Preamp out Power amp in OD Special

[roknroll]

In https://tubeamparchive.com/files/dumble ... ic_172.pdf with no loop insert the signal bypasses the 220k/250pf pair

In https://tubeamparchive.com/download/file.php?id=11313 with no loop insert the signal goes through the 220k/250pf pair

In https://tubeamparchive.com/files/124_schematic_182.pdf with no loop insert the signal bypasses the 220k/250pf pair

In https://tubeamparchive.com/files/124_sc ... 84_208.pdf no 220k/250pf pair at all
I understand that there are a few different versions of the Special. So my questions are
1- Is any one more correct or more accepted
2- Is there a possible typo on any of these schematics regarding this area
3- If Dogears were to build one, which version would he use?
Thanks
Jack

[dimitris]

Hi Jack
Don't know what Dogears would build but if you study the photos of 124
you will find that with no loop insert the signal bypasses the 220k/250pf pair.

[CHIP]

A little mentioned here, https://tubeamparchive.com/viewtopic.ph ... c&start=60

[dogears]

I'd use a bright cap on the master volume. Then use two tip shorting jacks on the back and insert a network to simulate loop cables on those jacks. Only in circuit shunting highs to ground when nothing is plugged in.

As far as I know, only 124 had the preemphasis network. But, many Dumbles had the bright cap and Dumbleator system. Such as Robbens.

Now, these amps did not have cable simulation on the jacks but it makes sense to do it as sometimes you just are too lazy to hook the rack up.

I've been simulating capacitance for years in my amps.

[roknroll]

Hi Jack
Don't know what Dogears would build but if you study the photos of 124
you will find that with no loop insert the signal bypasses the 220k/250pf pair.

I see where the disagreement is coming from. Look at this drawing I am correct based on this drawing, you are correct based on the other. If you notice the brown wire from the master volume is attached to the hot leg of the unswitched jack. In the one you are referring to the brown wire is attached to the switch of the switched jack. Maybe the version of the drawing changed over time and mine is an earlier one.
Thanks for everyones opinions.[/img]

[Max]

But, many Dumbles had the bright cap and Dumbleator system.

Hi Scott,

AFAIR I have never seen (first hand or pictures) a capacitor at the master volume or loop in any dumble ODS that has been origninally built with a "pre-classic" or "classic" tone stack (all ODS up to around 1987 and # approx. 15X) and still has this "pre-classic" or "classic" tone stack. If someone here knows of a "classic" or "pre-classc" ODS with such a kind of "loudness" capacitor at the master volume, please correct me, this would be interesting to know.

AFAIK only very very very few original Dumble ODS amps have ever been or still are used with a Dumblelator. Original Dumblelators are extremely rare. It is my personal opinion from taking into account the number of Dumblelators in relationship to the number of ODS, that have been offered "second hand" over the last 30 years, that Alexander made perhaps a total of 30 or even less mono and stereo Dumblelators.

AFAIK a lot of players used their Dumble ODS amps without any effects in the loop, or with effects in the loop but not with a Dumblelator but in a different buffered or not buffered setup. Steve Farris e. g. used a Korg SDD 3000 plugged just into the loop of his ODS #075 (stereo plug because the "ratio" is placed on the back, see the pictures of the back: http://www.maverick-music.com/scripts/v ... oduct=1968) and without a Dumblelator AFAIK.

All the best,

Max

[dogears]

Moot issue for me. I have pictures of maybe 10 Dumbles with bright caps at the master. All with either Skyline, Bluesmaster, or Skyline HRM configurations. Including #124 (upgraded by HAD).

Most importantly, for my grail tone (along the lines of the Robben horn thing), the bright cap and Dumbleator were most certainly a system. I personally verified it. One must have the other.

The OP was asking about 124 and that is an updated Skyliner. Hence my recommendation.

Regards....

But, many Dumbles had the bright cap and Dumbleator system.

Hi Scott,

AFAIR I have never seen (first hand or pictures) a capacitor at the master volume or loop in any dumble ODS that has been origninally built with a "pre-classic" or "classic" tone stack (all ODS up to around 1987 and # approx. 15X) and still has this "pre-classic" or "classic" tone stack. If someone here knows of a "classic" or "pre-classc" ODS with such a kind of "loudness" capacitor at the master volume, please correct me, this would be interesting to know.

