[Tekkaman]

Hello everyone!
 
Amp - LittleDot Mark IV (Non-SE)
 
Cans - HD-555/HD650
 
Other than sending this back to LittleDot, I was wondering if anybody might have experienced this issue as I'm sure it isn't isolated to just the LD Mk IV.
 
 
Description:
 
I purchased this amp from head-fi years ago. I haven't been able to use it for about 2 years. Anywho, right before I stopped using it, one of the channels had died. About a week ago I attempted to use the amp again and swapped the fuse as per instructions found online. Now I have 2 channels, however this is what I'm running into now - As a pre-amp/pass-through, the volume is perfect! It sounds nice and at times is a bit too loud for my taste.
 
However when I use it as an amp, I noticed that even when it isn't plugged in, I can still hear very faint audio (coming from my source) which is able to be increased slightly by turning the knob to max.
 
 
 
Things I have tried:
 
Changing fuse
 
Used all combinations offered by the Gain switches
 
Swapped multiple power and driver tubes (sorry if the names are wrong, but the big tubes and small tubes)
 
Tried multiple sources - Phone, computer, XBOX 360
 
Tried multiple power cables
 
Tried multiple RCA cables
 
Tried multiple cans
 
Cleaned the bottom of the tubes and as a last resort, lightly sprayed compressed air into the amp from a good distance away as to not damage anything on the PCB
 
 
 
Outside of those things, I'm not aware of what else I can do/not sure what I'm capable of doing.
 
 
 
Would you suggest I send it in or are there any solutions that you folks know of?
 
 
Thank you in advance! I will do my best to monitor this thread.

 

[NA Blur]

Seems like the amp and pre-amp sections are reversed which explains the loud volume in pre-amp mode and very quiet volume in headphone amp mode.
 
Perhaps the tubes are reversed?

 

[Tekkaman]

Hmmm, when plugged in as a pre-amp/pass-through, the volume knob does nothing to volume, which to my knowledge means it's working as intended. The line should be @ 100.
 
As for the tubes, due to the design, the tubes only fit in specific places, so reversing the tubes is not a possibility.

 

[kramer5150]

Sounds like your tubes are picking up radio broadcasts. Some tubes / amps will do this, behave like a radio antenna, picking up local radio waves from nearby stations. I dont have any first hand experience dealing with this though. I have read about others re-positioning and re-locating the amp to a different spot in the house. Good Luck!!

 

[Tekkaman]

@kramer5150
 
Interesting! I have edited the original post to mention that the audio I hear is coming from my source rather than a radio signal, but you definitely gave me a lot of reading to do hahaha. I'm interested in this entire tube amp radio signal reception.
 
Thanks either way ha.

 

[kramer5150]

Sure no prob... the condition can be tube dependent too, so just tube rolling can be a simple cure.
 
So your source is somehow "broadcasting" your music to your amp?... you can hear library / tunes as you play them?  whoa thats the first I have hear of that, without bluetooth, wifi or an AM/FM modulator.

 

[Tekkaman]

No no, what I mean is that the music from my source, plugged into the amp, is what I can hear. The issue is that the volume is so incredibly low and does not require my power plug to be plugged into the amp to hear it from my source. When I plug in the amp, the volume does not change. It only changes from silent to extremely low when I turn the knob all the way to max.

 

[Tekkaman]

Heya all!
 
Still looking for help if possible.
 
I may end up just using this as a pre-amp as I notice that there is still very nice sound quality being output that way and just scratch ever using it as an amp.
 
What do you guys think?

 

[kramer5150]

No fix huh?
 
Sounds like an output section + power / tube problem.  Blowing fuse I think could be a sign of something wrong internally, or it could simply mean your main coming in off the wall was unusually high at that moment.
 
If its still under warranty you should look into having it serviced.  If its out of warranty, (if it were me) I would get busy with the DIY repair.  Pop the cover and start Fluke-ing point to point in the amp, check for shorts and bad connections.
 
It could be nothing more than bad/blown power tubes... a shorted tube(s) can cause fuses to blow.
 
Are you sure the preamp output is not supposed to be volume controlled?  I always thought most of the chinese tube headphone/preamp models had volume controlled preamp outputs.  (my darkvoice certainly is) Might want to double check that too.. there could be some tell-tale signs of wrong-going there.

