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Acurus L10 problem

Ok, stupid question... Since I moved the 47Kohm to the back, i suspect i need a load on the output when probing the with signal? Somewhere between 10-100Kohm?
What's your wote @mondialfan

Also about my tryout regarding measuring the difference between 970/2240 and BC549/BC550 I the diff-section, it would have helped if I remembered to short the inputs by muting the unit instead of tracking all sorts noise..... I'll try again later
 
10K load... Squarewave:
1.4Vpp input, 100Hz/1kHz/10kHz/20kHz
IMG20240219153739~2.jpg
IMG20240219153724~2.jpg
IMG20240219153710~2.jpg
IMG20240219153655~2.jpg

10K load... Sinewave sweep (video):
1Vrms input, 5Hz-250.000kHz
photos.app.goo.gl

Acurus LS11 "k" · Monday, Feb 19, 2024

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10K load... Sinewave til clipping:
2Vrms input, 1kHz
IMG20240219160128~2.jpg

All tests (except clipping) was performed leaving the volume untouched at 12o'clock.

Please comment if I'm doing this wrong:)

EDIT: be aware that my probe is set to x10, but scope is set to x1, so 1 division is 5volts for all tests except till clipping where i spotted this. A mistake by me;)
 
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Current state as drawn. I haven't measured the raise-times yet.
The 10Kohm at the output just emulate the load and can be ignored.

1000003827.jpg
 
Since I'm talking to my self in the search for the very best this preamp might do, I might just continue doing so :D
I found the missing midrange that my previous owned "Ken Ealey-version" of this preamp did so well :)
The DC-offset adjustment do function, but the difference between the impedance at input vs outputstage does make it drift a bit more then I would normally approve.
I tried different settings for better performance at the differential stage without making the source seeing a load, but at best I saw some marginal phaseshift on the oscope, and returned to settings as posted above.
A cap of high value did the trick to meet F3 a the feedback/gainstage.
1000003853.jpg

Regards
 
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And to be fair, the topology in the Acurus with the diff-transistors that's NOT thermally coupled like the Aragon might (or will) make things harder to achieve a well set offset. With the cap installed the margin swings within ±0.05mV.

Good day
 
Stable and fully tested Acurus LS11, shared as inspiration.
It's a -3dB@1.7MHz preamp in the current configuration, yet also the most musical I've managed to do. Very easy listening, no edges.

Regards
1000003989.jpg
 
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Hello there, is anyone here? I didn't want to start a new thread about this topic if I didn't have to. I am experiencing this same volume/balance issue as OP. I am weighing my options, clean,lube reassemble,test, or replace volume control with something else, as the originals are not available. Can anyone tell me what I can use for that? Alos, would it make any sense at all to bypass my balance control? I have no use for it and it can be nothing but a maintenance item and lossy?

So is there a ALPs control I can replace my NOBLE with, as I cannot find any available? Thnaks for any help you all may offer. I love this pre, but the VC is maddening
 
33713 said:
Hello there, is anyone here? I didn't want to start a new thread about this topic if I didn't have to. I am experiencing this same volume/balance issue as OP. I am weighing my options, clean,lube reassemble,test, or replace volume control with something else, as the originals are not available. Can anyone tell me what I can use for that? Alos, would it make any sense at all to bypass my balance control? I have no use for it and it can be nothing but a maintenance item and lossy?

So is there a ALPs control I can replace my NOBLE with, as I cannot find any available? Thnaks for any help you all may offer. I love this pre, but the VC is maddening
Click to expand...
I have the big brother, or cousin to your pre; an Aurum. But with regards to your vc question … I bet Partsconnexion has a viable alternative, seems I remember researching for another pre, and TDK had a decent offering.

If it were mine I would go with a Goldpoint, if they are still available, outstanding product, albeit it will lighten your wallet. I have one hiding in a box somewhere, but still won’t sell it.
No matter your choice, be sure you have the space to fit whatever replacement you choose, mm’s can make the difference!
Best on your journey,

Celadon
 
ALPS Blue Velvet 20Kohm is a perfect substitute. But you'll need some additional wiring as shown here as the OEM volumepot that came with the Acurus has special longer legs.
That said I can't tell the difference between ALPS and the more expensive TDK which I bought in this thread. I did regret spending the extra money on a TDK.
A stepped attenuator might be interesting, but expensive. I have a DACT CT2 in my current preamplifier and it's the best investment I've done for years regarding volume control. Absolutely tight tolerances and perfect balance between channels no matter the volume setting.

