Title really should be Building Modifiable Circuits.

I've built an analog amplifier for my acoustic/electric guitar. The amplifier part uses a LM1875 chip amp, and is working great. Now I need to build a preamp, but it's challenging because I put the circuit on perfboard after testing in a breadboard, and there are many connections from the perfboard to the front panel of the amp, so it's challenging to do the work because of all the wires in the way. I have plenty of space on the perfboard to build a preamp, and the OPA2134 audio quality op-amps are on their way to my house, but wiring them into the circuit is going to be challenging.

I was looking at videos of people doing DIY builds of tube amps, and I saw they were using turret boards, where the components are soldered onto pins that are stuck in a fiberglass board. This is a lot easier to modify and work on than a board where the wires and components are on opposite sides.

I was wondering if anyone knew of techniques to either make many low noise (shielded wire) connections to the front plate easily removable, or to have the components and the connections all on the same side of the perfboard. One thought was the header pins that they use for things like an Arduino - just solder the short end of the pins in on the underside of the board, and then connect the wires to the tall parts of the pins. Any experience with this, or any other good method to build a component that can be modded without too much difficulty?

Regards,
Martin

 

One thought was the header pins that they use for things like an Arduino - just solder the short end of the pins in on the underside of the board, and then connect the wires to the tall parts of the pins. Any experience with this

I've done exactly that for a preamp I built. It has an ESP32 web UI for volume control and source selection, so I was already using 0.1" pitch dupont connectors for the digital wiring. You can buy a connector kit and suitable crimper to make cables with sockets to plug onto the headers

 

I've built an analog amplifier for my acoustic/electric guitar. The amplifier part uses a LM1875 chip amp, and is working great. Now I need to build a preamp

If the amp is working great, what is it that you want to do with a preamp?

What controls do you want in the front panel? These days, the controls and jacks are usually positioned on the edge of the board to line up with holes in the panel, hence no wiring.

 

Use 0.1” pitch pin and socket headers or even DIP IC sockets to connect a daughter board to the motherboard. You don’t need shielded cable of low impedance signals.

 

One thought was the header pins that they use for things like an Arduino - just solder the short end of the pins in on the underside of the board, and then connect the wires to the tall parts of the pins

Once you have the header in place, solder the external wires to a single-row strip socket that plugs onto the header. In this way, the perfboard can be removed easily for modification rather than trying to turn it over and unsolder/solder stuff with all of the external wires still attached.

ak

 

If the amp is working great, what is it that you want to do with a preamp?

What controls do you want in the front panel? These days, the controls and jacks are usually positioned on the edge of the board to line up with holes in the panel, hence no wiring.

Well, the amp works, but doesn't have enough gain. I need a preamp to get the signal out of the acoustic guitar up to a level that the power amp can amplify enough to make it more than barely audible.

 

S.c.h.e.m.a.t.i.c . . .

 

S.c.h.e.m.a.t.i.c . . .

Does that help?

Power supply for the preamp is a generic +/- 15 V using LM317/337, powered off the unregulated power amp supply. Replace the tone control on the power amp with the preamp as shown.