DIYstompboxes.com

I have a thing for the Lonestar amp. Never played it. Just heard it and seen it. Somehow I feel attracted to it. That is why I wanted to try to make a stompbox version of the amp, ala the guru's at AMZ, ROG, GEOFEX, and ofcourse the many examples at this board!

I took the original pre-amp schematic and replaced the tubes with J201's.

I know there is not such an thing as 'FET-for-Tube'-magic. However, I hope it results in a fun circuit and stompbox.

Here is the schematic of the Lonely Star:

(http://diy.2muchgear.com/LonelyStar/LonelyStarSchematicV0.5.png)

I have made a couple of modifications to the original schematic:

• Tubes have been replaced with FETs (J201)
• The amp has two tone-stacks. One for the normal chan, one for the lead channel. I combined those. You can have a lead channel->
• The lead channel has an extra gain-stage. I have opted for a switch that can bypass this stage to have the 'normal' channel
• SW LEAD A and B should b a DPDT, but for PCB-reasons I have a SPST in the schematic. If you bypass the lead-channel you go from Drain Q1 directly to C9 (the tonestack)
• I have added 220pF's (C13, C14, C15, C16) to emulate the millar capacitance (uhm, monkey see monkey do ;) )
• I scaled down the tonestack by a factor of 10
• R10 and R15 are 'optional'. I have added those because with them you can kill all the sound by turning the drive/gain completely down. With these resistors you always have a (little) bit drive/gain
• I have breadboarded this schematic and it works. However before putting it to pcb (which I already designed in Eagle) I love to hear your comments and improvements

I hope to receive some feedback to improve this circuit. And hopefully, once verified, I can finalize the  PCB and share it with the board! I want to make a 'modable' version where it is easy to leave pots out (who needs 7 pots???) by e.g. replace the tonestack with a one-knob version.


/edit: corrected SPST to DPDT

Hi, Thats an interesting looking circuit you have there, I am wondering how well the gain pot works from a quick look, it looks like both ends go to gnd. (through resistors). Secondly it might be better to just have the one tone stack in there. Do you have any sound clips of it to listen too.
Good work and i look forward to having a look at the finished layout.

Thanks for your reply.

I do not have any soundclips as of yet. The gain-pot is wired as in the amp, and it does work ;)

The tonestack is just one tonestack. It is the tonestack of the normal channel. In the amp the lead-channel has its own copy of the tonestack. So you would switch from tonestack-normal to tonestack-lead. That would be too much knobs for my liking. ;)

When the gain/drive pot is up full, you have a voltage divider comprised of R9 (220k) and the 1M pot in parallel with R11 (220k).  The way the drive pot is wired, as you turn the drive down, you end up with two cascaded voltage dividers.  So, imagine the 1M pot is set halfway (and omit that optional 100k resistor because the Lonestar does too).  You would now have one voltage divider comprised of 220k and 500k to ground, followed by 500k (the other side of the wiper) and 220k to ground.

I dont understand how the lead switch works. Looks like when it is open you get no signal passing at all.

I have the same question as Chris, though I think what is happening is that it is an spst switch and he just has the two different poles represented, so the signal leaves the first gain stage and then either goes through the second gain stage and gain pot, or jumps straight to the tonestack.  Someone correct me if I am wrong, though.

Quote from: Ripthorn on May 05, 2009, 05:44:38 PM
I have the same question as Chris, though I think what is happening is that it is an spst switch and he just has the two different poles represented, so the signal leaves the first gain stage and then either goes through the second gain stage and gain pot, or jumps straight to the tonestack.  Someone correct me if I am wrong, though.

I thought that too at first.

A DPDT would be needed though. Jumper the outside two lugs so the signal can bypass the extra gain stage though.

The switch is pretty unclear, I understand. And I made a mistake in the description.

It should be a DPDT.

Position 1 (normal channel): you bypass everything around Q2. From the Drain of Q1 you go the C9, the tonestack.
Position 2 (lead channel): you go from Drain of Q2 to C6, R8/R9. And the Drain of Q2 leads in to C9, the tonestack.

I'll make an updated schematic with a DPDT, just for clarity in the next couple of days.

Quote from: kurtlives on May 05, 2009, 05:53:49 PM
A DPDT would be needed though. Jumper the outside two lugs so the signal can bypass the extra gain stage though.

Spot on!

Quote from: kurtlives on May 05, 2009, 05:39:43 PM
I dont understand how the lead switch works. Looks like when it is open you get no signal passing at all.

I think we have to make the assumption the switch is a DPDT switch with parts not shown in the schematic.  It looks like the idea is to bypass one of the gain stages. EDIT: looks like 4 of us posted at the same time :)

Something to keep in mind about this circuit is that it will distort a lot more than the tube amp equal will distort.  The headroom is probably about one tenth of that in the MESA amp.  Remember the rails in the preamp section are often in excess of 100V.  It's possible to have a 50V-p-p signal, whereas in the 9V model your signal will be maybe 5V-p-p.

