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Message started by nico on 05/27/14 at 22:23:22

Title: No sound....
Post by nico on 05/27/14 at 22:23:22

I need some help guys.
One of my Zen mono amps [SE84C] stopped working last night.
All tubes glowing, no sound.
Problem is defenately the amp; switched amps, switched cables etc. to locate the problem.
Opened it up but nothing to see there what could cause it.
HOW TO CONTINUE?
HELP!

Nico

Title: Re: No sound....
Post by beowulf on 05/28/14 at 03:43:42

1. Did you switch tubes?

2. Did you check/swap fuses?

3. Did you check outlets?

Title: Re: No sound....
Post by Lonely Raven on 05/28/14 at 05:13:23

Lighting up, but no sound coming out sounds like the input tube or related circuit is having an issue, or the volume pot possibly. Try swapping the input tube, try flicking the bias switch a few times, try cranking the volume knob left right a few times and see if it comes back. That will hopefully help you narrow down the fault.

Title: Re: No sound....
Post by nico on 05/28/14 at 06:47:12

Just woke up over here. Thanks for the suggestions guys but yes, I already did what you suggested.
Tried two new sets of tubes, swapping cables , left amp to the right etc.
problem def. is in the amp itself.
It simply stopped playing without any extra noise, smell or whatever...
I know the basics of electronics but this is a mystery to me.
Any more idea's?
[since I'm in The Netherlands it's not so easy to send the amp over to Steve ]
Nico

Title: Re: No sound....
Post by marky on 05/28/14 at 09:32:24

I had a similar issue last week on bridged Rachaels. Took some hunting down to find a signal tube on the phono amp had just eased out a shade.

Title: Re: No sound....
Post by Lonely Raven on 05/28/14 at 17:06:23

Nico, since it's happening on both channels, you need to look at all points where the signal goes through *both* sides of the amp at the same time, I still think that's only input tube or volume pot.

I can't recommend opening it up and checking it yourself, but you might want to poke at the input tube socket, and verify the signal wires if you do open it up again. Make sure nothings come loose or looks burnt.

Beyond that, it might be time to either send it to Steve, or find a local tube amp tech to give it a look over. It's a very simple design, and any tube amp tech worth his salt should be able to diagnose it with an input signal and multi-meter.

Title: Re: No sound....
Post by 4krow on 05/28/14 at 18:53:59

Nico,
To recap, you own 2 mono amps, 1 of which is not working. The one not working has tubes glowing, so you know it is getting power. You have checked cables and tubes, finding no fault with them. There is one more thing to consider. The RCA input jack may have problem. You can take the cover off and pull on the wires going to the jack. These wires can be physically stressed when pulling off a tight interconnect cable, ESPECIALLY if the interconnect was being twisted trying to pull it off.

Title: Re: No sound....
Post by Lonely Raven on 05/28/14 at 19:06:49

Duh, for some reason I was assuming two regular SE84C that were simply run bridged for mono. If they are dedicated monoamps, then the whole signal path is suspect.

Title: Re: No sound....
Post by Lon on 05/28/14 at 19:19:39

4krow wrote on 05/28/14 at 18:53:59:

Good call. The interconnect itself could have a problem as well unless that has been eliminated as a problem.

Title: Re: No sound....
Post by 4krow on 05/28/14 at 19:53:57

Lon, well thanks. The twisting of the RCA connector itself is what I think is suspect. I just repaired a unit 3 days ago that the customer was using tight interconnects(monster cable turbin connectors), and to get them off, he was twisting the interconnect RCA . Well, as he twisted it, the AMP chassis mounted RCA twisted as well. This of course, caused the internal wire to detach. Also, I should mention that the chassis RCA signal connection was actually pushed in by forcing the interconnect into the CHASSIS mount RCA.
As an aside, I am in the process of replacing ALL 4 sets of inputs of my 34.3I because of the fact that the signal connection on some of them has come to be too loose for a good connection. Um yah, I am a BIG believer in high quality (not necc high priced) RCA connectors for the chassis of any component, and often change them out from stock.

Title: Re: No sound....
Post by Lonely Raven on 05/28/14 at 20:35:35

What chassis mount RCA do you like over stock?

Title: Re: No sound....
Post by 4krow on 05/28/14 at 21:35:57

LR,

Oh boy is that ever a hard question. There is a mountain of junk out there, and another mountain of over-priced parts as well. Just when I found an RCA that fit the bill, I can no longer get them. They had a solid body that was rhodium plated, and the fit was correct as well. I have tried the 'CMC' brand RCA jacks from China, and man, let me tell you, they are sized waaay too tight. Then the material is something that I tried to drill, and well, it wasn't copper, it wasn't brass, but it was hard! No more of them. Occasionally at Parts Connexion, there are some that work out to be ok. It is hit and miss, but I do not like the small 3/8" diameter type. I prefer 1/2" diameter, with a short barrel. I have some on the way from China that I have not used before. They should be here shortly. Yes, my fingers are crossed.

