Mod to 2nd/ 3rd generation build

[stevlech]

I hope I'm not being a pest, but I drew up a new idea borrowed from the HRM models. Would this approach work for individual master controls?

P.S. - I know the tonestack is wrong, I just threw this together...

[Structo]

Looks similar to the 101 HRM schematic.

I didn't look too carefully but the HRM amps have separate masters.

[stevlech]

That's what I had in mind, actually.

[Max]

Hey Max
AFAIK the pre trigger OD entrance design is I would consider a fairly low gain network... much of the signal get's attenuated at the front end and gets attenuated less on the back end of the OD circuit..

Getting the right balance between clean and OD and still have the OD serve up some real gain w/ sustain and bloom is rather difficult at low living room volumes(no FET).. When you get the amp to higher volumes the amp starts to better balance itself clean/OD and really starts to sing..Very Cool!! This is not a living room amp it's a gig amp tuned for slightly higher volumes..(The fet does help with this BTW) Max, Marcos would you agree..

Tony

Hi Tony,

I’ve played some of these early amps without a ratio control and some of them even for a longer period of time and never had any practical problems because they did not have a ratio control. Even at "living room levels" I got all the tones I wanted just by using all the inputs, switches and controls of these amps and all the controls of my guitars. And some of the professional players who use one of these early amps reported the same when I asked them concerning this. All these early Dumble ODS amps I know did clean up perfectly when turning down the volume controls of my guitars.

If you ever attended a Larry Carlton live concert in the last years you have most probably attended a demonstration, too, how to get different gain levels by just using the volume pots of the guitar and/or his Sho-Bud volume pedal in front of the amp – and even without channel switching at all.

And if you really fear that you will have serious volume level troubles when switching without a ratio control you could perhaps think of a HQ volume control in the loop. A loop done without coax cables but with twisted wires (ground wire connected only to the jack) would be an "original 2nd generation mod" that you find in real 2nd gen. amps, too.

A "HQ volume control" in the loop could perhaps be a midi controllable device that you can control with a midi pedal (advantage: short coax cables between the loop and the volume control device that you can place perhaps near or even on the amp as an example) or a high quality volume pedal in the loop – just what you think works better. Usually you can try such devices today and return them for a refund of the price paid if you don’t like them.

Another option to solve such a kind of volume level problem without a mod to the original "pre-classic" circuits would perhaps be the use of a HQ power attenuator with a switching option - perhaps something like Jim Kelly did use for his amps (FACS as an example).

IMO the different Dumble amps from different generations offer different options of tone, timbre and feel. So I would indeed recommend to

- listen to the tracks of the reference thread
- make a first decision which of these tracks are perhaps worth a second close look
- buy a CD or download a HQ file of these tracks to listen again in highest quality
- decide which one of the original circuits with which of their "original mods" (known from real amps) you want to begin with
- use the corresponding one of your four layouts for your build

If you should already have an amp you are rather happy with and are looking for a fun project, you could perhaps start a journey through the ODS history based on your layouts.

The big advantage of your four ODS layouts you've posted up to now (2nd, 3rd, 4th, skyline update of 4th) is, that they all are based on rather similar general structures: I you opt for a 100W or 50W model in the beginning, then the chassis, the PS, the transformers, the FET and many of the other structures could be used for each one of these four layouts.

Example for such a journey through the ODS history:

1st step:
You can start with a replica of a 2nd generation, but perhaps with the 100W power amp of your "low plate classic" layout if you are sure that you want a 100W amp from the very beginning of your journey (otherwise you could later update to the 100W power supply/amp).

2nd step (optional):
the "original 2nd generation" updates" (known from real 2nd gen. "pre-classic" amps - without a "classic" tone stack and/or a "classic" OD entrance). Some examples:
– the twisted wire loop
– a presence control of different sorts, like in #093 (option: the trim pot on the back) or with the small control knob on the front in the place of the former accent)
– 50W to 100W upgrade

3rd step:
3rd generation update just as in your 3rd generation layout

4th step (optional):
the "original 3rd generation updates" (known from real 3rd gen. "pre-classic" amps - without a "classic" tone stack and/or a "classic" OD entrance). Some examples:
– the twisted wire loop
– a presence control of different sorts, like in #093 (option: the trim pot on the back) or with the small control knob on the front in the place of the accent switch)
– 50W to 100W upgrade

5th step:
"transition generation 'classic' update" = your "low plate 'classic' layout" but with the ratio control on the back like #075 (coax of course) and a small presence on the front in the place of the accent and then perhaps a stereo jack loop (twisted wire), too, like in #075

6th step:
"skyline" update of this "transition generation 'classic' ODS" replica = your #124 "skyline" layout but with the ratio on the back, a small presence pot on the front and perhaps the stereo loop jack.

Optional steps:
- high plate versions of the "classic" and "skyline" circuits.
- HRM update of the skyline update circuit.

If you take a look again at your layouts, all these circuits could IMO be implanted in the same chassis just as in the original 2nd generation chassis of some of Alexander's customers that have later been updated to "classic" or "skyline" specs or some even to "classic-HRM" (I know of only one of these and with AFAIR fixed HRM EQ resitors instead of the trim pots, but I am no longer 100% sure of this) or "skyline-HRM" specs.

