ODS 124 - revisited for the 21C

[Stephen1966]

ODS #124 with Skyliner TS, 1988

PRIMARY DOCUMENTATION

Dumble ODS with layers-optimised.pdf

#124 Schematic_1988_Skyliner [marked up_2].pdf

See source: A Collection of #124 Information (Schematics, Layout, etc.) https://ampgarage.com/forum/viewtopic.php?f=5&t=5719

R&D
Note: Works in progress until marked "Final"

ODS components.xlsx

AMP SECTIONS

Precision Power Supply

ODS Main Power Supply 3.0.pdf

See source: ODS Eyelet Boardshttps://ampgarage.com/forum/viewtopic.php?f=5&t=29630


Skyliner Tone Stack

ODS_Clean Preamp Tone Stack 1.4.pdf

FET Boost Mod and Pedal Detail

ODS FET FS 1.4.pdf

See source: Footswitch-able FET Boost https://ampgarage.com/forum/viewtopic.php?f=5&t=31084
Also: FET Questions=Martin?
https://ampgarage.com/forum/viewtopic.php?f=4&t=34108
Method to set FET bias and supply voltage
https://ampgarage.com/forum/viewtopic.php?f=5&t=18389


Onboard FX Loop and OD

Normster's FX loop.pdf

Normster - 97_ODS_HRM_Loop[marked up].pdf

Good health!
Stephen

[Colossal]

Nice work, Stephen

[Stephen1966]

*EDIT: the Power Section thread with linked files has been moved to the first post (see above).

PS to Colossal - Cheers! I only know how to use one emoji

Good health!

Stephen

[norburybrook]

I think there's a reason HAD never built the dumbleator into the ODS amp. I've done it and I'm not sure I would again. It changes the amp. I think the a separate Dumbleator is the best way to go personally.


M

[xtian]

Hey, Stephen, please make edits to post #1 in this thread, to keep your documents updated and collected in that first post. That's a nice way to make your (excellent!) files easy to find, when this thread inevitably grows to many pages long.

[Stephen1966]

Hey, Stephen, please make edits to post #1 in this thread, to keep your documents updated and collected in that first post. That's a nice way to make your (excellent!) files easy to find, when this thread inevitably grows to many pages long.

Good point. I was thinking it might be easier to search for and find if there is a different subject line for each section but you're probably right.

[Stephen1966]

I think there's a reason HAD never built the dumbleator into the ODS amp. I've done it and I'm not sure I would again. It changes the amp. I think the a separate Dumbleator is the best way to go personally.


M

I hear you. I've hummed and hawed over this for ages but its easier to try it and "restore" it to stock design than to leave it out and live with the buyer's remorse if I don't do it.

[norburybrook]

I think there's a reason HAD never built the dumbleator into the ODS amp. I've done it and I'm not sure I would again. It changes the amp. I think the a separate Dumbleator is the best way to go personally.


M

I hear you. I've hummed and hawed over this for ages but its easier to try it and "restore" it to stock design than to leave it out and live with the buyer's remorse if I don't do it.

good point. there's nothing wrong with building in the loop but I couldn't bypass mine without added noise no matter what I tried so it was always on which makes for some complicated knob twiddling with the master now being the loop return volume on the back of the amp!!!



M

[Stephen1966]

I think there's a reason HAD never built the dumbleator into the ODS amp. I've done it and I'm not sure I would again. It changes the amp. I think the a separate Dumbleator is the best way to go personally.


M

I hear you. I've hummed and hawed over this for ages but its easier to try it and "restore" it to stock design than to leave it out and live with the buyer's remorse if I don't do it.

good point. there's nothing wrong with building in the loop but I couldn't bypass mine without added noise no matter what I tried so it was always on which makes for some complicated knob twiddling with the master now being the loop return volume on the back of the amp!!!



M

That's right... I remember the conversation. I'm working on a switching solution which will effectively take the loop out of the circuit but how the Master will interact with the loop activated seems to be down to where it's placed in the signal chain: before, in parallel, or after. I figure with the loop active it comes down to finding the unity level of the Send and Return of the loop circuit. The simplest solution seems to be before; Dumble's passive loop seems basically a switched bypass. This is all mostly theory at the moment... Lots of head-scratching. I'll have a schematic shortly. I'll follow xtian's suggestion and post it up top.

[talbany]

Just another players opinion here..I agree with Marcus the loop should be an add-on feature with it's own separate isolated power supply/star gnd system along with the "knob twiddling" FWIW
BTW. With the loop set at unity (no effects) and still in the signal path you no longer have an ODS?
it's something else now?

Tony

[Stephen1966]

Schematics for the OD, Master and FX loop moved to first post.

[Stephen1966]

Just another players opinion here..I agree with Marcus the loop should be an add-on feature with it's own separate isolated power supply/star gnd system along with the "knob twiddling" FWIW
BTW. With the loop set at unity (no effects) and still in the signal path you no longer have an ODS?
it's something else now?

Tony

I think I may have misunderstood what we mean by "unity", I mean as I understand it, unity doesn't remove the effect: it just balances the signal strength between the in and the out. The waveform of the signal may still be shaped by the effect. The Send and Return of the D-lator have a documented effect (on what would we call it? - the transient frequencies???) but I was thinking about that moment when we hit the footswitch and our ears start to bleed! It might be fun to have both the Master and the Return have some interaction and effect on tone, like the two volume controls on a stock 5E3 with a single channel active, but stuff like this is a little too ephemeral when all we want to do is get up and play. As for the power and grounding, I think that needs careful management and it's a puzzle I'm still working on. You're right and I've still not ruled it out, a separated power supply might be the simplest solution to avoid overtaxing the PT, but the grounding and RFI issues appear to me, to be a problem of topology: lead dress, orientation, routing...

Stephen

[Stephen1966]

I wonder if anyone could explain or at least point me in the direction of understanding the role of the 250pF / 220k RC network after the Master pot? It seems clear that its main purpose seems to be to affect the impedance of the signal coming from the preamp to the LTP that is, it seems more for the benefit of the PI than anything else. I am struggling to understand the effect of impedence at this stage and the effect of the negative phase angle. The phase angle changes with the frequency (higher is closer to 0 degrees) suggesting higher frequencies such as those across a guitar's strings meet more resistance. Does this mean it is behaving like a low pass filter?

Another possibility, and although all the evidence suggests it is not is, that if the RC net is disengaged when the loop is engaged it plays some role alongside cable capacitance and impedance. What, if any factors besides attenuation of gain for the PI are we looking at here?

It's discussed in another new post '#0124 capacitor/resistor combo' https://ampgarage.com/forum/viewtopic.php?f=4&t=34214 but I don't believe it is disengaged at any point. The connection is between the tip of the send jack and the shunt of the return, the brown wire from the Master pot is also connected to the shunt lug so when the circuit is open the RC network bridges across to the tip of the Send jack (i.e. it's kept in the circuit).



Stephen

[erwin_ve]

The rc combo is disengaged when nothing is in the loop. It really is, ,having it build exactly like in the pic.
It is engaged with something in the loop; having used this a few times: it has a positive effect on the highs and a give a more tight low end in combination with a external dumblelator. It is subtle tho...

Erwin

[Stephen1966]

The rc combo is disengaged when nothing is in the loop. It really is, ,having it build exactly like in the pic.
It is engaged with something in the loop; having used this a few times: it has a positive effect on the highs and a give a more tight low end in combination with a external dumblelator. It is subtle tho...

Erwin

Doh! Of course! If the send jack isn't plugged in, there is an open circuit on that end of the net. Anyway, that solves one mystery. I owe you a beer...

Stephen