Little Dot II+ impedance jumper?
Sep 20, 2006 at 12:18 AM Thread Starter Post #1 of 31

GotNoRice

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I was reading and found that the Little Dot II+ apparently has a jumper that is left in for high-impedance phones and can be removed for low-impedance phones. You can see what I mean here (I’ve also heard various tidbits about it in other threads here):

http://www.little-tube.com/forum/for...=30&PN=1&TPN=3

Now my questions are:

Has anyone removed the CN1/CN2 jumpers or whatever they are? What changed?

Where on the PCB are the jumpers? The manual is only in Chinese, and from the pictures on the little dot site I can’t identify the jumpers.

Would removing the jumper affect how the Little Dot II+ works when I use it as a preamp for my amp?

I asked this on the little dot forums as well and if I get a reply I’ll post it here. I’m just kinda confused, as it seems like it is something you should adjust if you need to but why then not make it accessible from the outside?
 
Sep 20, 2006 at 11:01 AM Post #2 of 31

Gradofan2

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Quote:

Originally Posted by GotNoRice
I was reading and found that the Little Dot II+ apparently has a jumper that is left in for high-impedance phones and can be removed for low-impedance phones. You can see what I mean here (I’ve also heard various tidbits about it in other threads here):

http://www.little-tube.com/forum/for...=30&PN=1&TPN=3

Now my questions are:

Has anyone removed the CN1/CN2 jumpers or whatever they are? What changed?

Where on the PCB are the jumpers? The manual is only in Chinese, and from the pictures on the little dot site I can’t identify the jumpers.

Would removing the jumper affect how the Little Dot II+ works when I use it as a preamp for my amp?

I asked this on the little dot forums as well and if I get a reply I’ll post it here. I’m just kinda confused, as it seems like it is something you should adjust if you need to but why then not make it accessible from the outside?



That's a good question. Can you, or someone, post the procedure for removing the jumper(s), or switching the jumper(s), or whatever... and maybe the pictures of the jumpers?
 
Sep 20, 2006 at 7:25 PM Post #4 of 31

m8o

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Quote:

Originally Posted by GotNoRice
Has anyone removed the CN1/CN2 jumpers or whatever they are? What changed?
...
Would removing the jumper affect how the Little Dot II+ works when I use it as a preamp for my amp?



Yes, I was surprised to hear about this too a few weeks ago. Only critical thing I have to say about Little Tube is they don't care much about making multilingual manuals. You only hear about these things as 'fables by the fireplace'.

The LD II+ has 12X gain with the jumper in and 9X gain with the jumper taken out. It has (and I'm not sure how) higher current capacity with the jumper out so can drive lower impedance phones better. Without question, keep it in when using it as a pre-amp driving an amp, as power amps usually have an input impedance in the multi Kilo ohm range to dozens of Kilo ohm range; you want the voltage gain and don't need the current gain driving a power amp.
 
Sep 22, 2006 at 12:00 PM Post #5 of 31

drxpert

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Unscrew the lower two screws of the front and back panels, and remove the bottom plate. From underneath, between the front plates and the mullard tube sockets, there are 2 black jumpers CN1 and CN2. For my set, gain is 9 with the jumpers on and 6 without.
 
Sep 22, 2006 at 6:22 PM Post #6 of 31

GotNoRice

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Quote:

Originally Posted by drxpert
Unscrew the lower two screws of the front and back panels, and remove the bottom plate. From underneath, between the front plates and the mullard tube sockets, there are 2 black jumpers CN1 and CN2. For my set, gain is 9 with the jumpers on and 6 without.


Thanks for the reply. David has also replied on the little-tube forums:

Quote:

Originally Posted by DavidZheZhe
Yes, for the easiest method, unscrew all screws and the top and bottom half of the casing should open up. Changing the jumpers will not negatively affect the pre-amp out


Interesting that it apparently doesn't affect the pre-amp out, because that would be a deal breaker. Can't wait to try it now
smily_headphones1.gif
 
Sep 22, 2006 at 7:21 PM Post #7 of 31

kramer5150

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can you replace the jumper with a toggle switch?

the more I read about this amp the more I want to try one... switchable gain setting would be a killer mod IMHO.
 
Oct 1, 2006 at 12:04 AM Post #10 of 31

vcoheda

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Can someone post some pictures of the inside and the jumpers. I want to know what they look like in case I decide to run my K701 through the amp.

Thanks
 
Oct 1, 2006 at 6:23 AM Post #12 of 31

Azure

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Quote:

Originally Posted by TheNew007
How high does the impedence have to be inorder to be called a "high impedence headphone" Is the HD595 high or low?


The HD595s are only 50 ohms which is somewhat low-ish. In my eyes, high impedance is 150+ ohms.
 
Oct 3, 2006 at 12:10 AM Post #13 of 31

Duc

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Sennheiser 650 has a 300 Ohm Impedence, thats high. I would say anybelow 100 would be considered low.

m8o you seem to be the resident LD2+ knowledge base, so I have a question, and maybe you can help. I have a set of AKG 701's (bought today!, yeah) they are 62 Ohm. I was running a pair of Senn 590's which were 120 Ohm. However I have to turn up the volume on the LD 2+ about twice that w/ the 701's as the 590's. So with the jumper off, should I not have to turn the volume up so much? Thanks! (though I could just do it and find out, huh?)

Oh, I can try it and take some pics!

blink.gif
B
 
Oct 3, 2006 at 12:52 AM Post #14 of 31

m8o

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Duc, I think with the jumper out you actually have to turn the volume up higher. This is because the voltage is reduced with the jumpers out; current is increased. But the amp operates more easily, with less 'compression' on loud musical passages.

I find so with my LD III+ which does impedance detection during startup. When my DT880s (250 ohm phones), are incorrectly detected as 32ohm or 60 ohm, I have to turn the volume a lot higher (to max) for the same amount of output from the same phone.

Now, I'm not sure you know what I mean by compression ...

...if you try to drive a low impedance in high impedance mode, the voltage swing of the signal is going to reduce (compress) on loud passages, because there's a limited amount of power the amp can deliver.

I don't know if you know ohm's law. And I don't think I'm doing a good job at explaining it in regards to power in this context. But basically, there's a fixed amount of 'power' the amp can deliver. V = I*R :: Voltage = Current Times Resistance ; P = V*I or R*I*I :: Power = Voltage times Current or Resistance times Current Squared. If you try to feed a low impedance load too much voltage and the tubes can't flow the current (I) to deliver the power the voltage is going to reduce on its own across the load to a point where the amp can deliver enough current to max out the power it can provide. ...compression.

(edit: I forgot my ohms law! I corrected it)
 
Oct 3, 2006 at 12:59 AM Post #15 of 31

odmanca

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Quote:

Originally Posted by vcoheda
Can someone post some pictures of the inside and the jumpers. I want to know what they look like in case I decide to run my K701 through the amp.

Thanks



Actually they are clearly marked on the PCB as CN1 and CN2 - works better than pictures
smily_headphones1.gif


Also a side note, on page 7 of the user manual it's stated these jumpers are to be used to configure the amp for "high-sensitivity" and "low-sensitivity" headphones, high-sensitivity headphones being the HD595 and HD650 and low-sensitivity ones being the AKG K501 and K240DF.

HTH.
 

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