Finally - The L5 Preamp

[Timko]

I have struggled with Aion's L5 preamp build since I mistakenly soldered the regulators on upside down (don't do that, BTW).  I had to run some trace wire, scrape parts of the trace mask off to reconnect them correctly.  Then, I was getting next to no sound out of channel 1.  Thinking I had fried a chip or fried some part of the board, I put the build down for a month or so.

A couple of nights ago, after finishing some other troubleshooting issues on some previous builds, I pulled this back out.  I had seen the Reverb.com video and decided to set the clean channel to the same settings as that video had.  And it worked!  I was getting these incredibly chimey cleans out of the channel.  The limiter seemed to work a lot better too; before I was getting very little compression unless I had it turned all the way down.  I'm still having some issues getting a noticeable effect from the multifilter, but I am going to play around with that later tonight.  A big thanks to everyone who helped me get this thing working after I was convinced I had fried it.

There's no fancy etching on this one; I was happy to not have to drill this template! The knobs are a little too big; I'll look at ordering something smaller sometime in the future, but for now, they work.

I took it up my my local store, and a couple of people couldn't believe it was a solid state amp.  For that matter, neither could I.  It's really a phenomenal pedal.

[gordo]

Timko, are you using this on 9vac?  I've built two of these now and can't get it to function unless I use 12vac.  Sounds awesome (both of them) but I've never been able to straighten this out.

[Timko]

Timko, are you using this on 9vac?  I've built two of these now and can't get it to function unless I use 12vac.  Sounds awesome (both of them) but I've never been able to straighten this out.

Yep, 9V AC adapter. 

Just to be clear, the MultiFilter doesn't work for you with a 9V AC, but works with a 12V AC?

[Boba7]

That looks great! The knobs are quite big I agree but I quite like them. I'm really curious about this circuit but I'm not sure I'd have use for it. What a great looking board though...

[Timko]

That looks great! The knobs are quite big I agree but I quite like them. I'm really curious about this circuit but I'm not sure I'd have use for it. What a great looking board though...

It's an amazing tone shaper.  While I'm not comparing it to a Color Box directly (JHS's Neve console in a box), it can can some of those things.

[darrenw6000]

great finish! how is it you get the perfect white letters on the black enclosures?

[dbp512]

great finish! how is it you get the perfect white letters on the black enclosures?

UV printing by mammoth electronics. There was a group buy for these enclosures last summer in conjunction with the release of the PCB. I believe you can find the template at Aion's site, so you just need to send it somewhere to get manufactured.

[gordo]

No, I can't get the whole pedal to work on 9vac.  Compressor locks on and I get an obnoxious hum.  Went with the Mouser BOM on the second one and exactly the same results.

[gordo]

Well now.  I've been using either a Line6 9vac power supply and a Yamaha 12vac power supply.  I just put both pedals on a T-Rex Fuel Tank with a 500ma 9vac output and dead quite and work like champs EXCEPT...within about 5 to 10 minutes they shut down when the regulators overheat.  Maybe 500ma is too low and the regs are working too hard?  Not sure that makes sense.

Any ideas here?

[Timko]

I'm using a Jameco adapter that Aion recommended to me. I don't have any issue with the compressor, but the Multifilter control has an effect on only the first and last 10% of the pot range. I'll keep tinkering. 

I got another couple hours in with this today and holy balls does it sound good. The clean channel has this amazing chime that I may start using as my base clean tone.  I'm still trying to tune in thr 2nd channel (the filter may help with that), but I could see this kicking my Nobels ODR-1 build off my board. Its got such a full sound in it, pushing the midrange a la Queens of the Stone Age.

[gordo]

My real L5 amp is similar.  The MultiFilter isn't a real dramatic effect.

[aion]

I got another couple hours in with this today and holy balls does it sound good. The clean channel has this amazing chime that I may start using as my base clean tone.

Yes! The 2nd channel has all the bells and whistles so it usually gets all the attention, but the first channel is a thing of beauty as well. My only complaint is I wish it could match the volume of the 2nd channel. I haven't experimented with it at all to see what it would take, but it seems like it'd be possible by raising R11.

