Splawn Quickrod Mods

[Bukak65]

Hi,

I have a 3 preamp Splawn Quickrod and love the thing but I wish it was thicker sounding. Does anyone have any mods that can fix this problem? Or any mods that I can do?
thank you.

[HTH]

imo C4 (1000pF) doesn't need to be there. you may need to remove C17 (1nF) or make it slightly smaller to your taste once C4 is removed - it'll take away a fair amount of thinness and chunk things up.

I'd probably look at bringing R22 (47k) down to 33k for a bit more low mids, but this will alter the 'bite' you have in the mids to more of a classic Marshall 'growl', experiment.

[Bukak65]

Hi,
Thank you for the reply. Run a jumper across C4? What value do you recommend for C17? I forgot to mention I'm using 6550 tubes.

[Tage]

Don't jumper C4, you want to remove it, otherwise the 470K resister will be shorted b your jumper. you wan't that resistance there to help attenuate some of the signal hitting the next stage, as it forms a potential divider with R12/R14 and helps limit the signal the second gain stage sees. that 470k also helps reduce blocking distortion, although I believe it was simply included here because it's what Marshal did. removing that cap is a common mod on jmp's and JCM800's.

I would reduce the coupling cap sizes to around 1/4 to 1/10 there size, a 22000pF for C1 and 47000pF for C5, not classic marshall/fender values but I think they help make a good mid strong sound IMHO

[Bukak65]

Hi,
Thanks for the reply. Would you reduce R22 (47k) down to 33k for a bit more low mids with your suggestions above? Also what would you do with C17?

[Tage]

well 33k is the marshall value, but you need to remember that in a marshall the tone stack is fed from a cathode follower, and because of it's low output impedance it does not get dragged down by the 33k slope resister. I'm sure the 47k was ettled on as a happy medium by the Splawn guys, after all most amps that use this tone stack without a cathode follower have a 100k resister in that position.

You should use the duncan amps tone stack calculator, use the "fender" one and input the values you have into it and see what it's response is like.

I'd also agree about C17, I think trying a 500p then a 220p would be a good way to start.