Looking for 102 w reverb layout?

[Stephen1966]

Hi Stephen,

You're coming from a reverb much like #60, don't you? I haven't build that one yet, but I guess that it would much sound like the reverb in my #94 and #124: spacious, but not sure at all.

One thing that is very different between the ODS with reverb amps and the clone of #005-clone (the Steel String Sultan from AN is a clone of the HPD of Bludotone, which is a clone of the original #005) I've build: the reverb. The reverb in the #005 is much more like a Fender reverb and consequently sounds like that too. I wouldn't call it sure per se, but it is less spacious, ambient and controllable than the reverb in my ODS reverb amps.

I have to put it out there that I don't have any real experience with different flavours of reverb. There is a nice thick tone on the clean channel in the reverb I built (after the #060, yes) but I can't get rid of the hum when the return, intensity is dialled way up. I have it sounding okay, when I dial back the return and dial up the send level. It isn't too intense though, which is or would be okay 95% of the time. I really don't dig the surf sound anyway. I just need the reverb to add a little spatial (ambient) dimension to the notes, and it does that beautifully, so much so that after a while, you forget its there and your ears take you completely into the tonal landscape it creates. It's only when you then turn it off, that you realise where you have been! When the Volume and Master go up to the sweet spot where the notes sustain and bloom, that hum becomes even more noticable and so to control it, I have to dial back the reverb to barely present. To be happy with it that is. I know some would say that noise is just one of the features of tube amps. I have a dead quiet amp when the return is at zero on the reverb though, and its only the reverb which I find doesn't have (or allow) the headroom. Tonally, it seems all there, just a noise penalty that is less than satisfactory. Perhaps if you build the circuit you will find an easy solution to the hum. But it's for that, and because of my experiences with the passive loop, that I am looking at a two tube layout.

I looked at the Metroamps loop several times and I am sure it deserves its good reputation. I was almost tempted, but then as one of our brothers here put it, the Dumbleator isn't just an FX loop, because of the tone shaping possibilities it offers, it is really an effect in its own right. It's that, that draws me to it. I might put the metroamps loop in a Fender or a Marshall, or any of the other generic names out there, but the sweet Dumble sound deserves its own, sweet loop: The Dumbleator. This design has been tossed around so many times now with inspirational mods that it has developed into one of the more mature designs. Not a single Classic design perhaps, but uniquely amenable to adaptation with features that are well understood. I have no hesitation building a Dumbleator in this amp. The one thing [edit: one of the things] I like about the CF model, is the low impedance, single phase of the signal through the circuit.

Just for completeness, here is the schematic of my Dumblator circuit. More or less there, maybe a couple of adjusted values more:

SKYLINER_FX LOOP - 2.1.pdf

[Edit: updated to include more stock values and a three position bright switch on the send to compensate for high frequency roll-off]

Stephen, here's an idea for a 2 tube reverb that is reminiscent of the one in #60. This frees up a tube for a built in Dumbleator.

I'm not at all clear about what caused the hum in my three tube design, I tried many things so it leaves me in a grey area of possibility where the problem may have been regarding the impedance of the circuit in combination with sections before and after. True, this does resemble the #060, perhaps you could give us more of your thoughts on that. I still like the idea that both triodes of the 12AT7 drive the signal though. Do you see any advantages of splitting the 12AT7 as you did here, to perform a dual duty - sending and recovering the signal perhaps? And the 12AX7 mixing? I guess this application of the 12AT7 most neatly encapsulates the heavy lifting part of the circuit where the signal pulls and produces a lot of current (never measured it - just speculating). Do you think this would give a better SNR compared to your early sim? Would it give the signal increased depth and a more "acoustic like" intensity? In some ways, I think the only way to find out is to build it and listen. I like what the #060 circuit does with the tonal presence of the notes so maybe this slightly different perspective on the two tube topology is what it takes to preserve the space, ambience and control in a more economical package. That's what I need to do. You are a damn fine sparky so I have no hesitation building either of these designs. They are all but guaranteed to work just fine. But like a good single malt, you never forget its distinctiveness.

I simply need to make a choice.

