Acurus P10 phono stage mod/rebuild

[KNielsen]

Hey AK

I'm planning af full rebuild on my Acurus P10.
One thing I've learned from my earlier amp project https://audiokarma.org/forums/index.php?threads/acurus-a250-and-starground.815860/ is that I'll prepare better this time... Meaning I wouldn't have to wait for new parts constantly, but order a big pile right from start.

But what can be done to this thing?

The PSU screams for an udgrade, and I know I'll change all the resistors with Dale RN60 series and a full recap.

Any more suggestions?
Is there any thing I can duplicate from the better sounding Aragon 47K?

Btw I can't find a schematic for this thing

Regards

 

[KNielsen]

Took the lid of the P10... Somebody has been messing with it before me
But luckily it can be reversed.

I need to know the correct values (or what to aim for when ordering) on R7/R8/R9/C10 and C13. All has been changed by the previous owner.
The PSU caps has been changed to 2x10.000uf.

Regards

 

[mondialfan]

Many of the schematics are available for legacy Acurus & Aragon components at Indy Audio under discontinued products. Here's the link, just click on P10 and it'll open a file browser.

The 47k and P10 are identical as far as the circuit goes. In fact there's a small amount of P10's out there that have the 47k copper colored board in them and not the standard P10 green board. I guess Mondial ran out of the green board and used the 47k board for a short period of time. The 47k of course has the bare copper colored pcb and also uses RN-60 resistors throughout. Inside the 47k under the same steel transformer cover as the P10 the holes in the main board for the internal transformer are present but those holes are empty because of the external PS. The 47K is hard wired from the back panel DC power input to the corresponding hole that the transformer secondary would feed. If you want to go with an external PS then you'll need to feed +/- 24vdc into the unit. At one time I had a picture of the 47k with that cover removed on one of my computers. If I can find it I'll post it.

 

[KNielsen]

So as you say, obviously the external PSU and better parts are the only difference between the two.

C10/C13: are there any higher values I should consider?

Thanks Mondialfan

 

[mondialfan]

Here's the 47k wiring underneath the steel cover. Pretty simple setup, red wire +24, Blue wire -24, green wire common. The large resistors set up the CRC filter between the external PS and the internal primary storage caps.

C10/C13??? Do you mean C10/C11? I'd stick with 1k uF.

 

[KNielsen]

.

 

[KNielsen]

I deleted last post, as there were some issues to correct. It picked up high frequency noise and some hum delivered to the speakers constantly ... I don't really know exactly how I reduced the hum, for long time i thought the wire between the 2xCCS was the problem acting like an antenna, and tried different approaches with straight wire and so forth. I ended up matching a complete new set of current sources with a slightly more boost then the first I did, and altered their location away from the inputstage by soldering my homemade PCB's with the components on the opposite side, flipping the boards. The diodes I'm using is 2mA-types, and the first CCS's I tried the diodes were run at 800μA. Some tests at DIYAudio suggest that lowest noise is reached at maximum mA from LED-diodes. The new CCS as pictured the diodes are set to 2mA sharp and the current output is 486μA... On the pictures as is now its Duelund Copper/Cotton wire between the CCS..
-And I think the resistors on the main PCB did the last part of reducing noise for the better?
It's all good now dead quiet background. The signature of the RIAA has definitely raised to the better.. and I'm home safe with the following

Heres what I did so far (and a few missing items):
-Removed R15/16 and added constant current sources at this location.
-Replaced the carbon resistors with metalfilms. I haven't got enough 25.5ohms, so these hasn't been replaced at the diff section and the output stage yet. I haven't worked on the Load/Gain-stage, as I want Dale RN55 due to space and haven't got these in stock. That said I never gave to much about changing resistors, but I really feel I can hear an improvement in sound with those resistors I've changed so far!(??).
-Replaced the 470uf BP cap with Nichocon Muse of same value.
-Replaced the 5VA transformer with a 10VA-type. Minor drilling was needed, but fitted like a charm beneath the internal PSU lid.
-Replaced the 1A diodes and installed 2A ultra-fast type at the bridge rectifier.
- I left the original 3300uf e.caps for now, but will replace these with 4700-6800uf e.caps... I did however add 1uf bypass to the 3300uf on the back of the PCB.
- Haven't touched the 6x1000uf caps. These will be replaced with better spec'ed Chemi-Con KZN-series of same value. The 10uf filmcaps will be replaced with ClarityCap ESA (if these will fit??? Haven't meassured yet )

Regards and sounds awesome

 

[KNielsen]

.

