Generic PCB designs - Preamp, LTPI, FX, Power
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Generic PCB designs - Preamp, LTPI, FX, Power
Last year I set about designing a generic PCB design for a dual triode - so a pair of stages on one PCB that could be configured in as many ways as possible (gain stage as well as CF) with places for all the usual components. Merlin did his own (and undoubtedly better) design around the same time, but I persevered with mine - with many of Merlin's tips / tricks adopted.
The idea was that I could try many differing topologies / values without having to do extensive rewiring. So going from a 4 stage high gain design to a 3 stage + CF to a plexi would be just swapping a couple of boards.
I then also made a generic LTPI and power supply board. And then an Effects loop (both tube and solid state) and also a Belton reverb board. Phew.
Some pictures of early versions: https://www.tristancollins.me/ax84/Mutineer/PCBv3/
I'm finally getting round to building the result:
This is my take on an AX84 October along with a JCM800 cold clipper preamp feeding a pair of 6V6s - so basically "Sluckey's Dual Marshall" mentioned on EL34world. Two inputs so I can use an external AB switch.
More details at http://www.ax84.com/bbs/index.php?id=501185 & http://www.diyaudio.com/forums/instrume ... l-amp.html.
https://www.tristancollins.me/ax84/Mutineer/Build/
I would be happy to share the designs etc if this build works OK and I haven't made a stupid mistake somewhere. The PCB design and physical chassis layout took quite a while, but the populating was very, very quick.
Tristan
The idea was that I could try many differing topologies / values without having to do extensive rewiring. So going from a 4 stage high gain design to a 3 stage + CF to a plexi would be just swapping a couple of boards.
I then also made a generic LTPI and power supply board. And then an Effects loop (both tube and solid state) and also a Belton reverb board. Phew.
Some pictures of early versions: https://www.tristancollins.me/ax84/Mutineer/PCBv3/
I'm finally getting round to building the result:
This is my take on an AX84 October along with a JCM800 cold clipper preamp feeding a pair of 6V6s - so basically "Sluckey's Dual Marshall" mentioned on EL34world. Two inputs so I can use an external AB switch.
More details at http://www.ax84.com/bbs/index.php?id=501185 & http://www.diyaudio.com/forums/instrume ... l-amp.html.
https://www.tristancollins.me/ax84/Mutineer/Build/
I would be happy to share the designs etc if this build works OK and I haven't made a stupid mistake somewhere. The PCB design and physical chassis layout took quite a while, but the populating was very, very quick.
Tristan
Last edited by tristanc on Sat Aug 25, 2018 8:31 pm, edited 2 times in total.
Re: Generic PCB designs - Preamp, LTPI, FX, Power
Oh, and I did all the design in KiCad - would totally recommend the latest version.
Also forgot to mention I made a board for the tone stack (Merlin's Bone Ray) so this could be hot-swappable too.
Also forgot to mention I made a board for the tone stack (Merlin's Bone Ray) so this could be hot-swappable too.
Re: Generic PCB designs - Preamp, LTPI, FX, Power
Really nice work! What company did you use for mfg the PCB's. And if you don't mind sharing, what does the cost of having these made up look like?
Steve
Re: Generic PCB designs - Preamp, LTPI, FX, Power
I used PCBway in China. Haven’t had an issue - fast and cheap.
I get 10 of each board for $5 as they are all <100mm per side. So $30 for the picture above and lots spare! Shipping to the UK is ~$25.
I get 10 of each board for $5 as they are all <100mm per side. So $30 for the picture above and lots spare! Shipping to the UK is ~$25.
Re: Generic PCB designs - Preamp, LTPI, FX, Power
I had forgotten that I had seen this post previously on AX84 . Are your KiCad files shareable? I'm trying to learn it, your right about the steep learning curve.
Steve
- chief mushroom cloud
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Re: Generic PCB designs - Preamp, LTPI, FX, Power
Nice work! I like those Phoenix/Weidmuller type screw terminals, too. But be sure to dab a dot of flexible acrylic nail polish into the setscrew wells....they can vibrate loose. I know this from experience.
