ODS 124 - revisited for the 21C

[martin manning]

Interesting.....so filters in a box with a Dumbleator would that give me the same feel/sound as the SSS then as I presume the dumbleator is acting as the driver/CF?

Filters in a box would let you see what EQ effects are available. Using a Dumbleator would provide the recovery stage to bring the level back up for the power amp input. You're still missing the CF driver.

[talbany]

If you used the filters in the Send and Return of the D-lator you would be driving the filters with the low impedance buffer (5f6-A Bassman style) so the frequency response will be different (filters would actually work better)
To get the actual affect in a real SSS?, use the send (back of the amp) to go in the filter box out of the filter box into the return of your D-lator and out of the D-lator to the return of the amp.This way your not using the buffer just the return amplifier in the Lator. This way your filters will respond the same as the filters in the SSS.
It might not be ideal because your filters will be wet with reverb (altering the frequency response of the reverb) but it will give you a frame of reference

BTW.If you wanted to do something more permanent you could break the connection after the tone stack recovery run that through a separate loop on the back (labeled filters) and use the return to feed the dry side of your mixer (recovery amp) this way you are filtering just the dry signal
Tony

[norburybrook]

thanks fellas looking at the Ceriatone SSS and the JM I can see that there's no voltage divider with the 1m (68K-JM sig) on the SSS. is that because the signal is going to the filters and therefore doesn't need to be cut as the filters reduce the gain instead? I presume then that's another reason there's no need for CF driver as well? I have a pot there on my amp and I can drive that stage into distortion if I turn it up, perhaps that would be all that's needed to drive an external filter box?



M

[mojotom]

thanks fellas looking at the Ceriatone SSS and the JM I can see that there's no voltage divider with the 1m (68K-JM sig) on the SSS. is that because the signal is going to the filters and therefore doesn't need to be cut as the filters reduce the gain instead? I presume then that's another reason there's no need for CF driver as well? I have a pot there on my amp and I can drive that stage into distortion if I turn it up, perhaps that would be all that's needed to drive an external filter box?



M

The filter section got a voltage divider built-in. Two Rock removed the filter part but kept the attenuation with that voltage divider.
Take a look at 13 schematic, there is a voltage divider at that same spot (to balance the dry and reverb signals).
From memory the guys at Two Rock didn’t like the CF driver sound so they remove them on the JM.
And last but not least the power resistors values are quite higher in the JM (less voltage on preamp tubes) and that changes a lot soundwise. The JM preamp will break up sooner due to the 22K+2K2 resistors while the SSS preamp will remain cleaner due to the lower R values (and higher preamp voltages).
A bit like comparing a Vibrolux to a Super Reverb. Vibrolux got two 10k vs 1k/4k7 on the Super Reverb. The SR will feel cleaner and less fuzzy. Off course the output sections are different as well as transformers size but reducing R values on the power supply change a lot in the feel of the amp.

[norburybrook]

thanks fellas looking at the Ceriatone SSS and the JM I can see that there's no voltage divider with the 1m (68K-JM sig) on the SSS. is that because the signal is going to the filters and therefore doesn't need to be cut as the filters reduce the gain instead? I presume then that's another reason there's no need for CF driver as well? I have a pot there on my amp and I can drive that stage into distortion if I turn it up, perhaps that would be all that's needed to drive an external filter box?



M

The filter section got a voltage divider built in. I think guys at Two Rock remove the filter part and keep the attenuation.
Take a look at 13 schematic too, there is a voltage divider (to balance the dry and reverb signals).
From memory the guys at Two Rock didn’t like the CF drivers so they remove them on the JM.
And last but not least the power resistors and quite higher in the JM (less voltage on preamp tubes) and that changes a lot soundwise. The JM preamp will break up sooner due to the 22K resistor where the SSS will remain clean due to the lower R values (and higher preamp voltage).
A bit like comparing a Vibrolux to a Super Reverb. Vibrolux got two 10k vs 1k/4k7 on the Super Reverb. The SR will feel cleaner and less fuzzy. Off course the output sections are different as wells as transformers size but reducing R value on the power supply change a lot of the feel of the amp.

thanks Tom, Interesting the guys at 2 rock didn't like the cathode follower!

