the truth and wait till it arrives, then it's a question of buy cheap but get the best in a few months or try to get something excellent at a decent price now. It's so frustrating having already v waited 3 months for the amp to be sorted.

The point is to remove the variables and perform tests in a methodical way that will gradually give us a good picture of what is going on. A complex problem is usually a series of simple problems all combined together. Forget the Truth for the moment, we can get to measuring that later.

[Jazid]

What about the phone idea? Costs nothing (if you have a smart phone), just a simple cable. At least you will know the power amp is working fine and have music.

Alternative solutions include cheap class d amps which can be had on amazon for £25, next day delivery, that you can plug the (checked for dc) Vida into and off you go, music. If the amp complains then it's the Vida, if not connect the Vida to the Truth and then the cheapo amp. If the amp now complains, it's the Truth. If all's ok it's between the ARC and the Truth, so you could either buy a cap coupled buffer with volume control, Pass B1 &c is probably available reasonably cheaply and pretty transparent, or even a pair of line level 1:1 transformers to isolate the dc between Truth and Arc. This will get you going. But using two dc coupled components in series is a recipe for disaster, most especially if one kicks out 10V when it's unhappy.



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[farflungstar]

The point is to remove the variables and perform tests in a methodical way that will gradually give us a good picture of what is going on. A complex problem is usually a series of simple problems all combined together. Forget the Truth for the moment, we can get to measuring that later.

Hmmm, I don't like the idea of shorting the inputs on a 5K phonostage - but I just tried something.

With the truth switched off (it cannot be on without a source and the vida is the source) I measured the Vida at switch on, only for DC, set at 200m. Both channels behaved the same at start up, fluctuating between -00.0/00.0/00.1/00.2/00.0 - then between 00.0/00.1 for the few minutes I monitored. This may be the noise you mentioned?
Set at 2000m the readings were 000.

Then i reconnected it to the truth and monitored the truth at start up, set at 200m.
01.8, gradually falling to 00.4 on one channel, - 00.4 the other.
Set at 2000m, 000.

Now, I dont understand what 01.8 means at the 200m setting - I'm stupid and it's Chinese to me.

What I do know is that although I never turn off the truth so it shouldn't get that initial spike, here in Spain, in summer and winter the electricity often goes down 2 or 3 times in a day. It can drop for only a second and has happened with the system on.

Now, when I first measured the truth the other week the offending channel was reading 01.7 at 200m 'steady state' meaning not at switch on, so this could have doubled when electricity failed and the unit switched back on before dropping back to 01.7.

Could this the problem.....

Jazid - the amp should be fine after a 900€ service and soak test. It just needs to be switched on and the new tubes biased. I get the phone thing, but my phone headphone Jack doesn't work.

I've posted a wanted ad for a transformer based volume controller. I'm also waiting for Pieter from Tribute to get back to me about pricing for two mono units. My preference is the Slagle Emia, but at 3k I just can't afford that until September. Im kicking myself for selling my old slagle, and for backing out of the LM VO2 from Jake last year. We live and learn. But looking at those numbers from the Truth, and knowing the vagaries of the supply here in Spain I think I have to ditch the Truth.

[Primalsea]

I’m sorry Adrian, but I cannot help you. I feel for what you are dealing with, I really do. As I have explained you need to have a methodical approach to solving this, especially if you have limited knowledge of the technical issues. Performing shotgun tests the results of which you don’t know how to interpret is not helping.