102 Feedback City

[llemtt]

I think Jelle could share some knowledge about the "rock city" mod cause he offers a "rock city" optional switch on his amps..

[tjauernig]

Talbany,

I have to admit, I'm a terrible one when it comes to taking notes. But, I know I do have a few on Kimbos amp. I need to did through all my stuff from my days at Peavey and find them. I'll post them here if I can dig them up.

From what I remember, Kimbo bought the amp in 82-83. I do remeber seeing the original reciept for $2780. The amp was a head covered in a orange/brown suede. (I think I have pictures from when his daughter had it for sale on Craigs List about a year ago....she still has it, as well as the 50 watt combo Kimbo had AFAIK) If I remeber right, Kimbo said it was modded in 88-89, when it had the "Rock City" mod done as well as tone stack mods. (Rock City was what Kimbo called it.....I'm not sure if that was an actual Dumble given name to the mod)

Whenever Kimbo was around Meridian for sales meetings, etc. or at several of the Texas Guitar Shows he would often attend with me, he would bring the Dumbles around. He only let me pull the chassis one time. There was a LOT of goop. I remember being amazed because tube sockets and pots were about all you could see. (I'll make a point to find the pics. I know I have some)

I always felt fortunate that Kimbo would bring the amp around for me to play. The experience of playing that amp was what inspired the Masterpiece 50 (one of the Peavey custom shop amps I did while I was there. Always hated that name by the way. HP came up with that. He always said it was from some old gun. Reminds me of BBQ sauce) The Masterpiece was Dumble-esque in nature from a schematic viewpoint, but far more Rock N Roll in tone IMO. (I was sort of forced in that direction due to the Peavey customer base..........don't get me started, then why did Peavey attach the $2500+ price tag?.............Arghhh!!!!) As far as I know, no one else at Peavey ever got to play either of Kimbos Dumbles.

I also remeber the mid control was a push/pull, but I have no idea what t did. It seemed to only be enabled when the PAB was on, and it seemed reduce gain, but not volume. Sort of cleaned things up a bit if that makes sense. Kimbo said he never used it.

The most memorable thing was that feedback. It was really cool. Looks like the veil on that mystery may be removed.

I'll dig out that info for the forum that I have on Kimbos amp.

[talbany]

T. Jauernig
Thanks for the background on Kimbo's amp..I do not believe the source of the feedback to be in the output section FWIW.. It would then make sense that Dumble would then goop the entire pre amp section..As you probably already know there must be a number of different things Dumble did to cause this sort of feedback effect..We'll find out soon enough..Looking forward to your notes and pics..

BTW..I can only imagine the frustration you went through while working at Peavey..Hand extended!!

Tony

[ayan]

I can offer these pictures. This amp was for sale at Overland Express a few years ago, and it was said to have undergone the rock city mod. Look at the funky box on the left, it looks like it would plug into the 6-pin XLR socket. Sorry, I have no other definitive details on this amp, other than the suspicion that it had something funny going on on the cathode of V2A which was footswitchable. It could perhaps be a bigger resistor, a la Soldano or Rectifier, or some funky network involving clipping diodes.

Gil

T. Jauernig
Thanks for the background on Kimbo's amp..I do not believe the source of the feedback to be in the output section FWIW.. It would then make sense that Dumble would then goop the entire pre amp section..As you probably already know there must be a number of different things Dumble did to cause this sort of feedback effect..We'll find out soon enough..Looking forward to your notes and pics..

BTW..I can only imagine the frustration you went through while working at Peavey..Hand extended!!

Tony

[talbany]

Gill
Humm!!.. Interesting!!..My guess would be various clippers (different gain) at the input V1A you plug your guitar in to (1/4 jack on the side and the amount of cable is a good clue)..with perhaps some sort of buffer as well..Maybe Max knows?

Tony

[tjauernig]

now that I see the little box, I do remeber a device like that. Seems to me I remeber Kimbo plugging that into the fx loop.

And yes Peavey was a strange test in patience. We could start a new forum for just that topic.

[talbany]

now that I see the little box, I do remeber a device like that. Seems to me I remeber Kimbo plugging that into the fx loop.

And yes Peavey was a strange test in patience. We could start a new forum for just that topic.

I assume Kimbo didn't need this device plugged in to get that feedback correct?

Tony

[Max]

This amp was for sale at Overland Express a few years ago, and it was said to have undergone the rock city mod. Look at the funky box on the left, it looks like it would plug into the 6-pin XLR socket.

