Sunday, 20 January 2013

AMZ Mini-Booster

Jack Orman's DIY classic that has been inspiring many builders and businessmen alike over the years. Simple as Fuzz Face, but very big, strong, lively sound. There must be tens or even hundreds of variations around, just as there must be tens or even hundreds layouts around. Still we didn't have this one covered yet. Now we do.




And Geiri's demo! Sounds great doesn't it!


37 comments:

  1. Verified. I'm really getting into these booster circuits and it's nice to be reminded that I'm playing guitar and enjoying the beautiful clear chime that instrument has. Nice simple one, too. Cheers!

    Mark

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  2. Hi Miro. What's the orientation on the 3.3uf cap? Thanks.

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    1. All the schematics i've seen state that it's non-polar...
      +m

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  3. I've actually got a 3.3 polarized (but no non-polar) and wanted to make sure I oriented it properly.

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    1. Build it to that point and measure which side has the bigger dc voltage.
      +m

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    2. You would usually expect the source of Q2 to be at a lower voltage than the gate, but I'm not sure if that is still the case with muamp configurations like this. But that's the way I would try it first, with the positive lead on the bottom row.

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    3. The schematic here: http://www.muzique.com/amz/miniboo.gif indicates that the negative pin on the cap goes to the bottom rail, to connect to the 1M R3 that goes to ground. The positive goes to S of Q1 and D of Q2.

      Having said that, I've just built this layout and gotten nothing (and tried the 3.3 polarised cap both ways)- I've used a 500k pot instead of 100k, and 2n5459s but that shouldn't make a difference as they're the same pinout. Oh well, back to troubleshooting.

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  4. If anyone doesn't have 3.3uf non-polarised, try using 1uf. I do it and I like it. I haven't tried using the correct value so I'm not sure how big of a difference there is. Oh and I don't have a 10pf so I use a 15pf. Other than that, the components are right.

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  5. 1u (non-polar) for that position and 5p for the ceramic seems to work fine. 3n3 chiclet :-o was ear bleeding-bumblebee-transistor radio-esque....and not in a good way

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  6. Verified(+). Sounds very profesional. A clean boost, it adds clarity and definition. It would be a must, 20% or 30% more output volume.

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  7. It 's normal that if the volume control is set to 0 will not come out any sound, and if the pot set to the 100% is lower than the input volume?

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    1. Yes in virtually all these layouts, when the volume control is fully counter clockwise all the signal is dumped to ground and so it is silent. Fully clockwise should be much louder than the bypassed signal so you must have an error somewhere.

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  8. AMZ Mini Booster: is there a mod to increase the overall volume a bit?

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    1. Try J201 instead of the 2N5457.
      That should give you quite a bit more volume and a slightly dirtier tone.
      Mine is insanly loud and unity level is about 10 o'clock, and it is capable of pushing my amp beyond overdrive and into fuzz territory.
      I actuall has never dared to turn it all way up, being afraid that it might be too much for my amp to handle...

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  9. Thank you Neil, good idea.. maybe i try change one 2n5457 for J201, and see what happens.

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  10. I finished this today and my attempt is definitely not a clean boost, even at unity to the bypassed sound. It has more of a mild overdrive sound. I have 2N5457's in it at the moment. I tried J201's but those are even dirtier. It's almost there, it just adds a little hair to the sound. Any suggestions as to make the circuit cleaner? I know I could try it at 18v, but that is not the best option for me.

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    1. Try to change 1k resistor for another with a higher value (10k)

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    2. Thank you, Boratto. That totally worked!

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    3. Sounds like the MOSFet Boost might be more to your liking. It's reportedly much more a "clean" boost. I don't see it here but it may be under a variation on the name. Here's the original AMZ page (I hope this is ok to point at)
      http://www.muzique.com/schem/mosfet.htm

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  11. Perhaps there is a mistake in the vero. According to GGG, 22n should be 220n (0.22 uF): http://www.generalguitargadgets.com/pdf/ggg_joam_a_bom.pdf

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  12. What are some other options, if any, to the J201/2n5457 transistors? I am just curious what other transistors would do. What would a bjt do or a mosfet do? Could I pop a BS170 in there or a 2n7000?

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    1. Alternatives might be any one of:

      2N3819
      2N5246
      2N5458
      2N5484
      2N5485
      2N5952
      2SK117
      2SK170
      2SK208
      2SK246
      2SK30A
      2SK30A
      BF244
      BF245
      BF256
      J111
      J112
      J113
      J202
      J310
      MPF102

      But it's a case of trial and error to which will work well in the circuit. Through hole JFETs are getting more and more difficult to source at reasonable prices, so I'd seriously recommend all builders to take the plunge and buy some surface mount J201 and 2N5457 and a batch of through hole adapters. They're in current manufacture and made by the billion so we won't run out any time soon and before long when the Chinese seller realise that we will buy them you'll probably get 100 for £2 as they all go into competition with each other. You can't get them quite that cheap at the moment, but I recently bought 25 x MMBFJ201 and paid about £4 for them delivered off eBay. For the adapters I bought 30 of these from OSH Park for $4.50 delivered:

      https://oshpark.com/shared_projects/8bf7XW05

      Yeah the soldering is a bit of a pain, but it's not that hard and you would very quickly get used to it. Plus you could do them in batches so you have them stocked up and ready for builds and then not have to think about SMD soldering for a while.

