[blakean]

Hello!

I recently bought a Little Dot Mk III from its original buyer. I bought it knowing there was a buzzing issue, but thought that the buzzing was an easily correctable ground loop fault. However, after using a "cheater" plug and an actual ground loop isolator without any success, I am wondering what the problem might be. I have the unit powered on with only headphones, connected to nothing but the wall socket (and I have a tried a few sockets throughout the house--with the same result). I have read through page after page of forum posts describing buzzing issues with Little Dot amps, but I am posting my specific details because nothing I have read has helped me up to this point.


The buzzing is in both channels--quite loud, but it gets quieter as I increase the volume. I can hear the music at a reasonable level, but the noise is constant.

I have given all the tubes a thorough cleaning--first a gentle scrape on each pin with an Xacto knife to eliminate possible oxidation residue, then a thorough cleaning with DeOxit. No results!

The jumper pins seem situated properly, and the gain settings are all in place. I have tried several different power cables and even a UPS battery surge unit which I thought may isolate any electrical interference. No results!

I took off the front and back panels to have a peek for disconnected wires and saw none, except one leading to one of the RCA output ports which I think I tore myself when opening. (If I did not do it, would this be the cause of the buzzing? I have not yet reconnected it with solder.)

Could it be the tubes themselves that are giving this constant buzzing? They were apparently out of use for at least a year and put in storage.
They all glow and heat up, and there is no white residue on the glass that I can see. Just in case, I have already ordered both driver and power tubes from Ebay, hoping that it would be a simple fix. I will have to wait and see.

Could a disconnected wire or broken solder joint on the inside be the cause? I hesitate to even try to take the board out for a look because it is so tightly packed in and I haven't found any instructions on how to safely do so.

Anyway, these are all the details I can share. I have spent a long time searching for the remedy, but haven't found it yet.

Any input on this issue will be much appreciated. I'd like to actually use the amp, since I have some HD650s on the way.

Thanks!

 

[buldogge]

First things first...You need to fix the broken wire @ the RCA. Is it the signal or ground wire?

Either way...the outputs are active and volume pot controlled...you need that wire repaired.

-Mark in St. Louis

 

[blakean]

Yes, I will repair the wire, which I think is the signal. I'm fairly certain it was me who did it, so that particular problem post-dates my original issue.

 

[buldogge]

There is always the possibility that it was already compromised.

The wires are thin, and they are packed in there tight.

Personally, if I keep my modded MKIII (have been listening to the BHC Crack mainly), I might machine the bottom of the case off to make space and make it a lift off top, and then add a wood base. Would also give room for additional cap mods.

Good luck.

-Mark

 

[blakean]

That sounds like a great modification, but a bit beyond my meagre skill set. Would that loose output wire create a buzzing noise even though I'm not using the output plugs?

 

[buldogge]

Assuming the RCAs are active even with headphones plugged in...not positive on that front.

I can test it out a little later today.

-Mark

 

[blakean]

Great, thanks.

 

[buldogge]

Confirmed...Signal to the RCA outputs with or without headphones plugged in on LD MKIII...volume pot controlled, as I believed.

-Mark

 

[blakean]

Thanks for checking that out. I do think that I ripped it out in the process of checking inside, but I will of course re-connect it. If the buzzing ever ends, I'll want to use the LD as a preamp as well.

 

[buldogge]

One other thing to check...If I remember correctly, there is a single chassis ground spot. I have gotten intermittent ground hum, in the past, and was able to eliminate it by introducing an external ground wire (or checking it by touching the RCA and chassis simultaneously)...FWIW.

-Mark

 

[blakean]

That's good to know. Where did you introduce the wire? Perhaps I can manage to do the same thing. I do realize, however, that the build design has changed over the years. I'm not sure which one I purchased or when the original was bought.

I did touch the chassis and RCA simultaneously, but nothing happened. I also made sure all the screws were tightened (the front right top screw when loose emits a different sort of buzzing in addition to my normal buzzing problem).

 

[buldogge]

Wire was just introduced as a test...not installed. Same bridge mentioned, as my body.

If your buzz is different then the front right screw buzz...then we're probably dealing with something different.

Let us know how it is after you fix the solder point.

-Mark

 

[blakean]

I will, thanks.

 

[blakean]

Just a quick update. I resoldered that loose wire with no change to the humming sound.

I also received some new driver tubes and put them in: no change. I'm still waiting for some new power tubes before I decide whether I want to pull the thing apart and have a look (with the eyes of an amateur).