Messages

Please take a look at this. Q1 and Q2 run of the normal VCC line again, the BBD and clock are powered from a separate regulated supply. The bias for the BBD is taken from that power supply aswel and placed right in front of the BBD. More parts, but a better design. Bias is further stabilised by a 10uF cap. This should be pretty solid. After the BBD there is a coupling cap and Q2 gets its bias from the regular power supply again. In theory it should now be possible to safely run the pedal at 9, 12, 15 or 18 volts without having to adjust anything. I upped the first filter cap to 220uF/25V. The BBD is always safe at 8V2, as is the clock.

You can socket the BBD. I just confirmed that the total height of IC + socket is 8.5 mm, so there is 1.5 mm room left between the BBD and the enclosure.

Who wants to actually see me build this thing? 

That would obviously be the better way to do the biasing; just like in the CS9, but with Small Clone values. CE-2 is done trough the first filter too. Any reason why the bias won't be stable when looking at the second image below? Anyway, I'm going back to the drawing board and see what I can come up with.

The LT1761 is adjustable and set for just above 8V. I saw in the datasheet that the sweet spot should be there ;-) and thank you for the confirmation!

All schematics in LTspice

LT1761 regulated Small clone

pre-emphasis outputs

pedal outputs

A big thanks for that valuable information! Seems I was thinking in the right direction: take the bias for the BBD from the power that supplies it. Power CD4047 and BBD from the same point. Hence my (most recent) thoughts: either maximise the whole power supply to 9 volts via a LDO regulator or supply Q1, Q2, the BBD and the CD4047 from a regulated supply via a LDO. The latter gives the option to run the pedal as high a voltage as the other parts allow. The BBD will be safe and the bias will be steady. Last but not least, the LDO will have almost no drop when using a 9V supply.

Another option would be to regulate the clock, BBD, Q1 and Q2 (and the bias network for them) to 5V. Seems to be the sweet spot for the BBD according to some (or many, I don't know). Distortion in Q1 and Q2 will rapidly rise in this config, mainly 2nd and some 3rd. Not necessarily a bad thing... Is there a very good reason to run the aforementioned parts on 5V?

I always liked the idea of 9V over 5V better for the BBD and clock. For no apparent reasons whatsoever...

Brings me to the last point you note here: bass content to the BBD. In a CE-2 or CS9 e.g. the bass is greatly reduced by the 33n cap decoupling the first opamp to the pre-emphasis filter. Now that opamp is already unity gain at bass frequencies, the 33n cap drops even more lower bass (below 40 Hz IIRC). In that same place in the Small Clone is a 1u cap, which let everything pass (except DC off course). Other than that, I can't come up why a MN3207 would get more of a beating in a Small Clone than in a CS9 (5kHz at +18dB right before the BBD in the latter).

I'll post some simulations I made in LTspice, so you can better judge/see the ideas I had and the results of different filtering methods according to simulations. I know, simulations......

That idea on the trimmer was clever! I should have thought of that and moved it to the other board side. Done that now.

You might want to also consider putting the BBD on the opposite side (socketed of course) It would make for easy repairs as that is the most likely fail item.

I was thinking about lowering the signal because of the CE-3 from Boss. Much less signal to the BBD. Seemed to be a the way to go for a MN3207 with its lower dynamic range. Then I looked at the CS5 and CS9 from Ibanez. Both build around the MN3207 and in a very similar fashion to the others. The signal going to the BBD of the CS5/9 is at least as strong as in a stock Small Clone. Now those Ibanez chorusses are highly praised, right? I haven't read any mentions about noise and distortion.

The CS5/9 run the BBD regulated to 5 V. I think it's more logical to regulate the entire pedal to 9V instead, or regulate everything that is dc coupled to the BBD. The Pork Barrel has the BBD and clock regulated to 9.1V (zener) in case of using a MN3207, but the bias for the BBD is taken from the the main power supply. This means that when the pedal is powered from a 12V (for what ever reason you'd do that) supply the BBD still has 9V and is misbiased because the bias changed with the PS voltage. Not to mention you'd probably fry a dropping resistor and zener diode...

