Crown D75

Part substitutions and replacements, rebuilds, before/after measurements, challenges encountered discussed here.
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John Warren
Posts: 14
Joined: Sat Feb 10, 2018 8:58 pm

Crown D75

Post by John Warren » Mon Feb 12, 2018 11:34 pm

Very early unit with manually laid out PCB traces (gold plated), composition resistors.
Picked this unit up locally. Front panel is as good as new.

Plan will be to measure the unit as is then decide where to go with it!
Attachments
D75_3.jpg
D75_3.jpg (765.46 KiB) Viewed 2713 times
D75_2.jpg
D75_2.jpg (701.16 KiB) Viewed 2713 times
D75_1.jpg
D75_1.jpg (516.78 KiB) Viewed 2713 times
North Reading Engineering
email: audio@northreadingeng.com
cell: 978 795 7172

John Warren
Posts: 14
Joined: Sat Feb 10, 2018 8:58 pm

Crown D75

Post by John Warren » Mon Feb 12, 2018 11:41 pm

Photo of unit here (top) and a somewhat later production unit (bottom, photo pulled from the net). Note differences in PC boards.
Attachments
D75_4.jpg
D75_4.jpg (385.02 KiB) Viewed 2707 times
D75_internet.jpg
D75_internet.jpg (1.35 MiB) Viewed 2708 times
North Reading Engineering
email: audio@northreadingeng.com
cell: 978 795 7172

John Warren
Posts: 14
Joined: Sat Feb 10, 2018 8:58 pm

Re: Crown D75

Post by John Warren » Sat Feb 17, 2018 5:09 pm

Setup for distortion measurements.

Amplifier module board is early unit.
Attachments
D75-9.jpg
D75-9.jpg (676.23 KiB) Viewed 2609 times
D75-8.jpg
D75-8.jpg (1017.08 KiB) Viewed 2609 times
D75-7.jpg
D75-7.jpg (649.39 KiB) Viewed 2609 times
D75-6.jpg
D75-6.jpg (588.57 KiB) Viewed 2609 times
North Reading Engineering
email: audio@northreadingeng.com
cell: 978 795 7172

John Warren
Posts: 14
Joined: Sat Feb 10, 2018 8:58 pm

Re: Crown D75

Post by John Warren » Sat Feb 17, 2018 5:22 pm

As-received, no mods, all factory parts. 1kHz FFT at full power, each channel.
Attachments
ch2_1kHz-full.jpg
ch2_1kHz-full.jpg (74.88 KiB) Viewed 2607 times
ch1_1kHz-full.jpg
ch1_1kHz-full.jpg (76 KiB) Viewed 2607 times
North Reading Engineering
email: audio@northreadingeng.com
cell: 978 795 7172

John Warren
Posts: 14
Joined: Sat Feb 10, 2018 8:58 pm

Re: Crown D75

Post by John Warren » Sun Feb 18, 2018 3:26 pm

Amplifier board wire connections and color codes, early D75.
Attachments
color_codes.jpg
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North Reading Engineering
email: audio@northreadingeng.com
cell: 978 795 7172

John Warren
Posts: 14
Joined: Sat Feb 10, 2018 8:58 pm

Re: Crown D75

Post by John Warren » Mon Feb 19, 2018 11:37 am

%THD at 1k (bottom) and 10kHz (top) to full power comparing two op-amp front end packages, NE5532P and LME49720. Balanced inputs. No significant differences.
Attachments
ch2_1k-10kHz-_recap_LME49720_NE5532P_frontend.jpg
ch2_1k-10kHz-_recap_LME49720_NE5532P_frontend.jpg (143.49 KiB) Viewed 2554 times
Last edited by John Warren on Mon Feb 19, 2018 11:39 am, edited 1 time in total.
North Reading Engineering
email: audio@northreadingeng.com
cell: 978 795 7172

John Warren
Posts: 14
Joined: Sat Feb 10, 2018 8:58 pm

Re: Crown D75

Post by John Warren » Mon Feb 19, 2018 11:38 am

10kHz FFT at 1Vrms and full power out into 8Ohm power resistor. Front end LME49720, balanced inputs. Higher distortion at 1V out as seen above.
Attachments
ch2_10kHz_full.jpg
ch2_10kHz_full.jpg (91.93 KiB) Viewed 2554 times
North Reading Engineering
email: audio@northreadingeng.com
cell: 978 795 7172

codewritinfool
Posts: 2
Joined: Sun Feb 11, 2018 5:37 pm

Re: Crown D75

Post by codewritinfool » Sat Mar 31, 2018 5:17 pm

That early PCB artwork is beautiful. I did some of it back in the day, but nothing that beautiful.

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