Preamp Modifications

[topround]

I bought a Audible Ilusions Modulas 2D for $400.
It is a very nice sounding preamp, especially for the money.

I am going to mod it....of course, and I am going to document all the changes and the percieved sonic differences I hear.

Later today I will post pictures of the unit bone stock.

I will perform one mod at a time in a certain order, photograph the mod and document what I hear. I am open to suggestions.

First mod will be the volume controls. The volume controls look like Alps blue, but may be something else. I ordered Dale Vishay stepped attenuators on eBay for $51 for the pair! with resistors!. Shallco 43 stepped attenuators with resistors are $348 from Michael Percy. These I am sure are the cats meow, but at the price of what the preamp almost cost me it seemed too over the top, even though I knew it would be the best volume control. I decided to do this on a budget, try to get great performance without buying the most expensive boutique parts.

Next up in mods will be power supply:
There are two sets of electrolytics that will be replaced. Since the unit was built in 1989 it probably is just good audio hygiene to replace these. I will do this in the 2 steps that are there. I will not use Black Gates which are impossible find and are not caps I like anyway, and I know I am in the minority here. Probably elna or Nichicon, or maybe some oil caps!

Next in the power supply will be the diodes, new diodes are .just faster and quieter, never a bad thing.


After the power supply I will look at some of the coupling caps, there are a lot of them in there and good quality caps can add up quick, I will address the ones I deem important and leave the phono section alone as it is not that great anyway.

Next we will look at hookup wire, this will be replaced with Neotech cabling. I am definetly open to suggestions on this topic.

Again it will be a slow process, and one at a time, allowing the parts to burn in, I usually replace a bunch of stuff at once, and we all know that is the wrong thing to do.

Hopefully it will turn out nice, perhaps it may get ruined, but there is alot to learned along the way.

Here is alink to the volume controls I bought, the first step for great sound in a preamp.

http://www.ebay.com/itm/Dale-23-Step-Ladder-Type-Attenuator-Potentiometer-POT-Log-100K-Ohms-Mono-x-2-/221094036357?pt=US_Home_Audio_Amplifiers_Preamps&hash=item337a3b4385


Final step will be a deep cryogenic treatment of the whole unit

[StereoNut]

Sounds like (pardon the pun) like we're in for a ride!  Should be a very interesting "bang for the bu¢k" pre-amp mod/re-build that will allow everyone to learn something along the way.  Keep us posted step by step, as you said you will and don't forget the photos. 

Good luck and "may the flux be with you!"

SN

[rollo]

    Cool. The character of the AI is warm and or dark in stock form. A very colored preamp. It will be interesting to hear the sonic differences wrought by each mod.
     My suggestions to consider are; Slagle chokes in the power supply, Hexfred diodes, silver hook up wire [ DH labs or Deulund ], Deulund Alexandra coupling caps,
    Tubes recommended are Siemens or another brighter side of neutral tubes. Teles would be the cats meow but not cheap.
    I owned the IA #A for quite some time used it with SS amps to add some lushness to them. Tubes made a huge difference with that preamp. You may just start there and then see what each mod offers in change.
    Have fun a cool thing to do.  BTW Penny & Giles are the so called best attenuators around.


charles

[sleepyguy24]

Yes. Please definitely keep us posted with all the pics to boot. I enjoy reading threads like this since I can't DIY much.

I've always been curious about refurbing/modifying the older gear.

Is this just a fun project or to prove that with refurbing older gear you can create a giant killer?

[richidoo]

Nice preamp. This will be fun!

The attenuator steps are not very even, but the price is right. I wouldn't dip them in nitrogen though because the plastic might not take it well.

These are very nice rectifier diodes, I have used them several times with great results.
http://www.mouser.com/Search/ProductDetail.aspx?R=FFP08S60SNTUvirtualkey51210000virtualkey512-FFP08S60SNTU

Nichicon KL are good for coupling electrolytics, if electros are needed in the signal.

