Power Tube Driver Configuration: Dumbleland vs. Steel String Singer?

[jfs322]

Hey Everyone,

I'm wondering if anyone can share their expertise on the pros/con of the two different driver tube configurations seen on Dumble amps:

(1) Dumbleland 12AU7 Phase Inverter and 12BH7 Driver configuration (not configured as a DC-Coupled Cathode Follower) (ala Odyssey and Winterland) versus

(2) Steel String Singer 12AX7 Phase Inverter and 12AX7 DC-Coupled Cathode Follower configuration (in SSS #002, I believe both tubes are 12AX7, whereas in #005 Dumble used a 12AT7 in both spots, though I could be wrong).

The reason I ask is I'm looking to incorporate one as a driver in an amp build, and I'm trying to get a sense of the pros and con of each configuration. I get the sense that tone/feel wise, they achieve similar results, even if their circuit functions are quite different. I believe Bludotone uses the first method in his SRV voiced Hi-Plains Drifter (perhaps a nod to historical Dumble interviews where Dumble hints that SRV's SSS is setup more like a Dumbleland than a SSS), and for Bludotone's EJ Voiced Hi-Plains Drifter, I believe it uses the second method (with 12AT7s).

Anyone have technical expertise and/or experience with both configurations to be able to opine on the pros and cons of each?

Thanks!

[talbany]

I used a 12AT in my #002 after going through an AX and BH7

Tony

[Aaron]

Even though both circuits are different, I prefer the Odyssey/Winterland style PI/Driver.
Or to put it another way, out of my five builds those are the two that I play most.

Aaron

[jfs322]

Even though both circuits are different, I prefer the Odyssey/Winterland style PI/Driver.
Or to put it another way, out of my five builds those are the two that I play most.

Aaron

Thanks, Aaron! The Odyssey/Winterland style PI/Driver is what I'm leaning towards, actually. Any chance you don't mind sharing what you noticed/like about that style PI/Driver circuit as compared to the SSS style DCCF driver? Any observations?

Thanks again.

[Mr. dB]

Even though both circuits are different, I prefer the Odyssey/Winterland style PI/Driver.
Or to put it another way, out of my five builds those are the two that I play most.

Aaron

Thanks, Aaron! The Odyssey/Winterland style PI/Driver is what I'm leaning towards, actually. Any chance you don't mind sharing what you noticed/like about that style PI/Driver circuit as compared to the SSS style DCCF driver? Any observations?

Thanks again.

6L6s aren't so hard to drive that they'd really need the cathode followers. 6550s might benefit. Which output tubes were used with which driver?

The two stage diff amp would have more open loop gain, so when you close the loop there's more feedback.

[jfs322]

6L6s aren't so hard to drive that they'd really need the cathode followers. 6550s might benefit. Which output tubes were used with which driver?

The two stage diff amp would have more open loop gain, so when you close the loop there's more feedback.

I believe there's a fair amount of variance for his builds, but my understanding is that Steel String Singers #001 through #004 were all 100-watt, 4x6L6, each having a DCCF driver, I believe (but not certain) that they were 12AX7 for both the PI and CF. The DCCF was dropped from SSS #004, which was a standard 12AX7 LTPI. Whether that was because Dumble by then thought a CF was unecessary for driving 6L6s tubes, I can't speculate. But from SSS #005 and on, they were all 150-watts, 4x6550/KT88 based. And I believe with #005 the DCCF topology returned, with a 12AT7 PI and 12AT7 CF for #005. The main exception from these post-#005 SSS amps were SRV's SSS amps, I believe, for which there is some indication from Dumble himself that SRV's SSS amps may have used the older, Dumbleland style driver topology.

By contrast, the Dumbleland/Odyssey driver topology is a bit different, more akin to a McIntosh amp 12BH7 driver topology, I'm told. Most Dumblelands/Odyssey amps I've seen with that driver topology are 12AU7 PI and 12BH7 driver; the Odyssey amps I've seen are 100-watt 6L6, but I think the Dumblelands were either 150-watt 6550/KT88 or 300-watt (i.e. no 100-watt Dumblelands).

[talbany]

SO BASICALLY ONE IS AC COUPLED AND THE OTHER IS DC COUPLED. WHAT'S THE DIFFERENCE?


