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Old 16th November 2011, 05:18 PM   #2081
Bensen is offline Bensen  Belgium
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Default Crescendo 1982 - 2pairs of output devices

In my first builds of this amp I had some oscillation issues. Since my last rebuild (+-2001) everything runs fine.
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Old 24th November 2011, 08:43 PM   #2082
Salas is offline Salas  Greece
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Default 20 years old chip wine

A 20 years old chip preamp this one. Came for changing log pot from the friend I had given it a long time ago. It is an OPA627 unity gain buffer feeding an OPA637 X6 gain stage sandwiching the volume control. Fully DC coupled with offset trimmers for each stage. Had made a large hand drawn PCB for it back then including routing for many inputs and rec out select all the way back to a row of RCA's meeting the board. Had simply cut out some aluminum panels and put it together with stainless steel screws and Fender Tele knobs. Automotive paint job non the less. I remember to had selected the 627-637 just from a BB brochure on intuition. Too expensive to stock, the official representative company had told me in yr 1991. Two months on the wait on special order and many dollars for the era... Very good passive components like Holco and Vishay, separate PSU, Teflon silver wiring, and what do you know, still measures and sounds clean as a whistle, and smooth. Especially with the new pot, very good imaging. Can pass a very nice 200kHz square wave, won't clip before 29V Pk-Pk sine wave, FFT attached (0dBFS=2VRMS). Nice to preserve an oldie.
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File Type: jpg CheapSwitchingPot.jpg (240.1 KB, 1503 views)
File Type: jpg CheapSwitchingPotBack.jpg (292.0 KB, 1269 views)
File Type: jpg ChipRow.jpg (154.9 KB, 1219 views)
File Type: jpg OPALIneOnRack.jpg (237.4 KB, 1238 views)
File Type: gif OPA627&637LinePreTHD.gif (14.0 KB, 489 views)
File Type: gif OPA627&637LinePreIMD.gif (14.1 KB, 188 views)
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Old 25th November 2011, 12:58 AM   #2083
rfj5106 is offline rfj5106  United States
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Hello Salas,

How did you do that beautiful paint job?
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Old 25th November 2011, 01:42 AM   #2084
Salas is offline Salas  Greece
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I gave the aluminum panels to a mate that was working in a paint shop at the time. And he used some leftover paint from when he had done his Vespa scooter. Really. Then it got renewed 15yrs later by the guy I gave it to. In an automotive paint shop. Check out how it reflects. Good in squares too. That one was a 20KHz square.
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Old 25th November 2011, 08:02 PM   #2085
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Salas: Other than those two buggers / harmonics @ 2k, ~3.3k ... ~120++ db down, all the way across, is still very impressive. All that plus a clean 20k square wave passthrough ...

Maybe a "re-visit" to this design is in order ... using plastic caps around the newer op-amps and other tweaks? (I might like to have one, me-self. )

Last edited by FastEddy; 25th November 2011 at 08:12 PM.
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Old 25th November 2011, 11:27 PM   #2086
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This one would have been a plain Blameless, but ended up a derivative of the DIYAmp (PCB layout is my own, transformer is only a 30-0-30 V unit).
http://www.diyaudio.com/forums/solid...-diyaudio.html
The performance is as promised. Big thanks to OS!

Case top and bottom are 2mm anodized aluminum sheets.
Front and back are sanded 100x6mm aluminum flat bar.
Heat sinks are Modushop/Hifi 2000 300x80mm, drilled and tapped 8-32 to hold the six sides together.

The power devices leads will be trimmed flush. They were left in case the mounting arrangement had to be changed.

The FFT was done with an emu0204 unit and has to be taken for what it is worth.
The 60/180/300/420/540 Hz noise visible seems to be coming directly from the transformer. It can be canceled almost totally by rotating the toroid around its bolt, at the expense of the other channel. Both channels are audibly silent.
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File Type: jpg ssIMG_3801.JPG (77.3 KB, 722 views)
File Type: jpg ssIMG_3804.JPG (101.4 KB, 609 views)
File Type: jpg ssIMG_3808.JPG (89.6 KB, 502 views)
File Type: jpg ssIMG_3812.JPG (63.6 KB, 473 views)
File Type: jpg ssIMG_3813.JPG (98.9 KB, 526 views)
File Type: jpg ssIMG_3825.JPG (98.9 KB, 661 views)
File Type: jpg ssIMG_3836.JPG (96.2 KB, 644 views)
File Type: png ss01 fft blame L, 10V, 10ohm, ifbox-20dB.png (120.2 KB, 477 views)
File Type: jpg ssfft emu0204 loopback, -12dB in_cr.jpg (98.6 KB, 244 views)
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Old 26th November 2011, 09:29 AM   #2087
Nrik is offline Nrik  Denmark
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Beautiful :-)
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Old 26th November 2011, 11:47 AM   #2088
kees52 is offline kees52  Netherlands
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also a beauty, very low thd, but how it sounds with so low thd because the first and second harmonic is importand for the amp character, maybe this one sounds very lean?

what do you use for measurement? of thd, I look for good software and mike.

it is beautifull made.

regards
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Old 26th November 2011, 01:41 PM   #2089
Salas is offline Salas  Greece
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Quote:
Originally Posted by FastEddy View Post
Salas: Other than those two buggers / harmonics @ 2k, ~3.3k ... ~120++ db down, all the way across, is still very impressive. All that plus a clean 20k square wave passthrough ...

Maybe a "re-visit" to this design is in order ... using plastic caps around the newer op-amps and other tweaks? (I might like to have one, me-self. )
I believe that the 10uF Stargets decouple it fine, there is no ringing in square waves, and there is no glassiness subjectively. A parallel regulator would make it more juicy. I must be having the hand drawn layout ''modules'' around the chips somewhere, but I could not readily find them to post them for you.
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Old 26th November 2011, 01:49 PM   #2090
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Quote:
Originally Posted by kees52 View Post
also a beauty, very low thd, but how it sounds with so low thd because the first and second harmonic is importand for the amp character, maybe this one sounds very lean?

what do you use for measurement? of thd, I look for good software and mike.

it is beautifull made.

regards
To me it sounds great - but I have tin ears
I do believe the speakers to be the bottleneck in the chain though.

The measurement is done using an E-MU0204 USB DAC/ADC unit at 24bit/192kHz:
E-MU 0204 USB

The input is routed via a homemade 0/-10/-20/-30/-40 dB attenuation box with zener clamps to protect the ADC.
The ADC can only take 2 Vrms maximum, so I use 20 dB attenuation in that graph. The software is SpectraPlus. The numbers shown on the graph do not mean much - the E-MU runs out of steam above 30 kHz.

10 V, 20 kHz square wave into 10ohm/47nF attached.
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Last edited by discrete; 26th November 2011 at 01:51 PM.
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