Greetings all
I post this request seeking the kind assistance of a fellow diy audio enthusiast.
Perhaps 25 years ago, I was purchasing some items from a local hifi shop in Brisbane, Australia when the owner showed me a schematic of Alan Kimmel’s Hybrid Mu (mosfet/tube) linestage. I believe it was published in a Welborne Labs catalogue.
The owner provided me with a single page photocopy and from that I built the preamp. I liked the idea of using a MOSFET and a tube. It keeps maintenance to a minimum! It sounded phenomenal to my ears! MIT foil/film coupling caps, Roedersteins & Vishay/Sfernice stereo pot etc. Please see photos.
I wish to again build Alan Kimmel’s Hybrid Mu Stage, however, after 25+ years I’m unable to find the schematic. The original build is still intact but I don’t wish to reverse engineer. I’d prefer the original schematic in case I missed some important detail 25 years ago!
I recently purchased a pdf copy of the Audio Express May 2019 issue hoping The Mu Stage Update by Alan Kimmel may include a schematic of the original design but it did not.
AudioXpress has very kindly provided me with a copy of the article: A. Kimmel "The Mu Stage" from Glass Audio, Volume 5, No. 2, 1993 but it lacks the detail found in the Welborne Labs schematic.
I have noted Welborne Labs has folded up so purchasing one of their old catalogues is not possible.
Would some kind soul please help by providing a scan of the linestage schematic from the old WLabs catalogue.
It would be impossible to exaggerate my appreciation for doing so.
Be well and stay safe.
Mark Perkins. (Brisbane, Australia)
I post this request seeking the kind assistance of a fellow diy audio enthusiast.
Perhaps 25 years ago, I was purchasing some items from a local hifi shop in Brisbane, Australia when the owner showed me a schematic of Alan Kimmel’s Hybrid Mu (mosfet/tube) linestage. I believe it was published in a Welborne Labs catalogue.
The owner provided me with a single page photocopy and from that I built the preamp. I liked the idea of using a MOSFET and a tube. It keeps maintenance to a minimum! It sounded phenomenal to my ears! MIT foil/film coupling caps, Roedersteins & Vishay/Sfernice stereo pot etc. Please see photos.
I wish to again build Alan Kimmel’s Hybrid Mu Stage, however, after 25+ years I’m unable to find the schematic. The original build is still intact but I don’t wish to reverse engineer. I’d prefer the original schematic in case I missed some important detail 25 years ago!
I recently purchased a pdf copy of the Audio Express May 2019 issue hoping The Mu Stage Update by Alan Kimmel may include a schematic of the original design but it did not.
AudioXpress has very kindly provided me with a copy of the article: A. Kimmel "The Mu Stage" from Glass Audio, Volume 5, No. 2, 1993 but it lacks the detail found in the Welborne Labs schematic.
I have noted Welborne Labs has folded up so purchasing one of their old catalogues is not possible.
Would some kind soul please help by providing a scan of the linestage schematic from the old WLabs catalogue.
It would be impossible to exaggerate my appreciation for doing so.
Be well and stay safe.
Mark Perkins. (Brisbane, Australia)
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Dear Andrewbee
Thank you very much indeed for your outstanding effort.
I truly appreciate your help. I'm very much obliged.
Rayma, thank you also for your interest.
You are both extremely kind and again, many thanks.
All my best.
Mark.
Thank you very much indeed for your outstanding effort.
I truly appreciate your help. I'm very much obliged.
Rayma, thank you also for your interest.
You are both extremely kind and again, many thanks.
All my best.
Mark.
Andrew,
You don’t happen to have the parts values for the schematic you uploaded do you? B+ is 300V. How about B2+, B3+ and B (-) ?
Best,
Anand.
You don’t happen to have the parts values for the schematic you uploaded do you? B+ is 300V. How about B2+, B3+ and B (-) ?
Best,
Anand.
Sorry no, If I had a parts list I would have included it. I posted what I have including the catalogue cover so its dated. Looks like you will have to reverse engineer but it will be much easier with a schematic now, just have to enter the values.
Edit. Eli D has a hybrid line stage posted here somewhere, you may want to take a look at it as well.
Edit again. Found it, 2nd post.https://www.diyaudio.com/community/threads/first-preamp-build.273495/
A little late to the party but here's a copy of the Welborne Kimmel Hybrid Linestage documentation.
Hi Gary
Thank you kindly for the pdf file.
Previously I had thanked several members for their contributions, but the info you've provided fills in a few gaps.
You’ve hit the ball out of the park so thank you.
I have recently ordered a NAD M23 power amp.
I'm sure the mosfet-tube line stage and the NAD Class-D power amp will be complementry.
My new setup will be:
Cambridge Audio CD transport (playing Steve Hoffman remasters 🙂 )
ifi Zen One Signature DAC
Alan Kimmel tube-mosfet linestage
NAD M23 power amp (awaiting delivery)
Audio quest speaker cables
Electro Voice Sentry 500 studio monitors, sitting on custom made steel stands.
Your kind post has been very, very helpful and I'm much obliged.
You have my respect and best wishes.
Mark. (Brisbane, Australia)
Thank you kindly for the pdf file.
Previously I had thanked several members for their contributions, but the info you've provided fills in a few gaps.
You’ve hit the ball out of the park so thank you.
I have recently ordered a NAD M23 power amp.
I'm sure the mosfet-tube line stage and the NAD Class-D power amp will be complementry.
My new setup will be:
Cambridge Audio CD transport (playing Steve Hoffman remasters 🙂 )
ifi Zen One Signature DAC
Alan Kimmel tube-mosfet linestage
NAD M23 power amp (awaiting delivery)
Audio quest speaker cables
Electro Voice Sentry 500 studio monitors, sitting on custom made steel stands.
Your kind post has been very, very helpful and I'm much obliged.
You have my respect and best wishes.
Mark. (Brisbane, Australia)
Something stood out in the second paragraph.
We have selected the 12AU7 as our preference of triode tube because of its very linear transfer characteristics
I thought the consensus here was the 12AU7 was not that linear?
Well the 12au7 isn't exactly. see if i remember correctly they also recommend the 6cg7/6fq7 which is electrically closer to a 6sn7. the 12au7 is a bit degraded because it was designed the fit in the context of the 12 series tubes.They were cheaper for a number of reasons the important one here is that the 12 series tubes all shared the same internal components, so you didn't have to retool the entire factory to produce a different tube. if you look close at the mica spacer of some of them you'll see unused holes, they were for different tube types. The 12 ax,at,au,....ect. were all common. The 12au7 was the replacement for the 6sn7 in the 12 series.
