NAD, Overdrive Special

Discussion in 'Amp Central Station' started by bullfrogblues, Jun 22, 2019.

  1. brookdalebill

    brookdalebill Tele Axpert Ad Free Member

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    Neato!
     
  2. telemnemonics

    telemnemonics Doctor of Teleocity Ad Free Member

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    I was wondering about that ratio knob as well.
    My D style has four volumes, and the ratio must be the gain knob for the dirt sound.
    Mine are called volume, drive, level, master.
    Volume is clean but affects the dirt as well, then drive and level set the dirt, while master sets both for the overall volume.
    It's one channel with the lead boost in the middle.

    (There may be a PAB preamp boost as well that removes the tone stack)
     
  3. homesick345

    homesick345 Poster Extraordinaire

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    Maybe the 183 (because of the EL34s)

    My understanding is that many D amps were de-gooed; & schematics are widely available now
     
  4. Silverface

    Silverface Poster Extraordinaire Ad Free Member

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    None have been de-gooped without destroying the parts values, so those "clones"and schematics are all guesses. Many of them are very good amps - no argument there. But (and I was in the coatings and adhesives business for almost 40 years and keep up on current technology) the epoxy resin Dumble used can't be removed or thinned to a transparent state without destroying readability - electronic or "eyeball" - of the parts values. Many Dumble owners - including well-known players - consider the whole "clone" claim insulting. Because they own very special amps and closes don't exist.

    They are NOT "clones" of actual Dumble-built amplifiers. If ANY had been successfully de-gooped most others would have as well - but they're not. Which is a pretty solid clue right there.

    The only actual parts values known are those in REALLY early amps, and Fender and Marshall amps that have been modified.

    This argument, BTW, has been going on for YEARS. And not a thing has changed. If it was possible there would be a database of dozens of Dumble schematics (since each amp is unique) with matching "clones" for sale.

    Where are they?
     
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  5. akuster777

    akuster777 TDPRI Member

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  6. L.A. Mike

    L.A. Mike Tele-Holic

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    You may not realize it but Mr. Dumble started out selling the ODS at music stores in L.A. and from ads he put in Guitar Player magazine. It wasn't until people started realizing how great they sounded, and his orders were exceeding his capabilities to fill, that he decided to limit who he would build one for. Before that anyone with a couple of thousand dollars could own a standard ODS amp that was not gooped.

    Regarding gooping circuits:
    The Urei 1176 compressor/limiter made in 1970 had a new LN (low noise) circuit added to it which was developed by Brad Plunkett. They encapsulated it in epoxy to stabilize the components and more importantly, protect the circuit until their patent was approved.
    So, we can see Mr. Dumble wasn't the first to use this process.

    The reason Mr. Dumble started epoxying the circuit was because of KittyHawk Amps. A company in Germany that imported Mesa Boogie and Dumble amps to Europe for a short period of time. Mr. Dumble wasn't selling a lot of amps here in the states at that time. So, selling them in Europe seemed like a good idea. Mr. Dumble decided to sell the completed ODS chassis to them and they would get cabinets made. These were ODS amps. In fact all ODS amps follow the same design. Any custom mods he does to the circuit to suit a particular customer are basically tweaks to the circuit. Things like more power, more headroom, more compression, different EQ capabilities, that sort of thing.
    Back to KittyHawk: He was still building all of these amps himself. KittyHawk wanted more amps than he was able to produce and he was falling behind in supplying them. So they had someone copy (try to) his circuit and cloned his amp without his permission or knowledge. They actually used a counterfeit nameplate for a while that said Dumble on it.
    The amps sounded terrible and were unreliable. Mr. Dumble found out about this and stopped shipping amps to them. He didn't know what else to do, so he started putting epoxy over the preamp circuit area to try and protect his design. He had already been sanding the values and mfg info off of the critical components as standard operating procedure. So the goop added some protection. And he knew that it also reinforced the components and made the amps more reliable.
     
    Last edited: Jun 24, 2019
  7. markal

    markal Tele-Holic

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    It sure LOOKS like a clone.

    Cool amp. Enjoy the heck out of it. Let us know how it sounds once you’re able to open it up and let it work.

    Interesting info on Dumble history. So much mystery and intrigue!
     