I took note of the changes you suggested to that earlier design and I get your drift. I will make an amended schematic though I think anyone could follow your advice without visual aids, and then perhaps I can give you a more detailed discussion. All makes sense though. I just need schematics for my brain to function properly. Damn fine work!

Stephen

[Stephen1966]

Stephen, here's an idea for a 2 tube reverb that is reminiscent of the one in #60. This frees up a tube for a built in Dumbleator.

Ahoy rootz! Here is the schematic I put together for your design:

TWO TUBE REVERB 60ish.jpg

The resemblance to the three tube #060 circuit as I understand it is the that signal is pulled or ported through a mixing filter which if I understand it correctly like the previous design, adds a little LNFB; reducing gain but increasing headroom. V4b (mixer triode) sends the signal out to the Master from the junction between the .005 cap off the plate and a 470k from just before the grid stopper. The .005 cap (C9) appears part component with the LNFB loop and part coupling cap for the next stage along the line (the Master pot). The last mixing stage of the #060 did this as well. The front end of this circuit has similar elements, where the signal comes in, from the OD relay in my design, the 1M pot is acting as a voltage divider with the 470k at the output side of the circuit; similar but it's a different topology. In the three tube design, I found reducing the fixed resistors 470k/470k down to 220k/220k brought up the gain and thus lowered the sound floor. Of course, I accept that reducing the input impedance of the circuit isn't necessarily the same as the effect we hear.

At the front end then, I am curious about the 470p anode bypass cap (as Blencowe calls it). Do you think it will be needed to reduce parasitic oscillation at high frequencies? You may have a different name for the cap, and Blencowe sees the lower leg of the cap attaching straight to ground (not in series with the cathode bypass cap) but it's the same net structure as in the OD stages and I can confirm that when you forget to solder those 270p caps in, you get a very shrill high end. (Don't ask me how I know ) So whether you call them this, or that, the effect is (audibly) the same. It gets tricky now, because a 470p puts more load on the tube than 270p would, reducing the gain and reducing the Miller effect. An alternative, might be to leave this cap out and rely on the Miller effect and adjust the 22k grid stopper higher instead for attenuation of the higher frequencies.

Anyway, I take what you say about the earlier design sounding a bit Fenderish or anaemic compared with the other ODSR circuits you have experienced, and I like this one, for it's distinctiveness.

For completeness however, here is the first design updated with your suggestions:

TWO TUBE REVERB 124-005 revised.jpg

*Please let me know if you see any errors; I will correct them if so.


Talking about zero loss loops though, what I liked about your first design was the comparable "zero loss" of the reverb circuit. Two questions here then: first, do you think the 470p anode bypass cap would be needed, and second, do we get a similar "zero loss" in the later 60ish circuit? I am guessing they don't display the same frequency response across the spectrum.

Stephen

[Guy77]

This is the loop currently in my #94 reverb. It is a Metroamps Zero loss fx loop. It goes in front of the master volume. I can't remember if your amp has a global master in front of the PI or if the reverb is right after the OD relay and in front of the clean master. This loop does not work well after the clean master. The objective of the driving LND150 of the loop is to attenuate a rather hot preamp signal to guitar fx level (not line level!).

I can vouch for the zero loss in the name. What goes in, comes out of the loop again. So signal strength wise it is transparant. Sound wise it is pretty good too. Adds a bit of 2nd harmonics, but as far as my ageing ears tell me, there is no loss in frequencies/adverse effect on the high end.

The biggest downside? Not the MOSFETS. Your effects in the loop are probably solid state as well. But it does not offer the tone shaping a Dumbleator does, none of it. No CF compression. No intended high end roll off.

Hi rootz, I am also thinking of installing a Metroamps Zero Loss fx loop in an Overdrive Special I am building. I wanted to ask you if there was any added noise/hiss with this loop?

Regarding the Dumbleator here is my impression of how I liked it. It is great but as mentioned here by rootz and else were buy others it ads some color to the sound. I found that I really liked it a lot in the Highplate Skyliner amps more so than in my Low plate Classic style amp. I realized that it made my High Plate amp sound more like my Low Plate amp and I always liked my Low Plate Classic amps more than the High Plate. There was added smoothness and compression with the Dumbleator. My Low Plate Classic did not need any more added smoothness, compression or high end roll off but my High Plate did.


