Ultimate Aragon 18K Rebuild

Dr K

Member
Hello, new member here. I wanted to post the rebuild of my Aragon 18K preamp here. Until recently, I have not been what you call a solid state fan or an active preamp fan. However, several months ago I had Ken Ealey rebuild an Acurus RL11 that I got for paltry $150 on eBay. I've been using passive preamps all along (stepped resistor, autoformer, and LDR) as I have found them to be more transparent and free of artifacts than any active preamp I have auditioned including 5 figure preamps. I was surprised to find out how good the Ken Ealey rebuilt RL11 is. In some respects, it surpassed the best passive preamps I have used (ie, better dynamics, both micro and macro, and more realistic high frequency performance). I asked myself if I achieve even better results, so I looked into its more sophisticated brother, Aragon 18K, which I found on eBay for around $300. But Ken Ealey has no mod for the 18K and was too backed up to even try.

This is where Kevin (aka Mondial Fan) comes in. As you may know, he is a prominent member here and has worked on many Mondial designs including the Aragon preamps. I contacted him to see if he would be willing to build the ultimate 18K. I wanted the following.

1) Critical signal pathway resistors to be replaced with naked Z-foil resistors from Vishay for low power circuitry and NOS US manufactured Mills MRA resistors for the output.
2) Bypass the large value electrolytic caps with good film caps and bypass the input coupling cap altogether.
3) Bypass the preamp's selector switch and balance control.
4) Use dual mono remote controlled autoformer volume control (amorphous core, hand wound by a specialist in the Netherlands). The dual mono volume control can also function as balance control.
5) Use Neotech Silver/gold hookup wire in the signal path.
6) The preamp can be either a PASSSIVE preamp going through the autoformer volume control only or an ACTIVE preamp going through the 18K circuitry, selected by simple relay switch.
7) RCA sockets are true copper (ie, 99.5% copper). Most audiophile RCA sockets that are claimed to be copper are actually alloys containing significant amount of other metals (eg, brass or bronze).
8) Kevin has his own version of Aragon preamp power supply, which is over spec'd using toroidal transformers and increased capacitance over the largest power supply Aragon built for Aurum preamp. So I decided to use his power supply with more mods including film cap bypass, AC filter, and additional supply for remote volume control.
9) This rebuild required entirely new PS and preamp chassis, so we designed new custom chassis for this project.

Here are some photos of the power supply. More to follow.
Powersupply1.jpg Powersupply2.jpg Powersupply3.jpg Powersupply1.jpg powersupplytop.jpg powersupplyback.jpg
 
Forgot to mention Kevin agreed to build this preamp, but obvious since I posted photos of his work. As you can see, his work is exemplary and has factory new appearance, actually miles better than what Aragon produced any modder work I've seen.
 
Here the plans for front and back plates.The front face plate is in the middle and will be chrome plated. The first image is the front panel with hole cutouts for the volume controls and switches.

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Here are the parts for the preamp project. First photo shows the mono inductive/autoformer volume controls with remote control units and stepper motor. Second photo shows the base Aragon 18K preamp from which we obtained the circuit board for this project seen in third photo. Fourth photo shows 100 uF Clarity film caps and 22 uF Mundorf Supreme caps, which will be used as bypass caps. Also Furutech and DH Labs RCA sockets and silver solder.

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Wow, you're going all out on this re-imagining of an 18K! Epic! Subscribed!

Also, thanks for posting the ClarityCap ESA (I think) and Mundorf Supreme pictures. I need both of those exact values, for a speaker recap, and I had no idea that they'd be THAT big. So while I do plan on a 22uF Supreme, I might have to rethink the 100uF ESA cap. It may not fit where it needs to go. Which reminds me, will you be using the stock 18K chassis? Or are the ClarityCap and Mundorf caps for the outboard power supply?

Oh yea, an Acurus RL11 for $150, and an Aragon 18K for $300! I must not be watching eBay closely enough. I've been wanting to replace my L10 with one of those for a long while now, and I must have missed those auctions. Good job!
 
Wow, you're going all out on this re-imagining of an 18K! Epic! Subscribed!

Also, thanks for posting the ClarityCap ESA (I think) and Mundorf Supreme pictures. I need both of those exact values, for a speaker recap, and I had no idea that they'd be THAT big. So while I do plan on a 22uF Supreme, I might have to rethink the 100uF ESA cap. It may not fit where it needs to go. Which reminds me, will you be using the stock 18K chassis? Or are the ClarityCap and Mundorf caps for the outboard power supply?

Oh yea, an Acurus RL11 for $150, and an Aragon 18K for $300! I must not be watching eBay closely enough. I've been wanting to replace my L10 with one of those for a long while now, and I must have missed those auctions. Good job!

Hi StimpyWan. Thanks for your response.

