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Discussion in 'The Workbench' started by Neddi, Jun 16, 2019.
Agree and there are so many other ways to shin that cat.
These works are on my short list More reading from Aiken, Fischer & Shaffer.
That is the spirit.
You want me to write you a book? Nah, just kidding. I have other things to do.
I have been using the practice of non co-planar. Using true point to point when & where I can to reduce unwanted capacitances.
? Yes, I do hear a difference. High gain tuning is a blast for an audiophile such as myself.
Harmonics matter. PCB is big business. But I am learning to minimize unwanted signal anomaly’s & enhance the clarity. I am a hobbyists that squeezes every shimmer I can get out of the amp.
Oh just to mention, there are so many ways to tap into and inject feedback.
Do not just read Aiken, Fischer and Shaffer. Get you some old tube manuals and text books. That is the way to understand more, much more.
Guitar Rocker told me to search out and buy the old RCA Manuals.
Ampmadscientist alludes to that practice all the time. Honestly to me it is just common sense.
Correct yourself. The right harmonics are what matters and is desired.
For tube amplifiers I would not use PCB if you did mean printed circuit boards. That is my preference. It does depend on design and components used. Its all about ease of installation and lead dress.
I think you are becoming more than a hobbyist.
Yes I have some.
I will locate what is needed. I now understand from the engineering view one is always in practice much like a Doctor or Scientist.
I still read certain chapters and subject matter repeatedly to ensure it sticks but I. Ever want to pigeonhole myself.
Thanks again David
I finally had some free time to catch up on threads and found this one. I was fortunate enough to get my hands on Mark Abrahamian’s #2 ‘Ground Up’ build using a Metro 12xxx chassis. I discussed the issue of using an FX loop with a PPIMV with George and he suggested placing it after the ‘master’ - so it ends up in between the ‘master’ and the PI since the master is adding another whole stage of gain before hitting the PI. Yes, you still do get some unpleasant artifacts when loading up the PI full tilt, but it is SURPRISINGLY quiet at ‘normal’ levels of drive. Without doubt it is vastly better than the traditional location between the pre and the master.
FWIW - I briefly owned a Bray 4550 Deluxe that the original owner ordered with a Zero Loss loop installed and it was literally un-usable. I am certain it had been installed in the traditional location between the pre and the master.
No doubt, running time effects at the board is always preferable, but having the Zero Loss Loop as George installed it allows reasonable and workable use of time based FX with this PPIMV head. I also had him include the switch so I am always one click away from having it entirely out of the circuit - as the amp was originally built.
It is best with a Master Volume after the effects loop and before the PI position.
What matters most however is signal level control and keeping it appropriate for each stage.
Any updates? Curious about this amp's situation.
David Hopkins has it - he sent me some pics and some info on just how bad things were - like i said before i don't like bashing anyone and i'm not trying to bad mouth someones reputation but the truth is the truth and i regret sending it to Michael who didn't respond to my emails about the loop problems - David has been in communication with me through every step - once i get the amp back i'll post a video of it
I hear you. You are in great hands now. Hoping to know more from David about what he found and his solution.
"PDC1 wrote - I finally had some free time to catch up on threads and found this one. I was fortunate enough to get my hands on Mark Abrahamian’s #2 ‘Ground Up’ build using a Metro 12xxx chassis. I discussed the issue of using an FX loop with a PPIMV with George and he suggested placing it after the ‘master’ - so it ends up in between the ‘master’ and the PI since the master is adding another whole stage of gain before hitting the PI."
So, what's happening here is a stardard pre-PI master has become a pad to dial-down preamp gain before it hits your pedals. Then, if you really want to slam the PI...park a clean boost at the end of your pedal chain. This all works IF you're using a passive loop. The Metro is buffered so you have to respect the expected signal provisions through the Metro's circuit. If not, you're going to blow some transistors along the way and a nasty distortion is to be expected from some not-so-nice clipping.
Since this amp won't begin to resemble a classic and the circuit is going to be dramatically changed anyways...if a loop is desired, might be interesting to convert the reverb section to a buffered tube loop with internal pots before and after so you can preset the level-IN to the loop and the level-boosted-OUT to get it back up to drive the PI to saturation if desired.
I guess my assumption is the Metro may now be compromised in some fashion. (?) David, you have your work cut out for you.
Let's see traveling through front to back .... PRE with OWM -> Leave the stock reverb if desired -> [internal pot with RC network to properly pad the PRE levels before the loop] -> LOOP (functioning at levels the pedals are friendly with) -> [post-LOOP boost to slam the PI all to hell, if desired] -> PI (suffering as it should) -> PPIMV (to prevent ear bleed and completely violate AMS' need for power tube distortion until max'd)
But, I'll assume David's going to scrap a typical OWM for the mods he typically does on the gain-side anyways. Have fun with that, David! Looking forward to seeing what you do to pad the PRE-gain levels to keep a loop friendly. Mark's suggestion of typical Master before the loop would be used as a pad. One problem with that is that it's accessible to the user and easy to slam (just to goose the circuit)...endangering pedals along the way.
The Metro loop is good, Steve Miller put a lot of work into it to suit the Metro/Marshall set up for both NMV and pre-pi MV arrangements, there are different versions for line level and pedals, the levels are also adjustable on the internal trim pot but it is needy regarding the supply voltage. If you are slamming the pi and relying on pppimv I do wonder whether the tube driven loop with in/out pots might be better.
Looking forwards to Dave’s report and solutions. Dealing with serial modders work is a nightmare (at least for an amateur like me!)
Hello Gentlemen. This is the current state of Neddi's amp.
Commentary and a video are available below.
I am not one to to speak poorly of another craftsman unless attacked first. I will say there were many anomalies that needed rectified to which I am uncertain as to who was/is responsible. I suspect there may be issues beyond someones control to not follow up on this work or address it here. Regardless we should move on from that. If that is to be addressed that is for Neddi to do.
I took time to remove and replace many components such as the TS Chiclet looking .022uf caps that turn to dust in addition to building the Pandora Mod 3 times to ensure I used the best brand & type of component to reach the owners request before settling on the entire overhaul. I also rebuilt the speaker out jacks and fabricated several "assemblies" used in my Pandora Mod.
In addition to that I also used two types of point to point work to offset the coplanar layout.
@ Brad. I too became familiar with the placing of the loop between the MV & PI however that still left the issues of Presence and TMB Tone Stack minimalism's. That simply will not due.
I asked Neddi to allow me to keep the amp over the week end to push it around a bit to which he agreed.
Forgive my playing as I am injured and must heal then regain my chops a bit.
Video Demo of Revision II on Page 6
Nice job, David! If I get lazy, I'm sending stuff your way! Good to hear the Metro was salvageable, too (you had a delay in that demo, right?)! I get your comment about Presence (why I suggested an after loop boost...all about getting the output level up to make that feedback voltage in the desired range). TMB circuit should be preceding the loop so not sure why that would be compromised.
Very clean rebuild! My hat's off to ya! Neddi - if you don't like it...there'll be plenty of takers here that will make some offers, I'm sure!
PS - Heal up, David! Pain stinks...