Clean Preamp for DIY practice amp - suggestions please

Grubb

Grubb

Well-known member
Hi folks, I have decided to build my kids a practice amp for Christmas seeing as they have started playing recently. So far the plan is to use Erik Vincent's 10 Minute Amp circuit (7W class A-B power amp) and a Belton brick reverb like the Boing. I just need a Fendery clean preamp as the front end of the amp, preferably something I can DIY. I was considering waiting for the Doxie but then I read that they perform best in front of a full guitar amp, whereas I want something that can go straight into the power amp section. Any suggestions?
 
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Yep, I think that's perfect, thank you @Elijah-Baley

Here's what I've got so far, the only part of the circuit I'm not confident about is the speaker protection segment. I found a circuit that uses a 555 timer IC to drive a relay closed for about 5 seconds, which I'm hoping will help me avoid thuds and pops through the speaker cabinet. I might try and trim it to 3 seconds if I can work out how to set the R and C values.

Amped.png

I took some visual cues from the Keeley Aria with the look of the enclosure design, it's currently planned for a 1590XX but I'll see how big it ends up. My daughter has no idea about this project and today asked for an amp for Christmas so there's a fair chance this will be a winner as far as presents go!

Amped v2.png
 
Updates: The good folks at DIY Stompboxes helped me simplify and improve the design. It now has a Mach 1-flavoured clipping section going into the Tonemender tonestack. Switching for the reverb was removed as the circuit has a dry path that is always on, so the knob can control whether or not the reverb is active. And the amplifier chip has built-in soft-start capability, so the speaker mute circuit was removed. Overall I'm pretty happy with the results so far.

Schematic:
Amped.png

Updated exterior (1590xx, Tayda light gold):
Amped V3.png

PCB:
Amped.png

Can anyone spot the neat symmetry cheat I learned from Robert? :LOL:
 
Grubb said:
Updates: The good folks at DIY Stompboxes helped me simplify and improve the design. It now has a Mach 1-flavoured clipping section going into the Tonemender tonestack. Switching for the reverb was removed as the circuit has a dry path that is always on, so the knob can control whether or not the reverb is active. And the amplifier chip has built-in soft-start capability, so the speaker mute circuit was removed. Overall I'm pretty happy with the results so far.

Schematic:
View attachment 34344

Updated exterior (1590xx, Tayda light gold):
View attachment 34347

PCB:
View attachment 34346

Can anyone spot the neat symmetry cheat I learned from Robert? :LOL:
Click to expand...
Re "symmetry cheat" ... you mean like where your lightning bolt logo is to replace an electrolytic and the "NRG" text & logo to make up for the cap and resistor ?
 
Grubb said:
Haha that's exactly right. I was looking at PCBs here the other day and I noticed some "caps" with logos rather than values and I was floored by the genius of it 😂
Click to expand...
Do I win one of your Christmas boards?


Seriously, though, I think your kids are gonna be well chuffed.


I might try to layout a perf of your schematic, if that's okay with you.
 
Feral Feline said:
Do I win one of your Christmas boards?
Seriously, though, I think your kids are gonna be well chuffed.
I might try to layout a perf of your schematic, if that's okay with you.
Click to expand...
There may well be spare boards that I'm unlikely to build. The downside with rolling my own PCBs is that I always end up with spares as there's a 5-board minimum order. But perf away if you prefer, I shared in the hope it would be useful to someone else. None of these circuits are mine in the first place!
 
Oops, so I made a slight mistake with my board for this project. I accidentally put the wrong DPDT switch DipTrace component in my PCB design and didn't pick up the error. Now I have physical boards that won't fit a mini or sub-mini DPDT toggle.

Anyone know what kind of DPDT switch might work with 2.54mm pin spacing in both horizontal and vertical directions?

1670133697435.png
 
Grubb said:
Oops, so I made a slight mistake with my board for this project. I accidentally put the wrong DPDT switch DipTrace component in my PCB design and didn't pick up the error. Now I have physical boards that won't fit a mini or sub-mini DPDT toggle.

Anyone know what kind of DPDT switch might work with 2.54mm pin spacing in both horizontal and vertical directions?

View attachment 37284
Click to expand...

What about a 3PDT toggle with one column of lugs cut off? Problem with that is the switch will be off-centre.

Offboard wire a micro-switch, if possible. Maybe... Offboard wire the mids switch & the Mids knob and manoeuvre their positions a tad, swapped or ?

I've looked at some slide switches, too, but nothing comes up with 2.54 on both X & Y axis.



How'bouit a pushbutton that you have to bend the pins a tad? This one has a 2.54 spacing vertically, and 2X that spacing horizontally, so maybe the pins could/would
be able to reach with a bit of bending...

LEAP#244 Switches/DPDT

all about double-pole, double-thow (DPDT) toggle switches
leap.tardate.com leap.tardate.com
Ahh never mind that one, it's common pins are 3 and 6. Never seen that before in a DPDT, common's always been 2 and 5.

...still, a pushbutton might be out there that fits...
 
Get on the SushiBox FX thread and check out the Echo Foxtrot for a simple clean TUBE driven preamp. It's got a EF86 preamp tube which is not a Fender approach. . . . BUT. . . . if you can wait I know that Nathan is working on a DIY blackface Fender preamp that I expect (hope) is not too far off from release. It should be a simple straightforward AB763 circuit w/ Gain, Bass, Mid, Treb, Vol. I am salivating just thinking about it.
 
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