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Old 20th August 2013, 11:30 PM   #1
ammel68 is offline ammel68  United States
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Default Acurus L10 Preamp Mods & Schematic

Does anyone here have or know where I can find a schematic for the Acurus L10 preamp?

Also, does anyone here have any experience with upgrading/modding the L10?

Thanks...
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Old 25th August 2013, 02:00 AM   #2
ammel68 is offline ammel68  United States
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So, 91 views and nobody knows anything about these preamps?

Interesting...
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Old 25th August 2013, 02:41 PM   #3
AVWERK is offline AVWERK  United States
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I think it was designed by William Synder who at one time was a production manager for Krell.
It was reviewed in the Audio Critic mag and got 2 thumbs up for the price.
I,m going from memory and might be off somewhat. There was a phono unit combination also and I might be thinking of that one...

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David
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Old 27th August 2013, 06:25 PM   #4
ammel68 is offline ammel68  United States
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Thanks for the info. David.

I'm interested in the changes I saw here:
Ken Ealey Audio - Rebuild Packages - Acurus L10 and RL11 Preamplifiers

I've sent this guy a couple of emails, but so far no reply.
Apparently his mods are "shrouded in secrecy".
Nonetheless, I'm not going to pay somebody $250 to change out a few components.

Here are the changes/mods he supposedly performs:

-First, he replaces the BJT transistors with some type of mosfets.
These mosfets are handmatched to the millivolt level and provide true differential performance. A circuit MUST have this to provide the best symmetry.

- Second, the idle current is increased putting them in that famous "Linear, Class A" mode. The stock version has to run barely turned on at nothing more than a trickle current for DC offset purposes. This mosfet upgrade fixes all that and then some. It has repercussions throughout the circuit.

- Third, active current sourcing is used to bias the mosfets and takes the place of the single stock resistor. All aspects of performance are improved and the result is a real front end the way a front end is supposed to be done. Most manufacturers don't budget for this step because it costs too much and demands special attention since it does not lend itself to mass production. As good as the stock version sounds, this sounds better with solidified imaging, soundstage, and clarity.

If mosfets sound so much better, then I wonder why Mr. Snyder didn't use them to begin with?

I wouldn't mind trying some of these things on my L10, but it may be difficult without a schematic to see the original circuit.
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Old 27th August 2013, 06:42 PM   #5
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There is a guy at the Danish HIFI forum who's had the mods done. There are schematics and some pictures of before and after in the thread. Quite interresting as it seems to me from those to you can deduce a lot about the mods. Link: HIFI4ALL Forum: Opgradere strømforsyning?

Martin
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Old 27th August 2013, 10:53 PM   #6
ammel68 is offline ammel68  United States
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Thank you Martin!

Now I have the schematic(s) and a PCB photo of the board after Ken's changes.
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Old 29th August 2013, 01:03 AM   #7
ammel68 is offline ammel68  United States
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Attached is the schematic for one channel thanks to Martin.

Will some of you experts on here please take a look at it and see what changes you would make to improve the sound?

I've outlined the changes ole' Kenny does above. Perhaps he's talking about replacing Q1 and Q3 with mosfets? Looks like Q2 and Q4 have been removed.

Also attached is an image of the board after his mods.
Attached Images
File Type: jpg Acurus-L10-schematic.jpg (128.6 KB, 343 views)
File Type: jpg Acurus-L10-mods.jpg (183.5 KB, 339 views)

Last edited by ammel68; 29th August 2013 at 01:08 AM.
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Old 29th August 2013, 10:23 AM   #8
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Hi ammel68, got your PM.

I will ask in the thread if he know the types of the semiconductors in his amp after the mod. If you look at the PSU mod it seems that he is removing the regulator and replacing it with some extra resistors and capacitors. I personally would rather keep the regulator and tweak the capacitors. Better yet rebuild the regulator as a shunt type (I like shuntregs).
It seems like he has changed Q3 and Q1, as well as removed Q2 and Q4, removing the symmetrical topology of the input-stage. I think this as well is a fairly drastic mod. It will almost certainly change the sound, but it changes the topology as well, making it essentially another amplifier, from my point of view.
Though I am skeptic, the mods might change the sound for the better, I am not knowledgeable enough to say. The guy in the Danish forum who's had the mods done, is very happy with the sound.

/Martin
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Old 29th August 2013, 04:11 PM   #9
ammel68 is offline ammel68  United States
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I agree, I'm not really interested in the power supply mods. I'm more interested in the changes to the amplifier section itself.

Looks like R14A,B have also been removed. I assume the trimmer pots are there for biasing the mosfet transistors, but not sure.

I'm wondering how similar the modded unit will be to the JC-2 clone on Ebay?
Symmetric Complementary J FET Preamplifier JC 2 KIT | eBay
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Old 29th August 2013, 05:45 PM   #10
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Before the mod it looked a lot like a jc-2 with BJT input... From a quick glance he removes the symmetry from input.

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