Cheers

Guy

[rootz]

There is a reason why Dumble choose the values you find in #60. The mixer stage is a summing stage, an (active) virtual earth mixer. At least sort of. I don't really get why Dumble used a 470k grid leak resistor. Shouldn't be needed per se. The mixer has a gain of -1 (inverting/anode follower). It is low noise and low distortion, can take the full signal the preamp produces, eliminates crosstalk between the dry and wet signals, has pretty good PSRR and is virtually immune for ageing tubes. What's not to like? Wel maybe the fact that the phase inverts, or added components in te signal chain.

Anyway, you shouldn't need to alter values to get the gain up: what goes in the mixer comes out inverted. No real loss in signal there.

470p 'snubber' on the reverb driver is there for 2 reasons: frequency tailoring (I don't like very bright reverbs) and damping oscillations when the reverb driver gets overdriven. To address that problem there is also the local feedback loop. All in all measures are taken to keep the reverb signal to the tank under control. I do like the sound of a tank driven hard, but strongly dislike distortion generated by clipping in the driver and recovery. Makes the reverb sound harsh, splatty and very unnatural to my old ears (I know, nothing really natural about spring reverb to begin with, just an approximation of real reflections). I place the snubber cap on the tube socket, much like the snubbers on the OD triodes. It just works. It does not load the tube in any relevant way, in the order of microamps in normal conditions. A large grid stopper only alters frequency response. It won't do much for oscillations, because the driver runs out of steam (goes into cutoff, long before you approach positive grid signals. If you want to avoid that, you need a much warmer bias than a 3k9 resistor on the driver gives you. That wil also put more stress on the driver. Hence Fender paralleled two 12at7 triodes.

I don't quite understand what you mean with 'The resemblance to the three tube #060 circuit as I understand it is the that signal is pulled or ported through a mixing filter which if I understand it correctly like the previous design, adds a little LNFB'. If you mean the mixer adds a little feedback: it adds a lot. So much that this is a follower stage. Was it Blencowe who calls it an anode follower? Or was it Aiken? John Broskie perhaps? Anyway, anode follower is the appropriate and right name for the circuit.

There's another thing I like about the mixer stage in #60 compared to passive mixing like in SSS#002 or the Wonderland (some call that the Tweed mixer). The wet signal path is comparatively much stronger in the #60 mixer. That is actually a good thing IMHO because now you don't need as much signal hitting the second reverb recovery stage, thus limiting clipping there. I don't really get why Dumble used a 1meg2 plate to plate feedback in #60. It gives relatively little feedback, so overdriving the second reverb recovery stage is rather easy. Now there is always a way to overdrive stages in the reverb circuit. If you don't want that, you'd need to design for a reverb that cannot overdrive with the send and return controls on 10 and the preamp maxed out. Luckily, you've got those reverb send and return controls, so you can dial out clipping in the reverb circuit.

I like that: "zero loss reverb mixer".

Not sure what you mean here 'I am guessing they don't display the same frequency response across the spectrum'. Frequency response of the #60 mixer should be ruler flat because of all the feedback.

[rootz]

This is the loop currently in my #94 reverb. It is a Metroamps Zero loss fx loop. It goes in front of the master volume. I can't remember if your amp has a global master in front of the PI or if the reverb is right after the OD relay and in front of the clean master. This loop does not work well after the clean master. The objective of the driving LND150 of the loop is to attenuate a rather hot preamp signal to guitar fx level (not line level!).

I can vouch for the zero loss in the name. What goes in, comes out of the loop again. So signal strength wise it is transparant. Sound wise it is pretty good too. Adds a bit of 2nd harmonics, but as far as my ageing ears tell me, there is no loss in frequencies/adverse effect on the high end.

The biggest downside? Not the MOSFETS. Your effects in the loop are probably solid state as well. But it does not offer the tone shaping a Dumbleator does, none of it. No CF compression. No intended high end roll off.

