[TrollDragon]

8 1/2 years have passed since these were generously gifted to me and I'm still running them in my MK IV. (EI Yugoslavia)

 

[Cognomen]

Like I stated earlier I don't have any experience with 1:1 audio transformers but have read a little on them when we were looking to solve the problem of hooking up a LD amp to a DC amp.

These are the transformers I would go with to test and see how well they work in your situation. https://edcorusa.com/collections/ma...-matching-transformers?variant=41117605331131 they have 3 wires per side so they can be used balanced or unbalanced but you will connect them up only using the + and - to an RCA leaving the CT not connected. You would need one for each channel. Edcor claims 20Hz - 20kHz in the specs so they should be fine.

I would connect these and power on the Little Dot first then power on your amp. If you were unhooking them I would power the amp off first then the Little Dot.

OTL amps come with the risk of DC on the output if a specific failure condition occurs (chances are rare but can happen), which will destroy a DC amp and probably just destroy the inputs of a non DC amp. The only way to avoid this issue completely is to use an OTC (Output Transformer Coupled) tube amp.

I am planning to buy them. I queried for an hour or so, hoping to find information about human safety but did not find much. Currently I am imagining running a limited amount of wiring between the transformers and male RCA plugs upstream and downstream and using an audio rca cable between them and the little dot and a second cable between them and the power amp. If the tranformer had been playing music without a problem and I turned everything off and waited a few minutes, would it be safe to touch the cable ends and the transformers? If the little dot emitted dc and they stopped working or were working poorly and I shut everything off and waited until everything was cold, would it be safe to touch things? If unhoused and playing music without a problem would it be safe to touch them?

I found some guidelines for working with them. They are fragile - do not pick up by the leads or drop them. They should not be exposed to magnetic tools, and twisting wiring might work well. Specifically I found it in Bill Whitlock's "Audio Transformers Handbook for Engineers," 3rd edition, p.28. https://www.jensen-transformers.com/wp-content/uploads/2014/08/Audio-Transformers-Chapter.pdf

 

[barbazz]

Currently using a LM4562 OpAmp.

These Sylvania 6HM5/6HA5 tubes are definitely not lacking on bass. Quite the contrary. I listen to a lot of bass-heavy music and push some of my headphones, like my DT770-Pro/80ohm headphones pretty hard, up to the limit of what the headphone drivers can handle. During my initial testing with the Sylvania 6HM5/6HA5 tubes I accidentally caused an over-excursion event with my DT770 headphones on a song that I play often, and where I'm very familiar with exactly how hard I can usually push them with most of my tubes.

Using the same opamp here (actually a LME49720, but that's exactly the same).

About the bass I probably should have said "compared to other tubes like the Voshkods, they lack some bass"

I have to agree with you when it comes to vocals, especially the female ones. They are excellent in that regard.

 

[TrollDragon]

I am planning to buy them. I queried for an hour or so, hoping to find information about human safety but did not find much. Currently I am imagining running a limited amount of wiring between the transformers and male RCA plugs upstream and downstream and using an audio rca cable between them and the little dot and a second cable between them and the power amp. If the tranformer had been playing music without a problem and I turned everything off and waited a few minutes, would it be safe to touch the cable ends and the transformers? If the little dot emitted dc and they stopped working or were working poorly and I shut everything off and waited until everything was cold, would it be safe to touch things? If unhoused and playing music without a problem would it be safe to touch them?

I found some guidelines for working with them. They are fragile - do not pick up by the leads or drop them. They should not be exposed to magnetic tools, and twisting wiring might work well. Specifically I found it in Bill Whitlock's "Audio Transformers Handbook for Engineers," 3rd edition, p.28. https://www.jensen-transformers.com/wp-content/uploads/2014/08/Audio-Transformers-Chapter.pdf

Its line level audio that comes out of the RCA jacks on the back of the Little Dot that amounts to 2V peak to peak... There is nothing dangerous about those connections, same for the transformers and RCA inputs on your amplifier.

