Verellen - Meatsmoke Preamp  [traced]

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vigilante397
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Post by vigilante397 »

Finished my layout. Tubes go into the empty spots on either side mounted on right angle headers, 3PDT (low profile) for bypass and 4PDT for channel, whole thing goes in a Hammond 1590XX. Bypass LEDs will be mounted under the tubes, channel LEDs will go in line with the pots so it's easy to see which channel's controls are active. I'll order it sometime in the next couple days and let everyone know how it goes when I get the hardware.

meatsmoke PCB.JPG

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Post by vigilante397 »

Ordered boards today. Another big benefit to SMD is I can pay a few bucks extra per board and have them assembled at the factory with a pick-and-place machine, so when the boards come I just add pots, tubes, and switches then throw it in a box and I'm ready to go.

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Post by Jarno »

Been wanting to try that as well, what are the mechanics of that? Do you need to use a certain library of components? Did you order in china or elsewhere?
"It crackles....., but that's ok"

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Post by vigilante397 »

Jarno wrote: 10 Sep 2021, 21:31 Been wanting to try that as well, what are the mechanics of that? Do you need to use a certain library of components? Did you order in china or elsewhere?
I use JLC in China, they have a library of components that I use. Every part in the library has a reference number that you add as a column in your BOM, then you upload your BOM and your centroid (pick-and-place) file. The centroid file is generated automatically by your CAD software and has the x/y coordinates and orientation of every component to be placed. Setting that all up right makes the whole process easy and fast, but they still have their engineers look over everything and verify your files, so they'll fix anything you messed up. Also if you don't list a reference number but have the value (i.e. 0.1uF 50V) and footprint (i.e. 0805) in the BOM then their system will automatically look for a match in their library.

I really like it because aside from saving me time assembling boards myself, JLC gets components direct from the manufacturers and they don't mark up prices, so I'm actually saving money as well. A board that would typically cost me $12-15 in components to assemble myself now costs $4-6 assembled from the factory. It's absolutely brilliant, I highly recommend it. I wish I had started doing it years ago.

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Post by Jarno »

Always figured it would be cost prohibitive, hard to do, but that sounds great! Might have a look at that as well, saves a bit of time and effort. And time is at a premium with two kids, and a very busy job :D
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Post by vigilante397 »

Alright, my Meatsmoke preamp PCBs are expected to finish production tomorrow. There are 8 designs on the order, 6 of which will have pick-and-place being done. I'm hoping to have boards in hand by the end of the week.

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Post by Reachahighernoon »

vigilante397 wrote: 09 Sep 2021, 16:04 Alright, final schematic. I left out the power supply, because frankly if you don't already know how to build a high-voltage supply then you shouldn't be learning it from me, you should do a lot of reading so you don't kill yourself. The original runs at 300V, I'll probably run around 240V so I can use 250V caps. Also the op-amp runs on a 25V supply; Verellen uses a fat resistor divider to get close then uses a 25V zener to keep it at 25V. I'm using an LM2733 to boost from the 9-12V input up to 24V, close enough for me.

Let me know if anything looks off, I'm not perfect and welcome any corrections, and I still have the unit so I can go back and double check anything that looks weird.


Verellen Meatsmoke.png
I have a question, I've seen some other schematics with a similar mosfet output buffer but with the diode in the opposite direction, how so?

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Post by vigilante397 »

Reachahighernoon wrote: 14 Sep 2021, 15:01
vigilante397 wrote: 09 Sep 2021, 16:04 Alright, final schematic. I left out the power supply, because frankly if you don't already know how to build a high-voltage supply then you shouldn't be learning it from me, you should do a lot of reading so you don't kill yourself. The original runs at 300V, I'll probably run around 240V so I can use 250V caps. Also the op-amp runs on a 25V supply; Verellen uses a fat resistor divider to get close then uses a 25V zener to keep it at 25V. I'm using an LM2733 to boost from the 9-12V input up to 24V, close enough for me.

