first amp build - choice of pre-amp and some really stupid questions

[incurably_optimistic]

Welcome back!
I finally bought myself a little dremel tool for cutting metal which allowed me to (almost) finish my project!
The head section of the amp is more or less ready. I didn't have a shielded wire at hand so I used a regular wire for all the wiring, but once I get myself some I'll surely fix it - however, the noise doesn't seem to be an issue so far. I may make some shielding for the preamp in the future if I feel like it. I don't have a dedicated guitar speaker, so I just connected it to the speaker from my stereo system - sounds quite nice, and it's going to sound only better with a real guitar speaker!

I live in a block of flats so I couldn't really test it at anything close to full volume, but after an hour of low-to-mid volume playing the heatsink didn't really get warm at all, so I think it's a good sign for the things to come. I think that heatsink should be enough for a single LM3886, right?

I haven't yet decided whether it's going to be just a standalone guitar head or a combo amp, so the speaker wiring is just temporary for test purposes, don't rip me for that!  :trouble But here are some pictures (click to make it larger):




I'm sorry exztinct01, but I cannot record any sound clips, because I don't have a microphone    It's all good though, because I'm a terrible guitar player so you don't have to listen to my terrible attempts to catch a clean chord  :lmao: however, when I'll figure out a way to record a sample with a good audio quality I'll make sure to invite a friend who can play well and post something here.

I tried it with a guitar plugged straight into the amp and with a modded tubescreamer I made and it sounds fine either way  :dbtu:

[exztinct01]

mine still squeals when I add a distortion pedal in front of the preamp. I'll try putting the distortion after the preamp and see if it minimizes noise.
Did you reduce the gain of your preamp from Rod's original 27db?

[incurably_optimistic]

no, I left the gain settings more or less unchanged.
I haven't yet tried it with master pot cranked up at maximum, I did however max the "volume" (or "gain") pot and noticed no squeal. Did you test your amp with different guitars? Sometimes a noisy/high output pickup + a lot of gain = squeal, so grab another guitar and see if the problem persists.

[exztinct01]

does the schematic of the p27 preamp have the supply bypass caps for the opamps or should I add it?
I didn't put 0.1uF caps there
or maybe Rod put it there but different values?

[incurably_optimistic]

it's C11 on this schematic:



in case you are asking about my layout for the preamp - yeah, I forgot to put it on the board, but it works fine as it is.