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Stratifier Schematic

The Stratifier is an amp that I built in the fall of 2012 and tweaked until I was happy with it in early 2013. I started out with a design by Honeydip on the Amp Garage forum. Honeydip had married a D-style preamp section having simplified tone control circuitry to a single ended EL84 poweramp taken from the AX84 website. I had been wanting to try a D-style amp but didn't need 50 - 100W so I thought I'd build his circuit.

Upon completion I tried the amp with and all my speakers and guitars. The immediate positives were the sustain and the way notes would hang, the touch sensitivity, and the clean tone with my strat, particularly through my Weber ceramic Signature 12 speaker. On the down side, to me the OD channel was quite bright and harsh and I felt that humbuckers had too much of an edge on the OD channel.

So, the mods started. I decided to sculpt the amp for the Weber Sig 12 ceramic speaker (which is a great value at just over $40) and single coil Fender style guitars. Here is sort of the path I followed:

1. Replaced both 12AX7's in the preamp with 12AY7's (new EH's).
2. Reworked Honeydip's "Mild" control on the OD channel to be a much more significant Low Pass shelving filter to mellow the OD harshness. I just call it OD Tone now.
3. Added switchable coupling caps between the first tube and second tube to control the amount of bass frequencies sent to the OD channel. I call it the OD Fat switch, which I labeled "Off - Medium - Max" fatness. Max fatness is the original Honeydip circuit.
4. Added a Dana Hall VVR board to allow dialing back the volume while maintaining tone. This worked so well that I changed the existing Master Volume to a clean volume so that the balance between the clean and OD channels can be easily set.
5. Added a slight treble cut to the clean channel and labeled it the bright switch.
6. Added a Weber low power switching relay board for footswitching bewteen the clean and OD channels (there is a front panel switch too that works when the footswitch is not plugged in).
Added a resistor to the bottom of the OD level pot. This prevents you from going to zero volume for the OD channel (who would need to?) but gets a little more output delivered to the Power Tube.

Stratifier Schematic

The result is very cool, I think. I have loaned it to several friends now and everyone really enjoys it. It is still a single coil, Strat and Tele kinda amp. Think "blues machine". The clean sound definitely impresses everyone - especially if you hang it on the edge of starting to break up - you know, the "warm clean" thing - both by cranking the preamp gain and by pushing the power tube a little. The only disadvantage when you get really into the "pushing the power tube thing for warm clean" is that the OD channel is slightly lower volume than the clean channel. Weird, but I remember Honeydip noticing something similar in his amp. However you can get a great match between the OD channel and a clean tone that doesn't push the power tube much and it sounds excellent on both channels.

Here are some sound clips from me and an excellent guitarist friend, Nate Hundley, from the prog rock band Hysterical Society. All mine are on a strat, Nate's are on a tele. I miked with an SM57 just off center at the speaker grill and a Rode NT1A back about 6 feet for ambience. Nate used a Fathead ribbon mic positioned a foot or two in front of the speaker cabinet (see below), which, by the way, is a little 1 x 12 combo open backed cabinet that at one point in its life had a Peavey Bandit transistor amp in it. Both of us used Reaper as our recording software and I added a tiny bit of reverb to my clips.

Clip 1: For those that can't wait to know how much distortion it generates, I start this clip clean on the mid/bridge combo pickup and then switch to the bridge pickup when I kick the distortion in about 7 seconds in. It's not a high gain amp, so don't expect that, but it does generate a nice thick OD tone.

Clip 2: The best demo of the warm clean tone was done by my friend Nate Hundley of the band Hysterical Society with his Tele. Nate plays finger style and really shows how touch sensitive the amp is.

Clip 3: This clip shows various clean and light to medium OD settings with the neck and neck/mid pickups

Clip 4: This clip is various clean and OD settings with the bridge, middle and bridge/mid combo pickups. The riff at 0:27 is clean and then repeated with light OD at 0:34. Same thing at 0:42 - first clean, then with OD at 0:49.

Here are two demos of the "OD Fat" switch effect. It is somewhat subtle, but you feel it a lot when you play it, both in the thickness of the notes and the fuzz of the bass strings. In each clip I play the same basic riff four times: (1) clean, (2) OD Fat off, (3) OD Fat Medium, and (4) OD Fat Max.

Clip 5     Clip 6

Clip 7: Another nice clip of the OD channel done by Nate.

Gut Shots and Construction
The amp was built in a 16 x 8 x 3 inch chassis that had previously housed my Firefly amp. I built an eyelet board and the initial build was very clean and nice. But then the mods started. I did my best to keep things tidy, but after moving controls around on the panel and adding the VVR and relay boards, it got a little messier. Thankfully, it is still pretty quiet.

Eyelet Board

Initial Build

Final Build

Labeled VVR and Relay boards

Closeup of board and controls

Front Panel Layout

Rear Panel Layout

And yes, it will go in a cabinet soon. Learned how to hand cut dovetails doing this one. And I am working on a faceplate.

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