Let me know if anything looks off, I'm not perfect and welcome any corrections, and I still have the unit so I can go back and double check anything that looks weird.


Verellen Meatsmoke.png
I have a question, I've seen some other schematics with a similar mosfet output buffer but with the diode in the opposite direction, how so?
In my understanding it depends on your goal. Based on some quick googling it looks like having the zener with the cathode connected to the gate is useful for transient voltage protection, but having the cathode on the source and anode on the drain prevents oscillation. I could be misunderstanding that, so if something doesn't work in the output buffer I can try flipping the diode around. Another (subjective) advantage to SMD, flipping around a component with a hot air station is easier than trying to desolder and resolder a through-hole part.

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Post by Reachahighernoon »

vigilante397 wrote: 14 Sep 2021, 17:38
Reachahighernoon wrote: 14 Sep 2021, 15:01
vigilante397 wrote: 09 Sep 2021, 16:04 Alright, final schematic. I left out the power supply, because frankly if you don't already know how to build a high-voltage supply then you shouldn't be learning it from me, you should do a lot of reading so you don't kill yourself. The original runs at 300V, I'll probably run around 240V so I can use 250V caps. Also the op-amp runs on a 25V supply; Verellen uses a fat resistor divider to get close then uses a 25V zener to keep it at 25V. I'm using an LM2733 to boost from the 9-12V input up to 24V, close enough for me.

Let me know if anything looks off, I'm not perfect and welcome any corrections, and I still have the unit so I can go back and double check anything that looks weird.


Verellen Meatsmoke.png
I have a question, I've seen some other schematics with a similar mosfet output buffer but with the diode in the opposite direction, how so?
In my understanding it depends on your goal. Based on some quick googling it looks like having the zener with the cathode connected to the gate is useful for transient voltage protection, but having the cathode on the source and anode on the drain prevents oscillation. I could be misunderstanding that, so if something doesn't work in the output buffer I can try flipping the diode around. Another (subjective) advantage to SMD, flipping around a component with a hot air station is easier than trying to desolder and resolder a through-hole part.
I see, thank you for the explanation

From what I've seen this is the only example with the diode in this direction, in all the cases I've seen so far the diode protected the gate of the mosfet

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Post by vigilante397 »

Reachahighernoon wrote: 14 Sep 2021, 18:14 I see, thank you for the explanation

From what I've seen this is the only example with the diode in this direction, in all the cases I've seen so far the diode protected the gate of the mosfet
This is where I found the mention of putting the zener the way I have it in the schematic: https://electronics.stackexchange.com/a/461673

But I agree it is unusual, and most articles I've found have the zener facing the other way. I will freely admit I may have just traced it wrong, I'll double check the original Meatsmoke unit when I get home from work to make sure. But the boards have already been fabricated and are in line for pick-and-place, so it's too late for me to fix on the first run, but if it is a mistake I will absolutely update this post with the correction and fix any future versions of the board. Easy enough fix on the board, hit it with the hot air station and flip the diode around. Thanks again for checking it out and letting me know :)

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Post by Reachahighernoon »

Hey guys I have a very weird issue with a circuit similar to the mosfet source follower here, the preamp sounds like a weird gated fuzz but I accidently touched the body of the mosfet(the drain) to the 12V line(sparks flew) and suddenly the preamp started sounding right, have you ever encountered something like this?

Here's the schematic of my preamp
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Post by Manfred »

Reachahighernoon wrote: 19 Sep 2021, 16:33 Hey guys I have a very weird issue with a circuit similar to the mosfet source follower here, the preamp sounds like a weird gated fuzz but I accidently touched the body of the mosfet(the drain) to the 12V line(sparks flew) and suddenly the preamp started sounding right, have you ever encountered something like this?
Have a look at the solder joints of the IRF830.

