Lumpy's Tone Shop - Lemon Drop  [traced]

General documentation, gut shot, schematic links, ongoing circuit tracing, deep thoughts ... all about boutique stompboxes.
User avatar
drewl
Breadboard Brother
Information
Posts: 110
Joined: 11 Feb 2010, 14:56
Been thanked: 8 times

Post by drewl »

Did a search but didn't find any info on it here.

Anyone ever see one, open it up?
Supposedly it's similiar to the Jellyroll but uses a silicon transistor to drive a FET?
just looking for something different to build.

thanks.

User avatar
Nocentelli
Tube Twister
Information
Posts: 2178
Joined: 09 Apr 2009, 07:06
Location: Leeds, UK
Has thanked: 1016 times
Been thanked: 870 times

Post by Nocentelli »

drewl wrote:Did a search but didn't find any info on it here.

Anyone ever see one, open it up?
Supposedly it's similiar to the Jellyroll but uses a silicon transistor to drive a FET?
just looking for something different to build.

thanks.
Weird :scratch:

I remember this well, I could have sworn there was a thread - Maybe it was a request that was never fulfilled so got deleted.
Anyway, I really liked the demo and was interested in building a workalike, but never got very far. However, I saved a description of the circuit from Lumpy himself:
Lumpy wrote:The Lemon Drop uses a similar idea as the Peppermill to push a JFET into overdrive,
but it does it differently and I didn't get the idea from the Peppermill either.
If the idea of overdriving a JFET is unique to ROG, then I guess I'm guilty.
The input stage on the Lemon Drop is a BJT, not a MOSFET.

It's practically the same as the 7 Series input stage simply biased for 9V.
Transistor is a BC108B rather than BC107s used in the amp.
As simple as that sounds, it's what makes the pedal sound the way it does.
The JFET is a 2N5457, similar stage setup as the Peppermill,
but that is so basic anyone could come up with that...
The tone control is set up like a range control on a Rangemaster copy.

There were 2 custom versions that were built with the 7 series tone stack.
The original prototype was a little more complex utilizing more features
of the 7 series preamp but it never quite got the sounds of the amp.
I've attached some relevant schems that I used as a starting point.
Attachments
Top_Boost_mictester.GIF
Top_Boost_mictester.GIF (9.08 KiB) Viewed 8705 times
VoxSeries7pre.jpg
VOX760pre.gif
vanessa wrote: 20 Aug 2007, 17:51 You can't arrest someone for reverse engineering something.

User avatar
Nocentelli
Tube Twister
Information
Posts: 2178
Joined: 09 Apr 2009, 07:06
Location: Leeds, UK
Has thanked: 1016 times
Been thanked: 870 times

Post by Nocentelli »

[edit]removed ROG peppermill schem - you can get that from ROG website easily[/edit]
vanessa wrote: 20 Aug 2007, 17:51 You can't arrest someone for reverse engineering something.

User avatar
Nocentelli
Tube Twister
Information
Posts: 2178
Joined: 09 Apr 2009, 07:06
Location: Leeds, UK
Has thanked: 1016 times
Been thanked: 870 times

Post by Nocentelli »

Aha, the thread is over at DIYSB, that's why I can't find it here:

https://www.diystompboxes.com/smfforum/ ... 249.0;wap2
vanessa wrote: 20 Aug 2007, 17:51 You can't arrest someone for reverse engineering something.

User avatar
Nocentelli
Tube Twister
Information
Posts: 2178
Joined: 09 Apr 2009, 07:06
Location: Leeds, UK
Has thanked: 1016 times
Been thanked: 870 times

Post by Nocentelli »

vanessa wrote: 20 Aug 2007, 17:51 You can't arrest someone for reverse engineering something.

User avatar
drewl
Breadboard Brother
Information
Posts: 110
Joined: 11 Feb 2010, 14:56
Been thanked: 8 times

Post by drewl »

Thanks.

If I ever get the time I want to build a 7 series preamp to go with some tube power amps I have that are similiar to the 7 series output section.
Someday, before I die :D


I've run Thomas Vox preamps into the power amps and they sound pretty good.

Thanks again.

User avatar
Nocentelli
Tube Twister
Information
Posts: 2178
Joined: 09 Apr 2009, 07:06
Location: Leeds, UK
Has thanked: 1016 times
Been thanked: 870 times

Post by Nocentelli »

No problem: I think the upshot is that the Lemon drop is just a single BC108c stage taken from the 7 series input and adapted for 9v bias, driving a single 2N5457. I couldn't get anything but farty fuzz, but I know nothing about biasing transitors. I'd love it if someone could suggest a suitable bias arrangement for the first BJT stage.
vanessa wrote: 20 Aug 2007, 17:51 You can't arrest someone for reverse engineering something.

User avatar
sciencefriction
Information
Posts: 3
Joined: 26 Jan 2013, 05:31
Has thanked: 2 times
Been thanked: 1 time

Post by sciencefriction »

Necro Bump. With Lumpy awol, has anyone thought about giving this circuit another look? Would be fun to build and tweak.

User avatar
Nocentelli
Tube Twister
Information
Posts: 2178
Joined: 09 Apr 2009, 07:06
Location: Leeds, UK
Has thanked: 1016 times
Been thanked: 870 times

Post by Nocentelli »

sciencefriction wrote:....has anyone thought about giving this circuit another look?
If anyone could post gutshots, that would be great.
vanessa wrote: 20 Aug 2007, 17:51 You can't arrest someone for reverse engineering something.