Best regards
 
Hey folks, thanks for the responses. So the original has 8 pins and the alps has 6 pins. I am good at soldering R&R, not reading schematics how do I go from 8 pins to 6 pins, or asked another way, why are there 8 pins in the first place? Ty
 
The Acurus only uses 6 of the 8 pins. This photo might help you.
If you zoom in you can see one unused solderpad at the outer row. At the same location at the inner row there is one unused solderpad with the new volpot installled. You cant see the inner row on the photo.
Best regards
IMG20230123193743~2.jpg
 
Ok, I did see this picture, but since it was a modification, I wasn't sure what i was looking at. I assume they are in the right order haha?
 
Correct. The pins on the volumeopot will match the layout of the PCB, just skip the first solderpads as on the photo:)
 
Thanks so very much to @KNielsen for creating this thread with the great documentation throughout!
Seems I have the same Siglent scope, and a close enough (more or less) Pre.
I was getting to know this scope, and then life got in the way. Bought it direct from Siglent (thanks Ruby). < Big boss at Siglent USA.

Looks like I have more of that life getting in the way stuff, way to much work on necessary things…

Now more homework, reading this thread from the beginning :bigok:

Must have posted in the thread way back, just no time to …
Oops back to work, the house maintenance is calling, and waiting on silly UPS to deliver rear brake rotors— I hate working on cars, AND houses.

Once again major gratitude to the op for helping us learn here at AK— The best audio site, bar none.

Best of luck @33713 the vc poster, it will be a simple task once you have part in hand.

Happy Listening,

Celadon
 
Celadon said:
Thanks so very much to @KNielsen for creating this thread with the great documentation throughout!
Seems I have the same Siglent scope, and a close enough (more or less) Pre.
I was getting to know this scope, and then life got in the way. Bought it direct from Siglent (thanks Ruby). < Big boss at Siglent USA.

Looks like I have more of that life getting in the way stuff, way to much work on necessary things…

Now more homework, reading this thread from the beginning :bigok:

Must have posted in the thread way back, just no time to …
Oops back to work, the house maintenance is calling, and waiting on silly UPS to deliver rear brake rotors— I hate working on cars, AND houses.

Once again major gratitude to the op for helping us learn here at AK— The best audio site, bar none.

Best of luck @33713 the vc poster, it will be a simple task once you have part in hand.

Happy Listening,

Celadon
Click to expand...
OK, pot should be here tomorrow. I am afraid that all I could find was this ALPS.

New Alps RK27 20K 20KA Metal Shaft Log Potentiometer: Amazon.com: Industrial & Scientific

New Alps RK27 20K 20KA Metal Shaft Log Potentiometer: Amazon.com: Industrial & Scientific
www.amazon.com

New Alps RK27 20K 20KA Metal Shaft Log Potentiometer​


I think the shaft is too long and may have to trim it. But the 211g model shown in picture above is not available (at least that I can find) at the moment, so I am hoping this one works. I also can't stop thinking about motorizing it!
 
One other question, I got into fixing this because of the output being off on balance. I have no need for a balance control and I really do not know who does. Can I just bypass it for better signal and no maintenance? if so, which pins do I bridge? I would ovbviously leave it installed for aesthetics
 
Thanks everyone. Bare in mind that a lot of testing is posted and ideas. Not everything survived the test of time since this thread started, mainly the posted schematics although it was a great way to learn new stuff for me :)
The LS11 works better with an output cap, but messing with the feedback did huge improvements.

For my LS11 the final schematic looks like this today and sound absolutely fantastic
1000006715.jpg
If I should solder the preamp today I would skip the 10uf at the current sources and replace with bigger 100uf/6.3V pr rail... But it really sounds so good I never bothered to open it up for the last year or more ;)

Best regards
 
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