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Old 28th March 2012, 08:24 PM   #1
JoeDJ is offline JoeDJ  United States
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Default Little dot and direct coupled amps......

Little dot pre amps are not to be use with direct coupled amps and I do understand why. Exactly how is one to know exactly which amps are direct coupled?

I have been told that most amps these day are direct coupled but, I do no know how true this is. Yes, I'm a bit confused over this born of my ignorance.

I ask this as I may get a Little Dot MKIII for headphone use.
However, I was wondering if I can also feed the LD output into an intergrated amp to boost low output sources such as an mp3 player.

What about T class amps? Are they considerd DC?
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Old 28th March 2012, 11:30 PM   #2
JoeDJ is offline JoeDJ  United States
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I have to assume that others are about as confused about this as I am.
Even on the LD forums, others can not get an answer to questions about DC amps.

Last edited by JoeDJ; 28th March 2012 at 11:32 PM.
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Old 28th March 2012, 11:46 PM   #3
godfrey is offline godfrey  South Africa
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Quote:
Originally Posted by JoeDJ View Post
Little dot pre amps are not to be use with direct coupled amps and I do understand why.
Why?
Quote:
Originally Posted by JoeDJ View Post
Exactly how is one to know exactly which amps are direct coupled?
Open it up and look inside, study the schematic, or ask the manufacturer.
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Old 29th March 2012, 12:35 AM   #4
JoeDJ is offline JoeDJ  United States
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Originally Posted by godfrey View Post
Why?

Open it up and look inside, study the schematic, or ask the manufacturer.
I've been told that with a DC amp, if a valve fails on the LD, it can send high dc current to the speakers.

To be honest I thought that here, among the "experts" someone would know about the T amps.

BTW, if I was competent in reading schematics, I would already know the answer .
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Old 29th March 2012, 08:41 AM   #5
Simon B is offline Simon B  United Kingdom
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I guess we must all just be too stupid Joe......

"Class-T" isn't a class at all, it's a trademark for a now bankrupt company's class D amp chips.

If you want to know if an amp you've got is dc coupled, you could always try putting some dc into it - not too much mind, and watching what happens at the output with a meter.

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Old 29th March 2012, 09:38 AM   #6
godfrey is offline godfrey  South Africa
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If in doubt, you can always do the AC coupling yourself; just put a suitable capacitor between the Little Dot's output and the power amp's input.
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Old 29th March 2012, 09:56 AM   #7
DF96 is offline DF96  England
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I thought the Little Dot was a headphone amp? Surely it has to include a DC blocker at the output? I realise the LD is strange: I believe one version of it is simply a solid-state amp with a variable-mu cathode follower to add some distortion.
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Old 29th March 2012, 10:33 AM   #8
godfrey is offline godfrey  South Africa
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I believe one version of it is simply a solid-state amp with a variable-mu cathode follower to add some distortion.
Aha! That's what I was suspecting. I guess they could leave out the output cap and use a DC servo or some other feedback arrangement to get rid of DC offset at the output, but I wouldn't want to own something like that.

If the valve fails the wrong way, you're screwed; there will be 100V or so on the output, and the feedback won't help. It's not just DC current through the speakers either; that kind of abuse would probably fry the input stage of a number of amps as well. (and an input coupling cap rated at 16V or so won't help either)
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Old 29th March 2012, 10:52 AM   #9
DF96 is offline DF96  England
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I understand that the different versions of the LD had quite different circuits, although details are hard to find. I saw on one website that someone had bypassed the CF and found that measured distortion roughly halved! (and it sounded better?)
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Old 29th March 2012, 04:26 PM   #10
JoeDJ is offline JoeDJ  United States
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As I said, even on the LD fourm there is confsion about the compatability of the LD amps when used as a preamp citing not to use them with a direct coupled amp. Even the moderators say "check with the amp's maufacture for compatabilty" to everyone who needs an answer..... never really adressing the issue.

BTW, I'm aware that T amps are a trade mark for amps using a Tripath chip but, they are a class of amps none the less with a certain architecture. My question was are they generally considered direct coupled designs.

I am interested in the LD MKIII.

Last edited by JoeDJ; 29th March 2012 at 04:40 PM.
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