A2D

Support for JLM Audio Kits

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living sounds
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Re: A2D

Postby living sounds » Thu Oct 16, 2014 1:06 am

Also, won't I have to attenuate the signal at some point so the converter doesn't clip?

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Joe Malone
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Re: A2D

Postby Joe Malone » Thu Oct 16, 2014 8:04 am

Thanks Joe! Is there a drawing of the JLM14 windings so I can understand the wiring? From your description I would imagine that yellow and blue are the primaries in a single winding, and red and green are two secondary windings with black the center tap?


You imagine correctly :-) We are using the JLM14 backwards in this case so there will be a 12dB loss of gain which works well as most A/D IC's only want a 1 or 2v peak to peak to hit 0dBFS. So you should at least need +12dBu or more to get 0dBFS.

if you want a exact input level to equal 0dBFS a 3 resistor pad can be added in between the XLR and Yellow , Blue wires. Just need to let me know the level you end up having to put in to hit 0dBFS.
Most common setup is +18dBu = 0dBFS for pro A/D, Next most common setup is +22dBu = 0dBFS. A pad would be added hit either of these exactly.
Joe :-)
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living sounds
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Re: A2D

Postby living sounds » Thu Oct 16, 2014 6:55 pm

Thank you Joe, sounds great. Just two more question: Will this configuration work well with balanced as well as unbalanced sources? Also, how much DC on the input can the transformer handle?

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Re: A2D

Postby Joe Malone » Thu Oct 16, 2014 7:32 pm

living sounds wrote:Thank you Joe, sounds great. Just two more question: Will this configuration work well with balanced as well as unbalanced sources? Also, how much DC on the input can the transformer handle?


Yes balanced in or unbalanced in doesn't matter as it is a floating transformer input so does not care. You should never have DC on the input as almost everything is capacitive coupled output and any DC servo outs will not have more than a few mV so will not matter.
Joe :-)

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living sounds
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Re: A2D

Postby living sounds » Sat Oct 18, 2014 3:45 am

Thanks Joe! I'll report back when I've got the JLM14 installed.

craigmorris74
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Re: A2D

Postby craigmorris74 » Tue Apr 23, 2019 6:10 am

I was always fascinated with this project, and hated to see that it wasn't issued as a kit. Were any components removed from the A/D board, or did the signal go through all the input circuitry before the A/D chip?

Thanks
Craig

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Joe Malone
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Re: A2D

Postby Joe Malone » Tue Apr 23, 2019 10:53 am

craigmorris74 wrote:I was always fascinated with this project, and hated to see that it wasn't issued as a kit. Were any components removed from the A/D board, or did the signal go through all the input circuitry before the A/D chip?

Thanks
Craig


A row of caps were removed to allow the input transformer to feed direct into the A/D chip. A2D PCB is no longer available unfortunately
Joe :-)

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craigmorris74
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Re: A2D

Postby craigmorris74 » Tue Apr 23, 2019 1:23 pm

Thanks for the reply Joe. Interesting stuff!

I have an old SM Pro Audio ADAT board, and would love try hooking up a couple of JLM14's to it and see what it sounded like.

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Re: A2D

Postby Joe Malone » Tue Apr 23, 2019 1:44 pm

craigmorris74 wrote:Thanks for the reply Joe. Interesting stuff!

I have an old SM Pro Audio ADAT board, and would love try hooking up a couple of JLM14's to it and see what it sounded like.


If you can take a large clear in focus photo of the top and bottom of the SM Pro PCB I am sure I can draw the mod on there for you to try.

If made a huge difference.
Joe :-)

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craigmorris74
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Re: A2D

Postby craigmorris74 » Wed Apr 24, 2019 10:03 am

Hey Joe,

Thanks again for your reply. I've attached photos of the top and the bottom of the board, as clear as I could get of the analog sections, and the schematic.

Thanks,
Craig
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Joe Malone
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Re: A2D

Postby Joe Malone » Thu Apr 25, 2019 1:32 pm

craigmorris74 wrote:Hey Joe,

Thanks again for your reply. I've attached photos of the top and the bottom of the board, as clear as I could get of the analog sections, and the schematic.

Thanks,
Craig


EDIT
We removed all 150R feeding 10uF and 9.53k resistors feeding opamp inputs and added wire under pcb between 10pin socket pin 1 to 4 and 7 to 10 going to each A/D input 1 to 8 via the 10uF just to make it easy to unplug the pcb.

JLM14 backwards giving -12dB loss so in front of the transformer we used a U pad made with 3 x 1k resistors to yellow and blue to give +18dBu input clip level. Green wires to 0v pin 5&6 on 10pin connector. Red wires in series with 120R or 220R to form filter with cap on A/D input.
Joe :-)

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