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  8. 3-Chord-Genius

    3-Chord-Genius Poster Extraordinaire

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    I remember Kitty Hawk amps. I saw them when I was stationed in Germany, and I think at least one of the famous guys who endorsed them (Reb Beach?) privately referred to them as "Sh**y Hawk" because of their quality problems. I had one of their combo amps for a while and didn't like it. It had an extra-high gain channel that was useless because it was so muddy.
     
    Last edited: Jun 25, 2019
  9. 4pickupguy

    4pickupguy Poster Extraordinaire

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    Wow, I’m very jealous. That looks like a great amp. I bet she sounds wonderful. Enjoy your amp!
     
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  10. rogb

    rogb Tele-Afflicted

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    Nice amp, take your time and give iit a good hard running-in, maybe think about some good tube choices, if you are running budget tubes.
    They take a little while to dial-in and some days to settle down, also I found picking technique and general playing style matters a LOT!

    With regards to some of the stuff you read about "gooping" and "epoxy", some of that is not quite correct.
    Here's #94, de-gooped, HAD used black silicone and later Permatex Blue RTV silicone. How would he be able to make changes for his clients if set in epoxy?

    gregor's D.jpg

    Here's one with the Permatex:

    image.jpeg

    And here is an earlier 1977 model with no goop:

    znibuqapcbna1p3axaff.png
     
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  11. homesick345

    homesick345 Poster Extraordinaire

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    I joined TDPRI in hope of amp knowledge of this caliber..

    Respect.
     
  12. Wally

    Wally Telefied Ad Free Member

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    I have a KittyHawk sitting around....all of the PCB mounted pots are shot and accurate replacements are not available.
    Hours of searching through mouser, digikey, etc have not been fruitful. the owner says the amp has not been played for 30 years!
     
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  13. scrimmer

    scrimmer Tele-Afflicted

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    Drool...
     
  14. monkeybanana

    monkeybanana Tele-Meister

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    I get the goo but what a shame for such beautifully layed out circuits.

    What are those thick thick wires? Shielded?
     
  15. rogb

    rogb Tele-Afflicted

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    The thick wires are shielded coax. He used various types according to availability I guess. I think the particular capacitance enabled tone shaping that added to the overall sound he was aiming at. The man is a genius no doubt.
    Eccentric yes but a genius.
     
  16. rogb

    rogb Tele-Afflicted

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    You could try Andy Fuchs Gary (Glaswerks) or Jelle Welagen. They might be able to give you a lead on those parts.
     
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  17. Wally

    Wally Telefied Ad Free Member

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    Thanks for that, Rogb, and perhaps that is a possibility. However, I checked with our brother Bendyha who lives in Germany and has his finger on the pulse of all things related to these guitar amps it seems, and he offered little hope that original Piher pots would be found. It may be a box that I don’t want to open, eh...specially with reports such as those above. Time will tell....
     
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  18. rogb

    rogb Tele-Afflicted

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    Do you think it would be possible to replace the conductive discs in order to renovate the pots? Just thinking aloud. It's something to maybe consider?
    Have you got a photo of the pots? Someone somewhere may be able to help out on the interwebs?
     
  19. telemnemonics

    telemnemonics Doctor of Teleocity Ad Free Member

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    Is that dead Kitty Hawk a superb amp, aside from being poorly built? (Irony intended)

    Does it seem to be one of their attempts at building a D style under their own name, or whatever they designed and built as well as importing actual Dumbles?

    Also, did Clapton play a Kitty Hawk in the past?
    Or maybe I'm mixing it up with Sundown?
    Seems like somebody from royalty used a KH at some point in time...
     
  20. Wally

    Wally Telefied Ad Free Member

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    Rogb, I appreciate your thoughts. Imho and 8me, the only recourse is to f8nd modern production pots that fit both the mounting and the specs...or to adapt the mounting. As for replacing the entrails, iirc, these are molded plastic bodied pots. Even if they were not, it would take a mighty fine amp for me to spend that much time just to get the pots working.

    Telemnemonics, this amp has been idle for three decades. I have not heard it process signal. My initial investigation and work hit a wall when the need for pots came up. If my calculations are correct and IF I could find pots that could be adapted, the work is worth more than the amp ever will be.

    Apologies for the hijack.
     
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