How to tame soldano's slo overdrive channel.

[FranciscoPerez]

Hi all!!

As a Chirstmas project, I recently rebuilt a 50Watt turret board version of the SLO I had taking dust on the shelf which had several hum issues due to a wrong grounding scheme. I've built a few of these for some friends but this was the first one back when I started building amps and was a complete mess ,so it called for a total rebuild!! Now it's working great, no hum issues.

I'm not a big fan of this amp, but after a few mods the clean/crunch channel is sounding good to my taste. However the overdrive channel in this amp is far too aggressive for me. I lowered v2b cathode resistor to 12k and changed the power rail resistor R63 ( the one that sets the voltage for v2) to 40K to get lower plate voltages. It helped but it's still too loud and too aggressive :(
The preamp and master volumes are practically useless at apartment levels, and there's too much gain present even at the lowest preamp knob settings.
I also thought about swapping v2 from a 12ax7 to a 5751 or even a 12ay7. Do you think it'd be a good idea in this situation?

How would you tame this beast??? Any ideas?
http://www.el34world.com/charts/Schematics/files/soldano/soldano_slo100.pdf

Thank you very much!!!!
Hope you're having a great Christmas!

Cheers,
Fran

[birt]

as an experiment you could try a 12AT7 or 12AY7 in V2.

my 2203 has a PPIMV and i have a 12AT7 in V1 to tame the gain a bit. (maybe also in V2, i'd have to check it)

[tubenit]

Change the 1M to ground between V2a &V2b to 470k or 330k,  then use a 5751 for V2.

with respect,  Tubenit

[FranciscoPerez]

Thanks birt and tubenit!!

I just tried both a 5751 and a 6072 and it improved indeed! There's still plenty of gain but now I can get close to what I like with very low preamp settings.
I'll go and change that voltage divider's resistor and let you know!

Thank you!!!!

[tubenit]

You can parallel another 1M across the existing 1M to get 500k.  IF you don't like it, just remove the paralleled 1M

with respect, Tubenit

[FranciscoPerez]

Thanks tubenit,
Yes, I did parallel a couple of also paralleled 1M resistors resulting in a total resistance of about 330k, as you suggested.
I'm really happy with the result!!!  The amp sounds great, still lots of gain if needed but without any harshness and the controls are quite more usable. What an improvement !!!!!

[alerich]

When I modded my old Peavey 5150/6505 (closely based on the SLO preamp) 330K was also the value I ended up with for that resistor. It was the sweet spot between taming the gain and strangling the preamp. Some people lower that resistor even further but I think that chokes the preamp dynamics. 500K was still to aggressive to me. It makes the gain control usable - still lots of gain on tap but you can actually use most of the range of the control. with the 1M resistor everything after 4 on the gain control was irrelevant because it was just mush. Several folks told me it was the best sounding 6505 they had ever heard and it's such a simple mod.

[tubenit]

Yes, I did parallel a couple of also paralleled 1M resistors resulting in a total resistance of about 330k, as you suggested.
I'm really happy with the result!!!  icon_biggrin The amp sounds great, still lots of gain if needed but without any harshness and the controls are quite more usable. What an improvement !!!!!

Very cool!  THANKS for taking the time to share the results of the experiment.  Glad to hear it worked out reasonably well for you.

With respect, Tubenit

[FranciscoPerez]

I totally agree with you  alerich! It's a really simple mod that makes such a big improvement.
I'm leaving the amp as it is now, for it's sounding great!!!
For lack of a speaker cabinet for the amp, I'm connecting the head to my 5e8a combo cabinet loaded with a pair of alnicos (weber 12A150 and 12A150B), and they're quite a good match.

Thanks you all for your tips and suggestions!!
Cheers,
Fran

[FranciscoPerez]

Took a couple of pictures of the amp before installing it into the head cab.
Hope you like it!!
It's a little messy but makes no hum at all, just some hiss with the overdrive channel cranked up.





And a picture of the mod, the extra two paralleled 1M resistors and 10K v2 cathode resistor

[smackoj]

If that bird is "a little messy" then I must be seeing things. Looks mighty tighty to me.

 

[darkbluemurder]

That lead channel in its stock format is indeed a monster.
A good mod is to lower the 22nf coupling cap after the 2nd gain stage to 4n7f and change the 470k/1M voltage divider to 470k/470k.
To tame the loudness of the OD channel, swap the 1MA pot for a 500kA and add a 470k resistor before the input/CW terminal of the OD master.
Cheers Stephan

[FranciscoPerez]

Thanks smackoj! :)
I'll try that Stephan, It'd be great to tame the OD channel a little bit more. Thank you!!