 

[KNielsen]

Done... Sounds fantastic

Last words on the work:
Since the PSU is internal I desided to skip the idea of investing big money in foilcaps (C12) and added the much smaller 10uf Nichicon Muse cap parallel with a 0.1uf Wima MKP4 here.
The Chemi-Con KNZ (C10/C11/C13/C14) is my first try with these capacitors, and I'm quite impressed!
I added 0.1uf Wima MKP4 to C10/C11 on the bottom and skipped the 1uf at the PSU e.caps as described added in previous post.
I skipped the looped Duelund Copper/Cotton wire at the CCS in favour of a solidcore copper/teflon wire straight between the two polarities, also for a smaller overall interference hopefully(?!)...
Lastly I lowered the current just a few μA at the CCS.
A small bonus was better internal offset after replacing all resistors with matched RN60D's at the input/output stage. I haven't touched the transistors itself.

Last thing to do is to replace the stock 3.300uf e.caps with 105°C 4.700uf Vishay Mal-series at the PSU. They have been ordered, but first stock is set to may2024, so a bit waiting for these. And I forgot to order RN55D 25.5ohms for the Loading-section, but my current cartridge doesn't need that value anyway, so not that important right now.

-It sounds sweet and with authority, yet very neutral without ANY fuzz..
I didn't know exactly what to expect when removing the "yellow" caps and replaced with aluminium ones, but it really didn't change the signature of the sound. Now I only see benefits for their size in a sensitive unit, and they are better at blocking DC after some monitoring at the outputs before and after the change.

Best regards

 

[Celadon]

Nice
Thanks for sharing, really appreciate your detailed write-up.

I have an Aurum; and a 47K - both stock.
Have a NOS faceplete for my Aurum ...

Happy listening
Celadon

 

[KNielsen]

Nice
Thanks for sharing, really appreciate your detailed write-up.

Thanks. Its my first try with a RIAA and I somehow neglected at the beginning how sensitive these devices are. The later in the build I got, the better I was using my scope to double check the results.
I ended up with a dead flat line, sadly I cannot measure THD for now, but I'll bet it's somewhat lower then before by the looks on the scope.
There were some pitfalls alone the way, one of them my cartridge(!) witch picks up hum from everything. It isn't elektro magnetic shielded, so even small interferences is amplified, and annoying when listening to the RIAA as the build progressed.
When I finally found the source for hum in my living room, things got a lot easier to hunt down on the workbench
That said, I feel the rewards has exceeded my expectations.

Best regards

 

[Celadon]

Awesome! Always great to hear a successful story - I learn alot, each and every day...

My luck yesterday, was needing to do a bit of final work on my McIntosh Mc2505, moved it from one end of the room onto my bench, all looked well, and damn if I hadn't lost one of the barrier strip screws -that stupid thing could be anywhere..... An hour or so later I go sit on the couch, and look down -- there's the crazy screw! Just shows how things like that, and springs... fly wherever.. Just getting ready to lug the McIntosh down into the rack.

I have quite a few other projects in the works right now, but my 47K is super clean, and I did just detail it.
It has the IPS power supply -- and that certainly needs to be opened up; and more than likely refreshed.

I really like my 47K -- it just gets outta the way, and I like the jumpers instead of switches for the adjustments.

 

[Celadon]

Aragon Fan Page <---- More than likely this has been posted before, but it's a pretty good place to visit for Aragon stuff ...
@mondialfan Has really contributed some awesome content at AK, and his work is pretty amazing. I spent many a read... Thank You!

 

[atlvalet]

Well @KNielsen now I know what your name is on DIYaudio lol

Since the 47K @mondialfan helped me modify is my only phono pre, has anyone compared their P10 or 47K to any other offerings out there, new or vintage?

Most reviews state the Aragon/Acurus units are really good, but I was looking to see if anyone had a direct comparison?