I'm sure they clip and respond differently. Advantage of the DC driven arrangement is the loss of the coupling cap, improved low end tightness, reducing Miller effect. I suspect (but don't know for certain) that the AC circuit might clip a little smoother and later than your standard LTP Schmitt but you still have the coupling cap on the way to the power tubes.
I think part of the clarity with the DC coupled is the added bandwidth and speed, no capacitor being present (and the sound any cap might bring). When you run regulated lower voltage screens the grid swing and bias voltage is somewhat lower, so I think the power tubes run out of power well before the driver starting doing strange things. 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. The amp is overall tighter without the time constant of the coupling caps.

There also seems to be an added transparency and overall sheen to the tone with with the lower impedance/ DC coupled. The amp sounds bigger and has more authority. Since the driver tube no longer has to drive a bias network or the miller effect of the multiple power tubes, I think overall bandwidth is improved a little bit as well. It can give a tighter more controlled and extended bass along with a very natural even compression that when releases causes the so called (breathing) singing effect with added sustain I've used it on 6L6's EL-34's and 6550's KT88's have KT100's in it now
I'm sure they both clip and respond differently but you still have the coupling cap on the way to the power tube vs the DC coupled..This is "basically" the same type ACC driver used in the Oddessy and IIRC Winterland, Super Twin, Marshall Major and some Mesa bass amps....Heath Kit/Mcintosh used this similar circuit used driving 6550's in the 60's.. The SVT is DC driven is a split-load inverter feeding two independent common cathode gain stages feeding two independent direct coupled CFs.
As far as which one I would recommend is totally up to the player.Apples and Oranges! At one point I built and ODS (Currently owned by Zac Brown) which was AC driven and he loves it! I prefer the DC driven in a totally clean amp due again to the added Bandwidth Clarity and singing sustain like compression it adds to a totally clean amp,although, I've heard many players say it's just too clean and clear sounding for them not to mention the volume it generates..This you will have to decide for yourself
I will say that I am not sure I would like it in an amp with built in overdrive (Although Dumble built one in the Todd Sharp ODS) and would maybe prefer the AC coupled better in an amp like that. You just have to play it for yourself to get where I am coming from..


Tony

[Aaron]

I should note, my builds have been slightly modded. The only way they resemble the circuit is the PI/Driver section.
Both amps have the Tone Filter circuit.

"Odyssey" inspired build is running a pair of KT88's with 700 volts on the plates and UL output transformer. And reverb.
"Winterland" inspired build is running 6550's.

Tonewise compared to my SSS #002 build, the louder they get, the more "body" there is to the sound. The low end isn't as tight compared to #002, but doesn't break up. Pedals are like an extension of the amp. Sound is more coloured?

With the #002 amp, the sound is more clean/hi-fi, retains the tone of the amp at any volume. With pedals, to me, the amp amplifies the tone of the pedal. It's like the amp amplifies the player? Theres nothing to hide behind.

If that makes any sense?

Aaron

[talbany]

I agree with the comment on the pedals in front of an #002 running AB2.
Pedals can take on a whole different vibe. You definitely get the natural sound of the pedal and unlike your typical LTP where the pedals can make the sound too compressed thin and a squishy and lack of clarity. Not with the DC follower The amp stays nice and punchy . The pedals I am mostly referring too are the Overdrive (Tube Screamer) op amp driven variants. The Fuzz Face types can be a bit brutal on the ears especially with single coils. (Nothing sounds like a Marshall Plexi with a Dallas in the front end) I can clearly see where Eric likes to use tube screamers in the front end of his SSS's you can (at fairly high vol's) get that smooth clear violin type sound out of it. Chorus and delays through those amps just gives it a HUGE sound! like the sound is coming from different directions. It's quite an amazing thing.
The band I was in we had a house gig in DC. Every fri night for a year. They actually liked me to play loud and was all to happy to appease! and bring the 002. I think I lost 1/2 my hearing but with a trio and that amp made those gigs a breeze and after that whenever I decided to take something else out like an ODS or my JTM's everyone in the band asked for me to bring back the SSS.After playing that amp for that long I can see where it changed how I played electric guitar. If you get too used to it it's hard going back to a 50w Blackface fender I can see why Stevie nicknamed his the "King Tone Consoul"

I can see where an Oddessy would also be a cool piece as well!

Tony

[Aaron]

Funny thing, when I was typing it I originally wrote overdrives! And agree with Fuzz Faces, always sounded raspy. To me anyway.
Although, the Pentode amp is AB2 and it sounds great!

Aaron