Point-to-point SLO preamp build w/ relay switching

[bancika]

Wanted to share my latest project - SLO preamp with relay switching instead of LDRs. I challenged myself to put it together in a relatively small enclosure (250 x 180 x 80mm) and wire the main circuit point-to-point. To make it even more challenging, I designed the layout in three dimensions to optimize signal path and minimize the space. There's a ground bus that everything is connected to. Components are arranged in three Z-layers - bottom layer with power supply components, the layer with components that go from tube sockets to ground, the layer with coupling and grid components. There are also few resistors that go between the top layer and ground bus.

Heaters are powered with 12.6VAC to reduce the current and they are elevated to ~50V. For relay switching I used a relatively simple method. Heater voltage is rectified and regulated to 12V. P-MOSFET is used to drive the multi-colored LED and toggle between two colors designating two main channels. Channels can be switched either using the panel switch or a footswitch.

I intentionally omitted the EQ because I want to use it either with a graphic EQ pedal or connected straight into the interface and have VST EQs applied. It's easy enough to add a shared EQ before the volume pots, slightly more complicated to do dedicated EQs with another DPDT relay.

As far as components go - custom toroidal transformers, alpha pots, russian PIO coupling capacitors, Panasonic HV electrolytics, xicon resistors, miyama switches, JJ tubes, panasonic film 1uF caps for cathodes...

It turned out great. There are no clicks or pops from the relay, voltages are pretty close to the official schematic and noise is very low for a high gain amp. The layout makes it easy to choose between having completely isolated channels or have clean bleed into the overdrive. There doesn't seem to be a big difference but I think I prefer to have them isolated. Connecting two terminals together makes the normal channel always on.

This is how the main module looks assembled. There's one aluminum L profile that holds tube sockets. Using four 50mm hex standoffs I connected two terminal strips with 13 contacts each.



and from the side showing different layers



A few components are mounted directly on the controls



The switching circuit is on a separate terminal strip.



The relay is mounted in a wire-wrap socket soldered directly on the main module



Here's the whole preamp assembled



And from the front. Knob color matches the color of the LED - blue for normal, red for overdrive channel.



The article with more pics and info is here http://diy-fever.com/amps/soldano-preamp-mk2/ will update it with more info and clips soon.

Full sized layout here http://diy-fever.com/wordpress/wp-conte ... out_v5.png

[M Fowler]

Incredible work which I really appreciate since I build preamps into old toasters and space is tight.

Mark

[xtian]

Fully OCD. I love it.

[ChopSauce]

Awesome

Thanks for sharing

[pompeiisneaks]

HOLY

CRAP

Outstanding work!

~Phil

[bancika]

Thanks everyone!

Adding few quick recordings. The first one is preamp straight into the interface. In reaper I added some EQ, Marshall JTM45 sim and a touch of reverb. The second one is pretty much the same settings but with Timmy overdrive at the front with gain set pretty low and Bass above noon to tighten up the sound.



Cheers

Edit: pompeiisneaks edited and linked the MP3 so it's playable from the site, just add mp3 tags around it by highlighting the link and clicking the "mp3" button in the editor mode.

[Deric]

Sounds great!

Thanks for sharing!

[pompeiisneaks]

Damn sounds good! I edited your post to link the MP3's inline so people can give them a listen right here.

~Phil

[bancika]

Thanks, good to know. Here's another one. Timmy OD with gain set pretty low to tighten the bass in front of the SLO (gain at noon). In Reaper I have clean marshall sim (LePou) and two rosen digital impulses panned hard left/right. Could probably tweak the EQ to sound better, but I prefer this to the previous recordings that have a bit of a "digital" quality to them.

[loctal]

Super nice PTP, thanks for the documentation. Makes me miss my SLO 100.

[bancika]

Thanks! Few more sounds

My mini telecaster with neck pickup on, crunch channel with a touch of overdrive at the front



Same guitar, similar settings



Another guitar with Dimarzio Fred in the bridge, lead channel with no boost at the front, gain set around noon



One more with ibanez, going after Petrucci's tone. Added V shaped EQ that mimics Mark graphic EQ settings and recto cab impulses. There's a touch of univibe (chorus settings) to fake double tracking.

[pompeiisneaks]

I saw you post that on FB and had someone wanting to have you build them one asap

~Phil

[dynaman]

This.....is awesome.

[tubeswell]

Pretty awesome indeed.

[ericlc]

Wow. Excellent piece of work