OD trim voltage value

[tubedogsmith]

Magic dust.....HHhhhhhhmmmmmm........

[talbany]

Thanks for the info Tony. Knowing that the typical Fender value is 68K and HADs' are generally 22K (33K-#124), I was curious as to the significance of the value when setting up the ODS for use with S/C p/u's. Reading through Aiken's words I get the impression that in these type of amps, the value is not too critical on V1a, as long as there is something within ballpark. I suppose the best way to find out is to have a go at changing the values in my amp!

Cheers,

Paul.

Paul


The treble response -3db roll off with 22k is 47.25 KHZ
With 68K -3db =15.2 KHZ

Keeping in mind audible range for human hearing is 20HZ-20KHZ If you don't play guitar in a loud band.. Normal range for guitar =82 to 1050
So looking at these numbers I doubt there will be an audiable difference.Now how this effects higher and lower order harmonics would be open for debate...
Tony VVT

[Guitarman18]

Tony,

I see where you are coming from, that makes a lot of sense. Even if it make any audible difference, there are obviously better places to 'start digging for treasure'.

Cheers,

Paul.

[BobW]

The treble response -3db roll off with 22k is 47.25 KHZ
With 68K -3db =15.2 KHZ

Based on the 151 pF Miller capacitance quoted earlier the knee:

w/ 22k Rgrid = 47.93 kHz
w/ 68k Rgrid = 15.5 kHz

[Structo]

You're going to quibble about 680Hz and 300Hz?

[BobW]

Here's something useful when discussing units and values.

http://ewh.ieee.org/soc/ias/pub-dept/abbreviation.pdf

Common mistakes:
k not K
Hz not HZ
pF not PF or pf

Quibbling, maybe but standards are standards.

[LPSGME]

I apologize if this post ends up in duplicate. But I'm reposting it as it seems my first try did not appear.

I'm new here but have been reading a lot trying to make a recent production Ceriatone HRM that I got (second hand) a bit more Dumble like.

While I've been modifying amps as far back as the 60's, I never heard the name Dumble until only 2 months ago. So excuse me if I'm not up to speed. BTY could someone please fill me in on the meanings of some of the common abbreviations and acronyms used regarding the Dumbles.

While reading this thread I kept thinking, how about just hooking up a scope and observing what happens when parts are changed? I don't think I've heard anyone ever talk about how the signal looks; only how it sounds.

As these 2 articles explain, the more pleasing 'even' 'second order' 'first' harmonics are generated by an asymmetrical soft clipping distortion of the wave form.

http://guitar.tyquinn.com/2009/lead-ton ... distortion
http://www.tangible-technology.com/tubes/altec.html

IMHO the easiest way to figure out what is going on is to drive the amp with a sine wave and look with a scope.

An amp can only do and deal with a few things like frequency and signal levels. It's not like it can 'core a apple'. So if there's any special secret, it's ultimately going to expose itself under thoughtful measured observation. If you can hear it, you can also see it. Right?

I seem to recall that it's possible to get both the positive and negative peaks of the waveform to round out and fatten nicely, as well as to go more asymmetrical, just as the signal clips - but don't recall if such coincidental form is optimal or not. Maybe it's best if the signal is asymmetrical at a low input level.

Besides every amp is probably different enough that each has to be individually tweaked.

[heisthl]

I wish it were that easy - what are you going to feed into the amp to judge how it sounds? Not a sine, not white, not pink - all are meaningless. Ok, so say you feed it with an actual guitar and have a storage scope so you can replay the waveforms - even then the "magic" cannot be seen. A good Dumble in addition to the just right amounts of harmonics and sustain has to have some almost unmusical "junk" that's almost random and for this humble writer has been impossible to capture on a scope trace.

[LPSGME]

I wish it were that easy - what are you going to feed into the amp to judge how it sounds? Not a sine, not white, not pink - all are meaningless. Ok, so say you feed it with an actual guitar and have a storage scope so you can replay the waveforms - even then the "magic" cannot be seen. A good Dumble in addition to the just right amounts of harmonics and sustain has to have some almost unmusical "junk" that's almost random and for this humble writer has been impossible to capture on a scope trace.

I wasn't thinking in terms of observing any formant changes as much figuring out the electrical changes and their effect on the an injected test signal.

It is really impossible to see (as the critical parts are changed) an observable identifiable and measurable change in the circuit or to an signal injected at various frequencies?

It seems that the effect of changing certain key parts has to be measurable and, perhaps, by ways that do not require much sophistication. For example, maybe a highly asymmetrical distortion is imparted to the top half of a signal in one stage but not in another. Who knows?

But knowing could provide interesting insight to the knowledge of what parts deliver the magic.

[heisthl]

I wasn't thinking in terms of observing any formant changes as much figuring out the electrical changes and their effect on the an injected test signal.

It is really impossible to see (as the critical parts are changed) an observable identifiable and measurable change in the circuit or to an signal injected at various frequencies?

It seems that the effect of changing certain key parts has to be measurable and, perhaps, by ways that do not require much sophistication. For example, maybe a highly asymmetrical distortion is imparted to the top half of a signal in one stage but not in another. Who knows?