      Plus an added bonus is someone mentioned the tolerances on the surface mount JFETs is very tight making it easy to get matched sets which would be fantastic for building a phaser with the minimum fuss.

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  13. But what happens if I don't use a jfet? Will it just not work at all? Smoke? Pyrotechnics to rival the greatest 4th of July display you've ever seen?

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  14. Can someone explain to me how one would add a tone control knob to this layout?

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    1. If you are willing to sacrifice some output volume (which shouldn't be an issue in this case) it's as simple as going into your tone control of choice from the output (Volume 1 link on the board) followed by an output cap (220n should do a good job there as well, but you can try more or less and see what changes it makes, if any noticeable ones) and finally into a volume pot (lug 1, while lug 3 will still go to ground and lug 2 will be your effect out/return).

      Not sure how clearly I explained it, hope it makes sense? :)

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  15. Can I sub a 47uf for the 100uf cap?

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    1. That's just a power filter cap, so yes.
      +m

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  16. Finally got this built and boxed up with a socket for both jfet transistors and the 3.3u cap. I don't have a 3.3u (polarized or non-polarized) so that's why I put a socket there. I've only tried as big as .1u but that seemed to be just fine. I really liked a .022 in there. Seems to be nice and bright for me and sounds good with my setup. My question is, what does that 3.3u cap? Sounds like it really affects the tone and wondering if a tone control there with two caps being swept with a pot would be doable. Also, it isn't very clean and it breaks up pretty much at the lowest setting.
    Going into a Rivera clean channel and wondering if different transistors would do the trick. I've got J201s in there and a slew of J202s, but I was told they are higher gain. Is there another component, a resistor perhaps, that would affect the breakup? Was really hoping for a clean boost on this, but what I do have is a nice one-knob overdrive for my particular setup. Super loud, though, but useable for the time being for me with a .022u cap in place of the 3.3u.
    Just curious why such a high value for that cap and if I'm doing something wrong with the .022 in its place.

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  17. Okay, so about to unload a slew of questions. Hope it doesn't get annoying.
    Reading on the geofex page (http://www.geofex.com/Article_Folders/modmuamp/modmuamp.htm) about the circuit and wondering what a 10M resistor to bias the first transistor (the one with the input going thru the input cap to the gate) would do. Guess all these questions could be answered by actually doing this, but my day is kinda crazy (stay-at-home dad with a 3 year old and a 1 year old, whose nap times can't be disrupted by me cranking a mini-booster to test my "mods").

    Also, the geofex article schematic uses 10M resistors for the voltage divider halving the voltage to the gate of the second resistor. Any other affect that would have on the circuit? The 2N5457 transistors seem to be getting harder to source, but I've heard a lot of folks like that in this circuit better than the J201.

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  18. okay, and one more for ya...
    The last schematic on the geofex page (http://www.geofex.com/Article_Folders/modmuamp/modmuamp.htm) has an unmarked capacitor going from the voltage divider to ground. Any idea what value should be there? It doesn't mention it in the schematic or notes. Drawing up a new schematic to breadboard that basically merges the bottom schematic with the mini-boost schematic. Changes that 3.3uf to .1uf and uses two 10K resistors for the divider fed into a 4.7M resistor to the gate of the bottom transistor (when I refer to top and bottom transistor, I'm referring to them as they appear on the veroboard in the layout above). Anyway, wondering if that capacitor is needed because of the lower resistor values of the voltage divider.

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    1. Try something like 10u. The notes say that using the 2 x 10Ks and the 4M7 "offers the ability to shunt thermal noise from the junction of the two 10K's to ground" which is what that cap will be doing.

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  19. built this, replaced 3.3u with NP 1u and 10pf with 6.8pf. Result is a non fully transparent boost. Treble and definition are definitely reduced and seems like bass is increased. Which of these changes are the culprit, if any? All other values are fine... thanks!

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  22. Has anyone seen the Fat and Fatter mod for the AMZ Mini Booster? I'm a bit of a noob and want to know would it be hard to incorporate it into this build? I mean, it looks like I can just have it off-board between the power and the board, but wouldn't I need any extra resistors to protect the LEDs? I am aware of the general concept, the power going to the board is dropped in voltage by one or two LED's, giving the pedal lower headroom. I just don't understand fully how I'd add it to this build. All help and noob guides for doing this would be highly appreciated. Cheers. http://www.muzique.com/news/mini-booster-fat-and-fatter/

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