Jimmy and Tony Boxed

spi

Well-known member
Here's a double build report to wrap up 2022.

Up first is the GuitarPCB "Black Dog", which is their adaptation of the RAH. This is marketed as a "Jimmy Page in a Box" pedal, mimicking his Hiwatt sound from 1970 recordings. I was interested for several reasons: First, as a lifelong fan of Led Zeppelin it just sounds cool. Second, I always wanted to try one of the Howard designs from Catalinbread. Lastly, the circuit is a variation on the Box of Rock. I have the Van Pelt, which is also a BoR variant (using 3 cascading mosfet boosts for gain). The Van Pelt grew on me over time, and has become one of my favorites. The RAH is similar but adds a feedback loop, and I was curious what it would do to the sound. A blowout price when BarryGPCB cleared out old revisions of this board ended up the deciding factor.

This one sounds pretty good to my ears. It has that stacked-mosfet gain sound I've come to know from the Van Pelt, but a bit more touch sensitivity. It's not a high-gainer, which is to be expected from an amp of that era, but has the gain for LZ type tones.

Second up is the Dark Esbat. I wasn't sure what to expect from this. It's not really a "Tony Iommi in Box", as it's not trying to replicate his amp or sound, rather it's marketed as a boost endorsed (and presumably used) by Tony. It's supposed to capture his Rangemaster tone--but with three op-amps it's definitely not a Rangemaster (It calls for MC33178s, and a common sub is TL072, but I used 4580Ds). And with bass and treble controls, and mid-range switch, it's way more versatile than a treble booster. After getting it boxed up last night, I got on this forum and found this fresh post by @MattG: Ember Boost and Dark Esbat: same circuit. He recognized that this is really a Spark Boost in disguise.

Last night while playing around I found it's very effective as a tweak-able boost, but it also does a great job of fattening Strat single coils when at unity volume. There's lots of settings to explore and I only got the tip. The odd thing is the output and gain knobs--both seem to impact the volume level, but there isn't really a lot of overdrive gain--bumping up the gain only adds volume, and sometimes a mild amount of grit, but other times not really noticeable. I don't think it's an issue with my build because I see some other build reports confirm the same.

Both these use waterslide decals (LZ and BS themed, my favorite part was finding matching fonts, which are obscured by the knobs in my pictures), with a top coat of Envirotex. This was my second attempt to use Envirotex and while I learned a bit the first time, I realized I'm still on the upward learning curve with this coating. The coating could be better, but the imperfections don't bother me.

The knobs on the Dark Esbat are temporary. The knobs I ordered were too large and hung over the side... I had to borrow ones planned for a different build in the meantime, until I can order replacements. Embarrassingly, there's a burnt capacitor box in there too 😊.

I should also mention these two sounded great together, stacking the boost into the OD.

IMG_20221212_195810192.jpg IMG_20221212_195822961_HDR.jpg IMG_20221213_202133070.jpg IMG_20221213_202139546_HDR.jpg
 
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Great builds and great write-up! Thanks for sharing!

Up first is the GuitarPCB "Black Dog", which is their adaptation of the RAH. This is marketed as a "Jimmy Page in a Box" pedal, mimicking his Hiwatt sound from 1970 recordings. I was interested for several reasons: First, as a lifelong fan of Led Zeppelin it just sounds cool. Second, I always wanted to try one of the Howard designs from Catalinbread. Lastly, the circuit is a variation on the Box of Rock. I have the Van Pelt, which is also a BoR variant (using 3 cascading mosfet boosts for gain). The Van Pelt grew on me over time, and has become one of my favorites. The RAH is similar but adds a feedback loop, and I was curious what it would do to the sound. A blowout price when BarryGPCB cleared out old revisions of this board ended up the deciding factor.

When you say "adaptation of the RAH", do mean same circuit, just a different PCB layout? Or has the circuit been tweaked/modified? Just curious. The Prince Albert is PedalPCB's version (adaptation?) of the RAH. It's on my Xmas list, hoping Santa brings it!


Last night while playing around I found it's very effective as a tweak-able boost, but it also does a great job of fattening Strat single coils when at unity volume. There's lots of settings to explore and I only got the tip. The odd thing is the output and gain knobs--both seem to impact the volume level, but there isn't really a lot of overdrive gain--bumping up the gain only adds volume, and sometimes a mild amount of grit, but other times not really noticeable. I don't think it's an issue with my build because I see some other build reports confirm the same.

Emphasis added. I built the essentially-the-same Ember Boost not too long ago. I've really taken a liking to this pedal, and here's my take: the tone controls are active boost/cut (i.e. classic Bandaxall tone controls), and they always do their thing regardless of where the toggle switch is set. But for the toggle, in the middle ("off") position, the "drive" knob has very minimal impact on the tone and volume - it's not zero impact, but, at least with single coils, even with the drive all the way up, I get only the slightest hint of dirt (I would expect to have a bit more break up with humbuckers or any higher-output pickups). So I consider the pedal truly a "clean boost with EQ" in the middle switch position.