AFAIR this is ODS #119. AFAIR it was updated to skyline specs around '88 and with this update it got what Alexander Dumble called a "Fat City mod", too. AFAIR the small box with the three jacks plugs indeed into the 6-pin XLR socket and it then has the usual function of a three-way footswitch if you connect the three jacks in this box with some external switching device (or three usual footswitchs e.g.). And AFAIR this "Fat City Mod" is some kind of mid boost that can be activated by this footswitch. So you can switch OD, PB and MB ("Fat City") with this three-way footswitch. If this footswitchable "Fat City" mid boost of #119 is technically the same as the usual mid boost of the skyline tone stack, I don't know.

Cheers,

Max

[jelle]

This amp was for sale at Overland Express a few years ago, and it was said to have undergone the rock city mod. Look at the funky box on the left, it looks like it would plug into the 6-pin XLR socket.

AFAIR this is ODS #119. AFAIR it was updated to skyline specs around '88 and with this update it got what Alexander Dumble called a "Fat City mod", too. AFAIR the small box with the three jacks plugs indeed into the 6-pin XLR socket and it then has the usual function of a three-way footswitch if you connect the three jacks in this box with some external switching device (or three usual footswitchs e.g.). And AFAIR this "Fat City Mod" is some kind of mid boost that can be activated by this footswitch. So you can switch OD, PB and MB ("Fat City") with this three-way footswitch. If this footswitchable "Fat City" mid boost of #119 is technically the same as the usual mid boost of the skyline tone stack, I don't know.

Cheers,

Max

It is my understanding that the Rock City mod is placing the usual mid boost that is on the front on a relay.

Jelle

[talbany]

Thanks Max/Jelle for the clarification!!

One would think it would make things easier to convert it to a 3 button FS

Tony

[ayan]

Now that Max mentioned Fat City, maybe that's what that amp has as opposed to Rock City. I too believe that the external box with the three LED's is for 3 separate footwiches. The amp is a Skyliner, and apparently a high plate version.

The extra stuff going on in that amp seems could be related to V2A's cathode wire. However, having a closer look, there definitely is an extra yellow wire running underneath the board from the front of the chassis, and I think it is the one feeding the XLR 6th pin. I am now more inclined to believe perhaps HAD had a footswitchable ground-lift on the middle pot, or maybe the Mid switch as Jelle suggested. The bass pot is typical Skyliner, with a cap across its ends and a 10K resistor to ground on the tail; can't see the middle pot too well.

Now, if the mod is just a ground lift on the middle pot, then what might have happened is that HAD may have mangled up the cathode wire while modding the amp. If so, it looks like he spliced it, shrink-wrapped it and gooped it to the chassis. I would love to know what's actually going on in this amp.

Cheers,

Gil

This amp was for sale at Overland Express a few years ago, and it was said to have undergone the rock city mod. Look at the funky box on the left, it looks like it would plug into the 6-pin XLR socket.

AFAIR this is ODS #119. AFAIR it was updated to skyline specs around '88 and with this update it got what Alexander Dumble called a "Fat City mod", too. AFAIR the small box with the three jacks plugs indeed into the 6-pin XLR socket and it then has the usual function of a three-way footswitch if you connect the three jacks in this box with some external switching device (or three usual footswitchs e.g.). And AFAIR this "Fat City Mod" is some kind of mid boost that can be activated by this footswitch. So you can switch OD, PB and MB ("Fat City") with this three-way footswitch. If this footswitchable "Fat City" mid boost of #119 is technically the same as the usual mid boost of the skyline tone stack, I don't know.

Cheers,

Max

It is my understanding that the Rock City mod is placing the usual mid boost that is on the front on a relay.

Jelle

[scotto]

Wonder if Brandon or Scott L. have any insights on this feedback enigma? You guys out there?

[tjauernig]

now that I see the little box, I do remeber a device like that. Seems to me I remeber Kimbo plugging that into the fx loop.

And yes Peavey was a strange test in patience. We could start a new forum for just that topic.

I assume Kimbo didn't need this device plugged in to get that feedback correct?

Tony

That is correct. I did it all the time.

[llemtt]

Another test for Tony...

what if you connect a "silicon" buffer stage between guitar and amp input such as a clean booster or something equivalent?

does the feedback improve? does it lessen?

thanks
teo

[talbany]

Another test for Tony...

what if you connect a "silicon" buffer stage between guitar and amp input such as a clean booster or something equivalent?

does the feedback improve? does it lessen?

thanks
teo

Teo
What are you thinking?..

Bridge & Middle EJ Strat w/Dlator

http://www.youtube.com/watch?v=wx42veOplwM

Tony