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AKSA's Lender Preamp with 40Vpp Ouput GB

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#542
Vunce said:
Just thinking….
Your 25W choke loaded THF51S SIT source follower amplifier probably takes about 30 mins for the heatsinks to reach equilibrium temperature. Would that be a coincidence or a condition that starts the interaction with ALP? And why?
This is a strange one
Click to expand...
That had crossed my mind but I must admit to being perplexed as to where to begin investigation of a potential interaction. Tonight I hooked up the ALP to a NuHybrid headphone amp/preamp (Pete Millett design) to see if the noise was present when driving a different amp, albeit a low power headphone amp. Not surprisingly, it wasn't, even after being on for several hours. Just total black silence between tracks. I also tried feeding the ALP into the power amp of an Audiolab 6000A (pre and main can be separated on this unit), with the same result. So I'm now doubting whether the ALP is to blame. My SIT amp is based on a design by Ben Mah (https://www.diyaudio.com/community/...d-193v-choke-loaded-2sk180-lamp.366312/page-6). See post #109 for schematic. I am using THF51S instead of 2SK180, Hammond 195T5 choke in place of 193V, Meanwell LRS-150-36 SMPS, three stage LC SMPS filter (design by Mello4) and 15mF of additional DC filtering. To date it has worked flawlessly with everything I've connected to it, with the unfortunate exception of ALP. But I haven't investigated its operation with an oscilloscope. This may reveal a different story.
Click to expand...
 
#543
Problem has been solved, or at least, gone away. I removed the SMPS filter I had been using for some time from the SIT amplifier and replaced it with PO89ZB SMPS filter designed by Mark Johnson. No more noise, even after operating for several hours The entire chain (source, preamp, power amp) is dead silent with no signal, on speakers or headphones, just as it should be. Oddly, the original SMPS filter is now operating without issues (noise or otherwise) in the ALP power chain, between the SMPS and DC-DC power converter. I can only guess that there was some strange interaction between the filter, power amp and preamp that was causing the noise, as nothing else has been altered. I have been listening to the system for a few days and it is performing superbly. I can only echo comments by X and others regarding the musicality and natural sound of the ALP with the source follower SIT amplifier. I now need to properly house the ALP in a suitable case as its definitely a keeper.
Thanks again to all for comments and suggestions regarding this issue.
 
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#551
There’s 562 units of the above cable when I click on the link above. Are we talking about a different cable because this PCB has only that one 8pin male-male cable. Those cables make a foolproof connection.

If you want to make your own you will have to figure out the matching part. It’s tricky - I ordered the wrongs ones several times before getting it right. This was years ago though.

Maybe someone who has recently built this knows the exact parts.

There are male/female and through hole and SMT and 0deg and 90 deg. Many permutations.
 
#554
I just finished putting together the SMT daughter boards using the BOM linked in the first post. Very challenging using only a fine tip solder iron and regular solder but everything is in place with the exception of the V102 diode. The pad is tiny and the part spec'd in the BOM is beyond small. How do you deal with something this minuscule? I gave up and dug out some through hole diodes and somehow got those soldered onto the pads.

My AKSA Lender was running as the HPA version so I cranked up the PSU to bring the voltage from 24V to 50V and all seems good. It's working well as a pre for my Modulus-86 right now. Next step is to bring it back into the workshop and see what it can do connected as the front end for some tubes.

AKSA_Lender_SMT.jpg
 
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#555
Nice work Spiggs!
I had trouble with that pesky little diode too. It’s really meant for solder paste and hot air/hot plate install and is best installed by a robot pick and place. My request to JPS64 would be never to use this type of footprint for DIY projects or anytime someone needs to install by hand. They have tiny little legs that make them fall over or stand up when the solder paste surface tension kicks in.

Good luck on using this as a preamp. I think you will find it very nice sounding and powerful enough to drive any amplifier.
 
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