LPB-1

[thermionix]

In tonight's installment of "What Can I Whip Up with Parts I Already Have," I made this as yet unboxed LPB-1.  I have quite a selection of old high voltage (aka Large) coupling caps, so I designed the eyelet board to accommodate some of the bigger ones.

From the various schematics I saw online, there doesn't seem to be agreement on the two base resistors, but I went with 470K and 47K.  Don't know how much difference it makes.  Anyone know what the "original" combo is?





This thing sounds pretty good, but just a wee bit too bassy for me.  I might swap both caps for 47n.  What do y'all like in there?

[Ben Lyman]

Whoa! that's cool. I wonder if you could put it right in a guitar with a battery like an active pickup... except with mojo... and way more boost.
Imagine plugging right into a little amp and cranking it, no pedals visible... people are all, "What?!?!"

[Kipper4]

It's a super little circuit. Per parts count it delivers on the boost count.
A circuit. I Would not hesitate to plaguerise and use as an add on.
I'm not big on mojo parts. Just too expensive for my needs. Not to denigrate. If I harvested some I would use them.
I do like the pcb kinda shaped like a doggy bone.
IMO the lpb1 into a bright fender tube amp is a thing of beauty.

[Elijah-Baley]

I never built it, but I'm planning to build a Blue Box, and want to solve the volume/tone issue adding a LPB-1 with tone control in the end of the circuit. This is another way to use this booster.

[Kipper4]

Check out Ben Lyman's Green ringer variant. IIRC he did something similar.
Maybe he has a link to the thread for you Elijah.

[Gus]

Look at the first post in this link http://www.diystompboxes.com/smfforum/index.php?topic=104730.msg940166#msg940166

[thermionix]

Look at the first post in this link http://www.diystompboxes.com/smfforum/index.php?topic=104730.msg940166#msg940166

Thanks Gus, good reading in that thread.  I guess I need to try this with a buffer in front before I start swapping caps.

[Elijah-Baley]

Check out Ben Lyman's Green ringer variant. IIRC he did something similar.
Maybe he has a link to the thread for you Elijah.

I meant to build a kind of the Blue Box by PedalParts.co.uk, the Blue Fool. This version have replaced the final output pot with a LPB-1, but this has some variations and some parts omitted.
I should build the Blue Box and the LPB-1 in two separated veroboard layout, and the LPB-1 have a tone control just after its input.
I don't have to see yet if I have simply to put a stock LPB-1 before the output, or I have to modify it like the PedalParts.co.uk's schematic. I guess it is modded for some reasons.
Sorry the slight off topic.

[Fndr8875]

where did u get that board? thats awesome. sometimes i get tired of ow things are like everything has to be super tiny.

[PRR]

> base resistors, ...470K and 47K.  ....Anyone know what the "original" combo is?

The circuit is "bad" in that different transistors want different bias resistors. In the "original" production runs I suspect he got 1,000 transistors which all biased good-enuff on the same resistors, then got a different transistor (type or just batch) which needed different resistors, so he changed.

Get the Collector roughly halfway up the battery voltage. That works with maximum output. A bit low or high may give different overdrive flavor. I suspect the "originals" all had somewhat flavor, as the idle voltage is not well controlled.

[thermionix]

where did u get that board? thats awesome. sometimes i get tired of ow things are like everything has to be super tiny.

I made the eyelet board.  I get the G10 fiberboard and eyelets from Doug Hoffman, drill holes, and I have a little hand press to set the eyelets.  It could have been much smaller, but I made space for big caps, because I have a lot of them.

The weird, curvy "dogbone" thing is something I do sometimes for the heck of it.  Weight relief?  LOL.  I suppose the first time I did it was to cover for some not-so-straight dremel cuts.  Okay, maybe every time.

[thermionix]

> base resistors, ...470K and 47K.  ....Anyone know what the "original" combo is?

The circuit is "bad" in that different transistors want different bias resistors. In the "original" production runs I suspect he got 1,000 transistors which all biased good-enuff on the same resistors, then got a different transistor (type or just batch) which needed different resistors, so he changed.

Get the Collector roughly halfway up the battery voltage. That works with maximum output. A bit low or high may give different overdrive flavor. I suspect the "originals" all had somewhat flavor, as the idle voltage is not well controlled.