I have lower resistors on my amp like the SSS so have a higher voltage on my pre amp tubes. I'm pretty sure my amp sounds more SSS than the standard JM but unless I play one i wouldn't know for sure. As long as it's close enough them I'm Ok with that but I'm interested in the differences for sure.

M



M

[mojotom]

You should build an SSS with CF and be done with it
SSS002 seems to be the one to build and it should sound different than a JM (tonestack, filters, CF, etc)

I think you’re not far from SSS 004 now (without filters).
Try to disconnect the Cut control too.

I can’t speak much about the SSS and CF as I haven’t build one yet but I tried a few things over the couple of years I build the JM and kept coming back to the stock amp (with a 1K8 to ground on the bass pot).
I should build an SSS too.

[Guy77]

I also played around with the voltages on V1 with the JM and I experienced the same things that you mentioned mojotom.
A significant change in tone from running V1 at 166v and then bringing it to 200v

Higher V1 gave me more clean headroom.

G

[talbany]

thanks fellas looking at the Ceriatone SSS and the JM I can see that there's no voltage divider with the 1m (68K-JM sig) on the SSS. is that because the signal is going to the filters and therefore doesn't need to be cut as the filters reduce the gain instead? I presume then that's another reason there's no need for CF driver as well? I have a pot there on my amp and I can drive that stage into distortion if I turn it up, perhaps that would be all that's needed to drive an external filter box?



M

The filter section got a voltage divider built in. I think guys at Two Rock remove the filter part and keep the attenuation.
Take a look at 13 schematic too, there is a voltage divider (to balance the dry and reverb signals).
From memory the guys at Two Rock didn’t like the CF drivers so they remove them on the JM.
And last but not least the power resistors and quite higher in the JM (less voltage on preamp tubes) and that changes a lot soundwise. The JM preamp will break up sooner due to the 22K resistor where the SSS will remain clean due to the lower R values (and higher preamp voltage).
A bit like comparing a Vibrolux to a Super Reverb. Vibrolux got two 10k vs 1k/4k7 on the Super Reverb. The SR will feel cleaner and less fuzzy. Off course the output sections are different as wells as transformers size but reducing R value on the power supply change a lot of the feel of the amp.

thanks Tom, Interesting the guys at 2 rock didn't like the cathode follower!

I have lower resistors on my amp like the SSS so have a higher voltage on my pre amp tubes. I'm pretty sure my amp sounds more SSS than the standard JM but unless I play one i wouldn't know for sure. As long as it's close enough them I'm Ok with that but I'm interested in the differences for sure.

M



M

Marcus
Some of the SSS's and D-lands AFAIK have this trimmer/voltage divider feeding the filters so this is a Dumble thing and Yes you could put in this trimmer before the filter box to control the amount of gain being fed to the filters..Maybe you could put this pot on the back so you can adjust it with or without the filter box installed..IMO I think the gain stage from the mixer should be OK for recovering the losses from the filters, however you might have to play around with the mixing resistors if this effects the reverb recovery. The filters are cool and does change the character of the amp although IMO the driver has a larger impact on the sound and feel than the filters do. Increased sustain compression and bandwidth should be rather obvious to you.

Tony

[talbany]

Here is a simpler way of doing it..Super Twin method..I've built this one and works pretty well!

Fender-Super-Twin-180W-Schematic.pdf

[Stephen1966]

Getting back to the ODS...

Here is the schematic for the two tube reverb:

ODS RVB 2.7.pdf

"I'd consider the option to just ground the reverb return tube grid. That way you keep the loading the same at the grid of the mixer tube (virtual earth mixer)".

Rootz, in this one, I've followed your advice and placed a SPDT relay just before the grid resistor on the recovery tube. I know your LTSpice model shows it after but I would like to use the added resistance to deflect the signal to ground when the relay is off. I've also got hold of a 12V 1A transformer for the relay power supply so this also has an LED indicator. The relay is shown in the off position.

I know there's a lot of love for the #002 reverb especially, and the beefier 3 and 4 tube designs generally. The intention is still to park this reverb in a standard chassis though, and I doubt there would be room there for the fully-fledged SSS type reverb. I might squeeze the filters in, but three/four extra tubes may cause coupling issues, mechanical in nature, which would be more difficult a problem to solve than swapping out caps and resistors for a better balanced sound. I figure if the #005 was good enough for Carlos, it is probably going to be good enough for me. (And yeah! before you say it, I know he sold the amp on.)