But I'm curious....did you allow for creepage clearance around power supply diodes? When you fire it up, watch for potential arcing....just turn off the lights to really see it. If you don't see it, don't worry about it.
What copper thickness did you specify in your fabrication guidelines doc?
On the PI board....what PI variations can it accommodate?
Also, I would recommend adding a wirepad/Fast-on or ??? right at the neg side of 1st rectifier filter cap....and run PT HT CT there or neg side of bridge rectifier, whichever is pertinent. Reference a second gnd wire to the chassis from there. I always put two wirepads (or fast-ons) at this point on every power supply. The rest of gnd plane can attach here as well.
If you have gnd planes on both sides...it's good practice to stitch them with additional vias, regardless of signal rise times (or frequency, in this case).
Not pcb related (but it can be)....regarding 1/4in jacks. We have found that using TRS types, tying ring & sleeve to gnd....improves reliability. In fact, we don't use TS jacks on anything for this very reason.
Good to know we have a KiCad expert in da haus....
But I'm curious....did you allow for creepage clearance around power supply diodes? When you fire it up, watch for potential arcing....just turn off the lights to really see it. If you don't see it, don't worry about it.
What copper thickness did you specify in your fabrication guidelines doc?
On the PI board....what PI variations can it accommodate?
Also, I would recommend adding a wirepad/Fast-on or ??? right at the neg side of 1st rectifier filter cap....and run PT HT CT there or neg side of bridge rectifier, whichever is pertinent. Reference a second gnd wire to the chassis from there. I always put two wirepads (or fast-ons) at this point on every power supply. The rest of gnd plane can attach here as well.
If you have gnd planes on both sides...it's good practice to stitch them with additional vias, regardless of signal rise times (or frequency, in this case).
Not pcb related (but it can be)....regarding 1/4in jacks. We have found that using TRS types, tying ring & sleeve to gnd....improves reliability. In fact, we don't use TS jacks on anything for this very reason.
Good to know we have a KiCad expert in da haus....
Don't overthink it. Just drink it.
Re: Generic PCB designs - Preamp, LTPI, FX, Power
Thanks and good tips! I've added some comments below:chief mushroom cloud wrote: ↑Sun Aug 26, 2018 3:34 pm Nice work! I like those Phoenix/Weidmuller type screw terminals, too. But be sure to dab a dot of flexible acrylic nail polish into the setscrew wells....they can vibrate loose. I know this from experience.
Ah, this is a great point - I'll be sure to check on first power-up. It's this sort of input that would have been valuable early on! There's always a v2.But I'm curious....did you allow for creepage clearance around power supply diodes? When you fire it up, watch for potential arcing....just turn off the lights to really see it. If you don't see it, don't worry about it.
The high current traces (so heaters and B+) are 2mm wide on 1oz copper. The rest of the traces are 1mm.What copper thickness did you specify in your fabrication guidelines doc?
Restricting to a traditional LTPI, it has spaces for negative feedback / presence control, as well as pads for a fizz cap and space for a 'scale' control as mentioned in Merlin's book. I've also added the heater elevation components to this board as the grounding for it returns to the PI filter cap. Schematic attached.On the PI board....what PI variations can it accommodate?
My grounding is a bit overkill. I have separate audio and chassis grounds throughout. On the power supply board I have multiple connecting points so each filter cap's ground for B+1 and B+2 isn't actually connected through the PCB - they can be configured as required - with the OT connection made to point x or y, e.g., whatever you prefer. Scheme attached.Also, I would recommend adding a wirepad/Fast-on or ??? right at the neg side of 1st rectifier filter cap....and run PT HT CT there or neg side of bridge rectifier, whichever is pertinent. Reference a second gnd wire to the chassis from there. I always put two wirepads (or fast-ons) at this point on every power supply. The rest of gnd plane can attach here as well.
If you have gnd planes on both sides...it's good practice to stitch them with additional vias, regardless of signal rise times (or frequency, in this case).