If and that a really big if, one of your output tubes developed a short on the anode then there could be 150V DC on the RCA jacks of the side that shorted. You would immediately know this as the transformer would be too hot to touch, smoke would be coming from it and there would be a very acrid smell in the air. So touching the RCA jacks while this is happening is obviously not advisable, yanking the power cable out of the wall is probably what most people would do along with airing out the room from the nasty smell of exploded capacitors, burnt resistors and transformer.

I don't understand the big concern with all the safety aspects. The chance of that specific catastrophic failure with your amp is extremely rare. People don't realise that if it happens while you are listening to headphones it will definitely destroy the headphones as well.

Little Dot puts the warning in the manual about not connecting it to DC amplifiers as a CYA clause. They don't want to be held accountable for a user plugging in some shorted tube they bought off eBay and taking out an expensive audio system.

 

[Cognomen]

Its line level audio that comes out of the RCA jacks on the back of the Little Dot that amounts to 2V peak to peak... There is nothing dangerous about those connections, same for the transformers and RCA inputs on your amplifier.

If and that a really big if, one of your output tubes developed a short on the anode then there could be 150V DC on the RCA jacks of the side that shorted. You would immediately know this as the transformer would be too hot to touch, smoke would be coming from it and there would be a very acrid smell in the air. So touching the RCA jacks while this is happening is obviously not advisable, yanking the power cable out of the wall is probably what most people would do along with airing out the room from the nasty smell of exploded capacitors, burnt resistors and transformer.

I don't understand the big concern with all the safety aspects. The chance of that specific catastrophic failure with your amp is extremely rare. People don't realise that if it happens while you are listening to headphones it will definitely destroy the headphones as well.

Little Dot puts the warning in the manual about not connecting it to DC amplifiers as a CYA clause. They don't want to be held accountable for a user plugging in some shorted tube they bought off eBay and taking out an expensive audio system.

I lack knowledge and experience about such things. Thank you. Your note was very helpful.

 

[g0ldl10n]

So, I actually built myself a custom adapter for dual 12SA7GT strapped as triode running a Eufonika H5M (default 6SN7 input) with just normal 8 pin octal sockets and I tell you what, they sound freakin' fantastic, lol (Currently using external PS for the heaters since they run on 12.6v).

I was actually searching the entire Head-fi forum to see if I could come across any impressions out there, and found this. This is obviously a very old comment/post, but thought I would chime in, in case anyone else was wondering. A custom adapter can be built as easy as one is built for say, strapping dual EL32 pentodes -> 6SN7 and they're wonderful drivers.

Kinda funny story how I came to need an adapter for this tube type - I was shopping for 12SR7 tubes actually - bought a listing that I thought was two pairs of 12SR7GTs, and once I received them, realized I read the listing too fast, and one of the pairs were the 12SA7GTs.. so I thought, wth, let's see if I can build an adapter for these for fun - and results were much better than I expected!

Currently have a pair a pair of blacked out Sylvania's and a pair branded as Westinghouse coinbase variants (seller said they came in a sealed box marked as Sylvania, so guess both pairs could be Sylvania's) - both pairs sound wonderful.



Because of their SQ performance, I have some Tung-Sol, National Union, 'Los Gatos' (I believe these might be Tung-Sol looking at them, but might never be sure) and some "Fapesa/Miniwatt made on Philips tooling in Argentina" types on their way. I would assume the 6SA7 variants have the same SQ, so also grabbed a few pairs of those too (obviously run on 6.3v instead).

For anyone following this, the 12SA7GT (and the 6SA7GT) are super good imo. All varieties there listed sound great, however, the NU and Fapesa/Miniwatt are my favorite. The adapter for these is simple dual adapter connecting the plate to grid 2 and 3 internally in the adapter, and using g1 for the control grid. Amazing SQ. Definitely competing with some of my favorites out there.

 

[Cognomen]

I just got a pair of Sylvania 6HM5/6HA5 (tall version) tubes for my Little-Dot I+ and I'm very impressed so far... These are the first non- EF95/6J1/6AK5(W)/5654/403B tubes that I've ever used with that jumper setting. I had been switching back and forth between a pair of Sylvania Gold Brand 408A tubes and a pair of Ultron EF92 tubes for a long time, but I like these new 6HM5/6HA5 tubes better than both of those, and they are my new favorites at this point.