What do you think, is this going to work?

Good health!

Stephen

[rootz]

Stephen, there are a couple of mistakes in your schematic. Your signal chain should be: relay-output --> reverb input (cap) and 1meg/82k combo. The output from the recovery tube should go to the master and from there to the PI-input. The reverb on/off should work. Not exactly sure how quiet it will be (popping) but I guess pretty quiet.

You should think of the reverb as an add-on that goed between the relay and master volume.

You could make two reverb versions. One more along the lines of the 002 (without the CF's/tweed mixer) and one more along the lines of a standard Fender reverb. If you place the reverb components on a separate board, testing will be possible (although still rather complicated).

You should be able to easily squeeze 5 preamp tubes and 4 power tubes in an ODS chassis. I'd say 6 preamp tubes is also possible, if you want to keep them in line. Things will be different when you use boards like in the SSS. I made a design based on 'The Don', a PCB based ODS. I got the board sizes almost exactly like the original and could easily use 5 preamp tubes. Now if you were to use smaller caps and a different layout, much more would be possible. But, how much do you want to stray from the original ODS designs?

Speaking about original designs. 002 uses a filter section, cf based wet/dry mixers, dc coupled power tube drivers (class AB2), a dual triode reverb driver, a pre driver coming from the volume pot wiper. Some of those features could be added to an ODS based design (should be interesting to see what it gets you), if you'd have the space to do so. The pre reverb driver, hmmm. How would that go in an ODS?

I think that is where you'd enter Two Rock Bloomfield drive territory. Last time I took a look at the one gut shot I could find, it looks like the amp has the triode in front of the reverb driver. That could mean that it is either an pre OD reverb ODRS, where the wet/dry signal is going through the OD (#13?), or where the clean reverberated signal is mixed in with either clean or OD dry signal.

Anyway, long story short, with some final adjustments your design will work. I added the drawing by Larry I talked about earlier, in case you don't have it. Clearly, also Fender based, but with a Dumbleator like recovery triode/stage.

[rootz]

The filter section got a voltage divider built in. I think guys at Two Rock remove the filter part and keep the attenuation.
Take a look at 13 schematic too, there is a voltage divider (to balance the dry and reverb signals).
From memory the guys at Two Rock didn’t like the CF drivers so they remove them on the JM.
And last but not least the power resistors and quite higher in the JM (less voltage on preamp tubes) and that changes a lot soundwise. The JM preamp will break up sooner due to the 22K resistor where the SSS will remain clean due to the lower R values (and higher preamp voltage).
A bit like comparing a Vibrolux to a Super Reverb. Vibrolux got two 10k vs 1k/4k7 on the Super Reverb. The SR will feel cleaner and less fuzzy. Off course the output sections are different as wells as transformers size but reducing R value on the power supply change a lot of the feel of the amp.

thanks Tom, Interesting the guys at 2 rock didn't like the cathode follower!

I have lower resistors on my amp like the SSS so have a higher voltage on my pre amp tubes. I'm pretty sure my amp sounds more SSS than the standard JM but unless I play one i wouldn't know for sure. As long as it's close enough them I'm Ok with that but I'm interested in the differences for sure.

M



M

Marcus
Some of the SSS's and D-lands AFAIK have this trimmer/voltage divider feeding the filters so this is a Dumble thing and Yes you could put in this trimmer before the filter box to control the amount of gain being fed to the filters..Maybe you could put this pot on the back so you can adjust it with or without the filter box installed..IMO I think the gain stage from the mixer should be OK for recovering the losses from the filters, however you might have to play around with the mixing resistors if this effects the reverb recovery. The filters are cool and does change the character of the amp although IMO the driver has a larger impact on the sound and feel than the filters do. Increased sustain compression and bandwidth should be rather obvious to you.

Tony

I've seen that trimmer before the Filters in some SSS designs. It greatly increases the output-impedance of the preceding triode and doesn't just adjust the gain before/of the filter. I could see a pretty dramatic effect on the bass/treble balance in the filter too depending on the setting of the trimmer. Higher settings --> more bass/less treble.

