Breadboarding (and modding) the High Top

Chuck D. Bones

Well-known member
I became curious about the High Top (J. Rockett Top Boost), so I breadboarded it. Sounded nothing like the demos, so after a little visual inspection I found one capacitor (C7) hooked up wrong. Once I had that sorted, it sounded great. I read Rockett's manual and it pretty much works as advertised, although I could not verify whether the Alnico setting was more "swampy." The CERAMIC/ALNICO switch is mainly a boost between the 1st & 2nd stages with a tiny bit of the top and bottom rolled off in Alnico mode. With the EF86 switch off, it's fairly clean unless you're playing very hard. The tone controls are all very effective and it takes some fiddling to find the right balance between the TREBLE & CUT controls.

Although it works great in stock form, there were four little things I changed to make it more to my liking.

1. Changed VOLUME from B50K to A50K. With B50K, unity was down below 9:00. This pedal is pretty loud, even with over 20dB loss in the BASS & TREBLE controls.
2. Replaced R18 with a jumper. Now the EF86 knob "goes to eleven." Try it, you'll like it.
3. Increased R20 to 56K. This centers the bias on Q2 and improves the clean headroom.
4. The bandwidth of the 2nd stage extends beyond the range of human hearing. I observed ringing above 20KHz, which may have been an artifact of the breadboard. I'm always pleasantly surprised when a breadboard doesn't oscillate. Anyway, I added 10nF in parallel with R12 to roll off the gain above 20KHz and that fixed it.
5. OK, 5 things. I installed one 499R resistor in place of R3 and left out R16. Either way works the same and I was building a breadboard. Apparently Rockett had too many 1K resistors.

I ended up using low gain transistors for Q2 & Q3 as recommended in the BOM. I tried higher gain transistors and noticed very little difference. Tried germanium for Q2, made no difference.

It's a very nice clean or dirty boost. Works well with single coil pickups or humbuckers. I could see putting either the EF86 or the ALNICO switch on a stomp switch. NB Rockett has ALNICO on a stomp switch.
 
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cooder

Well-known member
Dude! I was eye balling that circuit, seems you can read my shriveled up mind.

And you certainly made me spill my morning coffee: "I could not verify whether the Alnico setting was more "swampy.""
That's probably because you didn't have your gumboots on...
"I observed ringing above 20KHz," means probably on a scope or do you have your dog or pet bat trained to tell you? ;)

In any case lots of thanks again Chuck!
 

cooder

Well-known member
Just glaring at the build doc again now, what transistors did you use for Q 2 and 3, listed as 2N708. Those seem to be quite low gain ones and you said higher gains didn't make much difference. So it seems the circuit is really open for replacements, rightyo?
Could 2N3903 be a good replacement candidate?
 

Chuck D. Bones

Well-known member
I used 2N6517 because I had a bunch from a "surprise pack." 2N3903 should work fine. Like I said, hFE didn't seem to make much difference to my ears. YMMV.

I tried BS170, 2N7000 and VN0610L for Q1 and they all sounded the same too.
 

jjjimi84

Well-known member
I love this circuit especially into a fender blackface style amp. I thought having the alnico/ceramic on a footswitch was a missed opportunity, having the ef86 on a fs would have been much better.
Thanks for the recommendations Chuck, I look forward to checking these out.
 

daeg

Active member
I've been looking to build a Top Boost style pedal. Is this one of the better ones?
 

music6000

Well-known member
I became curious about the High Top (J. Rockett Top Boost), so I breadboarded it. Sounded nothing like the demos, so after a little visual inspection I found one capacitor (C7) hooked up wrong. Once I had that sorted, it sounded great. I read Rockett's manual and it pretty much works as advertised, although I could not verify whether the Alnico setting was more "swampy." The CERAMIC/ALNICO switch is mainly a boost between the 1st & 2nd stages with a tiny bit of the top and bottom rolled off in Alnico mode. With the EF86 switch off, it's fairly clean unless you're playing very hard. The tone controls are all very effective and it takes some fiddling to find the right balance between the TREBLE & CUT controls.

Although it works great in stock form, there were four little things I changed to make it more to my liking.

1. Changed VOLUME from B50K to A50K. With B50K, unity was down below 9:00. This pedal is pretty loud, even with over 20dB loss in the BASS & TREBLE controls.
2. Replaced R18 with a jumper. Now the EF86 knob "goes to eleven." Try it, you'll like it.
3. Increased R20 to 56K. This centers the bias on Q2 and improves the clean headroom.
4. The bandwidth of the 2nd stage extends beyond the range of human hearing. I observed ringing above 20KHz, which may have been an artifact of the breadboard. I'm always pleasantly surprised when a breadboard doesn't oscillate. Anyway, I added 10nF in parallel with R12 to roll off the gain above 20KHz and that fixed it.
5. OK, 5 things. I installed one 499R resistor in place of R3 and left out R16. Either way works the same and I was building a breadboard. Apparently Rockett had too many 1K resistors.

I ended up using low gain transistors for Q2 & Q3 as recommended in the BOM. I tried higher gain transistors and noticed very little difference. Tried germanium for Q2, made no difference.

It's a very nice clean or dirty boost. Works well with single coil pickups or humbuckers. I could see putting either the EF86 or the ALNICO switch on a stomp switch. NB Rockett has ALNICO on a stomp switch.
Something like This:
PopTop Mockup Pedal.jpg
 

Paradox916

Well-known member
The exceptional hubris of a average moron... gave this one a go on the Breadboarding... this the second circuit I have ever done on a breadboard... that kind of got away from me.... I’m surprised it worked! Still have to play with it a little bit to see how it sounds I’m sure I messed up somewhere and it will shine through when I start playing. As of now though it seems to sound good at very low volume( the kid is taking a nap.) thanks Chuck! 39AC7770-A6BE-423C-8874-0745547E2D8C.jpeg
 

Paradox916

Well-known member
Ok so I went wrong somewhere I think, the EF86 controls doesn’t seem to clean up. but the rest of the circuit is very lively and responsive.... I’ll have to try an go back over that rats nest and see if I can figure it out.
 
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