A way to account for this would be to put a 10:1  voltage divider on the input to scale the signal back so it clips at about the same place as it would in the real thing.   Without the gain reduction on the front end, the input stage will probably clip, when in the real amp it likely does not clip on the input stage.  Clipping the input will make it sound more "fuzzy" and loose.  You may find the thing is more useful just the way it is.

Quote from: Auke Haarsma on May 05, 2009, 05:01:12 PM
Thanks for your reply.

I do not have any soundclips as of yet. The gain-pot is wired as in the amp, and it does work ;)

The tonestack is just one tonestack. It is the tonestack of the normal channel. In the amp the lead-channel has its own copy of the tonestack. So you would switch from tonestack-normal to tonestack-lead. That would be too much knobs for my liking. ;)

Oh yeah sorry ! I didn't look closely enough, i misread the second gain pot after the tone controls, i saw it as a BM tone stack. I'll have to get some glasses.

Quote from: Transmogrifox on May 05, 2009, 06:07:09 PM
Something to keep in mind about this circuit is that it will distort a lot more than the tube amp equal will distort.  The headroom is probably about one tenth of that in the MESA amp.  Remember the rails in the preamp section are often in excess of 100V.  It's possible to have a 50V-p-p signal, whereas in the 9V model your signal will be maybe 5V-p-p.

A way to account for this would be to put a 10:1  voltage divider on the input to scale the signal back so it clips at about the same place as it would in the real thing.   Without the gain reduction on the front end, the input stage will probably clip, when in the real amp it likely does not clip on the input stage.  Clipping the input will make it sound more "fuzzy" and loose.  You may find the thing is more useful just the way it is.

With the trimpot you can set the voltage on the drain to such a setting that Q1 stays clean a long time.

However, would increasing R3 (currently 68k) help in getting closer to the amp?

I took a look at the original schem and it looks like a project for submini tubes to me, but then again, I'm really into them at the moment.  Looks like a great design.

Quote from: Auke Haarsma on May 06, 2009, 02:44:40 AM

Quote from: Transmogrifox on May 05, 2009, 06:07:09 PM
Something to keep in mind about this circuit is that it will distort a lot more than the tube amp equal will distort.  The headroom is probably about one tenth of that in the MESA amp.  Remember the rails in the preamp section are often in excess of 100V.  It's possible to have a 50V-p-p signal, whereas in the 9V model your signal will be maybe 5V-p-p.

A way to account for this would be to put a 10:1  voltage divider on the input to scale the signal back so it clips at about the same place as it would in the real thing.   Without the gain reduction on the front end, the input stage will probably clip, when in the real amp it likely does not clip on the input stage.  Clipping the input will make it sound more "fuzzy" and loose.  You may find the thing is more useful just the way it is.

With the trimpot you can set the voltage on the drain to such a setting that Q1 stays clean a long time.

However, would increasing R3 (currently 68k) help in getting closer to the amp?

The trimpot on the drain adjusts the bias.  I agree that you can change the gain by making it much smaller.  However,  this will change the high-pass cut-off frequency through C6 (4n7).  Additionally this will not prevent the first stage from distorting due to cut-off (ie, when the input signal is on the negative swing, it turns off the transistor).

Changing the 68k resistor won't really change the gain.  It will only change the cut-off frequency of the low-pass filter formed by the 220pF grid capacitance emulator (which actually might make it more likely to distort sooner). 

It doesn't seem as though it would be hard to put a divider on the input.
I would probably replace the 2.2M (R1) with two resistors: 511k and 68k.  The 511k would be in series with the input, the 68k goes to ground.  Take the center tap of the two directly to the input capacitor.  This configuration emulates the effect of having the guitar's volume knob turned down to about 9%.  The input impedance will be plenty high.

We're dealing with Alice in Wonderland fitting into two different sized rabbit holes.  One has a high ceiling, the other has a low ceiling.  If Alice is the same size going into the first hole, she's going to bonk her head on the roof of the smaller hole.  When she goes into the rabbit hole entering tube amp, she's just the right size.  Each tube stage she enters has a mushroom so she grows a little bit more.  Each FET stage in the FET amp has the same kind of mushroom, so her size increases by the same ratio as the tube amp...but if the ceiling is shorter, she'll whack her head.

Making a link with the analogy, when you shrink the power supply down from 150V to a 9V supply, you essentially make the entry rabbit hole 10 times smaller than it is for the tube amp.  If you shrink Alice before she goes into the FET amp so the same ratio of her body fills that hole the same as it does for the tube amp, then you have properly adjusted Alice for headroom.  She will grow proportionately in each FET stage thereafter and bonk her head on the roof at about the same bend in her legs as she would in the tube amp.

Without gain reduction on the front end, Alice is going to whack her head on the entry.  Give her a 10:1 mushroom. 

The notes say that the channel switching is done with a DPDT, but is represented as an SPST for eagle/pcb reasons,.

They say nobody reads anymore  ;)

Quote from: MikeH on May 06, 2009, 02:51:52 PM
The notes say that the channel switching is done with a DPDT, but is represented as an SPST for eagle/pcb reasons,.

