Marsh headphone amp from Linear Audio

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#521
I went the hardware route so it could be stand-alone. Would not have to use a computer to get it working. But, thats an individual preference and cost issue.

I got a new THD instrument here and learned the second harmonic (H2) is really about the only harmonic to increase as load Z goes down to 30 Ohms. The other harmonics are so far down it doesnt matter. In other words, the effect is benign.

BTW - if this was used as a line amp, instead, - driving high Z load like the input of power amp or what ever - the HTD+N is around .00025%.... H2 is .00015% of that total.
Thx-RNMarsh
 
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#522
RNMarsh said:
I went the hardware route so it could be stand-alone. Would not have to use a computer to get it working. But, thats an individual preference and cost issue.

I got a new THD instrument here and learned the second harmonic (H2) is really about the only harmonic to increase as load Z goes down to 30 Ohms. The other harmonics are so far down it doesnt matter. In other words, the effect is benign.

BTW - if this was used as a line amp, instead, - driving high Z load like the input of power amp or what ever - the HTD+N is around .00025%.... H2 is .00015% of that total.
Thx-RNMarsh
Click to expand...

True on individual taste but I would prefer a hardware solution over having to buy and debug software.

Nice to throw in the specs when using it as a pre-amp. I am tempted to use it as a pre-amp as well!

For some of us amateurs, we sometimes miss the little details. I see the regs that I bought (LT1963a) only like to run up to 20V max at the input. I am so used to just snapping up 18V secondary transformers that I missed that little bit of info. I should have picked something a bit lower on the secondary voltage.
 
#523
sonidos said:
For some of us amateurs, we sometimes miss the little details. I see the regs that I bought (LT1963a) only like to run up to 20V max at the input. I am so used to just snapping up 18V secondary transformers that I missed that little bit of info. I should have picked something a bit lower on the secondary voltage.
Click to expand...

You can use an LM317 or LM7815/MC7815 ahead of the LT1963A.
 
#525
question about heat from the regulators

jackinnj -

We know that the output transistors need to have heatsinking. How about the LT regs you mentioned? How much heat did they give off? I bought the dpak smt versions off ebay for a great price. I want to just 'dead bug' them on a proto board but how hot do they get with the head amp?
 
#527
both of which I have showed here on this forum

homemodder said:
Hmmm, this is just a combination of two well known circuits, both of which I have showed here on this forum. The input is the buffer as shown by JLH, the second part is as I described in Mpp thread to tweak JLHs headphone amp. Does this designer frequent DIY audio ??

Anyway it will sound and measure very well indeed.
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Could you provide the link?
 
#528
here is the original JLH headphone amp circuit --- RNMarsh

??
 

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#533
RNMarsh said:
here is the original JLH headphone amp circuit --- RNMarsh

??
Click to expand...

I bought about 2 yrs ago a JLH headphone amp being promoted on this DIYAudio site.... it doesnt measure as well, either. What else can i say. I even paid about $450 for a finished product off a headphone only site and wasnt pleased with the results, either. Now that one also sits unused as more wasted money. :-( It was all IC based.... but couldnt drive low Z headphones well... even with a buffer IC after the opamp. The sound matters. Measurements matter. Seemingly small changes matter.

Thx-RNMarsh
 
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#538
Telstar said:
JLH amp IC based? the sold u a fake.

A real JLH circuit is in my do do list (after yours, yay!)
Click to expand...

I just looked at my comment - some of it didnt come thru.... the JLH was bought off this forum/dyiaudio headphones here. Not IC. Others tried were IC based. There are many to choose from. Some are copies of others work- like JLH. Some are improvements on others work. I am here only to help with my headphone amp... its dirivation is discussed in detail in Linear Audio publication.
In another forum here in dyiaudio I am working on measuring the thd and harmonics and trying to come up with a signal source and thd meter to measure the headphone amp. each time I get something better to test with, the number drops. My older Audio-Precision wasnt up to the task. I now use a ShibaSoku AD725D which can measure directly, to -135db re 1 volt. Then I can add FFT and notch filters to drop that further. Now I need a better signal source and modifying an HP339A as a better (lower distortion) source. All started because I couldnt get an accurate number for my own headphone amp design with the A-P. Its been expensive but fun, too.

Thx-Richard Marsh
 
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#540
I've put together some kits of parts for the Marsh headphone amplifier -- you've got two choices: 1) Semiconductors and active components = $54;
2) Semiconductors = $27.50.
This will be sufficient for a pair of amplifiers -- one for each ear.

The JFETs are matched for Idss (that is you get a 2N5460 and 2N5457 which are matched for Idss +/- 0.1mA), bipolar output devices for hfe.

An externally hosted image should be here but it was not working when we last tested it.


Yes, there is a markup. Mother Theresa is dead.
 
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