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AKSA's Lender Preamp with 40Vpp Output
AKSA's Lender Preamp with 40Vpp Output
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Old 7th December 2017, 09:44 PM   #351
xrk971 is offline xrk971  United States
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AKSA's Lender Preamp with 40Vpp Output
Perhaps we should ask JPs64 to make a low/high gain selector switch in the future. It’s tricky though as you want the feedback path to be clean and short and not pass through a long wire and a switch on the panel. You could just have low gain and high gain daughter boards to swap in-out.
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Old 7th December 2017, 09:49 PM   #352
jwjarch is offline jwjarch  United States
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I wouldn't mind swappable daughter boards. That would be quick enough. Great idea!


I edited my previous post but you beat me to the punch. I was saying how a build guide with various gain settings would be awesome. Or maybe it would just be included on future BOM spreadsheets.
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Old 8th December 2017, 04:29 PM   #353
JPS64 is offline JPS64  Germany
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Hi X,

find attached schematics for checking before producing manufacturing data set.

JP
Attached Images
File Type: png DIY-AKSA-LENDER-PRE-SMD_0805_1206_PBA-TOP.png (885.4 KB, 198 views)
Attached Files
File Type: pdf AKSA-LENDER-PRE_SMD_0805_1206_SCH.pdf (19.2 KB, 31 views)
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Old 9th December 2017, 12:11 AM   #354
xrk971 is offline xrk971  United States
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AKSA's Lender Preamp with 40Vpp Output
GB MB & TH daughterboard verified working.

AKSA's Lender Preamp with 40Vpp Ouput GB-gb-th-demo-test-jpg

AKSA's Lender Preamp with 40Vpp Ouput GB-aksa-lender-pre-gb-mb-th-8vpp-7kohm-fft-png

AKSA's Lender Preamp with 40Vpp Ouput GB-aksa-lender-pre-gb-mb-th-20vpp-7kohm-fft-png

This is for TH board with R5=R6=10R, R9=100k, R10=12k (22dB gain). Decreasing R9 to 68k will increase H2 relative to H3. Increasing supply voltage will decrease THD. Currently at 45v Vcc.
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Old 9th December 2017, 12:13 AM   #355
xrk971 is offline xrk971  United States
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AKSA's Lender Preamp with 40Vpp Output
Quote:
Originally Posted by JPS64 View Post
Hi X,

find attached schematics for checking before producing manufacturing data set.

JP
Thank you, JPS64. We have a layout of 0805/1206 chip resistors now - for those of us who can't find the MELFs.
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Old 9th December 2017, 10:19 AM   #356
xrk971 is offline xrk971  United States
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AKSA's Lender Preamp with 40Vpp Output
Default There is truth to "Burn-In"

Well I let the Aksa Lender Pre stay on overnight for burn-in, mostly because I was lazy to turn it off. I come back in the morning and remeasure it to make sure everything is working and thought I made a mistake or something, but the distortion went down significantly.

Here is the FFT for 20Vpp into 7kohm load, the THD is now below 0.001% into the single digits ppm, whereas was at 0.0016% before. 38% reduction of an already low level...

AKSA's Lender Preamp with 40Vpp Output-aksa-lender-pre-gb-mb-th-20vpp-7kohm-fft-burn-in2-png
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File Type: png Aksa-Lender-Pre-GB-MB-TH-20Vpp-7kohm-FFT-Burn-In2.png (81.1 KB, 448 views)
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Last edited by xrk971; 9th December 2017 at 10:27 AM.
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Old 9th December 2017, 11:51 AM   #357
xrk971 is offline xrk971  United States
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AKSA's Lender Preamp with 40Vpp Output
Quote:
Originally Posted by JPS64 View Post
Hi X,

find attached schematics for checking before producing manufacturing data set.

JP
Hi JPS64,
Here are the suggested values that could be ordered in addition to everything else already shown. This will give the user some choices for level of gain (R10), emiter degeneration on R5/R6 LTP (more or less H2/H3 ratio), and relative level of H2 (R9). Otherwise looks great. The R10 is not a MELF so perhaps can simple 1/4W axial CF be used here with bent pins?

Thanks,
X

AKSA's Lender Preamp with 40Vpp Output-gb-smt-melf-values-v1-jpg
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File Type: jpg GB-SMT-MELF-Values-v1.jpg (118.2 KB, 214 views)
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Old 9th December 2017, 11:33 PM   #358
Harry3 is offline Harry3  Australia
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Hi X,
for us non technical folk - does decreasing the gain change the THD?

Thx
Harry
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Old 10th December 2017, 01:10 AM   #359
xrk971 is offline xrk971  United States
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AKSA's Lender Preamp with 40Vpp Output
Yes, it will lower it.
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Old 10th December 2017, 11:05 AM   #360
xrk971 is offline xrk971  United States
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AKSA's Lender Preamp with 40Vpp Output
Hi JPS64,
I noticed that the header pin spacing on the new 0805/1206 SMT version is different than the previous boards, can you make sure it is compatible? A few practical comments as I am attempting to build the MELF version using 0805. The diode part is unusually small and very close to capacitor and transistor pads. Solder paste from nearby pads can pool and surface tension from uneven heating can pull parts out of alignment easily. Would it be possible to make 1N4148 an 0805 part and move it farther away from others? Maybe place to the left where ground plane vias are - reduce ground plane there is OK. Also, would it be possible to cover all vias with solder mask? They are prone to sucking up loose solder and forming solder bridges.
Thanks,
X

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Last edited by xrk971; 10th December 2017 at 11:08 AM.
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