They say nobody reads anymore  ;)

The edit says that it used to not read dpdt... :icon_biggrin:

Hi,
Be aware that MB factory schems have deliberate errors in them, to the casual reader they don't seem apparent.
I believe that the Presence control may be attached to the top side of the master control not the wiper. (see MK1 reissue)
The mid boost is the same connection as for the MKI MB and goes to the top of the treble control, not the wiper??
Why just scale the Tone Stack why not the whole schem.............and are FET impedance's significantly lower than the tube schem ??
Just my observations and 2 cents worth.
John G

Quote from: Ripthorn on May 06, 2009, 05:04:47 PM

Quote from: MikeH on May 06, 2009, 02:51:52 PM
The notes say that the channel switching is done with a DPDT, but is represented as an SPST for eagle/pcb reasons,.

They say nobody reads anymore  ;)

The edit says that it used to not read dpdt... :icon_biggrin:

See?  Nobody DOES read anymore  :D

Quote from: Transmogrifox on May 06, 2009, 01:58:48 PM
Without gain reduction on the front end, Alice is going to whack her head on the entry.  Give her a 10:1 mushroom. 

Thanks for the story ;) Would Alice need an additional 1:10 mushroom at the end to bring back the level ?

Quote from: John G on May 06, 2009, 05:22:26 PM
Hi,
Be aware that MB factory schems have deliberate errors in them, to the casual reader they don't seem apparent.
I believe that the Presence control may be attached to the top side of the master control not the wiper. (see MK1 reissue)
The mid boost is the same connection as for the MKI MB and goes to the top of the treble control, not the wiper??

We would need some1 with the actual amp to verify, or a verified schematic. I have just based this schematic on the schematic I found online (at a well known source I guess).

Quote from: John G on May 06, 2009, 05:22:26 PM
Why just scale the Tone Stack why not the whole schem.............

While breadboarding I didn't have the required pots for the original values. Then I decided to down scale the TS as I saw in the Dr Boogey threads. It also helps with reducing noise I understand.

I was not aware that you could downscale more. Could all pots/gains be downscaled without affecting the overall response of the circuit? Could you point to some area' s and values that could be downscaled, and to what the added value is.

Quote from: John G on May 06, 2009, 05:22:26 PM
and are FET impedance's significantly lower than the tube schem ??
Just my observations and 2 cents worth.
John G

Thanks for thinking with me John. I do not understand what you mean with this remark. Could you elaborate?

Quote from: MikeH on May 06, 2009, 05:35:59 PM
See?  Nobody DOES read anymore  :D

Lol! And all this because I couldn' t find a suitable DPDT in Eagle ;) I didn' t want 2x3 pads as a DPDT has, b/c as said above, the bypass is easily done on the switch. I do not need those pads on the PCB. Waste of space I couldn't use.

IMO the best way to scale the gain would be to find out how much distortion the triode stages generate. For example a 60V p-p (say at 300hz) signal enters a triode stage, the gain is 60, the output signal should be 60X60=3600V, but the plate voltage is say 300V so we have 20xlog(3600/300)=21db of distortion. Now, we should design the fet stage so that is has the same amount of distortion and do that for every stage. The first stage would be a little more tricky, I think it would need an additional 'input trim' control to make it work with both single coils and humbuckers (assume input voltage 100mV p-p for single coils).

Quote from: the_stig on May 07, 2009, 11:08:46 AM
IMO the best way to scale the gain would be to find out how much distortion the triode stages generate. For example a 60V p-p (say at 300hz) signal enters a triode stage, the gain is 60, the output signal should be 60X60=3600V, but the plate voltage is say 300V so we have 20xlog(3600/300)=21db of distortion. Now, we should design the fet stage so that is has the same amount of distortion and do that for every stage. The first stage would be a little more tricky, I think it would need an additional 'input trim' control to make it work with both single coils and humbuckers (assume input voltage 100mV p-p for single coils).

We assume the guitar and pickup types are irrelevant.  If the amp itself behaves similar to the real thing, then it will have the same response to single coils as the real amp would have, and likewise with the humbuckers.

Secondly you don't have to think in dB for this.  It's as simple as my Alice in Wonderland story.  You just scale the magnitude of the input by the ratio of (clipped amplitude low voltage stompbox)/(clipped amplitude of high voltage tube amp).   It's like making a doll for a doll house.  If a room in the dollhouse is 1/96th the size of a real room, then you make the doll 1/96th the size of a real human, then the doll will fit properly into every room in the house as long as it's truly built to scale.

In other words, you don't need to adjust every single stage as long as the gain on each stage matches the gain on each stage in the tube amp.  We will assume these FET's are close (although I suspect the J201 may be a little higher).  A typical 12AX7 stage has a gain of about 100.  You can find out from a datasheet how this compares to the gain at the currents you're using.

QuoteWould Alice need an additional 1:10 mushroom at the end to bring back the level ?