After reading the thread Gus linked above, and your post in it, I dropped the 47K just a bit to get the collector voltage up some.  I didn't have the exact resistor so I paralleled the 47K with a 560K underneath the board.  I now have 4.75v on the collector with a battery reading about 8.8v.  Close enough I reckon.  I was at about 3.7v before and it sounded pretty good then.

FWIW, I tried this with my Boss TU-2 in front as a buffer, and it makes a world of difference.  I should have noticed the low input impedance before.  Now I'm wanting to add a permanent input buffer, but I don't have any suitable JFETs on hand.  Guess I'll get one whenever I order an enclosure.

[thermionix]

^I should add that earlier today I looked up gut shots of original vintage LPB-1s.  Almost every one had a different set of resistors, some even had a different emitter resistor, so it seems ol' Mike was taking the time to accommodate the various transistors, which were also different types.

Also noticed that the old units were PNP with positive ground, never see that in the common schematics floating around online.

[PRR]

> I now have 4.75v ..  I was at about 3.7v before and it sounded pretty good then.

So is there any difference 4.7 or 3.7?

I would be concerned if below 2V or over 7V. Between, the difference may be subtle.

> ol' Mike was taking the time to accommodate the various transistors

He was getting odd lots at low prices. Apparently so cheap he could cover the extra (un-skilled! but spot-trained) labor cost.

> the old units were PNP with positive ground

Odd lots of cheap parts. These are probably Germanium. Leftover rejects from days when AM radios were assembled in NY.

There is a time-line. In critical work, you can date gear by the transition from Ge to Si. When Mike was scouring the old inventory at every distributor in the city, he would have been finding Ge long after "everybody else" had gone Si.

> add a permanent input buffer

IMO: then it would not be an "LPB". The low Z off a passive guitar rolls-off the highs. Why? Put those overtones through distortion (in the LPB or in the amp) and they intermodulate to an annoying high haze. The low Z may be side-effect of low-gain devices (and the bias they need), but it IS the "tone" of the LPB.

If you have a Government impedance Spec you have to hit: use a Darlington and increase the Base resistors 10X or 20X. Will have to increase the lower one more to cover the higher Vbe. Should not be hard to get >500K. And indeed this would be "more clear, transparent". But that's not really the LPB's point.

[thermionix]

So is there any difference 4.7 or 3.7?

I honestly haven't listened to it since I made the change, been busy with other stuff.

> the old units were PNP with positive ground

Odd lots of cheap parts. These are probably Germanium. Leftover rejects from days when AM radios were assembled in NY.

There is a time-line. In critical work, you can date gear by the transition from Ge to Si. When Mike was scouring the old inventory at every distributor in the city, he would have been finding Ge long after "everybody else" had gone Si.

I guess I looked at gut shots of about 7 or 8 units, the early point-to-point (sloppy!) ones with the male plug at the output.  They looked to me like Si transistors, various packages, but I'm not sure of it.  All of them were positive ground though.  Google>Images>LPB-1

> add a permanent input buffer

IMO: then it would not be an "LPB". The low Z off a passive guitar rolls-off the highs. Why? Put those overtones through distortion (in the LPB or in the amp) and they intermodulate to an annoying high haze. The low Z may be side-effect of low-gain devices (and the bias they need), but it IS the "tone" of the LPB.

I was already thinking of making the input buffer bypassable (is that a word?).

[antonis]

bypassable (is that a word?).

Don't worry too much for that..

(if it isn't a word, duck_arse will proudly place it in the stomboxology vocabulary..) 

[thermionix]

Dead thread resurrection.

Finally got this boxed up.  I might be the first guy to make an LPB-1 that barely fits in a 125A.    After playing more with it, I decided against an input buffer.  Did go with a clipping switch, right now set up to choose between Si, clean, or Ge.  Sounds good, pretty fat.

Funny part is the footswitch and daughterboard are from an actual store-bought LPB-1.  I got one years ago, one of the Nano series IIRC, and I never did take a liking to it.  So I gutted it and built a Si FF in the box.  (Didn't like that either, so I gave it to a buddy).  I like this clone much better than the Nano/Reissue, which I think uses some extra caps compared to the vintage originals.





You can see I spent a lot of time on graphics!

[antonis]

I might be the first guy to make an LPB-1 that barely fits in a 125A.   

Maybe you should try with vertical caps of more than 1kV rating...

[Gus]

Something I posted in 2012
http://www.diystompboxes.com/smfforum/index.php?topic=99139.msg868712#msg868712