Title: Re: No sound....
Post by Lonely Raven on 05/28/14 at 21:51:25

Cool! Tell me how they fair.

Also looking for better power inlet for my Decware amps - Steve isn't happy with them either, so I've been keeping an eye out for a good IEC inlet with solid connectivity, that actually fits a standard IEC plug!

Title: Re: No sound....
Post by 4krow on 05/28/14 at 22:05:24

LR,

If you were to get into the inner circle at PS Audio, they might tell you where a good IEC inlet can be had. I know of no other company that strives for great connections.

Title: Re: No sound....
Post by SteveC on 05/28/14 at 22:44:45

This suggestion is only half serious....

you know how you can install some appliances, like dishwashers, by direct wiring to the box, or wiring a pigtail to the box and plugging it in? To eliminate weakness at iec contacts, you could hardwired a cord/plug (a nice one) into your amp (haven't thought about aesthetics or where it could come out, etc). It's one way of avoiding the problem entirely. No connector would have a better electrical connection. Would have to remember to handle the fuse. And you save having to buy a female iec plug if making your own cords.

Again, only half serious, but it seems like one of those "old way, better way" kind of situations.

Title: Re: No sound....
Post by Lonely Raven on 05/28/14 at 23:11:35

We are totally derailing nico's thread...sorry nico.

SteveC, I've already thought about that - had plans to do that with my little Zen amp, but Steve talked me out of it...keeps telling me my little Zen amp will be a collectors item some day and I shouldn't muck with it.

Title: Re: No sound....
Post by SteveC on 05/29/14 at 00:16:44

you're right.

Nico, So far:
you have opened the amp.
you are comfortable with electronics
you have switched in known good tubes
you have switched in known good cords and cables

... if you suspect the IC connections...
you can with the amp open and on, (be careful!) probe the wires at the RCA inputs with some wires carrying music signal. this will tell if your rca jack is somehow busted or bad contact.

if you suspect the volume pot(s)... it's just a resistor, you can short it with a piece of wire and that will provide instant "full volume". that'll tell you if the pot is broken.

personally I don't know enough about the lines going to the tubes and which are high voltage... so that's where my troubleshooting would end. (I guess with NO POWER, visually inspect for loose wires on tube sockets.) otherwise send home to Peoria.

Anyway, only do the above (plug in and operate a opened amp) if you know how not to kill yourself from high voltage.

Title: Re: No sound....
Post by SteveC on 05/29/14 at 00:42:53

Or to be safer... Just check continuity from the jack to the wire. And measure the varying resistance of the pot as you rotate it. Without power... Much safer ��

Title: Re: No sound....
Post by nico on 05/29/14 at 19:57:42

THANKS guys for your help.
Can you believe I had a bad night because of this..?
Listening to music is like a daily medicine for me against stress.
So today I decided to open both [mono bridged] amps, lay them on one side with tubes inserted and powered them up.

Taking my DMM, I started measuring the voltage across different points inside the working amp, and then in the defective one.
Soon I measured no voltage after the 1K resistor that feeds the OT's....
After shutting everything down I de-soldered that resistor and YES SIR, it is "open" .

That means the OT's did not get any power and that means tubes glowing but no sound.
So I stumbled upon the answer this way!

I asked a local tech and he confirmed that the bad resistor would indeed cause the problem I described.

As seen on the later schematics, this resistor has been upgraded by Steve from 1K10w to 1K50w. Maybe the 10w version prooved to be thermally stressed too much, I don't know.

What I do know is that tomorrow I'll be buying two 1K50w resistors, solder them in place and hope to get my daily dose of medicine again.

For all who own a older Zen; replace the resistor for a 50w version.
Nico

Title: Re: No sound....
Post by nico on 05/29/14 at 19:59:31

Here is where it's at, there's only one of those inside, you can't miss it!

Title: Re: No sound....
Post by 4krow on 05/29/14 at 20:00:23

Very good sir! I am pleased that you were able to find this problem./

Title: Re: No sound....
Post by Lon on 05/29/14 at 20:11:43

Good news Nico!

Title: Re: No sound....
Post by will on 05/29/14 at 21:32:31

Way to go Nico. It has been fun to watch the progress.

As to the side thread topic...loose IECs, I personally would not hardwire a cable since I find cable rolling very useful, especially with a new component introduced in the blend. I did make and buy cables with quality, but also diversity in mind though. All my nice PCs sound good but different, and depending on what they are plugged into, sometimes for inexplicable reasons, one will really match a component within the synergy of the whole. For example, I have a 10 AWG PI Audio cable I got while in development. It has Gold Furutech ends, and a really good damping and noise reduction design. It sounds (or doesn't sound) really good everywhere, transparent, dynamic and quiet, but in my DAC it is awesome. These strange synergistic things can be sort of shocking for me.

BUT LOOSE IECS.....until you find the right replacement, wrapping the Power Cord IEC connector with teflon tape until it fits snuggly will stabilize it in a dampened sort of way.