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Post by Reachahighernoon »

Manfred wrote: 20 Sep 2021, 05:58
Reachahighernoon wrote: 19 Sep 2021, 16:33 Hey guys I have a very weird issue with a circuit similar to the mosfet source follower here, the preamp sounds like a weird gated fuzz but I accidently touched the body of the mosfet(the drain) to the 12V line(sparks flew) and suddenly the preamp started sounding right, have you ever encountered something like this?
Have a look at the solder joints of the IRF830.
I did and nothing was out of the ordinary, I actually de-soldered the mosfet(I used a 740) and replaced it with a 840 and the problem still persisted

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Post by vigilante397 »

Reachahighernoon wrote: 19 Sep 2021, 16:33 Hey guys I have a very weird issue with a circuit similar to the mosfet source follower here, the preamp sounds like a weird gated fuzz but I accidently touched the body of the mosfet(the drain) to the 12V line(sparks flew) and suddenly the preamp started sounding right, have you ever encountered something like this?
Is there any DC bias on the gate? If you accidentally connected the drain to the gate, the zener could held it at 12V to bias the gate and work. So I still haven't opened the Meatsmoke back up to double check the orientation of that zener, but I think I do have it backwards and it's supposed to be regulating a 12V DC bias to the MOSFET gate. For your buffer you could try adding a 470k resistor between the drain and gate like the Meatsmoke has.

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Post by Reachahighernoon »

vigilante397 wrote: 20 Sep 2021, 17:26
Reachahighernoon wrote: 19 Sep 2021, 16:33 Hey guys I have a very weird issue with a circuit similar to the mosfet source follower here, the preamp sounds like a weird gated fuzz but I accidently touched the body of the mosfet(the drain) to the 12V line(sparks flew) and suddenly the preamp started sounding right, have you ever encountered something like this?
Is there any DC bias on the gate? If you accidentally connected the drain to the gate, the zener could held it at 12V to bias the gate and work. So I still haven't opened the Meatsmoke back up to double check the orientation of that zener, but I think I do have it backwards and it's supposed to be regulating a 12V DC bias to the MOSFET gate. For your buffer you could try adding a 470k resistor between the drain and gate like the Meatsmoke has.
Yeah...I opened a separate thread in debugging and the issue is indeed that I didnt have any dc bias to the gate, I thought the meatsmoke didnt either and same for another few schematics I looked at

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Post by vigilante397 »

My Meatsmoke PCBs are out for delivery!!!

EDIT: Just got the notification that the boards were delivered, but I still have 5 more hours of work. It's going to be a long day...

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Post by vigilante397 »

Board is on the bench, it's in my queue of boards to verify tonight so I will keep eberyone posted. Here's the board with the extra components the factory didn't stock added on:
IMG_20210921_202352.jpg
Also I got the original Meatsmoke back open to check the zener diode, and I do have it backwards, cathode should be facing gate and anode should be on the source. I'll update my files, but this batch of boards I'll just flip the diode around.

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Post by vigilante397 »

Board has been verified!

With the zener flipped around (I'll fix and re-upload schematic) this is a 100% functioning design. The owner of the original let me hang on to it so I can A/B test mine against it, so I'll try to get this boxed up tonight and A/B the two. By itself it sounds great, I tried it running into the front of my Lightning clone, and I tried the record output going direct into my interface. Both were great, but I've found that I like the dirty channel better into an amp and I like the clean channel better through the record out. Record out obviously is just a filter, but for how simple it is it does a good job. It doesn't sound like an IR, but I would definitely say good enough to be usable live.

For testing I wired straight in instead of hooking up bypass, but I did wire up the 4PDT for channel switching. I don't like excessive wires, so I made a daughter board for the 4PDT and mounted it to the board on header pins. Much tidier than 12 wires flapping around.
board top
board top
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board bottom

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Post by plush »

Nice build.

But, I'd consider rerouting C2. Just as a precaution.

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Post by vigilante397 »

plush wrote: 23 Sep 2021, 16:48 Nice build.

But, I'd consider rerouting C2. Just as a precaution.
Any particular reason?

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