What voltage and capacitance are the original storage caps?

Transformer output?        not cheap...

Some AI preamp mod ideas:
http://www.chimeralabs.com/audIllusmod.html

[AcidJazz]

Hey, we are moving along parallel paths Mike, I started mods on my CAT pre about a month ago. First mod was to eliminate the balance control and replace the stereo stepped pot with Khozmo mono pots, have to say it was a big jump in performance with just that one mod.
Since this CAT is circa 1990, I was also looking at the electrolytic caps as the next step. Hope we can compare notes on parts selections etc.
I will post some pics when I get back late January.

Good to know Rich, about the Nichicons. 

[topround]

This is a project, a logical, laid out plan to improve a design.
Will it be a giant killer? I doubt it. Can it be improved? I think so.
This is a project just for fun, since it did not cost much it has become sacrificial, besides the preamp I really want is the Dude, which i can't afford right now(new car and braces for the kids).

Martin, we are moving in parallel lines although I might zig zag about freely with this, with your Cat i would stay within the lines, don't ruin it! Besides Ken Stevens is kind of a prima donna and thinks you should not mess with his superior designs.
Volume control is key in a preamp, most manufacturers skimp here because the really good stuff is expensive and labor intensive,but the killer volume controls are stock equipment for the DIY crowd.

Pictures coming soon, volume pots are on there way and this preamp just might become a DHT tube version, if we decide to go crazy!

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I was looking at those Khozmo attenuators, they look very nice, and I was tempted , especially with 48 steps! but they were too expensive for this project, but I would like to try them in the future especially since Martin is having good results with them.

Electrolytics are next on the mod list

(3)  100 uf 350 v
(3) 10,000 uf 10 v
(1) 470 uf  16 v

I am open to suggestions, what would you guys like to try?

[richidoo]

This is what I would try

http://www.mouser.com/ProductDetail/Nichicon/UKL1C471KPD/?qs=sGAEpiMZZMtZ1n0r9vR22U0HJIc3SC%252bohOY9JOxTyFo%3d

http://www.mouser.com/ProductDetail/Panasonic-Electronic-Components/EEU-HD1A103/?qs=sGAEpiMZZMtZ1n0r9vR22QGha91sM8wWq6d5e4Jz2wY%3d

http://www.mouser.com/ProductDetail/Nichicon/UPW2G101MRD/?qs=sGAEpiMZZMtZ1n0r9vR22RxOeB5kHP9B6%252blgtsUaExA%3d

Check the sizes of the cans and lead spacing.

[topround]

Rich,
I will order these parts tomorrow.
BTW I like Panasonic Electrolytics

I will post fotos of the volume controls going out and the new ones in and  I will burn the steps that i like in the volume control with a cd player.
Rollo mentioned Deuland Alexander caps for the coupling caps in the signal path, these are very nice sounding caps but too expensive for this project, besides if I was to use Deuland it would be CAST as that is what they are famous for, the Alexanders are just an attempt to get more market share from the boutique market, they are rebranded Jensens, which make Deuland.
I was thinking more along the lines of the new Auricaps or maybe Dynamicaps. I am pretty familiar with the Dynamicap sound and it feels to me like it would be a good match for the AI circuit. I like Auricaps as well but I have never heard the new ones, but it seems they adressed the areas where the Auricap needed a little help(in the extremes), hopefully not at the expense of the Auricaps strength(midrange)

But coupling caps are a way off..much to do before that.

Mike

[Face]

Also consider Jensen or Mundorf for the power supply.

[richidoo]

For common parts like this digikey can ship 1st class mail, which is cheaper than mouser UPS.

For coupling I like the Jantzen Superior Z and Silver Z. They sound good and not too expensive. I avoid bypass caps.

For cheap coupling caps Vishay MKT1813 are pretty good for the money. http://www.vishay.com/docs/26013/mkt1813.pdf