Preamp Modifications

[WireNut]

I was looking at this preamp not long ago on Agon or USAudiomart
I believe. Thought is was a good deal. Almost beat you to it.

Congrats.

[topround]

This was sold from a private sale it was never listed so i did not beat anyone to it.
It is silly good for the money, even bone stock.
Just wait till i get my hands on it and mod it ..

and ruin it

[Carlman]

Good luck, Mike.  I had that preamp and it was modded when I bought it.  It tended to burn through tubes a bit quick, though.. I think whoever modded it might have done something to make the voltage too high on the tubes.  So, maybe that B+ think Bill was talking about is worth understanding.  I don't know, I don't mod preamps.

AllenZachary who frequents this board uses this preamp also.. and his was why I bought one.  It is a good destination in hifi equipment.  I could see someone being satisfied and stopping with this pre.

Unfortunately for me, there is no remote and 2 (that's two!) volume knobs... So much work!  I had to sell it. 

-C

[Response Audio]

Volume controls have arrived

Ii think you will really like that volume control. For the money and with the Dale RN resistors, it's worth every penny. I have used them in the past and never had any problems with them except for those who wanted remote

[tmazz]

 It tended to burn through tubes a bit quick, though. I think whoever modded it might have done something to make the voltage too high on the tubes.  So, maybe that B+ think Bill was talking about is worth understanding.  I don't know, I don't mod preamps.

We are running an AI pre in my son's Mini-mancave system and one of the things I noticed was that even when you shut down the unit with the front panel power switch the tubes remain hot. Seemed like an awful waste of tube hours , especially if you only use the system a couple of times a week. I suspect this may be why it has been known to eat tubes. I plug the unit into a power strip the has a switch on and use that switch to cut off power from the unit and thereby shut down the tubes when it is not in use. We have been running the unit on a set of tubes I pulled out of one of my ARC units after a year and it has been going for over 18 months now with no problem.

I realize that the results with one unit and one set of tubes certainly doesn't prove anything on a general basis, but if you pull the plug to power down the tubes when the pre is not in use you may very well significantly extend the tube life on an AI pre. All I can say is it works for me. YMMV

[topround]

Thanks Tom, very useful info.
I noticed that the unit is sort of always on, with the orange light that turns green, I had no idea the tubes were still warm.
Kind of a dopey design.
I have used a RM 200 amp that had cap forming switches that kept the power running thru the caps at very low voltage, so they were always ready for play, but the tubes were cold.
Seems a much smarter design for tube gear.

[tmazz]

Mike that AI pre has to be the biggest steal I ever made in this hobby. found it on the shelf at the Crack House with a price tag of $112 hanging from it. My son and I were planning to put together a second system for him to experiment with and I couldn't get my wallet out fast enough when I saw this. I figured at that price even if I had to put some repairs into it it would be a great deal. Well I took it home powered it up and it has played perfectly from day one.

See, the Crack House isn't just good for records...... 

[topround]

Tom,
I have a AudioNote kit preamp here as well, it is the L2 with phono, another very nice design and pretty reasonable.
This is another design that I think alot of people would like.

The AI is a bit better than the AN and build quality is a bit higher on the AI than the AudioNote. But the AudiuoNote is a kit and the chassis are crap and cheap

I paid $400 for the AI,and that is the going rate, the phono section is not that good on the AI, the phono in the AN is much better, but the linestage in the AI is better than the AN.
I use a separate phono anyway, so what is built in is not really necessary for me. But fro $400 the Linestage of the AI is quite good.  Not world class mind you but very good for no money in this hobby.

I will put the volume controls in this weekend and see what happens.

Mike

[richidoo]

Mike, here are 3 PS caps in stock at Mouser. It's a long link so I will put it in this link:

LINK

The Vishays are 26 x 67mm   axial leads, bipolar   $16.53 each 
The Nichicons are 22x40mm   axial bipolar   $7.04 each 

Based on smaller physical size that you need and lower price I think the Nichicons are the wtg. They're not in stock at Digikey.

[topround]

Here is a photo of the volume knob connected to the volume pot

[topround]

Here is a photo of the volume pot inside the chassis


and here



as you can see, they don't fit, so i am off to find some new electrlytic caps that are smaller, to replace the big blue mallory caps from the past.
New caps are smaller and better, and will give me wiggle room to fit the volume pots.
So the story takes a break until the caps arrive

[richidoo]

This might help with your hookups Mike:
http://www.beavishifi.com/articles/Volume_Control/

[rollo]

This might help with your hookups Mike:
http://www.beavishifi.com/articles/Volume_Control/

  Excellent read and info. The professor strikes gain.


charles

[AcidJazz]

Here is a shot of the Khozmos in my CAT...was worth all of its 200.$


 

[topround]

Looks good
I wanted to try those but they were too expensive for this project, especially since I will probably sell the Audible after the project.

Doesn't CAT use a ladder attenuator?