 

[Tekkaman]

Thanks for keeping up with this and thanks for the suggestions.
 
It is out of warranty so I more than likely will end up tinkering with it. I have been soldering for ~15 years so it shouldn't be much an issue. I could also just invest in a set of power tubes but unsure if I want to drop another $50 on the unit.
 
If someone else w/ the MK IV (non-SE) could chime in on the pre-amp not changing volume based on turning the volume knob but on the source's volume, please let us know!

 

[HeatFan12]

Quote:

Hmmm, when plugged in as a pre-amp/pass-through, the volume knob does nothing to volume, which to my knowledge means it's working as intended. The line should be @ 100.
 
As for the tubes, due to the design, the tubes only fit in specific places, so reversing the tubes is not a possibility.

 
 
Hey Tek,
 
Been reading this thread and trying to figure out what is going on.  When you connect to the 'output' from the rear of the amp, it will act as a preamp, however it needs to be connected to a power amp or powered speakers.  You control the volume from the MKIV.  I use my MKIV SE in this fashion quite frequently with powered speakers.
 
To use MKIV as a preamp- Connect 'output' on rear of MKIV to powered amp or powered speakers, then connect 'input' on rear of MKIV to source (ipod, cd player etc.).  Volume will be controlled by MKIV.
 
To use MKIV with headphones only- Connect 'input' on rear of MKIV to source (ipod, cd player etc.).  No need to connect anything to 'output' on rear of MKIV.
 
Cheers!!!

 

[Tekkaman]

Hey HeatFan12!
 
Well, looks like I had a few things right and a few things wrong regarding my setup hahaha.
 
What I had correct was of course how to use the amp with headphones. I had been using them for quite some time before the unit "broke" on me. Doh!
 
However what I had configured as a "pre-amp" was just plugging my source into "Output", which then would go straight to the headphones and made it incredibly loud. This would make sense as to why the volume knob did not work.
 
Anything plugged into the "Input" of the amp is brought down to literally 1-2% of the volume it should be. I tried swapping tubes with the set that I received and generally I either got the same result or I would have muffled music, signifying to me that whichever tube(s) I put in were defective/not working with my unit.
 
I sent an email to David a while back and he said he would only charge me shipping, so I think that's what I will end up doing.
 
Would you all advise me to do so? I was hoping for a quicker fix but if I have to wait, I have to wait hahaha.

 

[HeatFan12]

Well Tek, I've sent back gear to David before and no problems at all.

However, maybe a few quick checks first- your sources, how r u plugging them into the amp (dac, lineout dock with phone)?

The MKIV can use two families of tubes (EF95 & EF91 & 92 and all the variants). Jumpers need to be changed to use EF95 from EF91 & 92.

Just checking things before u have to ship.


Sent from my iPhone using Tapatalk

 

[Tekkaman]

Heya I will definitely be sure to check my, what I'm guessing you mean by jumpers, gain switches. If I am mistaken by what you mean by jumpers, please let me know!
 
The 2 sets of tubes, according to the forum post from the seller, are 6H30's. Excuse my ignorance for not being familiar with family those tubes belong to. If you could educate me on that, that wuold be awesome. My current guess is that the EF91, 92, and 95's are for the other smaller tubes? That seems to be what I've gathered but I could be wrong.
 
 
Regarding sources:
 
ASUS Xonar DX2 - Direct from Line-Out/Spear-Main
 
Galaxy Note 2 - Directly from headphone jack
 
XBOX 360 - RCA in from default A/V cable

 

[HeatFan12]

Hey Tek,
 
The 6H30s are the power tubes (larger ones) and no settings needed.  The driver tubes' (smaller) settings need to be changed if you use EF95 (and all variants) to EF91 & EF92 (and all variants).  EF95 family is different from EF91 & 92 family of tubes.
 
In reference to the sources, I can't really advise.  I don't use any of the ones you listed.  Check all your connections with the 'input' of the amp.  For the card, you are using the line out, so don't really know if you are bypassing the card's amp and not just double amping.  I usually test amps with an iDevice via line-out to bypass the internal amp of the device or a cd player (portable or full size).  That way, if the amp works great with a simple connection then when you throw it into another audio chain, if you have problems, you know it's not the amp but another component connection.