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I am looking for the schematics for this preamp. I am aware of The Tube Preamp Cookbook by Allen Wright, but where I can find a copy of it? I appreciate any guidance leads to the schematics of this preamp.
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So for the phono section a Dynaco PAS3 schematic will be helpful but not completely accurate.
If I recall right the Lazarus had a set of simple solid state regulators.
The line section is a 12AX7 where the first stage of gain is direct-coupled to a cathode follower output, much like the Last PAS (which was anything but...).
I've fixed a few of them but I saw the last one a good twenty-five years ago...
If we're talking about the same preamp, Allen Wright said:
"That unit's design was a direct ripoff from me"
Link to Allen's Asylum post is here and also below.
Here's the Last PAS phono (with David Vorhis corrections indicated), line stage and filament supply schematics, if anyone is looking for them. I may have the Vorhis / Jung regulated B+ schematic too, if someone needs it, although I showed it to Allen Wright once, and he wasn't too fond of it.
Note that for C43 and C44 in the filament supply, I use two 120,000 µF caps. I've had several people tell me that much capacitance shouldn't make an improvement, but it does.
- which would suggest that he had the design in the early 1980s.
I just remember working on several Lazarus preamps decades ago and being struck at how similar they were to the Last Pas preamp.
But thought I'd at least link to the late Mr. Wright's take on the situation.
I've always liked the sound of my Last PAS. The phono is OK, but the line stage I'd consider very good, certainly better than my stock PAS or Audio Research SP3-A-1.
I've often run a similar line stage, but dropped the negative feedback and used a 12AU7 (with values optimized for a 12AU7). It seems to sound better and has more voltage swing.
And had one guy tell me that it looked like a guitar grunge-box circuit.
No matter how it may look on paper, it sounds very good, better than my stock PAS and ARC SP3 etc. as I mentioned.
I wrote to thank David Vorhis (who sometimes posts here on the Asylum) for putting together such a detailed, well written article on modifying a Dynaco PAS. He took the time to write it like a kit assembly manual, rather than simply posting a couple of schematics and saying, "Have at it". I needed my hand held when I built it way back when. I don't know if I would have attempted it if he hadn't laid it out the way he did, and to have it turn out so well was gratifying.
-
You agree with the circuit's guitar grunge box assessment?
Nah, I'm just kidding, Ralph. It's always a pleasure interacting with you here on the Asylum
Look to the link below. Vacuum State is still running I believe. Probably better to send an email to ask.
Edits: 12/18/16 12/18/16
Yes! Make that Lazarus rise from the dead!
Dave
All he will have to do is say,preamp,wake up,just as Jesus did with Lazarus.
An Xmas miracle possibly?
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Edits: 12/20/16
It works to certain extent.
Phono section hums with 60hz motorboating/ oscillation at every 5 seconds apart that is volume dependent. After doing some measurements, HV regulator decoupling cap is the suspect for now.
The original parts in this preamp are marginal at best. The 250v metalized coupling/ decoupling caps everywhere are destined to be ruined with constant stress. The decoupling cap at HV regulator is constantly stressed at 280v with 250v specs. The filament cap is a cheap 50v cap but is designed to take 48v. What a joke!
In terms of the cookbook, to spend 50 EU from a foreign country simply doesn't make sense. I respect the designer's copyright, however he has passed away. I am actually very puzzled by the lack of info for this preamp. Schematics seems a secret of some sort purposely hidden by this manufacturer. I don't understand the mentality of that, and no wonder this company cannot survive the real world. I guess I will just hand trace it.
Your 50 Euro would have been spent in vain, there is no mention of a Lazarus preamp in Allen Wright's Tube Preamp CookBook. However, there is an article by Mike Vans Evers about this preamp in the March 1993 issue of Glass Audio.
Thank you for the pointer!
"In terms of the cookbook, to spend 50 EU from a foreign country simply doesn't make sense. I respect the designer's copyright, however he has passed away. I am actually very puzzled by the lack of info for this preamp. Schematics seems a secret of some sort purposely hidden by this manufacturer. I don't understand the mentality of that, and no wonder this company cannot survive the real world. I guess I will just hand trace it."
If you knew how Allen worked you would understand this.
Allen was generous with his knowledge, time and help. He had at one time (he passed some time ago)schematics posted on the Vacuum State web site. They were, by design, generic in nature so that others could not copy and implement his work on their own (read Chinese knockoffs). I know at one time he had several lawsuits regarding intellectual theft. If you were proficient you had a good chance of ciphering your layout from his basic premise.
As an aside, I was looking for a MC phono stage to work with my SP6 that did not use transformers. Allen was helpful to a fault setting things up to have it added to my preamp however he would not send me the schematic for my own use.
OK, I hear you But your solution is pretty much the standard solution. Replace the filter caps with new electolytics and replace the coupling caps. I don't mess with the resistors unless they are carbon composite. You don't have to spend a lot of money. you just have to solder carefully. Just youse defiant polly propylene capacitors as decouplers and dece t elecrp;tics in the power supply and clean all the pots and switches.. Even without the schematics, you should be able to read the values of the existing parts. Good luck!
Dave
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