But knowing could provide interesting insight to the knowledge of what parts deliver the magic.

The magic is the basic design, layout, component types and construction techniques and when you catch up on all the old posts here you will pretty much know all that is known.
Many here have pursued the scope each stage course, mostly for tweaking purposes and I think the variance of component values and their effect is already known by many here, Off the top of my head a search of old topics should reveal the tracing of the OD section and its impart on a sine wave as one example.

Study up and then build one using the ODS-101 schematic as a baseline - the folks here will help you every step of the way.

[butwhatif]

While reading this thread I kept thinking, how about just hooking up a scope and observing what happens when parts are changed? I don't think I've heard anyone ever talk about how the signal looks; only how it sounds.


IMHO the easiest way to figure out what is going on is to drive the amp with a sine wave and look with a scope.

I for one have tried to get some baseline bench information like pix of scope traces going on this forum, but alas, i think most guys here don't own one, and while it's not a requirement, it sure is a helpful tool, especially if one has experience using it, or get into trouble on a project. I use one every day, there's so much info that could be gleaned from this, as any bench tech will attest. I think those who do not own one never clue on the attributes. It's like an ICU heart monitor, you can listen thru a stethoscope, and hear a lot of things , but wouldn't you want to see the scope trace?
Ears are and will be the final judge on what works, but if I could get one of the guys lucky enough to either own or have on the bench a real ods to post some od traces w/a sine wave input, it would mean as much to me as
a listen to the thing. Haven't seen it happen yet. 'Clips' are the stock in trade here.

[LPSGME]

Thanks for all the feedback (for everyone's hard work). I agree as (I think) has been said, that the only needed key is to decipher which parts deliver which sound - and then just listen.

[Structo]

While reading this thread I kept thinking, how about just hooking up a scope and observing what happens when parts are changed? I don't think I've heard anyone ever talk about how the signal looks; only how it sounds.


IMHO the easiest way to figure out what is going on is to drive the amp with a sine wave and look with a scope.

I for one have tried to get some baseline bench information like pix of scope traces going on this forum, but alas, i think most guys here don't own one, and while it's not a requirement, it sure is a helpful tool, especially if one has experience using it, or get into trouble on a project. I use one every day, there's so much info that could be gleaned from this, as any bench tech will attest. I think those who do not own one never clue on the attributes. It's like an ICU heart monitor, you can listen thru a stethoscope, and hear a lot of things , but wouldn't you want to see the scope trace?
Ears are and will be the final judge on what works, but if I could get one of the guys lucky enough to either own or have on the bench a real ods to post some od traces w/a sine wave input, it would mean as much to me as
a listen to the thing. Haven't seen it happen yet. 'Clips' are the stock in trade here.

I would agree if I owned a scope.

Then there would be the learning curve in how to use it and to know what you are looking at.
I haven't used a scope since high school some 35 odd years ago.
I would love to buy one but just putting food on the table is hard enough right now.

[LPSGME]

I for one have tried to get some baseline bench information like pix of scope traces going on this forum, but alas, i think most guys here don't own one, and while it's not a requirement, it sure is a helpful tool, especially if one has experience using it, or get into trouble on a project. I use one every day, there's so much info that could be gleaned from this, as any bench tech will attest. I think those who do not own one never clue on the attributes. It's like an ICU heart monitor, you can listen thru a stethoscope, and hear a lot of things , but wouldn't you want to see the scope trace?
Ears are and will be the final judge on what works, but if I could get one of the guys lucky enough to either own or have on the bench a real ods to post some od traces w/a sine wave input, it would mean as much to me as
a listen to the thing. Haven't seen it happen yet. 'Clips' are the stock in trade here.

Yes there are so many useful things one might never clue into or find without a scope.

On a side note, somewhere I recently heard a sound clip of an early model dumble with a tremolo. It cause me to wonder if a tremolo could be subtly used to subliminally entrain the audience's mood.

A friend and I used to build 'brain' machines that utilized programs that we designed to fit particular new age music recordings. The programs were just recordings of the low periodicity 'beeps' that drove the light googles and which were also mixed into the headphones along with the music.

There was one tape in particular that would always cause people too break into a hugh smile and ecstatic laughter - always at the same point in the program.

Can you imagine if all it took to entrain the mood of an audience were some subtle tremolo progressions?

[BobW]

While reading this thread I kept thinking, how about just hooking up a scope and observing what happens when parts are changed? I don't think I've heard anyone ever talk about how the signal looks; only how it sounds.


IMHO the easiest way to figure out what is going on is to drive the amp with a sine wave and look with a scope.

I for one have tried to get some baseline bench information like pix of scope traces going on this forum, but alas, i think most guys here don't own one, and while it's not a requirement, it sure is a helpful tool, especially if one has experience using it, or get into trouble on a project.

'Clips' are the stock in trade here.

I agree, my scope / function generator is a valuable tool for finding parasitics, grid clipping, etc., but haven't been able to determine using traces alone if its the tone I want.