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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

AKSA's Lender Preamp with 40Vpp Output
AKSA's Lender Preamp with 40Vpp Output
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Old 19th July 2019, 10:38 AM   #1141
xrk971 is offline xrk971  United States
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AKSA's Lender Preamp with 40Vpp Output
FWIW, I found that using a linear class 2 wall wart PSU typically found on old routers ideal for this preamp. 12v 1000mA or 800mA works too. Step up to 52v then you get 48v our after the cap Mx. If you can find a 48v to 55v linear regulated PSU - even better - then you can skip the DC-DC. They are big and expensive though.

IHB48-0.5 - International Power - Linear Power Supplies | Galco Industrial Electronics

You could also make your own unregulated one with a 10VA trafo from Antek, a rectifier bridge, a 9600uF cap and feed that to the onboard cap Mx. Precise voltage is not necessary but good to have about 45v to 48v at input to actual amp daughterboard.
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Last edited by xrk971; 19th July 2019 at 10:46 AM.
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Old 19th July 2019, 11:42 AM   #1142
Skylar88 is offline Skylar88  South Africa
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Quote:
Originally Posted by xrk971 View Post
FWIW, I found that using a linear class 2 wall wart PSU typically found on old routers ideal for this preamp. 12v 1000mA or 800mA works too. Step up to 52v then you get 48v our after the cap Mx.

I can confirm that it works very well. As X has noted before, if mounted inside the chassis, it's not class 2 anymore, but who cares? I'm very happy that I've decided to mount a router linear PSU internally. It gets hot, though - so ventilation slots is a must.

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Old 19th July 2019, 01:48 PM   #1143
Shawnstium is offline Shawnstium  United States
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It wouldn't be that hard to make a simple regulated supply using a TL783. With some tweaks that regulator could be used in place of the cap Mx on the mother board. Would something like that be better option over the 48Vdc SMPS?
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Old 26th July 2019, 09:02 PM   #1144
Shawnstium is offline Shawnstium  United States
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Well, before I begin building the power supply the daughter board needs to work. I am measuring 20vdc on the input of the card. I double checked my transistors and they are in the correct spot and check out with the diode function on the Fluke.
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Old 7th August 2019, 02:03 AM   #1145
xrk971 is offline xrk971  United States
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AKSA's Lender Preamp with 40Vpp Output
Hi Skylar,
Wow, that’s a beautiful preamp! One of the best looking that I have seen. I know it sounds awesome too.
Congrats!
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Old 7th August 2019, 05:22 AM   #1146
Vunce is online now Vunce  United States
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AKSA's Lender Preamp with 40Vpp Output
I started assembling the new PCA daughter boards that member Twocents requested, and instantly a nice compact layout by JPS64 magically appeared!
Iím also able to use one of the Crown Jewels in my parts bin (2SK170) because GaryS had suggested that option
Itís a very easy low parts count board to make, but it took some tweaking to get the bias current across the quad paralleled resistors just right. Voltage after the onboard capMx is 21vdc and across the quad paralleled resistors is 11.6vdc.
I started at the 270R value from the schematic- WAY to hot!
Next up was 330R, better but still to hot at 127mV
Then up to 470R, almost there at 98mV
Last stop will be 560R, unfortunately Iím out of them now. A quad paralleled set of 560R will give a total resistance of 140R and that will bring down the bias current to approximately 83mV.
I havenít listened to music yet, so I have nothing to comment on there.....
This Aksa Lender Pre is setup for strictly preamp duty, no HPA use.
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Old 8th August 2019, 12:24 AM   #1147
xrk971 is offline xrk971  United States
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AKSA's Lender Preamp with 40Vpp Output
Nice work, Vunce! That’s a good looking board. Do you mean mA and not mV?

When you say hot, is the MOSFET too hot or the resistors too hot? If resistors hot, try using a pair of 1W resistors in parallel which should comfortably dissipate 1aw.
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Old 8th August 2019, 12:58 AM   #1148
Vunce is online now Vunce  United States
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AKSA's Lender Preamp with 40Vpp Output
Thanks X.
It was late when I posted, yes I meant mA
I canít pull those late nights as successful as you, lol!
The resistors seem fine, itís the Mosfet I want to run a bit cooler.
Iím finishing up the second board now and have the resistors set up just right for a paralleled value of 137R5
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Old 8th August 2019, 12:00 PM   #1149
xrk971 is offline xrk971  United States
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AKSA's Lender Preamp with 40Vpp Output
You can use a bigger heatsink - it’s ok for them to run 85C even - just be careful touching it. Electronics are fine at those temps relative to lifetime and all.
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Old 8th August 2019, 12:09 PM   #1150
Vunce is online now Vunce  United States
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AKSA's Lender Preamp with 40Vpp Output
My Aksa Lender preamp stuffed with PCA DBís is singing away!!
Sounds really good, Mosfet heatsinks are running 55įC.
Now time to enjoy the make-over
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