No.  At least not if you don't need 100V peak to peak to drive a power amp stage.  You don't want the output to burn up your $400 Line6 delay station.  Just think through what we're trying to do here.  On the output you want the waveform to look like a scaled-down version of the waveform that comes out of the tube preamp stage. 

Quote from: Transmogrifox on May 07, 2009, 01:21:34 PM
No.  At least not if you don't need 100V peak to peak to drive a power amp stage.  You don't want the output to burn up your $400 Line6 delay station.  Just think through what we're trying to do here.  On the output you want the waveform to look like a scaled-down version of the waveform that comes out of the tube preamp stage. 

Just tested it on the breadboard: you are right! There is no need to have another gain stage to compensate for the lower input level. And yes, 470k/82k (values I used) did lower the gain and 'sweetened' the sound up a bit. I am going to add this into the schematic and pcb as a mod. Higher gain, just  omit the 470k and replace 82k with 1M, lower gain (more 'real' amp like), use Transmogrifox's suggestion. (see edit at end of this post)

Btw, with this circuit realy responds well to the guitar volume. You can go from clean to crunch with just your volume knob on the guitar!

I am now going to look for a suitable 1-knob tone section to include as a possible mod.

edit:
I just tried the '470k-at-the-input'-mod with a single coil guitar: it does have quite an effect on the available distortion. With humbuckers you can still go from pretty clean to distortion, with SCs it goes in to OD / mild distortion max. But hey, maybe that is what the amp is supposed to do ;)

Well, the BMP tonestack can be used. Since the TS is followed by two gain stages, there is no need for a gain recovery stage after the BMP tonestack.

Whoo

This looks like alot of fun!  Looks like this will be on my "must build" list.

Quote from: the_stig on May 07, 2009, 11:08:46 AM
IMO the best way to scale the gain would be to find out how much distortion the triode stages generate. For example a 60V p-p (say at 300hz) signal enters a triode stage, the gain is 60, the output signal should be 60X60=3600V, but the plate voltage is say 300V so we have 20xlog(3600/300)=21db of distortion. Now, we should design the fet stage so that is has the same amount of distortion and do that for every stage. The first stage would be a little more tricky, I think it would need an additional 'input trim' control to make it work with both single coils and humbuckers (assume input voltage 100mV p-p for single coils).

As soon as the triode entering voltage exceeds the grid-cathode voltage, distortion starts (roughly between 1.5 and 3v in typical applications)
and absolute voltage amplification factor drops rapidly.

Ok, here is the updated schematic and the proposed PCB layout.

Schematic has the added input resistor as mentioned above.

A note about the PCB: I have not attempted to make it as small as possible. But instead, I have made it as small as possible while trying to keep it not a very tight, complex fit. My goal is that even a relatively unexperienced builder should be able to use this pcb layout. That is also the reason why, with the final version, I want to offer a full-out 7 knob version as well as a simple three-knob version (and notes for anything in between).

I have tried to keep the traces thick and the spacing a bit wider than I normally do.

(http://diy.2muchgear.com/LonelyStar/LSSchematic06.png)

(http://diy.2muchgear.com/LonelyStar/LSCutePCB06.png)

C1      0.1uF    C2      15uF    C3      15uF    C4      15uF    C5      15uF    C6      4n7    C7      2n5    C8      5n    C9      2n5    C10      1uF    C11      0.47uF    C12      120pF    C13      220pF    C14      220pF    C15      220pF    C16      220pF    C17      47nF    C18      120pF    C19      47nF    C20      10n    C21      1n2    C22      100uF    C23      5n

R1-A      82k / 2M2 R1-B      470k R2      2M2 R3      68K R4      1K5 R5      1K5 R6      1K5 R7      1K5 R8      1M R9      220K R10      100K optional R11      220K R12      10K R13      10M R14      10M R15      100K optional R16      82k R17      100k R18      2M2 R19      1M R20      220k R21      100R

Q1      J201 Q2      J201 Q3      J201 Q4      J201 J1-J2      jumper    D1      1N4001 POT1      1M   drive POT2      25k   treb POT3      25k   bass POT4      1k   mid POT5      1M   gain POT6      100k   master POT7      100k   presence SW1      On/Off/On TRIM1      100k TRIM2      100k TRIM3      100k TRIM4      100k

Nice work!

You have turned around the PCB pretty fast

Thanks!

I must say that I now see that I again failed to put the lead-switch correct in the schematic. SW_B should ofcourse be mirrored  :icon_redface: :icon_redface:

But other than that, does the PCB look like it is 'project-ready'? If so, I'll go and make the PCB to verify it probably this weekend.

Ziet er goed uit Auke!
Ik ben benieuwd hoe het uiteindelijk wordt en klinkt!
(weer een project voor de toekomst  ;))

Just some Dutch chit chat! ;D

Dank je ;)

Andre etched me a PCB very quickly! I haven't received it yet, but he made a photo, which ofcourse, I cannot keep just for myself!

(http://diy.2muchgear.com/LonelyStar/LonelyStarPCBandre.jpg)

Quote from: Auke Haarsma on May 10, 2009, 04:25:39 AM
Andre etched me a PCB very quickly! I haven't received it yet, but he made a photo, which of course, I cannot keep just for myself!