When you flip to either up or down position on the switch, you'll notice an obvious jump in volume, and also, the drive knob starts having noticeably more effect. With the same single coils I mentioned, I get some breakup around noon, and with the drive knob maxed, some might call it "mid gain". So with the switch in either of the "on" positions, I think of the pedal as a "light overdrive with switchable mid emphasis".

If I am interpreting the schematic correctly, with the switch in the middle/off position, one of the opamp gain stages is essentially removed (not literally removed, but I think the feedback loop is set such that the gain is nearly 1). And with either of the on positions, that opamp stage takes a more prominent/deliberate role. Also, with the switch either of the on positions, the switched-in opamp stage and the following one (which has the clipping diodes), together start to look like the basic topology of a Bluesbreaker-style circuit.

Another thing that I think is sort of uncommon, it looks like one of the opamps is being used as a regulator for VREF. Maybe the designer had a "spare" opamp after the signal path was designed? I can't help but feel this circuit could be simplified a bit, without taking away any tone or flexibility.

Anyway - I'm really liking this pedal. I in fact use it as my low gain/edge-of-breakup into a clean amp. The mid-emphasis switch is the killer feature for me, I feel that makes it very adaptable to different guitars and amps. The only thing I don't like: the overdrive/dirt it generates sounds great into two of the actual tube guitar amps I've used it with. But it sounds pretty awful going through my headphone practice "amp" (DSM Simplifier). But that goes for lots of dirt pedals, it's not unique to the Ember Boost. But other dirt pedals sound find through the Simplifier, and I haven't been able to figure out why one sounds good and the next sounds bad.
 
When you say "adaptation of the RAH", do mean same circuit, just a different PCB layout? Or has the circuit been tweaked/modified? Just curious. The Prince Albert is PedalPCB's version (adaptation?) of the RAH. It's on my Xmas list, hoping Santa brings it!
There's some minor differences compared to Prince Albert--it looks like GPCB added pulldown resistors at the input and between gain stages. Also a different input capacitor. For the rest of the circuit, I don't see other differences in components.

As for the Dark Esbat, I'll have to give it more exploration with the different settings, I really only had about 20 minutes messing with it so far, and spent most of the time on the up position (which I think corresponds to the high-end boost, assuming PPCB switch positions are true to the original).
 
used a socket for C19, but left it unpopulated. This was mentioned in this thread. I haven't tested with a C19 populated. I own the actual COTS TC Spark Booster, and with C19 omitted, and my build sounds so close that I don't feel it's worth taking the time to experiment. Plus I'm saving a few pennies by using one less component!

Hey @MattG one interesting thing I notice is that 1n C19 in the Spark Booster is replaced by a 270p in the Dark Esbat. C10 was also changed to 100p. Maybe Chuck had a hand in designing it?
 
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Hey @MattG one interesting thing I notice is that 1n C19 in the Spark Booster is replaced by a 270p in the Dark Esbat. C10 was also changed to 100p. Maybe Chuck had a hand in designing it?

For the handful of Ember Boost build reports I've read here, it seems the consensus is that those "mods" are universally preferred. That in turn makes me suspect that the values listed for the Ember Boost are probably incorrect versus an actual Spark Booster, i.e. tracing error.
 
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FWIW I have built two Dark Esbats. The first was totally stock, and the second one has a tiny mod which I quite like. All I did was use two pairs of clipping diodes instead of three. I found the clipping a bit harsh in the stock version so tried using just two pairs of diodes and it does sound slightly smoother.
 
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FWIW I have built two Dark Esbats. The first was totally stock, and the second one has a tiny mod which I quite like. All I did was use two pairs of clipping diodes instead of three. I found the clipping a bit harsh in the stock version so tried using just two pairs of diodes and it does sound slightly smoother.

In which mode (i.e. toggle switch position) are you typically using your Dark Esbat? And through what amp are you playing?

Having originally played the commercial TC Spark Booster, I had a similar thought when I built my Ember Boost. So I socketed all the clipping diodes. Off and on, I played with a handful of different combinations, but ultimately went back to the stock config.

What I found, was when using fewer than three clipping diodes per side, that middle toggle position (the "clean" setting on the Ember/Spark) became less of a clean boost, and more of a light overdrive. That was expected, but I ultimately wasn't too fond of it like that.

The reason I ask about the amp: the overdrive sounds of my Ember Boost sound like poo through my headphone amp (DSM Simplifier), "harsh" is truly the appropriate word - it's just distortion, the unpleasing, non-musical kind, nothing like the kind we are trying to achieve with all these overdrive circuits. However, I've played this pedal through two tube amps now (Hiwatt DR504 clone and Peavey Custom 30), and there is no hint of harshness. In fact, in the mid or fat switch positions, this has become my favorite low gain overdrive pedal. I have a fair number of overdrive pedals that sound good or even great through a tube amp, but have this unpleasant harshness through the Simplifier.
 
I'm mainly using the Dark Esbat through low wattage tweed style amps or the occasional Marshall 18W. Once some dirt has been established it sounds great, but using it as the only form of dirt is not so good. It seems to prefer HBs IME. I use either the clean setting or medium - never full blown.

The other thing I do out of habit is use a mix of diodes, rarely four of the same. In this case it was my go-to 2x1N4001 and 2x1N4148.
 
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