 

[KNielsen]

My real name is Kaare Nielsen. My username on DIYAudio was created almost 20years ago in my youth... If I should create a new account today I would do it by my name, just as here...
That said, the Aragon should sound even better with the external power supply. The rest is identical between the two

 

[KNielsen]

Just received the final missing part that was ordered before refurbing the P10, the Vishay Mal 6800uf 105°C e.caps...
Since the phonostage doesn't take much current I didn't suspect a noticeable effect by replying the stock 3300uf.
I can recommend the MAL-series as a good replacement combo with a 10VA xformer. New life and and only positive impact on the sound

 

[Celadon]

Just received the final missing part that was ordered before refurbing the P10, the Vishay Mal 6800uf 105°C e.caps...
Since the phonostage doesn't take much current I didn't suspect a noticeable effect by replying the stock 3300uf.
I can recommend the MAL-series as a good replacement combo with a 10VA xformer. New life and and only positive impact on the sound

Good to hear you are on your way to completion with this project!

I was hoping you could point me in the direction of where you sourced the particular Vishay Mal's --
With a quick look, I was only coming up with screw type caps, at much higher voltages. I assume these are snap in type caps, though.

Height under the inner metal cover is a concern to me, or rather lack thereof.

I had my Aurum apart and did some work on it -- In the same board position as yours, there are 2 low (in height) and wide caps (filter caps?) that are 10,000Uf 35V -- that measure approx 26mm in height, (there is no inner cover) -- but, don't know how much room I have to work with under either the Aurum or the caps under the cover on the 47K.

Thanks in advance,

Celadon

 

[KNielsen]

Good to hear you are on your way to completion with this project!

I was hoping you could point me in the direction of where you sourced the particular Vishay Mal's --
With a quick look, I was only coming up with screw type caps, at much higher voltages. I assume these are snap in type caps, though.

Height under the inner metal cover is a concern to me, or rather lack thereof.

I had my Aurum apart and did some work on it -- In the same board position as yours, there are 2 low (in height) and wide caps (filter caps?) that are 10,000Uf 35V -- that measure approx 26mm in height, (there is no inner cover) -- but, don't know how much room I have to work with under either the Aurum or the caps under the cover on the 47K.

Thanks in advance,

Celadon

I always source my parts from Mouser. Some specials are only available through Digikey due to my location, such as the 10VA transformer I use.

Here's the Mouser Part-NO for the Vishay MAL: 594-MAL225630682E3
There's 323psc available at this moment.

Since they discounted the Nichicon LKG snap-in series witch I liked alot I've tried different brands as replacement. One I would not recommend although data seems very good, is the Kemet ALC80 (this might be only be true for Acurus gear?!)....
I've got these Kemet's in 10.000uf/40V and tested in my Acurus preamplifier with very similar PSU design, and the soundstage just sounded so harsh. I left them in the pre for almost a month without any improvement before removing them again.
The Kemet's might perform better in the Aragon 47K and Aurum with their better external PSU/bigger transformer, where I'll bet they would at least fit in your Aurum, also in main chassis: Kemet ALC80 10.000uf/40V dimensions is 40mm(H)x30mm(D).
Mouser Part-NO: 80-ALC80A103CD040

The 47K is same chassis as the P10, but can't remember the total internal hight from PCB to lit.
For now I'll stick to the MAL-series also in future upgrades in my own gear, I'm quite pleased.

Best Regards

 

[KNielsen]

@Celadon for the Aurum these might be of your interest: 594-MAL225640103E3
90pcs in stock at Mouser, measuring 30mm(H)x30mm(D), 10.000uf/35V.

You'll have to confirm the dimensions your self by measuring in the preamp as I never worked with a Aragon Aurum.

Regards

 

[Celadon]

@KNielsen Thank you so very much --
just looked over data sheets kinda quick -- and gives me some figures to work with.

I myself look away from Kemet -- never really a fan.

Vishay, on the other hand have always treated me well --
I get a chuckle out of all the talk over the Vishay MKP1837's that were all the rage a few years back - sorting through stuff today, there were a quad of them, along with some Sonicraft Gen I caps i found...

There was A special resistor that I wanted to use for the 47K -- if I remember correct it was either a nude Vishay, or maybe another close brand --
It may have been Texas Instruments-- you contact them with the value, and they make the particular resistor I am thinking of, I have specifics somewhere. <--- I was going this direction.

Then There's Speco, if they are still around, but they may not do the kind of items needed -- well worth looking into though.

Thanks on the info about the caps for the Aurum -- looks like I would have ~4mm more... More homework.

I am currently trying to concentrate on my Technics RS1500 R2R -- but the Aurum and the 47K sound damn good --but a bit long in the tooth, I must admit ---

Eating the elephant, one bite at a time -- thanks again,

All my very best -

~C




Unbelievable the kindness and generosity of folks here -but after all this IS AK.....