Very Nice PCB Auke!
So with the layout you were already aware that the PCB would become blue!

So, which one of you distinguished veroboarders feels like veroboarding this circuit? I'd like to try it against my Dr Boogey I just made.

Sounds like a great plan! However, I still need to verify the build. In a couple of days I can tell if the circuit really works well.

Quote from: Jimmy-H on May 10, 2009, 07:59:16 AM
So with the layout you were already aware that the PCB would become blue!

Well, I wasn't aware of that. Just a lucky guess. In my opinion gold/copper looks better against a blue background ;)

Quote from: Scruffie on May 10, 2009, 09:38:59 AM
I'd like to try it against my Dr Boogey I just made.

Also, keep in mind the Dr Boogie is high gain, the lonestar has less gain. It still has plenty of gain on tap for my liking.

Yea I want something with a little less gain to go with it, I just wanna compare its Mesa sound in comparisson with the boogey, but as I say need a vero to test it.

Well, Andre shipped the PCB fast... however I had supplied him with my old address. How stupid can I be??? I moved months ago, and still I mixed up the addresses... But, I got the PCB finally and man, it is gorgeous!!

(http://diy.2muchgear.com/LonelyStar/pcb_foto_1.jpg)

(http://diy.2muchgear.com/LonelyStar/pcb_foto_2.jpg)


And another close up to show how good this etch is. This is a really close close up ;)

(http://diy.2muchgear.com/LonelyStar/pcb_foto_3.jpg)

I plan on populating the board this coming weekend. Stay tuned!

The board is being populated. Next step is to connect all the pots...

All pots wired: it works on first attempt! I have been playing around with the pots and been tweaking some. Ofcourse, despite many breadboard verifications, I still manage to flip the lugs of the pots on the pcb ;) some corrections need here. The pots are very interactive, but you can get some nice tones out of it.

I wasn't completely blown away by the sound though... until I tweaked the 2M2/120pF (R18, C18) after Q3. The sound much improved when I just bypassed those. So, I checked the amp schematic. The 2M2/120pf is in between the send and return of the Reverb. Send is before R18/C18, Return right after R18/C18

What is the function of the 2M2/120pF in the original schematic?

Since we are not using the reverb (I left it completely out), can we also ditch the 2M2/120pF?  (I am gonna do that anyway, it sounds much fuller! but I do like to understand the function).

So, I deigned a new version of the PCB. The changes:

• Dropped the 2M2/120pF (R18, C18). This gives a much fuller sound.
• Relocated some components. The PCB is now smaller, but still not extremely tight. Should be an easy build, component-placement wise. I gues it could fit in a B sized enclosure. (In case you want to build the 3-knob version...:)
• Added a switch. Yeah, another one! I made the input resistors switchable. You can use the reduced level input, or the 'hot' input. The hot input sounds good with weaker pickups, or if you want extra gain
• Added an (optional) resistor and pad for a status LED.
• The current version now has: 7 pots, 2 footswichtes, 2 toggle switches...

Any suggestions?

Quote from: Auke Haarsma on May 17, 2009, 12:03:09 PM
All pots wired: it works on first attempt! I have been playing around with the pots and been tweaking some. Ofcourse, despite many breadboard verifications, I still manage to flip the lugs of the pots on the pcb ;) some corrections need here. The pots are very interactive, but you can get some nice tones out of it.

I wasn't completely blown away by the sound though... until I tweaked the 2M2/120pF (R18, C18) after Q3. The sound much improved when I just bypassed those. So, I checked the amp schematic. The 2M2/120pf is in between the send and return of the Reverb. Send is before R18/C18, Return right after R18/C18

What is the function of the 2M2/120pF in the original schematic?

Since we are not using the reverb (I left it completely out), can we also ditch the 2M2/120pF?  (I am gonna do that anyway, it sounds much fuller! but I do like to understand the function).

Try a smaller value resistor than 2M2.

I like the Marshall 470pF/470K. 300pF/470K also sounds very good imo.

I can do that.

But what are that resistor and cap for? Some kind of filter?

Ya just a filter. Another form of coupling.

Personally I would remove C17 and jumper it. Then you dont have the "extra" coupling.

Ok thanks. I will experiment some more with different values. I'll report back ;)

I replaced C17, C18 and R18 with sockets. I tried some different values. If I remove C17, and use the 'marshall'-values, I loose the bias on Q4 completely. The 100k trim can't get it to ~5V. So it seems I have to keep C17.

I tried some different values from C17. To me 0,1uF sounded best. So that's double the original value.

André will etch me a new pcb for version 1.1.

And, I also corrected an error on the schematic (and thus the V1 pcb). The 'Thick' setting should lead between C7 and R13. Not as on the v0.6 schematic to before C7.

Hope to share the full project in the coming days!

that's great! keep it up!

Quote from: brunocbicalho on May 19, 2009, 11:49:11 AM
that's great! keep it up!

