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LSK pre - BAF 2013
LSK pre - BAF 2013
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Old 3rd January 2018, 04:41 AM   #531
needtubes is offline needtubes  United States
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I've had the opposite experience with Silmics - they start really bassy and then calm down within a couple hours. Though, this was for coupling duty, and not on the rails.
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Old 3rd January 2018, 05:02 AM   #532
Hikari1 is offline Hikari1  United States
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Originally Posted by needtubes View Post
I've had the opposite experience with Silmics - they start really bassy and then calm down within a couple hours. Though, this was for coupling duty, and not on the rails.
I have had the preamp on for 24 hours or so...I almost always use silmics on the rails and usually they open up a lot in the first couple of days. The PSU of this preamp (Nichicon KG followed by KZ) and regulator have been used for a couple years before so they are broken in.

Honestly, the bass is not bad. It's actually better than some other preamps I have heard. I could totally live with it. But I also have the Salas DCG3 which I have been using before Juma's preamp. It has drill-like bass that is deep and powerful. It's kind of the opposite flavor...Also excellent. Probably my two favorite preamps I've tried. But I haven't tried them all.
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Old 3rd January 2018, 08:52 AM   #533
juma is offline juma  Germany
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Originally Posted by Hikari1 View Post
... I wasn’t expecting it to be this good...
I'm glad you like it.

About the bass response, I like it clean and natural, the way I experience it in live acoustic performances. If your preferences are somewhat different or you are a fan of electronic music - see post #521 (3rd paragraph), check also the value of your output caps (if the Zin of your amp is 10k caps should be 10u at least, 1u for 100k and so on...). For tougher loads (very long cables, headphones, very low Zin amps), Emitter/Source follower can be added at the output. BJTs at the input, instead of JFETs tend to change sound in the direction you described (drill-like bass). Power supply/decoupling plays a role too. Volume pot (10-20k) should be at the preamp's input.There's a lot of room for experimenting, have fun with it...
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Old 3rd January 2018, 04:31 PM   #534
Hikari1 is offline Hikari1  United States
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Power amp is very light load (Pass F5T/100K), output caps are 8.2UF. I am sure a follower on the output would be interesting but another stage might ruin what I have now...especially since the power amp load is so light. But definitely room for experimentation there.

I will play with the feedback resistor values like you have suggested...but really it might be perfect as-is. I was listening last night and it was really live sounding. So open and clean.
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Old 3rd January 2018, 08:14 PM   #535
vdi_nenna is offline vdi_nenna  United States
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Hey, have a question about post number 1.

In the board trace the parts placement can be seen.
Is there a trick to getting the parts placement to go away or does the PCB image need to be edited to remove the parts placement to get a clean PCB transfer?

Thanks,

Vince
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Old 3rd January 2018, 08:56 PM   #536
Hikari1 is offline Hikari1  United States
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Originally Posted by vdi_nenna View Post
Hey, have a question about post number 1.

In the board trace the parts placement can be seen.
Is there a trick to getting the parts placement to go away or does the PCB image need to be edited to remove the parts placement to get a clean PCB transfer?

Thanks,

Vince
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Old 3rd January 2018, 08:58 PM   #537
vdi_nenna is offline vdi_nenna  United States
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Like that. Was it automated or did you edit the traces?

I keep thinking there's a printer function where only pure black and white will print.
I see these type of PCB traces all the time and was just wondering if it's done with the software that made the PCB, or a 3rd party such myself could automate the removal of the parts placement.

Make sense?
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Last edited by vdi_nenna; 3rd January 2018 at 09:00 PM.
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Old 3rd January 2018, 09:06 PM   #538
Hikari1 is offline Hikari1  United States
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I edited it in photoshop. Took out the red and filled in the traces. There is really no automated way to do it unless you start from a "Layered" file. If you printed only black the red will cut the traces. The red does not "overprint" over the black. It just cuts through it. I am a graphic designer...so finally we can talk about something I know lots about on this forum. Ha.

If you use the software that created this file I am sure you can turn off and on the parts you want.

The easy way would be just to tell adobe acrobat or whatever printer program you use to only print pure black and then fill in the traces with a sharpie.

In other news, I'd consider Juma's Current Mirror version instead...seriously.
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Old 9th January 2018, 04:55 AM   #539
Hikari1 is offline Hikari1  United States
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LSKpre-CM+FB.gif
Quote:
Originally Posted by juma View Post
I'm glad you like it.

About the bass response, I like it clean and natural, the way I experience it in live acoustic performances. If your preferences are somewhat different or you are a fan of electronic music - see post #521 (3rd paragraph), check also the value of your output caps (if the Zin of your amp is 10k caps should be 10u at least, 1u for 100k and so on...). For tougher loads (very long cables, headphones, very low Zin amps), Emitter/Source follower can be added at the output. BJTs at the input, instead of JFETs tend to change sound in the direction you described (drill-like bass). Power supply/decoupling plays a role too. Volume pot (10-20k) should be at the preamp's input.There's a lot of room for experimenting, have fun with it...
I did in fact add more feedback...520R/150R was as close as I could get to what you suggested. The sound is a little bit more lively now. Seems like a little less gain too? Not sure which I prefer, the original has a smoothness and silkiness I like. But I will have to listen for a while and see.

Also, while the circuit seems DC stable in a temp controlled situation it does fluctuate a bit (20mv or so) with temp changes. It probably doesn't help that my phono amp with shut regs is on top of it. I will leave the cps for now.

Still impressed. Thanks Juma.

Last edited by Hikari1; 9th January 2018 at 04:58 AM.
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Old 9th January 2018, 09:17 AM   #540
juma is offline juma  Germany
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Yes, R7/R6 ratio defines the gain and the total value of those resistors sets the load for BJT transconductance stage. Test and find out what you like the best.
I didn't bother much with small DC fluctuations at the output - I used coupling caps (Silmic at first, WIMA MKP 10 later). Thermal coupling and tight matching will help (closing the preamp's case goes without saying). DC servo can be used too.
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