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Marsh headphone amp from Linear Audio
Marsh headphone amp from Linear Audio
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Old 17th January 2018, 04:25 PM   #1421
RNMarsh is online now RNMarsh  United States
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Marsh headphone amp from Linear Audio
Hi,

Well I hope you looked at some of the pcb layouts or bought a kit by now and are building your HPA. In the layouts and kits you can get a sense of what the Wattage for R's is. Basically, All can be 1/4w except those in the output stage - they should be 1-2W resistors..... the 4.7 and 18 Ohm.

To lower the gain, you can increase R5 to maybe 2K.

Increasing OPS bias beyond what is used in original isn't needed. The distortion is already extreamly low and you might have to change output devices.


THx- Richard
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Old 20th January 2018, 04:21 AM   #1422
ammel68 is offline ammel68  United States
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Marsh headphone amp from Linear Audio
Richard, what's up with wearing that dumb-looking cowboy hat in your latest avatar??
Did you recently visit Texas?
You look like you're really p_$$ed and ready to gun down some other cowboy.

Just having a little fun with you Mr. Marsh, so don't take it seriously.

Now...let's bust out the moonshine and soldering iron and build something!
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Old 20th January 2018, 10:07 AM   #1423
BuckarooBanzai is offline BuckarooBanzai
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Thank you for the reply .

I reckon your hat looks spiffy
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Old 23rd January 2018, 09:36 PM   #1424
CometCKO is offline CometCKO  United States
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Originally Posted by jackinnj View Post
A couple of folks have asked about boards. Restating, they are $3 and have two amplifiers. Shipping varies all over the world. Here is a picture of what they look like:

Hi jackinnj, I sent you a PM; looking forward to building this! I've never been a headphone guy, but lots of DIY turntables, phono stages & the like. Do you have any recommendations for power supply?
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Old 24th January 2018, 02:09 PM   #1425
jackinnj is offline jackinnj  United States
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Marsh headphone amp from Linear Audio
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Originally Posted by CometCKO View Post
Hi jackinnj, I sent you a PM; looking forward to building this! I've never been a headphone guy, but lots of DIY turntables, phono stages & the like. Do you have any recommendations for power supply?
I used a Lambda brick for the first one. Another has an Amveco torroid and CRC filter.

You can use a wallwart and DC-DC converter with a low noise post-regulator I've used Murata and Meanwell, but thesedual output devices should work, and cost ~$16.

https://www.recom-power.com/pdf/Econoline/RS6.pdf

I think Jan's "Simpleswitcher" isn't quite up to the task as it will only source 150mA.
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Old 28th January 2018, 06:56 AM   #1426
RNMarsh is online now RNMarsh  United States
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Quote:
Originally Posted by ammel68 View Post
Richard, what's up with wearing that dumb-looking cowboy hat in your latest avatar??
Did you recently visit Texas?
You look like you're really p_$$ed and ready to gun down some other cowboy.

Just having a little fun with you Mr. Marsh, so don't take it seriously.

Now...let's bust out the moonshine and soldering iron and build something!
I don't know what possessed me. Goofy mood, I guess.


-Richard
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Old 28th January 2018, 02:37 PM   #1427
craigtone is offline craigtone  United States
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Originally Posted by CometCKO View Post
Do you have any recommendations for power supply?
I used this one with great success:

Positive and Negative +/- 1.25~37V DC Adjustable Voltage Regulator Module | eBay
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Old 5th February 2018, 04:00 AM   #1428
RNMarsh is online now RNMarsh  United States
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Hello Craigtone. How would you describe the sound and performance?


THx-Richard
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Old 26th February 2018, 09:52 PM   #1429
Caiparinha is offline Caiparinha  United States
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Originally Posted by jackinnj View Post
I used the devices from your article. JFET's usually matched to 100uA Idss, 2N's matched for vbe or hfe. the output transistors matched similarly -- MJE's are slightly quieter than 2SD/2SB but the latter have higher gain and show less distortion.

Transistors/diodes for 2 channels $27.50, complete set of parts (no power supply) $54.00. PM if interested.

I have 2 complimentary transistor matchers -- very twitchy.

FWIW, I think I mentioned way back in this thread that even with randomly selected devices the performance is really excellent.
PM Sent. With all the rave reviews I am in for the full kit if still available.

Thanks... Chris
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Old 23rd March 2018, 07:34 PM   #1430
RNMarsh is online now RNMarsh  United States
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Gilding the lily ---

i think, since I found the THD lowered with higher DC ps voltage, other higher voltage rated output transistors should be used at +/- 22-24vdc at 250mA minimum per channel. 300mA or more should be enough.

The suggested alternative transistors seem fine for use with higher voltage PS. be sure that the pS cap voltage is high enough.

What I found specifically, is the 3H drops more than 2H as PS voltage is increased. Just going from 15v to 22-24 vdc dropped the 3H about 15dB.

The reason for this drop in HD is because the FET device C's continue to go down as PS voltage goes up. These C's are quit non-linear. Another factor is the topology -- the push-pull complimentary input makes C of gate-drain cancel at input with input connected together. So we dont need to cascode with the spec'ed jFET devices. .

Dont get too excited - we are talking about levels already below -110--120dB to -135dB. The residual mismatch in C's can be trimmed further

You can add some small C with a trimmer cap to one side to balance the C values which then cancel. Or, since the C's are voltage dependent, a drop in the - Vs of 3 diodes in series with neg PS will change the C enough to make + and - equal and null.

But, just run at higher voltage will do the most good for the least effort. Be sure heat and voltage rating on caps and transistors etc are adequate. I added small heat-sinks to the second stage (Av).

Enjoy.



THx-Rnmarsh

Last edited by RNMarsh; 23rd March 2018 at 07:52 PM.
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