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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Neurochrome Differential preamp build
Neurochrome Differential preamp build
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Old 18th April 2016, 05:52 PM   #1
IanLenco is offline IanLenco  United Kingdom
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Default Neurochrome Differential preamp build

My first venture into DIY amp building was Tom Christiansen's Modulus-86 power amp with which I was very pleased. So when he announced he was releasing a differential pre-amp I just had to have a go. Initially I was put off given the large number of SMD's to solder but I bought a practice board off ebay and it didn't seem impossible to do so I bought Tom's pre amp board.
A chat with a friend from Lenco Heaven at a recent get together resulted in him offering to do the SMD soldering for me as he does it all the time in his work for a Formula 1 Grand Prix team. What to do? Imagining how difficult fault finding might be I quickly chickened out Here's his excellent work.

Click the image to open in full size.

So I was left to do some simple through hole soldering and the case work/wiring.

I bought a case off ebay which eventually arrived with the wrong coloured on off switch - a replacement is on its way but it didn't stop me getting on with the hole cutting. Given everything is mounted on the circuit board it requires some precision to get all the holes in the right place - something I lack! Eventually I plucked up the courage made myself a template and loaded the stepper drill bit ready for action.

Click the image to open in full size.

Click the image to open in full size.

Miracle of miracles it fits!

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Tom's design has a Alps blue on the board but I wanted remote control and the motorised Alps wouldn't fit so I went with this arrangement.

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...and it all works when powered up!

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It's been in the system all day and I've played quite a bit of music. What does it sound like? One word, nothing Another word, transparent.

Thanks Tom!
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Old 18th April 2016, 06:43 PM   #2
zman01 is offline zman01  Bangladesh
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Neurochrome Differential preamp build
Nice work Ian. Enjoy!
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Old 18th April 2016, 08:50 PM   #3
tomchr is offline tomchr  Canada
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Very cool. Thank you for sharing. I'm glad you like it. Sonic transparency was indeed the design goal for that preamp.

Those stepped drills really are worth their weight in gold. I use one as well. As long as you pre-drill with a bit that's a touch larger than the starting diameter of the stepped drill, you'll end up with holes perfectly centred where you want them.

The full spec sheet for the Differential Preamp 8x2 can be found here: DIFF PRE 8x2 (link).

Tom
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Modulus-686: 240W/8Ω @ <0.00025% THD. Modulus-86: 40W/8Ω @ 0.000054% THD. DG300B & Other Tube Circuits.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old 18th April 2016, 09:26 PM   #4
IanLenco is offline IanLenco  United Kingdom
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Thank you Tom. You do all the hard design work I just do a painting by numbers exercise and pray it works.
I've learnt an awful lot building your amps and your help has been invaluable.

Cheers, Ian
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Old 19th April 2016, 08:51 AM   #5
billshurv is online now billshurv  United Kingdom
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Neurochrome Differential preamp build
The measured performance sounds much better in parts per billion!
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Old 3rd May 2016, 11:37 PM   #6
tomchr is offline tomchr  Canada
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Indeed. I just had an opportunity to measure the IMD. The input is an Audio Precision 32-tone test signal consisting of 32 logarithmically spaced tones from 16 Hz to 20 kHz. The output amplitude is +20 dBu.

The IMD residuals check in at -120 dBu; 140 dB below the output signal amplitude.

Tom
Attached Images
File Type: png DIFF PRE 8x2 R1.0_ Multi-Tone Test (Vout = +20 dBu).png (69.1 KB, 179 views)
__________________
Modulus-686: 240W/8Ω @ <0.00025% THD. Modulus-86: 40W/8Ω @ 0.000054% THD. DG300B & Other Tube Circuits.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old 28th July 2016, 06:06 PM   #7
tomchr is offline tomchr  Canada
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Another DIFF PRE 8x2 build coming together:
https://dashpuppy.wordpress.com/2016...pre-amplifier/

Tom
__________________
Modulus-686: 240W/8Ω @ <0.00025% THD. Modulus-86: 40W/8Ω @ 0.000054% THD. DG300B & Other Tube Circuits.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old 28th October 2016, 09:53 AM   #8
cspirou is offline cspirou  United States
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I see this a balanced preamp but it uses a 2-gang pot instead of a 4 gang pot. How does the volume control work for this kit?
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Old 28th October 2016, 09:55 AM   #9
billshurv is online now billshurv  United Kingdom
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Neurochrome Differential preamp build
Balanced in and out. Single ended gain stage.
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Old 28th October 2016, 01:46 PM   #10
cspirou is offline cspirou  United States
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So BAL -> SE , pot and then SE - > BAL? Not the type where the pot is part of the feedback loop?
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