trinityamps.com

Hello,

I'm new to this forum.
I'm modifying my 18w combo that I built years ago. I'm turning it into a plexi style 18w (based on Richard Johnson schematic). Regarding all the mods in these pages, I have a question about the "clean boost switch". Can this switch be installed on the front panel? I mean, is there any advice about how to wire it (twisted wire, shielded wire?) in order to avoid any hum?

thanks,

rgds,

Ed

Take look at mapmaker's n5x schematic and layout for front switching. You can do it with or without the charge resistors. no pop or with pop when flicked.

Rhos os the referred to schematic. Let us know how it works for you.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Hello coco and sazafraz,

thanks for your help. I did put the switch at the rear for a first test. But with the combo version, it's not the best location...
I'll try to wire it for front switching.
As the amp has now two free holes on the face plate (there are two inputs now, high and low), I can put two switches. One is dedicated for the cascade mod, and I wasn't sure if a bright switch should be usefull, the amp has quite enough sparkle already. And if we want more treble, we just turn the treble pot.

I'm amazed about how it sounds. It's LOUD and the cleans are beautifull. It's not as "brownish" as the audio clip posted by Unimind but that's the reason I haven't done all these mods. Just wanted to keep a 70s taste for that amp.

thanks,

rgds,

Ed.

just a question about the RX5,

the charge resistors are R5 and R6 here?

thanks,

Yes

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Hello,

sorry for this noob question but there is something i don't understand in NX5 schematic.
The boost is actually a cap (.68uF) in parallel with the 2k7 resistor, isn't it?
So, according to the schematic, applied to an on/off switch or two position, if we consider C2 (.68uF), in series with R6 resistor (47K) :

1)right position : R6 is shunt and ground is directly linked to C2. That's the boost position.
2)off position (we don't want the effect of the cap) : R6 will be at the ground, but the cap is still in series. So does it mean that this R6 resistor cancels the effect of the cap by discharging it? it would end with 2 resistors (2k7 and 47k in //, so more or less 2k5)

thanks,

rgds

cap's pass ac but block dc

So with the 47k in series with the cap you just have the 2k7 resistor and because the potentional voltage at the cathode of the tube is positive compared to ground the cap gets a positive charge

With the 47k bypassed the cap has a path to ground and can boost the higher frequency . with the nx5 the other cap 47uf will also boost lower frequencys i.e. fat

Hello,

thanks for these technical informations.
I've found this site that explains this :

http://sound.westhost.com/valves/bias-gain.html

But i don't know if by using Rcathode = 2.7k in // with (0.68uF in series with 47k), i will have the same gain (specially when switch is off) as found on Stephen's schematic/layout...

rgds,

Hello,

finally done the front wiring for the boost switch and it works fine. And there is no "pop" anymore.
I've also made some changes (because I found normal channel too dark and muddy): coupling caps for the first stage : .022uF for bright channel, .01uF for normal channel (but it has still more bass than bright channel), and put 47uF for the cathode bypass cap for normal channel (instead of 220uF before the change). It may not feel brownish like this but cleans are really great (which i'm using most on my amps) and fat.
I wait to test it like this at high volume (this amp is LOUD as hell for a 18W!), maybe I'll have to change some values, but I like it like this.

thanks,

Ed