Thanks!

I received the version 1.1 PCB today. The size is quite perfect now, it can even fit a Hammond B-size enclosure. Ideal for the 3-knob version or a Zvex-BoR style enclosure layout.

Populating the board:

and a picture showing the size of the pcb (and the v1.1 pcb traces) in a 'zvex'-style layout with 1 bypass switch and 1 lead/normal channel switch.

WOW this really looks tempting ha ha  :P
I cant wait to see how it will turn out

Keep me posted


Dave

are you gonna be making boards to sell or putting in a group order somewhere?  me-likey

Quote from: aziltz on May 20, 2009, 07:23:55 PM
are you gonna be making boards to sell or putting in a group order somewhere?  me-likey

yeah, pcb's will be available. Most likely I will not make them myself, but I am sure André (who has made the pcb's shown on the pics in this thread) or some of the other great pcb makers here (John Lyons springs to my mind) can provide high quality PCB's at a fair price.

As of now, I have populated the V1.1 PCB, all pots wired and have been playing with it for the last couple of hours.

I am trying some different values here and there, and the results are good. I have changed the values around the 'thick, thicker' switch. It now allows for a lot more gain. I wrote somewhere above that this beasty has a lot less gain than the Dr Boogey. Well, it has less gain, but it gets really close with the mods. And the cool thing is, if you flip the hot-switch to normal or flip the Thick-switch to another position, you can change the gain on tap easily. It is a really adjustable pedal!

I'll continue testing and will probably put it in an enclosure to check on the 'noise' it picks up. Release of the project file (in a new thread) is still on track for this weekend ;)

Here is a pic with all seven pots and three switches. The blue switch at the top would normally be a footswitch. It is used to switch from normal to lead channel:


Stay tuned!

looks wonderfundle!   i must build this, eventually.

Quote from: aziltz on May 20, 2009, 07:23:55 PM
are you gonna be making boards to sell or putting in a group order somewhere?  me-likey

As Auke already mentioned, I can make boards for this project.
The price for green ones will be €11.- excl. shipping.
The blue ones will be €12.40 excl. shipping.

For shipping I will charge the same price TNT charges me.

looks good, but how does it sound? i'm dying to hear some clips...

cheers buddy

If all goes well I hope to have at least some basic soundclips up when the project is released.

Quote from: Auke Haarsma on May 22, 2009, 10:37:06 AM
If all goes well I hope to have at least some basic soundclips up when the project is released.

Cool! Your projects looks like it might sounds good. The PCB etching is flawless, and i really hope it sounds killer. I love this F4T projects (I'm doin' the same with the Marshall JCM900SL-X)

I just cannabalized an old enclosure to quickly box up the Lonely Star. Funny coincidence... the enclosure used to house an OmniDrive. The first effect I ever build! And now that same enclosure gets the honour of housing, well temoporarily housing my first ever own 'designed' effect. Here's a pic of this historic moment :D


But man, I do like how this pedal sounds. It has such a wide range of sounds. From clean all the way into high gain territory! And a lot of steps in between. The controls work really nice. The tone-controls are highly interactive (you have to get used to it), but together with the presence control you can shape the sound to suit your style.

While it was still outside of the enclosure I got some squeeling at the highest gain settings (Hot, Thicker, Lead and max gain and drive). But inside the enclosure there is no squeeling at all!

I need to finetune the Thick/Thicker switch a little more. But I have a feeling I am getting close to finishing the design.

Finetuning of the Thick(er)-switch is finished. I am pretty pleased with it.

Gonna let is rest for a night (gotta get some sleep) and check how it sounds in the morning (you know what beer does to your ears). If it still sounds good I'll write up the project file, make some soundclips and post it in a new thread here at diystomp!

yeay cant wait. im new to this but this project has me on the edge of my seat.

I hope I am not asking too much of your patience, dear viewer! I was already working on the project file... But, the project will take a couple more days.

Why is that?

Well, after finetuning some more (changed the tonestack a little, to reduce some of the bass. Still plenty of bass available), I tried the circuit at a higher supply voltage. 16V to be precise. And, not really to my surprise, this circuit really benefits from the added headroom. It sounds great at 9V (imho) and it sounds even better at 16V (or 18V).

So, what did I do? I decided to add a charge pump to the PCB. Ofcourse, it is optional, you can still runs this effect at 9V. And, it does NOT require a special adapter or power supply. Just the normal 9V 'we' often use. The charge pump takes care of getting the 9V to18V. But since I want a single PCB for the different versions of the project, I recreated the PCB. No fancy colours this time, just a PCB layout image straight out of Eagle:


It is getting more and more crowded, but I still think the PCB can keep its 'easy-to-solder'-ness. To make place for the Charge pump I dropped the onboard LED_resistor, but I do not think anyone will mind.

I also stuck the trimpots much closer together. Still more than enough space for each trimpot, just look at some of the pics of my builds. I use pretty small trimpots which do not require a lot of space.

Any comments regarding the charge pump or the new pcb?

So, it looks OK I guess?