One thing that I noticed right away about the Sylvania 6HM5/6HA5 tubes is that the bass seems to have a lot more texture to it (in a good way). Very open and airy top-end and amazing vocals.

I've always liked my Little-Dot I+ a lot, especially for my lower-impedance headphones, but it never quite seemed to match that true tube sound that my Little-Dot II+ (OTL tube amp, predecessor to the MKII) had. With these 6HM5/6HA5 tubes it really seems to have helped close that gap, which I didn't think was really possible.

I just got a pair of Sylvania 6HM5/6HA5 (tall version) tubes for my Little-Dot I+ and I'm very impressed so far... These are the first non- EF95/6J1/6AK5(W)/5654/403B tubes that I've ever used with that jumper setting. I had been switching back and forth between a pair of Sylvania Gold Brand 408A tubes and a pair of Ultron EF92 tubes for a long time, but I like these new 6HM5/6HA5 tubes better than both of those, and they are my new favorites at this point.

One thing that I noticed right away about the Sylvania 6HM5/6HA5 tubes is that the bass seems to have a lot more texture to it (in a good way). Very open and airy top-end and amazing vocals.

I've always liked my Little-Dot I+ a lot, especially for my lower-impedance headphones, but it never quite seemed to match that true tube sound that my Little-Dot II+ (OTL tube amp, predecessor to the MKII) had. With these 6HM5/6HA5 tubes it really seems to have helped close that gap, which I didn't think was really possible.

I like the Westinghouse tall bottle 6HQ5 which is similar to 6HA5 / 6HM5. I have the Yugo EI 6HM5 and like it also. It would be interesting to compare - I can't do that well enough from memory. There are many variants that have hardly been reported on compared to the Yugo. I recall a post where tall bottles sounded better than some small bottles. Perhaps the short ones are "Trabant."

 

[Kerouac]

Last week I started using the LD2 as pre-amp in this set-up:

PC (+foobar) => Burson Swing (dac) => LD2 (as pre-amp) => Burson Fun (amp) => headphones.

Sometimes when I used the LD2 I already got some loud (electrical?) pops on my headphones a few times in the past when I (dis)connected them. But the headphones were still fine after that, so I thought that it wasn't a huge problem after all. But maybe this already was a bad sign? And how to avoid this?

Now, did I understand correctly from some posts over the past few pages in this thread that there's a (high?) risk involved using the LD2 as pre-amp?
That I might damage the other parts in this system (including the headphones) in case that there would go something wrong with the tube connection?

If this is the case, than I guess that I might better not use the LD2 like this anymore, although I really liked the synergy sound result of this set up

Thanks in advance for any advice regarding the above!

 

[warp2600]

Last week I started using the LD2 as pre-amp in this set-up:

PC (+foobar) => Burson Swing (dac) => LD2 (as pre-amp) => Burson Fun (amp) => headphones.

Sometimes when I used the LD2 I already got some loud (electrical?) pops on my headphones a few times in the past when I (dis)connected them. But the headphones were still fine after that, so I thought that it wasn't a huge problem after all. But maybe this already was a bad sign? And how to avoid this?

Now, did I understand correctly from some posts over the past few pages in this thread that there's a (high?) risk involved using the LD2 as pre-amp?
That I might damage the other parts in this system (including the headphones) in case that there would go something wrong with the tube connection?

If this is the case, than I guess that I might better not use the LD2 like this anymore, although I really liked the synergy sound result of this set up

Thanks in advance for any advice regarding the above!

There is a warning in the LD manual that using the LD as a preamp with a DC coupled amp is not safe. You should know or ask the manufacturer if your Burson amp is built DC coupled or not.

 

[Cognomen]

There is a warning in the LD manual that using the LD as a preamp with a DC coupled amp is not safe. You should know or ask the manufacturer if your Burson amp is built DC coupled or not.

