Steve Farris ODS #075

[martin manning]

Max, #124's rear panel manual PAB switch will not engage the PAB wired as shown in the photos. This is a bit of a mystery, and might be adequately explained if the R/J switch has a middle position that can be used to engage PAB manually from the front panel (the rear panel switch would not be needed). Since #124 was updated at some point, perhaps the three position R/J was one of the updates. There is no difference electrically between the center off position of the R/J switch and the PAB relay function. Both methods leave the top and the wiper of the bass pot, and the bottom of the treble pot floating (disconnected).

[Max]

Max, #124's rear panel manual PAB switch will not engage the PAB wired as shown in the photos. This is a bit of a mystery, and might be adequately explained if the R/J switch has a middle position that can be used to engage PAB manually from the front panel (the rear panel switch would not be needed). Since #124 was updated at some point, perhaps the three position R/J was one of the updates. There is no difference electrically between the center off position of the R/J switch and the PAB relay function. Both methods leave the top and the wiper of the bass pot, and the bottom of the treble pot floating (disconnected).

Martin,

first of all thanks for your answer.

I don't think that the middle position of the R/J switch of #124 is a part of the skyline update, as I've met this R/J PB middle position in all the transition generation and 4th generation "classic" ODS amps I am familiar with. BTW: All these haven't been labeled "PB". Only #121 has a "PB" label at the J/R middle position AFAIR.

And as AFAIR the 5th generation skyline ODS amps I know didn't have the three position R/J switch anymore.

Now as far as I understood Tony's post correctly, he obviously thinks that there is a technical difference in the way the R/J switch and the relais work:

R/J switch PB position = "lifting the stack"
Relais = "break bass pot wiper".

Do you think Tony is wrong and the R/J switch PB position and the relais work likewise (that is how I understand your post, Martin)?

@ Mac Daddy, Mr Dumble, Scott and maybe others who played a 5th generation skyline ODS (like #183) lately:

Did they have a three position R/J switch with a PB middle position? Or just the PB relais switch on the back?

Cheers,

Max

[martin manning]

The schematic is a little hard to follow even if you are used to looking at them. In the attached I clipped the tone stack section from icracer's #124 schematic and traced the floating paths for R/J in center off and for PAB relay engaged. As you can see the result is the same either way. Note that there is a difference as far as the 22M resistors still being in the circuit using the PAB relay, but they are only there to silence the switching and can be ignored.

[talbany]

It's an easy thing to try even if you don't have the center off switch.. You can find the sweet spot between R and J setting where the switches don't make contact(essentially center off) it will stay there..Martin is right the results are basically the same.. The mid control works just the same as center off as it does in PAB mode..Technically it's different but the results are the same.. It's a good trick to know if your in the studio and the relay goes..The Classic stack may be different though.. I don't know..Maybe someone here w/ Classic stack can give it a try..I am out of town!!Try it..as far as the 124 layout I did the switches on the back energize the relays both PAB and OD

Max
Lifting the stack( in the common sense of the word) really only applies to TS such as the Marshall & Fender where the ground reference to the entire stack is at the bottom of the Mid pot. Take a look at TS simulator or schemo..As you raise the ground potential you lift the whole stack from the circuit..
The Skyliner is a different animal in the way that the mid pot is independent from the treble and bass controls so you can't lift the entire stack just by lifting the mids you can however take some of the load off the stack by breaking certain connections such is the case with the bass pot in the Skyliner..If I said the center off lifts the stack I was wrong and certainly apologize..

Tony

[Max]

@martin manning and talbany:

Hi Martin, Hi Tony,

thanks a lot for the explanation. Got it.

Do you perhaps know, or can find out by asking someone, if I remember right and the 5th generation (Mid switch) skyline amps like #155 or #183 etc. don't have such a three position R/J switch any longer?

Thanks again and all the best,

Max

[ayan]

Max, #124's rear panel manual PAB switch will not engage the PAB wired as shown in the photos. This is a bit of a mystery, and might be adequately explained if the R/J switch has a middle position that can be used to engage PAB manually from the front panel (the rear panel switch would not be needed). Since #124 was updated at some point, perhaps the three position R/J was one of the updates. There is no difference electrically between the center off position of the R/J switch and the PAB relay function. Both methods leave the top and the wiper of the bass pot, and the bottom of the treble pot floating (disconnected).