It will be the third PCB I will populate for this project. Wanna make sure this is the final one!

It's looking pretty good, though if it were me (and probably just for me) I would put in a voltage select switch so I could run it at either 9 or 18V with the flick of a switch.  Maybe that is why my submini amp has taken 4 months so far... :icon_biggrin:

as if we do not have enough switches already  :icon_mrgreen: :icon_mrgreen:

Why would one want to switch from 9V to 18V? Or from 18V to 9V?

I would include a switch to change the headroom and thus the amount of distortion available.

Ah yeah, I understand.

I'll stick to the current pcb I think, there is already plenty of 'gain-shaping' available (lead/normal chan, hot/norm input, norm/thick/thicker-switch). However, it sure is a great add-on, for those interested in even more 'shaping' options!

Quote from: Auke Haarsma on May 26, 2009, 06:24:46 PM
as if we do not have enough switches already  :icon_mrgreen: :icon_mrgreen:

Why would one want to switch from 9V to 18V? Or from 18V to 9V?

Ya I was thinking that as well.

I think a little DIP switch on the PCB would be nice. Kind of set it and forget it kinda thing.

Quote from: kurtlives on May 26, 2009, 08:04:40 PM

Quote from: Auke Haarsma on May 26, 2009, 06:24:46 PM
as if we do not have enough switches already  :icon_mrgreen: :icon_mrgreen:

Why would one want to switch from 9V to 18V? Or from 18V to 9V?

Ya I was thinking that as well.

I think a little DIP switch on the PCB would be nice. Kind of set it and forget it kinda thing.

exactly, but still you would have the option of changing it without any desoldering, etc.

Looking good Auke!  8)
I would like to build one when you're finished and happy with it and André has the final PCB available!  ;D

Did the members from Run Off Groove react to this design yet? They have lots of experience with this amp simulation stuff...

Quote from: Ripthorn on May 26, 2009, 09:21:04 PM

Quote from: kurtlives on May 26, 2009, 08:04:40 PM

Quote from: Auke Haarsma on May 26, 2009, 06:24:46 PM
as if we do not have enough switches already  :icon_mrgreen: :icon_mrgreen:

Why would one want to switch from 9V to 18V? Or from 18V to 9V?

Ya I was thinking that as well.

I think a little DIP switch on the PCB would be nice. Kind of set it and forget it kinda thing.

exactly, but still you would have the option of changing it without any desoldering, etc.

I like this idea, using a dipswitch. However, it will be a challenge to fit it onto the pcb. I'll have a look at it. The pcb *must* fit in a Hammond B-sized enclosure. As you can see on the pics of the V1.1 PCB, there is some room left to enlarge the pcb, but I doubt there is enough room...  We'll see ;)

Quote from: flo on May 26, 2009, 09:31:52 PM
Looking good Auke!  8)
I would like to build one when you're finished and happy with it and André has the final PCB available!  ;D

Did the members from Run Off Groove react to this design yet? They have lots of experience with this amp simulation stuff...

Thanks Flo. Not sure if the ROG-crew has seen this thread. However, I have read most articles and checked most 'amp-sim' designs by ROG. They do have made great amp-sim pedals.

I've been trying to get a charge pump working. My initial test at 16V was with my own PSU, not an onboard charge pump. I have now breadboarded several versions of the chargepump with several IC's, but each an all of them give me squels when I bias either Q3 or Q4 around 1/2 Vcc. Unworkable sadly. And I have no clue why.

At first I thought it may have to do with the (way too) long wires I used in my test build. But no, that's not it. It must something related to using a charge pump. So for now I think I will go back to the previous version of the pcb (without charge pump, running at plain 9V, sounding great!) unless someone has an explanation for my 'squeels' at biassing Q3/4.

Did you make sure to engage the boost function on the charge pumps?  You might be getting the switching frequency into your nearest jfets which would then get amplified and could become a squeal.

Yeah, that is not it. I've tried acouple of variants of the MAX1044, all with boost function.

And, I must correct my previous post: I now notice the squeels also happen with my own PSU's. So it is not charge pump related.

It must be something in:
1) the circuit itself: it squeels when fed with 18V
2) my test-setup (chaos to the outsider, very organized to me :D )

Option 2) seems unlikely.

Just to add some more info to this mystery...

This is what happens when I put a higher voltage on the circuit.

Vcc = 18V
Q1 Drain: biasses nicely at ~10V
Q2 Drain: no probs to get it to ~10V
Q3 Drain: trimpot is still on the 9V setting, so it starts high (15V). I trim it down and I can hear the squeel coming up. If I keep it at 15V, I do not have a squeel. Just a not so nicely biased sound.
Q4 = same as Q3.

well, I've had a bad vibe. Sometimes I have that, nothing seems to work... plain bad luck all the time. That vibe is over. It is time for gooood vibrations!

I abandoned the charge pump, went back to the 9V design. Changed the thick/thicker-switch so that there is a bigger difference between thick and thicker and a smaller difference between normal-thick.