On the CF drivers Tony, I just can't get my head around to why it would compress more than AC-coupling. I mean, there is more driving capabilities for the power tube grids, which would only be very noticeable when approaching positive grid territory. You could push the grids positive with DC coupling, class AB, so you'd only get extra headroom. However, the SSS designs with a CF driver don't seem optimised for class ab2. What am I missing here?

[talbany]

thanks Tom, Interesting the guys at 2 rock didn't like the cathode follower!

I have lower resistors on my amp like the SSS so have a higher voltage on my pre amp tubes. I'm pretty sure my amp sounds more SSS than the standard JM but unless I play one i wouldn't know for sure. As long as it's close enough them I'm Ok with that but I'm interested in the differences for sure.

M



M

Marcus
Some of the SSS's and D-lands AFAIK have this trimmer/voltage divider feeding the filters so this is a Dumble thing and Yes you could put in this trimmer before the filter box to control the amount of gain being fed to the filters..Maybe you could put this pot on the back so you can adjust it with or without the filter box installed..IMO I think the gain stage from the mixer should be OK for recovering the losses from the filters, however you might have to play around with the mixing resistors if this effects the reverb recovery. The filters are cool and does change the character of the amp although IMO the driver has a larger impact on the sound and feel than the filters do. Increased sustain compression and bandwidth should be rather obvious to you.

Tony

I've seen that trimmer before the Filters in some SSS designs. It greatly increases the output-impedance of the preceding triode and doesn't just adjust the gain before/of the filter. I could see a pretty dramatic effect on the bass/treble balance in the filter too depending on the setting of the trimmer. Higher settings --> more bass/less treble.

On the CF drivers Tony, I just can't get my head around to why it would compress more than AC-coupling. I mean, there is more driving capabilities for the power tube grids, which would only be very noticeable when approaching positive grid territory. You could push the grids positive with DC coupling, class AB, so you'd only get extra headroom. However, the SSS designs with a CF driver don't seem optimised for class ab2. What am I missing here?

Rootz Here is some good reading if you want to know more about DC coupling using followers

Compression/
So we now have a cathode follower that is permanently 'stealing' current from the previous stage; what is the result? If a down-going signal appears at the gain stage's anode the grid voltage of the follower is pushed down back into the area of "normal operation", and grid current stops flowing more or less immediately, for the duration of that cycle. But when the incoming signal is positive going the grid is pushed more positive, which induces even more grid current to flow into the cathode follower as it tries to maintain bias, which in turn 'drags down' the anode voltage of the gain stage which is trying to move positive! In other words, the up-going cycles are very heavily compressed but the down going ones are not, which generates a lot of second harmonic distortion.

http://www.valvewizard.co.uk/dccf.html
+
The AC Coupling Dumble used in both Odyssey and the Winterland were both plate driven https://ampgarage.com/forum/viewtopic.p ... 27#p426427

However, the SSS designs with a CF driver don't seem optimised for class ab2. What am I missing here?

They may not be optimized for AB2 however technically they still are AFAIK (sinking for grid current)

Class A2/AB2/or B2 requires a very low impedance, transformer-coupled or DC-coupled driver stage. The standard AC-coupled phase inverter or single-ended driver stages used in nearly all guitar amplifiers will not allow grid current flow, so they are class A1/AB1/B1 amplifiers.
The advantage of class A2, AB2, or B2 is the complete lack of "blocking distortion", or transient intermodulation distortion. The disadvantage is the extra complexity of the output stage required to source current to drive the output tube grids into the positive region.The main advantage to the cathode follower directly into power tube grids is losing the effects of grid-blocking from the coupling caps recharging and causing momentary distortion when power tube grid current occurs

BTW..There may be a few other things adding to this compression effect however? you just asked about the C.F

Tony

[Stephen1966]

Stephen, there are a couple of mistakes in your schematic. Your signal chain should be: relay-output --> reverb input (cap) and 1meg/82k combo. The output from the recovery tube should go to the master and from there to the PI-input. The reverb on/off should work. Not exactly sure how quiet it will be (popping) but I guess pretty quiet.

You should think of the reverb as an add-on that goed between the relay and master volume.

You could make two reverb versions. One more along the lines of the 002 (without the CF's/tweed mixer) and one more along the lines of a standard Fender reverb. If you place the reverb components on a separate board, testing will be possible (although still rather complicated).

