ODS 124 - revisited for the 21C

[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

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

I have 2 amps w/built in loops Bluesmaster and 2nd Generation and here is what I found..
Stephen
(Yes I was referring to unity as in both the master and return levels are balanced with no effects [jumped send return]. Of course the loop would be in the signal path and not bypassed! )
In Very Simple Terms

Impedance.. Even with the lator set at "unity" several things happen. First the CF buffer alters/lowers impedance and since impedance is frequency dependant this alters frequency response.

"Harmonic" content?.. When cathode followers are driven hard enough they tend to generate 2nd order harmonics this will or can change the harmonic structure of the amp..Followers will also impart a kind of soft compression as well that an change the feel of the amp..

The Return amp. Adding another gain stage just before the PI will reverse the phase of the preamp,You might also discover the tone controls on the front of the amp don't really respond the same..The extra gain stage will also increase headroom so the amp will be a bit punchier and have a more sterilizing kind of effect ( especially with the "return set higher than the Master like you mention)

Noise? Regardless as to how careful you are with the design layout lead dress etc etc..You are still going to add noise ..Anytime you add a voltage amplifier you exponentially increase any noise you might have picked up from the previous stages and your putting another one just before the PI, so get ready it will add noise!. I Guarantee it, the only question is how bad will it be?

Another thing if you have not yet used a Dumbleator the return pot (now Master) just after the last gainstage and being only 250 k makes for an extremely sensitive pot value for a master, this lowers the range you have to work with at a given volume level so adjusting on the fly can be at times a bit tricky IMO It also seems to work better for lower vol settings.

BTW? I'm not really worried about overtaxing the P.S due to the added current draw? I am more concerned about the added stray RF/Noise /ground loops when you try cramming 5 gain stages into 1 chassis with 1 power supply in a non PCB type amp.

Not trying to talk you out of it just telling you what I wish someone would have told me before I did a built in loop.

Tony

[Stephen1966]

I have 2 amps w/built in loops Bluesmaster and 2nd Generation and here is what I found...

Not trying to talk you out of it just telling you what I wish someone would have told me before I did a built in loop.

Tony

... Before you did it (twice)

When I look at it now, I see problems of impedance and harmonic distortion and clipping that require a whole new level of understanding. I wish I knew more to understand what it is that I know I don't know! I have a hunch the got-ya is in the recovery stage as the cathode follower seems to follow the "good practice" design principles I've seen elsewhere, but that would only be the half of it and I would need to understand how impedance affects the signal before and the consequences of distortion on the waveform of the inverted phase. Problems which you seem to be saying, are less evident at lower volume settings where the tube has more headroom but which increase as the signal becomes more compressed. In short, I seem to offering a solution, in search of a problem(s).

Darn it! You've done a good job of not talking me out of it

In any case, I see some interest in Normster's design so I will finish the schematics though it is really not much different from the original D-lator as far as I gather. After that, I will relegate it to a side project. Build it separately and use that as a test bed for understanding the problem of integration, better.

As the old Chinese proverb says: When ten men tell you "you are dead," lie down.

Good health,

Stephen

[norburybrook]

Interesting that back in the day Larry Carlton hated the Dumbleator. He didnt like what it did to his sound.

He's recently changed his mind though with the amps and dumbleator that Brandon made for him (Bludotone) so i wonder what the difference is? My guess is perhaps it's a parallel path through the dumbleator so the dry signal stays 100% pure.

I agree 100% with Tony's explanation of the sound and feel of the ODS with the loop in, he did try talk me out of it but it was an itch I had to scratch myself. I sold that amp during lockdown by the way and I don't miss it at all.

The dumbleator is very useful in certain situations and can be a great additional tone shaping tool so I think everyone with an ODS amp should have one.
I've ended up going down the wet dry path so I can keep my ODS amp 100% dry and pure then add reverb/Delay 100% wet on another amp.

as with all these things there's no right or wrong so whatever gives you what you hear in your head is ultimately 'right'


M

[talbany]

Again..Not trying to talk anyone into it or out of it..Just what to expect so we don't regret something later
All The Best!
Tony

[Stephen1966]

Again..Not trying to talk anyone into it or out of it..Just what to expect so you don't regret something later

All The Best!

Tony

Well you talk the talk and you've walked the walk but as the Bangles opined, can you "Walk like an electrode"? Seems you can. You certainly talk like a node and it's my guess there is an ode to Cathy in there as well

[Stephen1966]

Just a thought. I guess many of you have used a prefabricated chassis for this amp with the hole for the PT already made. Has anyone mounted the PT in another place in a head. Like the PSU in a computer, could it be mounted in the bottom of the head? It could free up a lot of space in the chassis for other goodies.

Good health,

Stephen

[Mainetone]

regarding the loops, Im not much of a poster so forgive me if Im not as tech smart as most, I just built a 2nd/3rd generation based amp out of a fender 75 combo cab and chassis. I used a slighlty modded two tube hammond reverb design and Merlins 1/2 a dumbleator and it sounds killer, Merlins loop for me was simple and I had real estate on the board and again it sounds killer. I could post some pics if its helpful
Holy crap its cold in Maine today

[norburybrook]

regarding the loops, Im not much of a poster so forgive me if Im not as tech smart as most, I just built a 2nd/3rd generation based amp out of a fender 75 combo cab and chassis. I used a slighlty modded two tube hammond reverb design and Merlins 1/2 a dumbleator and it sounds killer, Merlins loop for me was simple and I had real estate on the board and again it sounds killer. I could post some pics if its helpful
Holy crap its cold in Maine today

Pic's are always helpful and schematics/layouts especially if it's a great sounding amp


M

[Stephen1966]

regarding the loops, Im not much of a poster so forgive me if Im not as tech smart as most, I just built a 2nd/3rd generation based amp out of a fender 75 combo cab and chassis. I used a slighlty modded two tube hammond reverb design and Merlins 1/2 a dumbleator and it sounds killer, Merlins loop for me was simple and I had real estate on the board and again it sounds killer. I could post some pics if its helpful
Holy crap its cold in Maine today

Isn't it cold in Maine, every day?

Trust me, I'm not as tech-smart as I wish I was either. It's great when someone with real chops chimes in, but what's really great about this forum is that it isn't elitist and amateurs like me, aren't looked down on when they ask what must be incredibly simple questions for others who have had the training, and the experience. I've seen some snotty views expressed, mainly in the past, but they were the minority and trolls don't seem to last five minutes here. It's why I joined this forum, and why I stay, because the people who contribute are fundamentally decent people. A rare thing in today's internet landscape. It kinda restores your faith in basic human goodness.

So, please, if you can find a way, do share your photos. I'm looking at photos of the 124 now and they really are worth a thousand words (sometimes).

[Mainetone]

Ill post some pics tonight for you to check out, I found the layout here on the forum as for the schematic
I used the layouts on the dumble file section.
Best
Shawn

[Mainetone]

I attached the pics of the loop layout,

[Stephen1966]

I attached the pics of the loop layout,

Thank you Shawn, that's interesting, what did you do with the power filter caps?

Good health,

Stephen

[Mainetone]

i used a 50/50 for the ot and output tubes, the remaining five are under the chassis

[Stephen1966]

I'm indebted to Rob Livesey for posting photos of the 124. There are a 109 photos on his site: https://thesubjectmatter.com/dumblearchive.html

[Stephen1966]

Going through the schematic for the tonestack now, I came across a couple of interesting links:

Looking at high and low pass filters: https://www.tubesandmore.com/tech-artic ... -high-pass
And https://www.guitarscience.net/tsc/dumble_jazz2.htm