Oh, I also received some submini tubes yesterday.... (no, I won't try to fit them into this design :D )

If the problem happens with any kind of 18V power supply, then it is probably just oscillation.  This is because 1) 18V provides more headroom and thus more volume and 2) biasing the jfets at 1/2 supply voltage is the ballpark for max gain on the fets.  So what you are probably seeing is that you are getting tons of boost through those last two stages when all is biased "correctly" and that starts the circuit oscillating.  Still looks like a good project.

Thanks Brian, that's reassuring!

What I don't understand is that it even happens even at mininum gain. At that setting you have to dial up the volume control to not drop the output level compared to the bypass signal.

Try increasing the value of the source resistors, just a bit?

It's my inderstanding that increasing the source caps will even further increase the gain.

What do you expect from raising the source caps?

Maybe lowerling the caps (currently 15uF to 10uF or 4,7uF) could help? But, that would also drop the gain in 'normal 9V-mode'.

My last post said resistors not capacitors.

Ya you would loose a bit of gain, thats why I said only increase them a little bit. I am just throwing ideas out here to try and help.

Ah apologies, I didn't read that carefully.

Quote from: kurtlives on May 29, 2009, 10:05:39 AM
I am just throwing ideas out here to try and help.

And that is much appreciated!

If my question "what do you expect from..." sounded a bit hars, that was unintentionally. I try to understand the reasons for changes to the circuit in an attempt to overcome my lack of knowledge ;) Especially if some1 knowledgeable like you gives a hint/tip I'd like to understand the reasoning behind that.

What I not yet understand is why increasing the supply voltage leads to oscilliation. I do get that :
-increasing supply voltage and biasing around 1/2 Vcc increases the available headroom
-more headroom means increased signal level before clipping

What I don't get is why it happens even at minimum gain. At the 9V supply voltage there is hardly any gain, I'd say it pretty much is a nice warm clean tone, with even a drop in volume (unless you set the volume pot at max). I'd expect to just have a nice clean tone at min gain settings and 18V.

Perhaps using an oscilloscope or an "audio probe" will help determining which gain stage is actually oscillating. It's there that gain and/or bandwidth must be reduced in order to remove the oscillation.

I know it has been brought up before, but that gain control is an interesting topology.  maybe try a traditional gain control on the breadboard to see if there are any differences.  Other than that, I can't think exactly why oscillation would occur on min gain unless there is enough gain after the gain control to induce it.   :icon_confused:

I still have 'a' version on the breadboard. Will fiddle some with the gain, source resistors and caps.

Also, I will prepare the 9V version for release. It is time that more people enjoy this circuit!

Mucho gracias for all the input, feedback and ideas guys!

Quote from: Auke Haarsma on May 31, 2009, 08:41:20 AM
I still have 'a' version on the breadboard. Will fiddle some with the gain, source resistors and caps.

Also, I will prepare the 9V version for release. It is time that more people enjoy this circuit!

Mucho gracias for all the input, feedback and ideas guys!

Dude, c'mon, this waitin' is killing me! /jk

@Anti-Idiot
If nothing weird happens I'll post the project tonite. I just want to make sure that what I post can actually be build and is useful ;). Parts layout and wiring is already done. Just need to beautify the schematic a bit and do a write up. Ah, also I need to prepare the parts-layout for a 3-knob version and describe the possible mods (that I see).


@Oscilliation
Well, I've used my scope to pinpoint the oscilliation. But, to no avail. I can't really see where it is comming from. It looks like it is already there on the input, but I see no reason why that would be the case. In the 9V-mode I don't see it at the input however...

I've tried different J201's in all Q's. Swapped them to 2n5457's (lower gain) to see if that would help. But no go.

And now for the weirdest thing: It seems somehow (indeed, as Brian mentioned above!) to be related to the Gain pot. The Drive-pot (from the lead channel) doesn't matter at all.

I wrote before that there was oscilliation at min gain. Well, that's not the case.... I somehow managed to swap the Volume pot and the Gain pot when I put back this board into the enclosure. Corrected that now, here are my findings:

Gain pot:

• from 7 o'clock to 9 o'clock: nothing, no oscilliation
• from 9 o'clock to 10 o'clock: faint oscilliation
• from 10 o'clock to 12 o'clock: increasing oscilliation
• from 12 o'clock to 2 o'clock: decreasing oscilliation
• from 2 o'clock to 5  o'clock: Max gain, but NO oscilliation.

So, it is NOT gain related. Or, there is no direct relatation to the amount of gain. If that would be the case you would expect max oscilliation at max gain. Well, at max gain: no oscciliation.

I don't really understand what is going on around the gain pot. Some1 with an idea?

Typically oscillation will  increase in frequency as the gain is increased, so it might be that the frequency of oscillation is just going above the audible spectrum (or high enough to get masked by the guitar).  Of course, I can't speak as to exactly what might be causing it.  If you post the project, then I will try to get it breadboarded over the next couple nights and see what I get.

sounclips would be nice! ;)

Have a look here (http://www.diystompboxes.com/smfforum/index.php?topic=76873.0)