IMO this would perhaps be really interesting and perhaps even educational for someone interested in building amps to start with exactly your 2nd generation layout and then to implant step by step all the updates of the 3rd, the 4th and the 5th generation (skyline/mid switch) into this amp, just as Alexander did this over the years with some of the 2nd generation amps of his customers.

By this you would IMO perhaps get a very meaningful impression concerning the influences on the tone and feel that all these step by step updates have. And I am rather sure that after such a kind of journey through the ODS history you will have a very solid basis for the decision which one of the ODS circuit versions you like best in the end for what you are looking for in a guitar amp.

If you should meet an amp on this journey that you really like, an obvious option would of course be to leave this one just as it is and build the next "step" as a complete new build in a new chassis and further proceed from there with the new chassis step by step - and so on.

As far as I remember Alexander Dumble once has recommended to Marcos some possible updates for a 2nd gen. "pre-classic" amp that are IMO steps from the "pre-classic" to the "transition generation 'classic' ODS" circuits and that IMO are "original 2nd gen. mods", too, as recommended for a try by Alexander himself. So perhaps you could ask Marcos to post again these "original 2nd generation mods/updates" and try these, too, somewhere between the steps 3,4 and 5 of this journey through the ODS history.

Have a nice day,

Max

[talbany]

Max
Thanks for the response.. Indeed a detailed review of each of the various modifications throughout the different generations would be of great value here .. However this would require modifying an existing amp I hold dear am hesistant to do so.. Perhaps sometime in the future I could build an amp for such an experiment would certianly be a wonderful learning experience and BIG fun.. I'll see what I can do to make this happen..
At the moment my collection consists of quite a few generations with various mods and features although the basic topology of each is as accurate as I could get with the info at the time.. Some of these were built on steel chassis and different coax was used and in some cases different transformer styles..These are not dead on replicas but very close and would be happy to review each of these or if someone has a question on one (in a post or PM) since they are already built..

Top Right....High Plate Music Man no loop EL-34 50w Classic stack w/ mid similar to #094

Bronze- 100W EL-34 HRM Bluesmaster w/OD tone controls on front built in loop

Green..2nd Generation/(deep & mid boost) 100w 6L6 /415 STR's Built in loop Vox style NFB

Black Clone-100w 5881 Music Man built off my 124 layout but high plate no loop

Flame Maple- PCB Design HRM Skyline stack Marshall Plexi Power and OPT style transformers Sozo tone coupling caps EL-34 100w built in loop

Bottom Left- Transition generation Classic w/ ratio on front updated high plate w/220k/100k trigger 4.7K /2K 390 1uf presence and PAB ..no loop currently running 6L6.. Amp has Traynor YBA-1A iron 520 on the plates..

Max.. Thanks for the tip on the Volume pedal in the loop.. I have used that in other amps with good results and will try it and report back if I find it useful..

Hope I can help..

Tony

[stevlech]

Wow. There are certainly many options, aren't there? Max, I like the idea of taking a build through the timeline of the ods. If done properly, it would indeed be very educational about the influence of various sections and even part values. With so many variations, one might even plan on more than one build. Maybe three or so chassis would be in order: one for 2nd/3rd generation, one for non HRM, and one for HRM/Bluesmaster. The builder would then have the advantage of comparing the chassis simultaneously to gain knowledge concerning the unique "feel" among the circuits. Hmm... I've got two chassis laying around...

Jeez, all I wanted was a ratio control and now I have new projects! Guess I have to finally build something.

Good day to you all

[Max]

With so many variations, one might even plan on more than one build. Maybe three or so chassis would be in order: one for 2nd/3rd generation, one for non HRM, and one for HRM/Bluesmaster. The builder would then have the advantage of comparing the chassis simultaneously to gain knowledge concerning the unique "feel" among the circuits. Hmm... I've got two chassis laying around...

Jeez, all I wanted was a ratio control and now I have new projects! Guess I have to finally build something.

Good day to you all

Hi stevlech,

I agree, to have two or even three chassis for such a journey from a replica of a 2nd generation "pre-classic" ODS to perhaps the latest skyline-HRM ODS amps with a precision power supply would indeed have the advantage of the possiblity for direct comparisions between different circuits like the 2nd and the 3rd generation circuit or the 3rd gen. "pre-classic" circuit with the low plate "classic" circuit or the low plate "classic" with the low plate "skyline" circuit etc.

With a single 2nd generation chassis for a start it would perhaps make some sense to document the step by step changes of the tone by meaningful high quality recordings.

Have fun,

Max

[groovtubin]

I hope I'm not being a pest, but I drew up a new idea borrowed from the HRM models. Would this approach work for individual master controls?

P.S. - I know the tonestack is wrong, I just threw this together...

May wanna try running the master just like a 80`s version, where it is a SGL master for both clean and OD, feeding the preamp out jack. On OD ratio and level, i run it like a 80`s as well....i forego the 180K to ground.

jim@Omegaamps

[jelle]

[quote="Max]

.....or some even to "classic-HRM" (I know of only one of these and with AFAIR fixed HRM EQ resitors instead of the trim pots, but I am no longer 100% sure of this) or "skyline-HRM" specs.