Hi rootz, I am also thinking of installing a Metroamps Zero Loss fx loop in an Overdrive Special I am building. I wanted to ask you if there was any added noise/hiss with this loop?

Regarding the Dumbleator here is my impression of how I liked it. It is great but as mentioned here by rootz and else were buy others it ads some color to the sound. I found that I really liked it a lot in the Highplate Skyliner amps more so than in my Low plate Classic style amp. I realized that it made my High Plate amp sound more like my Low Plate amp and I always liked my Low Plate Classic amps more than the High Plate. There was added smoothness and compression with the Dumbleator. My Low Plate Classic did not need any more added smoothness, compression or high end roll off but my High Plate did.


Cheers

Guy

No added hiss or noise to speak of. But I didn't really listen/test for it.

[Guy77]

This is the loop currently in my #94 reverb. It is a Metroamps Zero loss fx loop. It goes in front of the master volume. I can't remember if your amp has a global master in front of the PI or if the reverb is right after the OD relay and in front of the clean master. This loop does not work well after the clean master. The objective of the driving LND150 of the loop is to attenuate a rather hot preamp signal to guitar fx level (not line level!).

I can vouch for the zero loss in the name. What goes in, comes out of the loop again. So signal strength wise it is transparant. Sound wise it is pretty good too. Adds a bit of 2nd harmonics, but as far as my ageing ears tell me, there is no loss in frequencies/adverse effect on the high end.

The biggest downside? Not the MOSFETS. Your effects in the loop are probably solid state as well. But it does not offer the tone shaping a Dumbleator does, none of it. No CF compression. No intended high end roll off.

Hi rootz, I am also thinking of installing a Metroamps Zero Loss fx loop in an Overdrive Special I am building. I wanted to ask you if there was any added noise/hiss with this loop?

Regarding the Dumbleator here is my impression of how I liked it. It is great but as mentioned here by rootz and else were buy others it ads some color to the sound. I found that I really liked it a lot in the Highplate Skyliner amps more so than in my Low plate Classic style amp. I realized that it made my High Plate amp sound more like my Low Plate amp and I always liked my Low Plate Classic amps more than the High Plate. There was added smoothness and compression with the Dumbleator. My Low Plate Classic did not need any more added smoothness, compression or high end roll off but my High Plate did.


Cheers

Guy

No added hiss or noise to speak of. But I didn't really listen/test for it.

Great thanks, I will try it out.

[Stephen1966]

Not sure what you mean here 'I am guessing they don't display the same frequency response across the spectrum'. Frequency response of the #60 mixer should be ruler flat because of all the feedback.

I was referring back to the traces alongside the schematic you produced with your earlier simulation. I never figured out what the traces represent - it kind of looks like a Bode plot - one trace being the amp's signal frequency without reverb, and one with. I think you described it as having "mdB of difference". I've found too, that the 060 style reverb I have at the moment is (for lack of a better word), transparent. It doesn't change the tone, whether it's low and clean, or high and overdriven. I think if it clipped the signal, I would have heard it by now. Please disregard my feeble attempt at trying to explain what I think the 60 reverb is doing. I much prefer the way you explained it. That's an education right there

And... I will probably return to your analysis, in the future. For now, I need to go shopping I took an inventory of parts last night, and see I need to place a small order but it means I will be building the new board shortly with the 60ish two-tube design, shortly - holiday season permitting.

Many, many thanks...

Edit: before I remove the three-tube 060 reverb, I will have a look at the recovery stage for clipping. Hopefully, I made it clear that when it actually is dialled back, it sounds transparent regarding the tone, and spacious - I think you would like it. It would be a shame if I didn't try this one last thing before upgrading to the two-tube design. The hum sounds very much like an AC ground problem, but maybe, after all, it is the recovery stage clipping when the return is dialled up. I swapped out the 1.2M feeback resistor to a NOS Piher (from Xicon), it did sound slightly better then but it didn't solve the problem.

[Stephen1966]

Hi rootz, instead of derailing this member's thread, I'm send you a PM.

Stephen

[samtech60]

Please I'm looking for a 102 layout Reverb as well