Any tube experts here?

Kw6 · « **on:** 14 Jun 2020, 06:30 am »

Just got a Cayin A 300B Mk II integrated amplifier. When I turn off amp after listening i hear a small pop from left speaker only. The dealer says caps discharging is normal. But met a guy online he has same amp and he says he has no pop. What's causing the pop?

Thanks!

FullRangeMan · « **Reply #1 on:** 14 Jun 2020, 08:01 am »

No expert just as a audiophile: the caps discharging are normal, it is consequence of you having turned off the amp, what is not normal is to pass this signal to the speaker, in one channel they did the correct assembly but in the other channel of your amp it was discharging in the speaker.

Also may be the faulty channel have less than good selected caps or less than ideal performance. To a precise diagnosis could be useful the schematic. Do your outlet have a ground that works well? as aroun 1-2 ohms.

Kw6 · « **Reply #2 on:** 14 Jun 2020, 03:42 pm »

I don't know what you mean outlet have a ground that works well?

Kw6 · « **Reply #3 on:** 14 Jun 2020, 03:55 pm »

Could it be a bad tube?

Kw6 · « **Reply #4 on:** 14 Jun 2020, 04:51 pm »

My dealer suggest to see what happens when I use a line conditioner. I will update later. My other amps don't need it but will see what happens.

Tyson · « **Reply #5 on:** 14 Jun 2020, 05:22 pm »

Could be a bad tube. Switch all your left side tubes with your right side tubes and see if the popping moves with it.

Kw6 · « **Reply #6 on:** 14 Jun 2020, 07:26 pm »

Ok thanks I will give it a try as well!

Kw6 · « **Reply #7 on:** 14 Jun 2020, 09:35 pm »

I just want to clarify that the sound I am hearing is a speaker thump when turning off with power button from my integrated. On left side only and would say not too loud.

FullRangeMan · « **Reply #8 on:** 15 Jun 2020, 12:11 am »

Quote from: Kw6 on 14 Jun 2020, 03:55 pm

Could it be a bad tube?

Its not a bad tube but you can swap the tube to check.

FullRangeMan · « **Reply #9 on:** 15 Jun 2020, 12:15 am »

Quote from: Kw6 on 14 Jun 2020, 03:42 pm

I don't know what you mean outlet have a ground that works well?

Does your home have an electrical ground?

Kw6 · « **Reply #10 on:** 15 Jun 2020, 12:43 am »

It's plugged into a regular household outlet with ground. I am actually listening to my amp now. The dealer told me to plug into line conditioner and turn off with line conditioner power button to test the amp. A funny by product of using line conditioner is more details and musical ease.😀 It's probably DC offset at the terminals being sent to the speakers. I read anything over 1 volt at the terminal is faulty. I read disconnect the speakers and place probes to see if below 100 mv or best 10mv and compare to right side. I thought tube amps can't be turned on without a speaker load? I have a voltmeter but instructions say don't touch the red probe to positive terminal or chasis. This has me confused. I thought while amp on you use black probe to touch negative terminal and red probe to positive terminal to get reading? Please explain if you know? Thanks!

Kw6 · « **Reply #11 on:** 15 Jun 2020, 02:59 am »

Update is when I used the power button on the line conditioner to cut power while amp is still on I thought the sound came more from the center but will confirm next time. But for sure when I use amp power button louder on the left. Again will confirm next time.

Docere · « **Reply #12 on:** 15 Jun 2020, 03:27 am »

How long after switch-off does the sound occur? Is the sound a short "pop", a thud or a thrummm.

I'm not familiar with the design and can't provide specific advice.

Edit: removed advice.

Kw6 · « **Reply #13 on:** 15 Jun 2020, 05:44 am »

As soon as I turn off amp short pop comes. Right now its mostly left speaker. I will check next time. Another fellow online has same amp as mine and he says no pop through speakers.

FullRangeMan · « **Reply #14 on:** 15 Jun 2020, 12:26 pm »

Most tube amp designs can be turned on for short periods without speakers connected; not sure about the Cayin.
When a tube amp is connected without the speakers or a resistor of adequate value the output transformer starts to short circuit and warmup, what first heats up is the wiring of the windings, which can harm the protective varnish of the winding wiring. That was not a good recommendation them give to you.

dB Cooper · « **Reply #15 on:** 15 Jun 2020, 12:58 pm »

Quote from: Kw6 on 14 Jun 2020, 03:42 pm

I don't know what you mean outlet have a ground that works well?

It's irrelevant as a grounding issue would be unlikely to affect only one channel.

Tyson's suggestion to swap the tubes channel to channel is a good one. Do it one corresponding tube at a time- if you transpose them all at the same time, and the problem moves, you'll know it's a tube, but not which one.

Anything that is notably different channel-to-channel in a stereo amp is worth being cautious about, especially with tube equipment where high voltages are present.

Kw6 · « **Reply #16 on:** 15 Jun 2020, 03:35 pm »

Thanks for all your help! Issue i think is resloved. I swap the Full music 300b tube and now the soft pop is now on the right. What causes a 300b tube to pop on turn off only not make any sound while on standby or playing?

FullRangeMan · « **Reply #17 on:** 15 Jun 2020, 10:53 pm »

Propably shorter distance on internal elements than ideal.

Kw6 · « **Reply #18 on:** 16 Jun 2020, 04:18 am »

I don't know what that means but I am sure you are right!😊

jules · « **Reply #19 on:** 16 Jun 2020, 05:05 am »

I've noticed a slightly out of time from one side to the other, soft turn-off pop with my SS amp. My guess would be, that it relates to different rates of discharge with capacitors. Capacitors have quite a wide + and - specified range up to 20%, though for most applications the variability is not significant.

The slight time lapse would support this idea. Most components work instantaneously but you'll notice, in many situations, that when you switch a piece of equipment off, the LED indicator will stay alight for some seconds as the capacitor discharges.