I could see this kicking my Nobels ODR-1 build off my board. Its got such a full sound in it, pushing the midrange a la Queens of the Stone Age.

Keep 'em both! The ODR-1 is another magical box. Try it in front of channel 1. I've never done it myself, but it seems like they'd complement each other pretty well.

[aion]

Well now.  I've been using either a Line6 9vac power supply and a Yamaha 12vac power supply.  I just put both pedals on a T-Rex Fuel Tank with a 500ma 9vac output and dead quite and work like champs EXCEPT...within about 5 to 10 minutes they shut down when the regulators overheat.  Maybe 500ma is too low and the regs are working too hard?  Not sure that makes sense.

Any ideas here?

I've seen maybe 5-6 reports of this so far out of a couple hundred, which isn't a whole lot but is still too many. I gave it a bit more thought. It seems to be an issue with the total current draw of the circuit and the regulator's ability to keep up with the sudden change in current flowing through it, so there is a voltage sag that affects the whole circuit when the compressor/limiter kicks in. The 12VAC supply fixes it because there is more current available, but it causes its own set of problems, namely that the pedal can't be used very long! So I have a couple more ideas:

1. Make sure you are NOT using super-bright LEDs (although gordo, I think you're OK on this one if you used the ones from Mouser) - this was the case for some people though.

2. Try raising the values of R95, RX5, and RX6 (the LED current-limiting resistors) from 680R to 1.5k. They're running off 15 volts as it is, so you probably won't notice a difference in brightness. I use these vintage-style LEDs with 4k7 CLRs in my 9 volt pedals and they are plenty bright, so I imagine there's a fair amount of room for raising that resistor value even further and lowering the current. Might be able to get away with a heck of a lot higher than 1.5k but I'd start there.

3. Replace RX3 and RX4, the two 1.8k resistors in the power section, with diodes as follows:



By removing the resistors, you reduce the current draw of the circuit (the resistors are there to make sure the regulators have enough current to function, but in a working circuit they are just drawing unnecessary power) and by adding the diodes you're guarding against latch-up. This trick was buried in a datasheet - apparently certain physical devices are more susceptible to it, even same part number from the same manufacturer, so you may experience it rarely with some, often with others, and never with most - just luck of the draw. It only happens when the unit is first powered up, never while it's already running, but this fix is a two-for-one.

4. Use a different kind of regulator. The 7815 has been around since the 70s or 80s, but there are more modern ones that may work better, especially the low-dropout (LDO) variety. I haven't had a chance to research what are the "old reliables" or industry standbys of these type of LDOs—and Mouser is pretty daunting just browsing through the options for them—but if none of the above ideas help at all, this is what I'd do next.

Let me know if any/all of those help!

[gordo]

Thanks Kevin, I should get some decent bench time over the next couple of days. I think I mentioned that I was mistaken on the T-Rex, it's 12v. Explains the thermal problems. Will keep you posted.

[gordo]

Really don't mean to hijack this thread but for anyone else that had the same problems I did, this is an easy fix and it works like a champ.  I have both my L5 pedals running dead quiet at 9vac and I got them calibrated without issue.  Thanks for the fix on this Kevin, it was totally painless.

It can be done without removing the board (thankfully) and I didn't have any 1.5k resistors so I unsoldered R95, RX5, and RX6.  I unsoldered RX3 and RX4 and moved them to RX5 and RX6.  I had a spare 1.8K left over from the original Mouser order so I used that for R95.  I added a 1N4001 to RX3 and RX4, although I suspect just about any diode would do (1N914 maybe?).  I really don't notice much of a difference in LED brightness and the regulators are now running comfortably warm.  I'm THRILLED that my issue is solved and my only challenge now is to decide if I want the blue-green sparkle PPP UV printed one or the Aion textured black on my pedal board.

The fact that my live rig is a real L5 is testament to how thrilled I am to have it in pedal form as well.