AFAIK only very very very few original Dumble ODS amps have ever been or still are used with a Dumblelator. Original Dumblelators are extremely rare. It is my personal opinion from taking into account the number of Dumblelators in relationship to the number of ODS, that have been offered "second hand" over the last 30 years, that Alexander made perhaps a total of 30 or even less mono and stereo Dumblelators.

AFAIK a lot of players used their Dumble ODS amps without any effects in the loop, or with effects in the loop but not with a Dumblelator but in a different buffered or not buffered setup. Steve Farris e. g. used a Korg SDD 3000 plugged just into the loop of his ODS #075 (stereo plug because the "ratio" is placed on the back, see the pictures of the back: http://www.maverick-music.com/scripts/v ... oduct=1968) and without a Dumblelator AFAIK.

All the best,

Max

[Max]

I have pictures of maybe 10 Dumbles with bright caps at the master. All with either Skyline, Bluesmaster, or Skyline HRM configurations. Including #124 (upgraded by HAD).

Scott,

thanks for the info. Same with me. Just like you, I have only seen these master volume caps in "post classic" ODS, all built or modified after 1987. Btw: Robben Ford's Dumble ODS #102, a 4th generation "classic" updated to "skyline" specs, is such a specimen with a 68pF (as many) cap at the master volume AFAIR.

Have a nice day,

Max

[dimitris]

Roknrol wrote:

I see where the disagreement is coming from. Look at this drawing I am correct based on this drawing, you are correct based on the other. If you notice the brown wire from the master volume is attached to the hot leg of the unswitched jack. In the one you are referring to the brown wire is attached to the switch of the switched jack. Maybe the version of the drawing changed over time and mine is an earlier one.
Thanks for everyones opinions

Jack you have misunderstood me.I was talking about the real photos not layouts.Look at the attached photo where the brown wire is soldiered and the mystery will be solved.
Cheers

[Structo]

I brought up this same issue when I built my Dumbleator.
The layout had the brown wire going to the wrong jack.

There can be a lot of confusion when dealing with this stuff over the internet.
But you are correct the brown wire from the Master Volume wiper does indeed go to the middle lug on the switched jack.
It was difficult to see so I think that is why it was wrong on the layout.
So depending which layout you have it could be wrong.

I had this network on my amp for a while after I built my Dumbleator, but I couldn't discern any affect from it so I took it out.
I don't play my amp without the Dumbleator so it doesn't matter.

What is crucial though with the Dumbleator is to have a bright cap on the Master Volume, from the right lug to wiper, this helps the tone.
I believe I have a 47pf on mine.

This is a corrected layout.

[ChrisM]

Does that have the R/J switch fix in it as well Tom?

[Structo]

I don't know.
I didn't know there was an issue with that.
What is wrong? I have the Visio file for this so I can fix it if it is wrong.

[ChrisM]

I thought it was you who brought that issue up, or was it a PAB issue? I forget now.

[Max]

What is crucial though with the Dumbleator is to have a bright cap on the Master Volume, from the right lug to wiper, this helps the tone.
I believe I have a 47pf on mine.

This may be your personal taste of course.

My personal taste:

When playing an original "classic" ODS, I did never miss this master volume capacitor. Not without and not with a Dumblelator in the loop.

When playing an original "skyline" amp I always disliked the (usually 68pF) cap with MV settings below 09:00. Above 09:00 better up to "fine with me". With a Dumblelator in the loop: just great, as now you can use the settings of the MV and the "drive" pot of the Dumblelator to control the amount of brightness added by this cap.

All a matter of personal taste IMHO.

Have fun,

Max

[talbany]

Dimitris
There were several revisions to the layout I did on #124.. These were the loop wiring you refer(thanks to Tom).. The PAB and also the filter wiring for V1.. These were all addressed and corrected so you do have a non revised copy.. After making those revisions I sent the revised copy to IC-to be posted in the D-files sticky section but stayed in my outbox for several weeks and don't really know if IC updated this.. Here is the revised copy..Save it..

FWIW.. The 220k/bypass cap placed at the return before the PI helps insure the max voltage/signal transfer due to the lower impedance coming from the outboard effect..
In general, if the source impedance is at least 10 times lower than the load impedance, you're okay, because you'll get 90% of signal transfer. The lower the source impedance, the less high end you'll lose due to cable capacitance or load capacitance on the input of the effect, so the closer you get to a zero ohm source impedance, the better.If you don't use the loop and the 220k is in circuit (before PI) it helps with loading..Just to mention.. Hope all this helps..or confuses you more..

Tony