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AKSA's Lender Preamp with 40Vpp Output
AKSA's Lender Preamp with 40Vpp Output
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Old 9th August 2018, 03:55 PM   #771
JPS64 is offline JPS64  Germany
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AKSA's Lender Preamp with 40Vpp Output
@twocents

Could you post fotos from equipped top PCB?

I had same problem and had do mistake with two populated resistors.

JP
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Old 9th August 2018, 07:43 PM   #772
twocents is offline twocents  South Africa
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AKSA's Lender Preamp with 40Vpp Output
Quote:
Originally Posted by JPS64 View Post
@twocents

Could you post fotos from equipped top PCB?

I had same problem and had do mistake with two populated resistors.

JP
Awesome - thank you very much JP for also making mistakes - I now found the problem with mine! I tried to take some photos but cannot get clear photos with my cell phone camera and artificial light. I then checked the orientation of the resistors against X's stuffing guide, and whala - there it is - R3 and R4A are incorrectly orientated. But to fix this will require some delicate soldering surgery. Damn, second mistake on this build.
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Old 9th August 2018, 07:58 PM   #773
JPS64 is offline JPS64  Germany
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AKSA's Lender Preamp with 40Vpp Output
I did the same mistake! But good friend is expert solderer so problem solved quickly and now listing never ends.

JP
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Old 10th August 2018, 12:04 AM   #774
xrk971 is offline xrk971  United States
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AKSA's Lender Preamp with 40Vpp Output
Quote:
But to fix this will require some delicate soldering surgery.
Contrary to popular belief, desoldering is not delicate but actually sloppy and messy... add lots of extra solder to the pads you want to remove to enhance the heat capacity to get it to soften to liquidus on both legs. When hot enough, pull out the offending part. Use solder sucker or copper braid with flux to clean up excess. Trick is not to pull on part until it is really liquid or a pad will come off too.
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Old 10th August 2018, 09:24 AM   #775
twocents is offline twocents  South Africa
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AKSA's Lender Preamp with 40Vpp Output
Thank you X for the de-soldering tips. It's waiting time again for me since I don't have those resistor values in my parts bin. I my case the resistors were not the offending parts - it was the offending builder who did not consult the documentation properly!

Quote:
Originally Posted by JPS64 View Post
... and now listing never ends.

JP
Wow, this is promising and worth the wait.
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Old 10th August 2018, 11:49 AM   #776
bassmad is offline bassmad
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Hi everyone,

I am about to buy the PCBs kit to build this preamp. Will the PCB still contain errors (I have read earlier threads and saw some comments about a resistor and a diode I think)
or these were rectified in later revision PCBS (if there were any)?

Also, can someone tell me if this preamp is suitable to feed a valve amplifier? If so, should I isolate the preamp from the amp circuitry if I want to enclose this preamp IN the actual amp case? Aluminium case any good? Thanks a lot.
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Old 10th August 2018, 01:41 PM   #777
xrk971 is offline xrk971  United States
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AKSA's Lender Preamp with 40Vpp Output
Default Errata - Please Read

The PCBs themselves are fine, there was a typo on the schematic which had the V141 diode for the cap multiplier portion of the main board spec'd as a zener but it should just be a standard 1N400x or even a 1N4148 can work - it is a protection diode to protect the gate on the MOSFET.

These were noted in the main GB thread. Please consult Post 1 of this thread for updates to any errors.

As far as I know these are the only 3 errors or typos. A PCB error would actually mean that a trace was wired badly or missing.

1. Error on main PCB schematic: R141 Should be 10k not 220R.

2. Error on main PCB schematic: diode V141 should be standard 1N400X not breakdown or zener.

3. Revised BOM for MB (8-pin connector was incorrect), file here:
http://www.diyaudio.com/forums/attac...04_01_2018-zip

4. Error on SMT Daughterboard schematic: R102/103 were swapped, schematic updated now.

Here is the TH board stuffing guide - follow it exactly for pin placement:
Click the image to open in full size.
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Last edited by xrk971; 10th August 2018 at 01:51 PM.
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Old 13th August 2018, 07:44 PM   #778
twocents is offline twocents  South Africa
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AKSA's Lender Preamp with 40Vpp Output
I finally got my Lender working! After some sloppy solder surgery the implants were successful resistors R3 and R4A replaced, this time on the back of the boards. The rebellious twin daughters are doing what they are supposed to do now. The mother is no longer shorting and causing smoke in the house and the father provides clean power. My Lender family is happy and singing . Almost filed for divorce a month ago.

The only mod on my build is R11 = 2k2. With this mod I feel the gain is still a bit low for my 88dB speakers. Only a quick listening test was done using a TDA7297 amp and Tannoy monitors. Maybe I must try something like 1k8 for R11? But this operation might be even more daunting as R11 is in the middle of the board. Anyway, I will test the Lender first with the ACA which I built it for.

Many of the motherboard caps were mounted underneath the board. This was to make space for larger heatsinks on the daughter boards.

How does it sound? I only did a few quick songs using the TDA. Compared to the B1 the most notable differences are an increased soundstage and an enormous amount of bass! Really looking forward to connect the Lender to the ACA.
Attached Images
File Type: jpg Lender basement.jpg (194.3 KB, 52 views)
File Type: jpg Lender twins.jpg (74.9 KB, 50 views)
File Type: jpg Lender working.jpg (199.0 KB, 51 views)
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Old 14th August 2018, 05:25 AM   #779
xrk971 is offline xrk971  United States
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Great work, Twocents! Glad you finally got it working.
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