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 Ovation SK-M Preamp Recreation
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seesquare |
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| Okay, both. I will be engaging in some fun while I attempt to build a stacked-knob preamplifier. Since I can't find a specific SKM schematic, I was curious if I used one half of the Ovation Stereo Preamp to construct this device. Here are the images I think are relevant to the matter. I have added the tone control components to the Mono schematic, as the same structure on the Stereo schematic. Yes, I will have to figure out the plumbing diagram for the concentric potentiometer, too. So, is this kosher? Does this qualify for BFLG activity? Are they giants, or just windmills? Steve McCormick at RenOvation was kind enough to provide the Stereo schematic and I accessed the Mono VT circuit from Jerome's OvationTribute website. There is also the Ovation Volume-Only preamp schematic, but it appears identical to the Mono VT circuit, anyway. BTW, on the Stereo diagram, what are all those numbered "TP" sites identifying? And, what's the Reader's Digest explanation of what those 2 capacitors in parallel with the 100 Mh inductors in the JFET Source section do to the sound quality? Thanks for your bemused attention and any reality-testing comments. It may be a pipe dream that goes up in smoke, eh? Edited by seesquare 2025-02-10 7:14 PM (Ovation Mono VT schematic- smaller image.jpg) (Ovation Stereo VT Schematic 2nd copy- smaller image.jpg) Attachments ----------------  Ovation Mono VT schematic- smaller image.jpg (68KB - 0 downloads) Ovation Stereo VT Schematic 2nd copy- smaller image.jpg (77KB - 0 downloads) | |||
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| DanSavage |
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Joined: June 2012 Posts: 2322 Location: Pueblo West, CO | Personally, I think this is perfect BFLG material. Here's the schematic:
Looking closely at this schematic reveals that the only difference between it and the VTM schematic you posted is that it has a single 22K resister in place of the 15K resister and 50K pot. | ||
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| seesquare |
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| seesquare |
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| numbfingers |
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| I have a stacked-knob 1624 but don't want to take the strings off right now. It's possible that the output jack could have a switch built in instead of using the plug to connect the battery. The parallel inductors/capacitors look like LC bandpass filters. They're probably doing some tone shaping, but why are there two filters in series, and how do they work connected to the FET source and ground in parallel with the resistor? Too much thinking for me, discuss amongst yourselves.  -Steve W. Edited by numbfingers 2025-02-17 11:08 AM | |||
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| numbfingers |
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| CC, here are your reading assignments, written by real old-school electronics guys, not random "experts" on the web. Rufus P. Turner on FETs and LC Circuits - I paid too much for these books and now they're on the web https://www.worldradiohistory.com/BOOKSHELF-ARH/Technology/Sams-Book... https://www.worldradiohistory.com/BOOKSHELF-ARH/Technology/Author-Gr... https://www.worldradiohistory.com/BOOKSHELF-ARH/Technology/Author-Gr... Ray Marston's 4-part series on FETs. These are also out there in .PDF format. https://www.nutsvolts.com/magazine/article/fet_principles_and_circui... https://www.nutsvolts.com/magazine/article/fet_principles_and_circui... https://www.nutsvolts.com/magazine/article/fet_principles_and_circui... https://www.nutsvolts.com/magazine/article/fet_principles_and_circui... Unknown Somebody's JFET Amplifer and Filter Project that might be related. https://www.diyaudio.com/archive/blogs/synctronx/1424-jfet-amplifer-... -Steve W. Edited by numbfingers 2025-02-17 11:09 AM | |||
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| DanSavage |
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Joined: June 2012 Posts: 2322 Location: Pueblo West, CO | |||
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| seesquare |
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| Mr. Ovation |
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| Those inductor or filter components could be there for any of a variety of reasons. It's been a long time since I cared about components so you would have to do the maths, but they could be anything from tone shaping, to simple filtering to ensure outside influences of nearby electronics stay out. FWIW, I would get a push-pull booster and eq (two separate items) from Seymour Duncan or EMG and I'm sure there are others, and re-wire with a stacked pot running the appropriate pot to replace the appropriate pot on each board. They are small, and someone else already did all the maths. | |||
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| seesquare |
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| seesquare |
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On an allied note, I just did some minor surgery on an OCP pickup that came with an Ultra 1528 from a Goodwill auction in Miami (long FedEx trip). No cable on the device (drat!), and no other electronics, for that matter, so the pickup was carefully disassembled and the end wires exposed for reattachment of a replacement cable. Delicate technique would be the apt term. So, it appears to be functioning, but how well will await the reinstallation and restringing phase. I might need to make an extension cord for the short cable, though. Probably won't reach to the intended, newly-fabricated preamp can on the bowl edge. Worse things could happen than that, assuredly. IKYP (new text-speak for "I'll keep you posted" . | |||
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| FlySig |
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Joined: October 2005 Posts: 4055 Location: Utah | |||
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| seesquare |
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