Conclusion: it's doable to fit a MN3207 in a Small Clone without altering the signal path to the BBD much (if my simulations and thinking are correct).

Don't forget that all of the other pedals you mention used the companion MN3102 for clocking which could figure into the reasoning as to why they went with the 5V powering scheme. The SC used the 4047 capable of a higher voltage tolerance.

Food for thought... Good luck with this, it looks fantastic! 

Socketing the BBD, that's something I'd really like! Moving it to the other side would mean I've to relocate it between the pots as there's an output jack on the opposite side. That would mean a pretty big overhaul...

Maybe I should start looking into daughter board and or other jacks (smaller ones like the ones from Zwee) for complex designs. How nice would it be to shoehorn a flanger/chorus/vibrato hybrid into a 1590a? Or just clip all legs when the BBD is dead.Doesn't matter, it's dead already haha.


Sent from my iPhone using Tapatalk

That idea on the trimmer was clever! I should have thought of that and moved it to the other board side. Done that now.

I was thinking about lowering the signal because of the CE-3 from Boss. Much less signal to the BBD. Seemed to be a the way to go for a MN3207 with its lower dynamic range. Then I looked at the CS5 and CS9 from Ibanez. Both build around the MN3207 and in a very similar fashion to the others. The signal going to the BBD of the CS5/9 is at least as strong as in a stock Small Clone. Now those Ibanez chorusses are highly praised, right? I haven't read any mentions about noise and distortion.

The CS5/9 run the BBD regulated to 5 V. I think it's more logical to regulate the entire pedal to 9V instead, or regulate everything that is dc coupled to the BBD. The Pork Barrel has the BBD and clock regulated to 9.1V (zener) in case of using a MN3207, but the bias for the BBD is taken from the the main power supply. This means that when the pedal is powered from a 12V (for what ever reason you'd do that) supply the BBD still has 9V and is misbiased because the bias changed with the PS voltage. Not to mention you'd probably fry a dropping resistor and zener diode...

Conclusion: it's doable to fit a MN3207 in a Small Clone without altering the signal path to the BBD much (if my simulations and thinking are correct).

That looks awesome, excited to see how all your 1590A SMD projects end up (and to hopefully build some of them  )

Thanks man! The boards for the micro sized Triple Wreck are on my way at the moment. Got an upgrade to swift service from the guys at OSHpark. Really nice. I want to see how that build is gonna work out. So that's the first one...

Thanks wgc. What do you think about lowering the signal to the BBD as I did? Any other improvements to be made, especially to the mods I did?

I made a quick mockup. The board looks like this:

Not much of a response here  . I get that, it's not really groundbreaking either to just miniaturise an existing pedal.

However, I went ahead and converted the SC to MN3207. This meant redesigning the power supply for the digital parts, which isn't as simple as on a CE-2 where the Egg for the BBD is provided by the clock. I'll let the schematics speak for themselves when it comes to the other changes.

The first schematic is the most basic one with a simple zener regulator and intended for 9V use, with 9V max provided to the BBD. Should be safe for the BBD and in the optimum working range of the MN3207 (IF I understand the datasheet correctly; minimum THD at around 8V operation).



The second schematic is with a 7809 or 7805. Both should work, but when supplied 9V the 7809 will drop 2V and the BBD will run at a lower voltage.



The third schematic incorporates other changes as well. The digital components aswel as the bias for them runs of a low noise LDO regulator. The LT1761 has a max voltage drop of just 150mV when loaded as lightly as in this application. I ditched D2, which only provides a unnecessary voltage drop after Q1. Not needed as I used a NPN here and not an PNP. More true to the original would to use a PNP for Q1 and use D2. I just can't seem to find the reason why it was done that way.