I have a interesing story about the apparently miswired PAB rear-panel switch. Indeed, as wired, 124 did nothing when flipping the switch. It is NOT, however, the only amp with that peculiarity. I went through another amp in L.A. that, like 124, did not have a ground connection on the PAB rear-panel switch. I fixed that while I was in the amp, and pointed it out to the owner. He said that he'd never attempted to use the toggle switch, but that he had realized that the center position of the J/R switch yielded a similar sound to that achieved by the PAB footswitch. However, this guy said he felt the two resulting sounds were slightly different. [ Now, I do not agree with that and I believe that, electrically, the two connections would be equivalent, but that's not the point ] Being the original owner he called Dumble and explained his finding, and asked him about the two sounds being different. Dumble's response was: "I am surprised you are one of the ones that can hear the difference," and offered no further words of wisdom. True story. The amp in question was a 1982 high plate classic, supposedly like Robben Ford's original Dumble -- at least that's what the owner asked for when he ordered the amp.

Gil

[Max]

I have a interesing story about the apparently miswired PAB rear-panel switch. Indeed, as wired, 124 did nothing when flipping the switch. It is NOT, however, the only amp with that peculiarity. I went through another amp in L.A. that, like 124, did not have a ground connection on the PAB rear-panel switch. I fixed that while I was in the amp, and pointed it out to the owner. He said that he'd never attempted to use the toggle switch, but that he had realized that the center position of the J/R switch yielded a similar sound to that achieved by the PAB footswitch. However, this guy said he felt the two resulting sounds were slightly different. [ Now, I do not agree with that and I believe that, electrically, the two connections would be equivalent, but that's not the point ] Being the original owner he called Dumble and explained his finding, and asked him about the two sounds being different. Dumble's response was: "I am surprised you are one of the ones that can hear the difference," and offered no further words of wisdom. True story. The amp in question was a 1982 high plate classic, supposedly like Robben Ford's original Dumble -- at least that's what the owner asked for when he ordered the amp.

Gil

Hi Gil,

I can confirm this. I also know one other 4th generation high plate classic without a ground connection on the PAB rear pannel switch. And, indeed, my perception too was AFAIR that the sound was a tiny little bit different when I engaged the PB with the footswitch and with the R/J middle position. As I am no tech, I always thought that this may perhaps be because some voltages inside the amp change a tiny bit when the PB relais changes from on to off and vice versa. But indeed, there was a tiny bit of a difference AFAIR, but nothing obvious at a first glance and perhaps pure personal imagination anyway. Psychoacoustics. We really have a lot of luck that our perception can be fooled that simply. Otherwise we would hardly perceive mp3 files to be music as an example. LOL!

Hey Gil, great story, thank you for sharing!

Cheers,

Max

[Structo]

I don't see how it could sound different, it is a relay that is either switched on with the rear front panel switch or the footswitch.

Sounds like HAD was having a bit of fun with the customer.
I wonder how he explains the rear slider switch not being grounded?
No solder on the switch so it was never grounded.
And since there have been a few amps with the same mistake, I wonder what he was thinking?

[jelle]

Max, Gil,

There is a difference between the two PAB approaches. The one on the front is a tiny bit hotter and fuller.

Jelle

[Max]

Max, Gil,

There is a difference between the two PAB approaches. The one on the front is a tiny bit hotter and fuller.

Jelle

Hi Jelle,

that was exactly my impression. But why?

Have a nice weekend,

Max

[jelle]

I think Mr. Dumble found it to be too much of a pain to wire those pesky 22M resistors on the center off Rock/Jazz switch as well. Those lugs are quite small, you see? IMHO, the resistors are not needed there.

The lack of 22M resistors in the center off position reduces loading down of the signal but the difference is very subtle. But, some ODS amps do not have the 22M resistors on the PAB, and in those amps I'be amazed to find a difference between the two PAB approaches.

Jelle

[martin manning]

There is a little difference... The R/J version is a little bassier with the Mid Boost off, but there is almost no difference with Mid Boost on. Sorry about the plot resolution... major divisions are 3dB. The rear switch as wired on #124 (e.g.) does have a usable function... it disables the footswitch PAB!

[Structo]

Right, I didn't even think about the 22M resistors.
I don't have the R/J switch on my amp so I was going by that.

[groovtubin]

Straight from Eddie.

His main old Marshall Plexi Superlead!!! Plus he had a good laugh over the hearsay that never ends!!!!

Hope this helps.

Outstanding, Scott! Too funny.

Did I mention that I ghosted all of the solos on 'The Dark Side Of The Moon'? I'm claiming it and you're reading it, so it must be true....

Nix, LOVE your sound, is that a CAE OD-100?? Just great!

jim

[ayan]

Max, Gil,

There is a difference between the two PAB approaches. The one on the front is a tiny bit hotter and fuller.

Jelle

Well, due to the padding of the resistors in the PAB. Furthermore, the amp in question had, rather than 22 Meg resistors, 2x10Meg instead, so I suppose it would be ever more noticeable.

Cheers,

Gil