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JDS Atom amp - volume knob light not turning off ..anyone notice this?

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Feb 13, 2019
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#1
Noticed volume knob light does not turn off when volume knob is turned all the way counter-clockwise and clicked into off position. Can anyone else confirm this on theirs?? Thanks. The only way I can get the volume knob light to turn off is to unplug the amp itself from the back.
 

restorer-john

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#5
That's terrible. If the relays they are using tend to 'stick' with the tiny currents in that thing, the relays are crap or they aren't turning the coils fully off.

Seriously, banging the casework? Brilliant. What a joke.
 
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daftcombo

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#6
I had it the first time I tried to turn it off.
With the amount of chinese products I've been using in the last months, that was no surprise.

I turned it on again and off and the light went off too.
 
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#8
Someone sent me a link this morning to this thread, suggesting I chime in.

First, thanks for the feedback. I agree this behavior is unexpected. Sorry in advance for the long message.

The relays are produced by Kemet, rated for 2A. We have used the exact same line of relays in other products for years in various circuits (gain control, muting, and system power). I was just as surprised as everyone else when the behavior appeared while prototyping Atom Amp, so I spent considerable time studying the circuit, trying different relays (all with the same behavior), reviewing application notes, and reaching out to the relay manufacturers themselves.

The circuit is simple: a constant 12VDC regulator feeds the SPST switch of the Alps potentiometer to make or break relay coil current. A diode protects the coil.

If you're reading this message board, I do not need to explain to you that relays are an old mechanical technology. We chose to use a relay to toggle amplifier power because doing so permits a front mounted switch. The same level of performance without a relay would have required placing a 2A DPDT switch on the rear side of the amp. Customers over the years have complained about rear mounted power switches. Thus, Atom Amp's power is relay toggled.

After a relay stuck once in prototyping, I handed the board to a coworker and asked him to switch the amp on/off repeatedly. He came back after 100+ tries, convinced I was crazy. Nevertheless, I spent weeks seeking to understand the behavior. Relay contacts can stick under strong magnetic fields, or due to micro-arcing from high currents through the contacts, or from a sudden bump (i.e., relay dropped or hit). I was already aware of these basic possibilities--we've observed gain and muting relays stuck in the wrong position in various boards over the years, always resolved by cycling the relay once.

Anyway, the relay controlling power in Atom Amp was not being hit or dropped, and there was no extreme magnetic field, so this left micro-arcing as a possibility. Micro-arcing happens when strong inrush currents cause the relay contacts to temporarily stick. Thus, I delayed release of Atom Amp by two months to implement soft-start circuits in the AC/DC regulation circuits. Atom Amp's +/-15VDC rails slowly ramp up from 0V to their final value, minimizing inrush currents.

Still, we've observed about 1 in 200 Atom Amp relays stick in final Q/C. The vast majority of Atom Amps never exhibit a stuck relay contact. For those that do, allowing the contacts to stick, then power cycling several times is generally all that is required to ensure that the power switch works as intended there on out. Once the contacts break-in, they tend to be reliable. I placed a tip in the Instructions PDF in case more break-in was required.

The Atom Amp on my desk was one with a stuck relay when first powered on. I've been trying all week to replicate the behavior. It only works as expected. The good news is, relay sticking is limited to initial use of a small number of amps.

To be clear, I do not intend to downplay or otherwise justify this behavior. Yes, the power relay can stick when Atom Amp is new. When a design has Achilles' heel, people focus on that.

Although 99.5% of customers never experience a stuck power switch from Atom Amps, I am actively seeking advice from outside engineers. It's a challenge, as a single prototype is unlikely to prove consistency of relay operation. Even 100 prototypes is not definitive. And such an enhancement must also not compromise Atom Amp's leading performance and FCC/CE compliance.

Thank you all for the support!
 
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#9
I had this when my Aton arrived. This trick of tapping (more like hitting) solved the case for me.
Don't hit the Atom too hard, it might split! ..and we all know what happens when you split an atom ..especially if your headphones are plugged into it. You hear the deepest bass and crystal clear highs for a couple of seconds and then everything turns to dust (yourself included).
 

amirm

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#10
Although 99.5% of customers never experience a stuck power switch from Atom Amps, I am actively seeking advice from outside engineers.
Thanks so much for the honest post John. On this, have you tried to put a small cap right at the relay contacts? This was standard practice to stop the arcing.
 
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#11
Thanks so much for the honest post John. On this, have you tried to put a small cap right at the relay contacts? This was standard practice to stop the arcing.
Thanks, Amir. I believe I tried a capacitor on contacts months ago and observed similar consistency as with the soft-start circuit (which we kept). Will double check. It's frustratingly difficult to reproduce this behavior. By the time I get my hands on a stuck relay, it tends to self resolve. I may have to disable soft-start to exacerbate.
 

tired_guru

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#12
Thanks, Amir. I believe I tried a capacitor on contacts months ago and observed similar consistency as with the soft-start circuit (which we kept). Will double check. It's frustratingly difficult to reproduce this behavior. By the time I get my hands on a stuck relay, it tends to self resolve. I may have to disable soft-start to exacerbate.
It's been reported by many users in JDS ATOM AMP MEASUREMENTS thread. But for most of them it only appeared once at the beginning and never came back. It's been like after trying to power off the amp it clicked but the white LED light was still there, so I guess it was still on. I just simply turn it on again and off, and it was all fine this time. After this one incident it never happened again so this is not like a problem at all. Some people suggested it might be some residue of flux after production or some oxidation on switch connectors that's been scraped after first use but now we know this is about stuck relay contacts.
 
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restorer-john

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#13
The circuit is simple: a constant 12VDC regulator feeds the SPST switch of the Alps potentiometer to make or break relay coil current. A diode protects the coil.
So is this the final board below?
1550966395621.png


Are you relay switching the AC input, the half wave rectified AC prior to the 317/337 regulators or the regulated outputs of the 317/337s?

Why not post an excerpt of the power supply front end and we can help.
 
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#14
@restorer-john - Yes, that is the v1.00 production board. Your synopsis is correct. I've attached relevant portions of the AC/DC stage if you want to take a look (part #s and other circuitry omitted).

By the way, the same relay contact placement has been used for years now in Element, except with a latching relay. The separate reset coil must provide more release drive than the non-latching counterpart.
 

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