Have a nice day,

Max[/quote]

Max,

For the sake of simply having the data out there....there's a HRM with classic tonestack that has the trimmers for the HRM, not the fixed network. I have the impression, just my impression, that the fixed network was just on the very first HRM amps. But maybe there was another reason why the fixed networks were used.

All the best,
Jelle

[marcos]

Hey Max
AFAIK the pre trigger OD entrance design is I would consider a fairly low gain network... much of the signal get's attenuated at the front end and gets attenuated less on the back end of the OD circuit..

Getting the right balance between clean and OD and still have the OD serve up some real gain w/ sustain and bloom is rather difficult at low living room volumes(no FET).. When you get the amp to higher volumes the amp starts to better balance itself clean/OD and really starts to sing..Very Cool!! This is not a living room amp it's a gig amp tuned for slightly higher volumes..(The fet does help with this BTW) Max, Marcos would you agree..

Tony[/quote]

Hi Tony,
I definetely agree.The 70s circuit needs more volume (I was playing pretty loud back then, Master on 2 o´clock) to sound good, not a living room amp at all.Also, the balance between clean and overdrive is better at higher levels.Still,as you noted, difficult to get the balance.

Marcos

[marcos]

2. Adding presence. Just adding a 1uf cap and 10K on the standard PI (820/100 feedback) is going to do bumpkiss. The 100ohm swamps the the pot and it only works when the pot is maxed out.


Gary

Hi Gary,
for the presence mod HAD recommended a 500 ohm pot in series with the 1 µF cap.This is how I did it, a 1 K pot works here,too.

Marcos

[marcos]

. So perhaps you could ask Marcos to post again these "original 2nd generation mods/updates" and try these, too, somewhere between the steps 3,4 and 5 of this journey through the ODS history.

Have a nice day,

Max

Hi Max,

here are the changes recommended by HAD (for my 2nd generation ODS):
250 KL treble pot instead of 500 KL, treble cap 330 pF instead of 510 pF,
PI input coupler 20 nF instead of 5 nF, the presence mod (500 ohm pot in series with the presence cap).He also recommended changing the V1b
coupling cap to .05 µF.All useful mods, but not the whole picture.
My amp pretty much evolved the way you described, from 2nd to 3rd
generation.It is a low-plate Skyliner now(without the trim pots) and I like it better than ever.
Actually, I think the tone is not that different, but it has a more vocal quality, especially in the lower mids.Still, a matter of taste.
Hope this helps a bit
Marcos

[talbany]

Hey Max
AFAIK the pre trigger OD entrance design is I would consider a fairly low gain network... much of the signal get's attenuated at the front end and gets attenuated less on the back end of the OD circuit..

Getting the right balance between clean and OD and still have the OD serve up some real gain w/ sustain and bloom is rather difficult at low living room volumes(no FET).. When you get the amp to higher volumes the amp starts to better balance itself clean/OD and really starts to sing..Very Cool!! This is not a living room amp it's a gig amp tuned for slightly higher volumes..(The fet does help with this BTW) Max, Marcos would you agree..

Tony

Marcos thanks for the shout back.. I've messed around quite a bit with that OD circuit and one of the things you can do to increase gain at the 3 resistor OD entrance is to lower the bypass resistor (1.2m) you can even mount an internal trimmer there and adjust the right amount of gain at the proper volume level you like.. If you look at the Kitty hawk clone they lowered it to 500 something K this will serve up a decent amount of gain and put a little snarl as well.. This will also help to balance it out.. Fun to play around with too..
Hope this helps

Tony

[Max]

there's a HRM with classic tonestack that has the trimmers for the HRM, not the fixed network. I have the impression, just my impression, that the fixed network was just on the very first HRM amps. But maybe there was another reason why the fixed networks were used.

Hi Jelle,

just to avoid a misunderstanding:

I wrote of a 2nd generation "pre-classic" ODS that has at first been updated to "classic" specs at some point and then again - at a later point -got an additional post OD HRM circuit and without changing the "classic" tone stack to "skyline" specs.

Now my question is: The one with a "classic" stacks and the trimmers you know, was this originally a 2nd generation "pre-classic" amp, too, or originally a transition or 4th generation "classic" ODS, which has later been updated with a HRM circuit?

Did it still have the V2 snubbers after the HRM update?

And did it still have the "classic" ratio/master circuit or the sperate clean and OD masters like the later skyline-HRM amps in the series # 200 range?

All the best,

Max

[jborders5]

A couple of hints for creating separate masters for Clean and Overdrive.

1. Float the clean master potentiometer off of ground when OD is enabled. THis is very easy to do if you remember that the OD input is grounded when clean mode is enabled. I simply tap the OD input from the relay and connect it to the ground connection of the clean master. This assumes wiring the clean master before the relay.

When OD is selected the Clean master has the same signal on top and bottom and is taken out of the circuit.

Gary

Thanks for the tip Gary. How does this look?:
[img442]http://img530.imageshack.us/img530/7685 ... stersg.jpg[/img]