User avatar
sciencefriction
Information
Posts: 3
Joined: 26 Jan 2013, 05:31
Has thanked: 2 times
Been thanked: 1 time

Post by sciencefriction »

Nocentelli wrote:
sciencefriction wrote:....has anyone thought about giving this circuit another look?
If anyone could post gutshots, that would be great.
I don't own one anymore, but here are some images I found online. Looks to be some variations between them.


User avatar
MoonWatcher
Diode Debunker
Information
Posts: 715
Joined: 28 Jul 2008, 12:27
Has thanked: 40 times
Been thanked: 50 times

Post by MoonWatcher »

sciencefriction wrote:Necro Bump. With Lumpy awol, has anyone thought about giving this circuit another look? Would be fun to build and tweak.
How about starting with a Peppermill, substituting a bjt for q1, and changing component values as needed?

You could always get into the particulars with the tone circuit and biasing a 2n5457 instead of j201 as the tweaking progresses.

While I'm probably wrong, I don't think that q1 plays as big of a sonic role as q2 does. That said, a mosfet will have different gains, and a different input impedance, than a bjt will, so I think those will probably be the most significant differences.

So - depending on how much overdrive comes from the jbt/q1 itself, you could probably just start with any semi-standard configuration. Maybe something like a LPB-1 for the first round of tweaks? Or maybe the booster stage from a Big Muff? Or a silicon Rangemaster variation?

Even though it differs from the Peppermill, it seems like the same basic idea is the same - q1 is driving q2. Most of the "magic" should be happening at q2, I'd think.

User avatar
Nocentelli
Tube Twister
Information
Posts: 2178
Joined: 09 Apr 2009, 07:06
Location: Leeds, UK
Has thanked: 1016 times
Been thanked: 870 times

Post by Nocentelli »

Thanks for the pictures!

It makes sense if we assume it's vero, but I can't figure how the gain pot works:

Image

That assumes the filter is between the two stages, and is a cap blend between the orange cap straight from the collector (under the drawn-on brown wire, presumably > 100n) and the ceramic cap below the BJT (small, 4n7 or something, direct from the large orange cap to the FET gate). That would imply the gain pot involves the far-left electrolytic. That works ok, but I can't then understand why the gain pot would use two separate wires on lugs 2 and 3 AND a "stopper resistor" from lug 1 to ground. I also don't see a resistor from FET gate to ground (would normally be 1M or so, no sign of one).

Schematic in the works
Attachments
lemon drop pic_zpstx2uebyh.png
vanessa wrote: 20 Aug 2007, 17:51 You can't arrest someone for reverse engineering something.

User avatar
sciencefriction
Information
Posts: 3
Joined: 26 Jan 2013, 05:31
Has thanked: 2 times
Been thanked: 1 time

Post by sciencefriction »

If they hadn't recently become so hard to get, I would get another. I want to build one and see if I can get it to sound a little looser. There were a couple with a pre-gain knob added, but I've never seen guts for that version. It's a cool build, but yeah, I'm not sure what's going on there either. If one turns up for a good price I'll grab it again.

User avatar
randalp3000
Information
Posts: 3
Joined: 09 Feb 2016, 18:13
Has thanked: 3 times
Been thanked: 13 times

Post by randalp3000 »

New guy here, been lurking/learning for awhile. I've built 20+ tube amps and a dozen or more pedals.
Picked up a ZII last week to try and help this thread along.
Here are a couple picks to help get this moving. I did trace it to the best of my abilities. Could only read one of the electrolytics but measured the rest in circuit with a cap meter. Ceramics are marked 471 and 10J, blue cap is WIMA 3300 100-U, orange cap 4700k, red caps .022uF.
Attachments
lemon drop zII.jpg

User avatar
randalp3000
Information
Posts: 3
Joined: 09 Feb 2016, 18:13
Has thanked: 3 times
Been thanked: 13 times

Post by randalp3000 »

Schematic I came up with. Feel free to double check resistor color codes
Attachments
ZII Lemon Drop.pdf
(24.67 KiB) Downloaded 601 times

User avatar
Nocentelli
Tube Twister
Information
Posts: 2178
Joined: 09 Apr 2009, 07:06
Location: Leeds, UK
Has thanked: 1016 times
Been thanked: 870 times

Post by Nocentelli »

randalp3000 wrote:Schematic I came up with. Feel free to double check resistor color codes
Excellent work, many thanks! Could you measure the voltage on the drain of the JFET?
vanessa wrote: 20 Aug 2007, 17:51 You can't arrest someone for reverse engineering something.

User avatar
randalp3000
Information
Posts: 3
Joined: 09 Feb 2016, 18:13
Has thanked: 3 times
Been thanked: 13 times

Post by randalp3000 »

Q1
1 4.58vdc
2 .79
3 .2

Q2 JFET
1 4.84
2 .61
3

User avatar
drewl
Breadboard Brother
Information
Posts: 110
Joined: 11 Feb 2010, 14:56
Been thanked: 8 times

Post by drewl »

Very nice, I'll have try it.

User avatar
ch ra
Information
Posts: 2
Joined: 10 May 2017, 15:04
Has thanked: 2 times
Been thanked: 1 time

Post by ch ra »

Hello, I saw there is a newer version of this circuit with a pre-gain, and separate treble and bass pots. Does anyone know how those fit into the posted schematic?

Thanks!

User avatar
HamishR
Breadboard Brother
Information
Posts: 78
Joined: 31 May 2016, 14:51
Has thanked: 6 times
Been thanked: 41 times

Post by HamishR »

I have drawn vero layouts for both versions - FWIW I think the 3-knob version sounds better. I added a bias trimmer too. Easy enough to leave out.
Lemon Drop ver3.png
Lemon Drop 4-knob.png

Post Reply