The biggest change however is in the parts surrounding IC1. The MN3207 has a fair bit less dynamic range when compared to the MN3007. The SC by default boosts the high frequencies in IC1a by as much as 18 dB and compensates for this in IC1b. The Boss CE-3 is much tamer at this point and boosts the highs around 10 to 12 dB. To me that seems more reasonable and get some of the headroom back. All was simulated in LTSpice and by the end of the signal chain, the frequency characteristics between my tamed and a stock SC are the same. Apart from an obvious noise penalty, is there any reason to tame the signal to the BBD?

Yet another development topic by me. Well, development... It's just miniaturising an existing pedal, this time the Small Clone. The only mod incorporated so far is a depth pot. I might add a vibrato or intensity switch.

Again I need some help. Could anyone of you point me to more info about converting this circuit to accept MN3207 BBD's? I'd like to make it easily switchable like the Pork Barrel. Can that be done here?

I will stay away from the really small parts, for now 

Got some parts in today, so time to take some real life measurements and do a very quick mockup on a scrap piece of vero. Just measured the total height from the top side of the volume pot to the top side of the output jack: 27.1 mm. The inner height of a 1590a enclosure is 27.4 mm, so it's really tight fit. But it fits!

The Alpha DPDT footswitches are tiny when compared to a 3PDT by the way. Definitely the way to go for more crowded builds. Overall very nice, relatively silent switches.

When checking the placements of the jacks, I found that they were a bit far from the inner walls of the enclosure. The nut could barely be fastened. I'm glad I'm checking this kind of stuff before ordering the boards...

Haha nice. Do you want one with 0201 size components then? 

Are there must have mods for a small clone beside the depth knob? I've got room left for a sub miniature switch and maybe some trim pots...

Incredible attention to details in this build! Even the wiring looks like it was designed to be that neat. And that colour scheme, just wonderful!

looks good once again.

seems like you've got a very different approach to layouting than I do. I first put down all components that will have certain positions, like pots, switches, connector pads and the like. then I put down all components following the schematic more or less as close together as possible, also keeping an eye on possible routes for the traces. after parts placement I trim the pcb to size, space the components as evenly as possible and start laying down traces, which of course leads to some parts being shuffled around. long story short, I don't start putting down traces before all components are placed

Not too different then! The placement of pots, jacks, switches, status led, connector between switch board and main board are given. I then place the bigger parts based on their place in the schematic and group the accompanying parts around them. Then I 'pre' route some parts to visualise where I will run into problems. That's where the real fun begins: shifting parts and traces around to minimise trace length and get the most important parts as close to IC's as possible. I use the rip up tool a lot. Really, probably too much. I wish I could work out a better workflow.
When working on a board that isn't restricted to an exact size like these, I trim it after everything is placed.

It all looks awesome!  I'm always on the lookout for some cool, small SMD projects! (especially a 1590a chorus )

Ha yeah, me too! And I'm looking for cleaner solutions for wiring too, hence all the board mounted stuff. With standard placement of certain parts, drilling etc. should be a breeze too. I've got a Pork Barrel and love it and already wanted a Small Clone, so why not design one in a small package and have some fun (other fun than drinking a few beers with friends, but fun nonetheless).

Let's get on with some teasers of work in progress. Of these projects only the Lunar screwdriver (an extremely good design by Skreddy) is at a stage that I could start to order parts. The rest is still in board design phase. The 3D renders are also of the Lunar screwdriver.

Stay tuned for more updates about the TW. It takes long to see some real life results (and not just 3D renders) due to shipping and order processing times and the way I work, but those results will come!

Most of the parts for this build have been ordered, except for the passives. I really need to pay close attention to the small differences. For example not all Cliff style jacks are the same. The jacks of Cliff and Rean appear to be slightly wider and longer than the ones from Neutrik for which this board is designed. The same for pots: small differences between Alpha and Alps. Pots, jacks, switches, all should arrive tomorrow.

In the mean time I needed something to do, so I'm working on 1590a versions in the same fashion as this TW of the Skreddy Srewdriver/Lunar module, DBD, small clone and Fulltone '70. The small clone is a bit of a challenge, but hey, I like the toughest puzzles best :-;


Sent from my iPhone using Tapatalk