I will not be using the stock chassis. It has to be bigger so I'm having a custom chassis built. As you can see, I posted diagrams of what the front and back of the chassis will look like. You can also see the photos of custom power supply which has much larger chassis to accommodate the Clarity caps, two toroidal power transformers, etc. The Mundorfs will be in main preamp chassis as bypass for those large filter capacitors on the left side of the 18k circuit board.
 
Thanks. Are use using the main board as is, keeping the circuit design stock?

You're redesign reminds me of doing a computer upgrade. Just pull the motherboard, drop it into a new case, add more ram and a bigger hard drive, and you're good to go for a few more years.
 
Thanks. Are use using the main board as is, keeping the circuit design stock?

You're redesign reminds me of doing a computer upgrade. Just pull the motherboard, drop it into a new case, add more ram and a bigger hard drive, and you're good to go for a few more years.

Please see my OP. It describes what will be done to the circuit board and circuit. The preamp will be able to switch between active and passive mode, so you get two preamps in one.
 
Please see my OP. It describes what will be done to the circuit board and circuit. The preamp will be able to switch between active and passive mode, so you get two preamps in one.

Yes, I did read that section. But, I guess I didn't see those as major circuit changes. Though, I have to admit, I'd be loathe to remove the balance control. It comes in handy, with some poor recordings.
 
Yes, I did read that section. But, I guess I didn't see those as major circuit changes. Though, I have to admit, I'd be loathe to remove the balance control. It comes in handy, with some poor recordings.

Because the inductive volume control is dual mono, you automatically have balance control. Balance can be adjusted via remote.

I didn't want to do any major circuit changes because I like the basic sound of the circuit. It's never harsh sounding, but detailed and natural. I'm a tube guy so that's what drew me to this preamp,
 
Because the inductive volume control is dual mono, you automatically have balance control. Balance can be adjusted via remote.

I didn't want to do any major circuit changes because I like the basic sound of the circuit. It's never harsh sounding, but detailed and natural. I'm a tube guy so that's what drew me to this preamp,

Duh! Dual mono volume does also allow for a balance feature too! My bad...! :whip:
 
Yes, I did read that section. But, I guess I didn't see those as major circuit changes. Though, I have to admit, I'd be loathe to remove the balance control. It comes in handy, with some poor recordings.

No there are not any major circuit changes. The basic design of the Aragon circuit is quite good, the original discrete DC rail regulators, complementary differential inputs using low noise SC1583/SA798 Toshiba audio transistors with active current sources combined with the mosfet output stage, it all remains intact. The 18k circuit itself was not seen as a compromise. The Acurus Pre's had compromises in them most of which were to control costs, other compromises in the Acurus pre's, i.e. the lack of active current sources, was to limit the sound quality. Anyhow we knew that Mondial had to control costs somewhere in the Aragon and that occurred in the parts selection and power supply. So we decided to replace the main components where Mondial had to compromise due to cost. Dr. K spared no expense on this one. Everything he's putting in this custom 18k pre is top notch.
 
I have very good opinions of my Aragon equipment. But I have zero experience with a soldering iron and zero knowledge of how audio circuits work.

Your Aragon gear may be over 20 years old. It may be about time to recap them. Those electrolytic caps drys up over time and may go out of spec. Sound will probably improve too.
 
Your Aragon gear may be over 20 years old. It may be about time to recap them. Those electrolytic caps drys up over time and may go out of spec. Sound will probably improve too.
Can anyone recommend a technician in central NJ or eastern PA? :)
 
I couldn't possibly swing the bill on a rebuild like this :). so i will live vicariously through your thread, and be Thankful that I own a Mondialfan blessed Aurum preamp that had a little mini upgrade along with his powersupply board, still want to get a toroid in there but that may require a custom power supply case. If i remember correctly, there are some v-cap bypass caps in the pre itself.

There are quite a few aragon junkies here on AK. Ive bought and subsequently sold a bunch of what i acquired, but im still hanging on to a few units. I finally got my hands on a 47k, Next stop... A 4t2 tuner. To complete an 8008bb/ 18K MKII setup ive been putting together for fun - a bit of aragon pokemon go if you will, trying to catch the entire stack, which includes the 47k i mentioned and a d2a series II .

We use an 8008x3 in one space and then theres a pallladium / momdialfan Aurum combo hanging around in another space. Im glad there are no matching source units to match. Hahah. So ive pulled some strays together to complete that stack. magnum dynalab md108 tuner , sony xa-7es cd, essence hdaac dac blah blah blah etc etc...

Still debating on. Swapping original palladiums (004 based) for a set of version II (008 based) units. I dig the heatsinks on the 008 revison. Shallow and silly but true.

THat 18k project sounds epic. So did Kevin's. 28k remix. Loved that idea too. I can see myself getting into some updates but that will have to come a bit later, my little ones eat like hungry football players depite only being 2 and 3 :).

Keep the pics and updates coming.
 
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