 

[RaynFox]

Hey, I've been reading and reading, but I still wonder, could the Little Dot Mk3 take a 12V driver tube?
Another question I have is - I read that the 6SN7 should require the Little Dot to have a different power adapter than the stock one - I've been using 6SN7 with just the stock one and it's fine, so I'm not sure whether there could be any potential upgrade by using a different power adpater ?
And the last question I have is whether it's possible to somehow fix a permanent electrical hum that is not audible at all volume levels - I've tried switching all the tubes to the stock ones but it was still there. Also when the knob gets to ~95-100%, there starts to be some very audible buzzing noises - what could that cause ?
Thanks in advance for answers.

 

[mordy]

Hey, I've been reading and reading, but I still wonder, could the Little Dot Mk3 take a 12V driver tube?
Another question I have is - I read that the 6SN7 should require the Little Dot to have a different power adapter than the stock one - I've been using 6SN7 with just the stock one and it's fine, so I'm not sure whether there could be any potential upgrade by using a different power adpater ?
And the last question I have is whether it's possible to somehow fix a permanent electrical hum that is not audible at all volume levels - I've tried switching all the tubes to the stock ones but it was still there. Also when the knob gets to ~95-100%, there starts to be some very audible buzzing noises - what could that cause ?
Thanks in advance for answers.

You cannot use 12V tubes in the Little Dot MKIII unless you arrange for an external power source for those tubes.
The amp comes with power tubes that draw the same 0.6A as the 6SN7 tubes - no need for another power source with those tubes.
The hum issue is more tricky. The first step is to try to find a source of the hum. It could be a cordless phone, computer etc - try to move away the amp from such sources. You can also try a different electrical outlet.
For he buzz at high volume try the above and also don’t use the maximum volume.
Many vacuum tube amps produce noise with the volume at very high or maximum.

 

[RaynFox]

You cannot use 12V tubes in the Little Dot MKIII unless you arrange for an external power source for those tubes.
The amp comes with power tubes that draw the same 0.6A as the 6SN7 tubes - no need for another power source with those tubes.
The hum issue is more tricky. The first step is to try to find a source of the hum. It could be a cordless phone, computer etc - try to move away the amp from such sources. You can also try a different electrical outlet.
For he buzz at high volume try the above and also don’t use the maximum volume.
Many vacuum tube amps produce noise with the volume at very high or maximum.

Thanks for the answers! I don't use the amp at 100% ever, it's not optimal, I just wondered about the noise. The electrical hum, I'll try a different socket tomorrow to see whether it'll make a difference - the other stuff I tried already.

And about the external power source, how exsctly would that connect? Just use a different than stock power adapter for the LD or is it a different way for the tubes? I'm not really sure about that.

 

[mordy]

Thanks for the answers! I don't use the amp at 100% ever, it's not optimal, I just wondered about the noise. The electrical hum, I'll try a different socket tomorrow to see whether it'll make a difference - the other stuff I tried already.

And about the external power source, how exsctly would that connect? Just use a different than stock power adapter for the LD or is it a different way for the tubes? I'm not really sure about that.

In order to provide external power you need several things. First you need a power supply - an old computer power supply from a PC or laptop is fine. Then you need a voltmeter to identify the 12V leads on a PC power supply - many laptop power supplies are already 12V but not all. Or get a wall adapter that is made for 12V.
However, you have to learn how much current each tube draws (Amps). A 1A wall adapter is not going to cut it for a pair of 1.5A tubes which draw 3A together, as an example. A PS from a PC (or laptop) usually has more than enough current capability.
Next you may need a voltage regulator. You attach the leads from the power supply to the voltage adapter. The voltage adapter comes with a little set screw and you can adjust the voltage in a wide range depending on what you buy. Some of the voltage regulators have a built in LED voltmeter (and amp meter).
Finally, you need to connect two leads from the voltage regulator to the power pins in a socket where the power is disconnected to the amp itself.
It really isn't that difficult and doesn't have to cost a lot. A PS from a discarded PC is free, a voltage regulator can cost less than $15. The modified socket you can make yourself if you are handy, or buy for around $20.

 

[rprodrigues]

Does anyone know the rated power consumption of the Little dot mk II ?

It's claimed elsewhere as only 28W, but I don't trust it.