SLO Preamp layout

Fun circuit. Try playing with values on that 39k cold cathode stage (try 33k)
Also if you've got tons of fizz lower that 220k plate resister in the (right before) CF stage. It removes a ton of compression.
 
CrazyNutz said:
Fun circuit. Try playing with values on that 39k cold cathode stage (try 33k)
Also if you've got tons of fizz lower that 220k plate resister in the (right before) CF stage. It removes a ton of compression.
Click to expand...
Looking at the Simplified SLO preamp that eliminates the Clean Channel, FX loop and switching.

Looks like this would be perfect for me.
 
PLX said:
Looking at the Simplified SLO preamp that eliminates the Clean Channel, FX loop and switching.

Looks like this would be perfect for me.
Click to expand...

Yeah, I've built them with, and without the FX Loop. It does sound slightly different. I'd say more classic/open without the FX loop, and more modern with.

I will say this, use the orange drop polypropylene caps (the 400v are fine), and the vishay metal film resistors. I've used others, and they don't sound right.

BTW I have a new O'netics power transformer for 100w collecting dust if you're interested.
 
CrazyNutz said:
Yeah, I've built them with, and without the FX Loop. It does sound slightly different. I'd say more classic/open without the FX loop, and more modern with.

I will say this, use the orange drop polypropylene caps (the 400v are fine), and the vishay metal film resistors. I've used others, and they don't sound right.

BTW I have a new O'netics power transformer for 100w collecting dust if you're interested.
Click to expand...
I'd be building the preamp section only.. so I'll probably use a toroidal Antek AS-05T200 I already have on hand.
 
Would it be correct to route the 470kΩ attenuator / .002µF treble peaker network directly to the .02µF coupling cap to eliminate the "clean channel" input jack ?

:unsure:
 
PLX said:
Would it be correct to route the 470kΩ attenuator / .002µF treble peaker network directly to the .02µF coupling cap to eliminate the "clean channel" input jack ?

:unsure:
Click to expand...
You might be able to just use the 2n2 as the coupler and not even use the 470k or 22n. It’s been a while since I built mine but are you talking about that spot real early in the pre where it splits off to the 2 channels?
 
SpiderWars said:
You might be able to just use the 2n2 as the coupler and not even use the 470k or 22n. It’s been a while since I built mine but are you talking about that spot real early in the pre where it splits off to the 2 channels?
Click to expand...
Yes, that's exactly right.

I'm trying to eliminate the clean channel input, the FX loop, and all the switching.
 
Huh? No you need that 470k/2n2 to sound right. Do not eliminate it.

The 470k is attenuating the signal from the previous stage. The 2n2 across it is boosting the treble that is lost in the attenuation.

Do it exactly like this
Simplified_SLO-100_Schematic.png
 
CrazyNutz said:
Huh? No you need that 470k/2n2 to sound right. Do not eliminate it.

The 470k is attenuating the signal from the previous stage. The 2n2 across it is boosting the treble that is lost in the attenuation.

Do it exactly like this
Simplified_SLO-100_Schematic.png
Click to expand...
Yeah, that's how I figured it as well.

jCuKZwu.jpg
 
Also keep the back of that input jack as far away from the board as possible. You might consider bending a bit of copper sheet to shield the back side.

This is a massive source of noise, and oscillation.
 
At least somebody makes good use of those tags.

Since it looks like you’ll have less current flowing thru those 15k power supply droppers you could increase them to hit your voltages. But it might not make much difference.
 
SpiderWars said:
At least somebody makes good use of those tags.

Since it looks like you’ll have less current flowing thru those 15k power supply droppers you could increase them to hit your voltages. But it might not make much difference.
Click to expand...
Since I'm using the Antek toroidal power transformer with 200V secondary, I am gonna have to get that B+ up.

🤷‍♂️
 
SpiderWars said:
At least somebody makes good use of those tags.

Since it looks like you’ll have less current flowing thru those 15k power supply droppers you could increase them to hit your voltages. But it might not make much difference.
Click to expand...

Good idea. He actually only needs to increase the one on the input tube. Maybe 20k

But I would get it together, and measure. The voltage on pin 6 of V1 should be around 185v
 
PLX said:
Since I'm using the Antek toroidal power transformer with 200V secondary, I am gonna have to get that B+ up.

🤷‍♂️
Click to expand...

Yikes. You might want to reconsider that transformer.

I've done lower voltage SLO, you can get a nice brown sound. But you're way low.

if you do full bridge rectification you'll probably be around 280vdc
 
CrazyNutz said:
Yikes. You might want to reconsider that transformer.

I've done lower voltage SLO, you can get a nice brown sound. But you're way low.
Click to expand...
Thinking the same thing.

Plan calls for a Fender Princeton type PT.

Will be overkill because it's just a preamp (no power tubes)
 
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