The copper pours (chassis ground) can be attached to the chassis through normal standoffs, or isolated using a plastic one at one corner. Each board has its audio ground returning to the stage's filter cap negative. Also, there are connecting points on each board for the 'correct' returns to attach - ie, the gain control ground is returned to the following stage's filter cap -ve. The sole connection between audio ground and the chassis can be controlled as one wishes - I'll put it at the furthest point along the chain from the power supply. The grounds can all feed back to a central point (star) or daisy-chained. I tried to keep it generic!
Ha - I wish I was. Many hours of frustration and googling.Good to know we have a KiCad expert in da haus....
Once I know it all works as expected I'll tidy up the files and share - hopefully someone can improve them and we can all benefit with improved versions.
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- chief mushroom cloud
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- Location: Peenemunde CA
Re: Generic PCB designs - Preamp, LTPI, FX, Power
Nice touch w/ the test points. I think your grounding will be fine.
Yea, there's always V2 (or Rev2 if yer 'murican). If......there becomes a version2....I would suggest 1.5mm clearance around rectifier diodes and .75mm clearance around all HT voltage traces. Just to be safe
I have some other suggestions for the power supply...but I'll wait until you get this running, and post them then for 'V2'.
In the meantime, I have to get KiCad loaded up and go thru some Youtube tutorials......
Yea, there's always V2 (or Rev2 if yer 'murican). If......there becomes a version2....I would suggest 1.5mm clearance around rectifier diodes and .75mm clearance around all HT voltage traces. Just to be safe
I have some other suggestions for the power supply...but I'll wait until you get this running, and post them then for 'V2'.
In the meantime, I have to get KiCad loaded up and go thru some Youtube tutorials......
Don't overthink it. Just drink it.
-
- Posts: 136
- Joined: Mon Nov 21, 2016 4:56 pm
Re: Generic PCB designs - Preamp, LTPI, FX, Power
VERY COOL!! this would make prototyping so much faster
Re: Generic PCB designs - Preamp, LTPI, FX, Power
My biggest concern about building a PCB preamp was the use of small capacitors instead of the full size orange drop and mallory caps in the pre amp. I recently opened up a Egnater and Rivera amp to fix them and I noticed the caps were so tiny compared to what we are use to seeing on our hand wired amps. I see here you are using full size caps, that's great!
Thanks for posting Tristan!
Cheers
Guy
Thanks for posting Tristan!
Cheers
Guy
Re: Generic PCB designs - Preamp, LTPI, FX, Power
So an update. After all this time I've finally got it up and running. The wiring is a little messy as I was in a rush, and things started getting a bit tight in there!
More details http://ax84.com/bbs/dm.php?thread=499543 and http://ax84.com/bbs/dm.php?id=501730.
Pleasently surprised all round - all the PCBs worked very well, sounds great, and I haven't started to tweak it yet. No oscillations and worked 1st switch on apart from the OT wires needing to be reversed - boy is this thing loud!
Schematics etc here: https://www.tristancollins.me/ax84/Mutineer/Built/
And once things have settled I'll see how best to share the KiCad PCB files.
More details http://ax84.com/bbs/dm.php?thread=499543 and http://ax84.com/bbs/dm.php?id=501730.
Pleasently surprised all round - all the PCBs worked very well, sounds great, and I haven't started to tweak it yet. No oscillations and worked 1st switch on apart from the OT wires needing to be reversed - boy is this thing loud!
Schematics etc here: https://www.tristancollins.me/ax84/Mutineer/Built/
And once things have settled I'll see how best to share the KiCad PCB files.
You do not have the required permissions to view the files attached to this post.
Re: Generic PCB designs - Preamp, LTPI, FX, Power
Nice work! Were did you get your fx loop board from?
Guy
Guy
Re: Generic PCB designs - Preamp, LTPI, FX, Power
Thanks. Made it myself - borrowing a few designs from here and there, simulating it in LTSpice etc. It's basically Merlin's Practical Series Effects Loop but with LND150s. I wanted the board to be long and narrow so it would fit. Discussion here: https://www.diyaudio.com/forums/instrum ... l-amp.html
The reverb board is a modified form of the Rub-a-Dub Delux, but with extra power supply bits to take a spare 6.3V tap and rectify it to 9V and 5V using some regulators.
Re: Generic PCB designs - Preamp, LTPI, FX, Power
A few more now that it is more complete:
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