You should be able to easily squeeze 5 preamp tubes and 4 power tubes in an ODS chassis. I'd say 6 preamp tubes is also possible, if you want to keep them in line. Things will be different when you use boards like in the SSS. I made a design based on 'The Don', a PCB based ODS. I got the board sizes almost exactly like the original and could easily use 5 preamp tubes. Now if you were to use smaller caps and a different layout, much more would be possible. But, how much do you want to stray from the original ODS designs?

Speaking about original designs. 002 uses a filter section, cf based wet/dry mixers, dc coupled power tube drivers (class AB2), a dual triode reverb driver, a pre driver coming from the volume pot wiper. Some of those features could be added to an ODS based design (should be interesting to see what it gets you), if you'd have the space to do so. The pre reverb driver, hmmm. How would that go in an ODS?

I think that is where you'd enter Two Rock Bloomfield drive territory. Last time I took a look at the one gut shot I could find, it looks like the amp has the triode in front of the reverb driver. That could mean that it is either an pre OD reverb ODRS, where the wet/dry signal is going through the OD (#13?), or where the clean reverberated signal is mixed in with either clean or OD dry signal.

Anyway, long story short, with some final adjustments your design will work. I added the drawing by Larry I talked about earlier, in case you don't have it. Clearly, also Fender based, but with a Dumbleator like recovery triode/stage.

Thank you Rootz. Here is the next iteration of the 005 type circuit:

ODS RVB 2.8.pdf

Is this what you meant? Regarding the switching relay... I'm assuming it's a bad idea to place a snubber cap [edit, a smoothing cap - perhaps it's not such a bad idea, after all] on the contacts. But at the moment, it isn't altogether clear that switch popping would be a problem.

Because of voltage constants, I figured (in the schematic at least) it didn't matter where the master pulled its signal from. There is still an uninterrupted line for the signal between the input side of the reverb and after the coupling cap of the mixer. If I were to take this line away which if I understand your simulation well, you aren't suggesting, I don't see how I could get from the OD relay to the Master without some alternative switching. In keeping with the original, I'm keen to preserve the native 124 topology, and so any modifications should be switchable to achieve the signature 124 sound.

You have me thinking about the alternative 002 reverb now though. Phil's post https://ampgarage.com/forum/viewtopic.php?t=32047 seems a good place to begin. I also have an LTSpice schematic of the 002 from GitHub. Layout, hasn't been decided yet but one of the first things I did was study the topology of the 124 layout (see the first post of the topic) and I'm keen to preserve as far as is practicable, the original layout as seen in the photos even if it only has a minimal effect on what MrD called "circuit constants". However, I will be cutting the boards and preparing a blank chassis myself, so I'm free to shuffle things around.

Thanks for the link to the TwoRock sketch by Larry. Alas, it looks like the jacks to the reverb tank are placed after the recovery triode i.e. between the recovery triode and the mixer, if he literally meant his block diagram of "standard Fender" reverb is accurate. It might be a good place to start a design, but I sure wish he had invested in another sheet of paper

I need to sit down in front of Illustrator and start looking at some of these layouts from a more informed point of view.

Stephen

[rootz]

Thanks Tony. So 'current stealing might cause compression. This statement is very true in many guitar amps. By my knowledge current stealing is only a thing in DC coupled cathode followers though, because the biasing point of the CF is so close to 0V. AFAIK current stealing does not happen in a well biased Ac coupled CF. Now there could be compression in the 002 due to the dc coupled cf's in the reverb/dry mixers. Or it could be that the compression is there in the cf but just not because of current stealing. IDK, I trust your ears that there is compression and so it has to be explainable.

I've designed and build some class ab2 hifi amps. It's rather difficult to get all parameters right because many, if not most, tubes are not designed for ab2 and thus there is no info in the datasheets. However, every dc coupled output tube driver should be blocking distortion free because there is no coupling cap. If you want it optimised you will have to adjust loading impedance for your output tubes and screen voltage too (probably).

You should use a CF that has a healthy dose of power to provide current for the power tube grids. At least, if you want to use cf drivers for a bit of extra power and dynamic range. I'd consider the 12ax7 as not the best choice for that, but it will get rid of blocking distortion and farting out. It might even compress when there are gird resistors on the output tubes, but then again that would only be the case when reaching positive grid area at which point your amp would be ear bleeding loud.