Rosamp SLO50 Soldano Clone Clean Channel Issue

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Hello,

Wanting a Soldano amp I could afford, I looked into several approaches to building this amp. Among approaches investigated I dug into the Sloclone forum, read Rob Roninette’s web page, and bought the Kuehnel Soldano SLO book. I put my best foot forward into understanding how the amp was constructed and worked. In the end, the Rosamp SLO50 looked like a great way to go because it was a complete solution with the chassis and all elements in one package, and I am in fact happy that I went that direction.

I've reviewed a lot of successful Rosamp builds on this forum, and they don't seem to have this issue.

Once built, everything worked as expected. Almost. Clean, crunch, overdrive, tone controls, FX, and so on worked and it’s a very quiet amp. So, I feel great about the decision.

However, the volume output of the amp on the clean channel, with or without crunch enabled, is nowhere near the volume of the overdrive channel. Despite the attenuation difference, selecting clean or crunch makes no real difference in the audible volume level when the channel is selected.

Now, I understand the differences in the channels and that there will indeed be differences in the dB levels and as such the perceived volume level, but what I have is really beyond that. Individual preamp and master volume controls are there to help set similar audible levels when switching between the two.

These setting have similar audio volume levels to my ears.


PreAmp Gain setting​
Master volume setting​
Clean​
Overdrive​
Clean​
Overdrive​
11​
11​
8​
1​
8​
1​
11​
11​

So, what I’m saying here is:
· With both preamp gains set all the way up, setting the master volume of the clean channel to 8 gives the same audible level as the overdrive master set to 1.
· Similarly, with both master volumes all the way up, having the clean channel cranked to 8 gives the same audible level as the overdrive set to 1.

I watched videos on Youtube on Rosamp builds to note the gain and MV settings, and they don’t have to wide difference I have, they are somewhat close to each other. I’ve reviewed my work several times and just can’t find an issue I may have created. When building the amp I verified resistor values. I also believe the optical switches to be working correctly because the system does work. I’m hoping for help resolving and issue with the clean channel on this Rosamp SLO50 build.

Because I can't upload the full schematic pdf I've just included a screenshot of the Rosamp schematic up to the phase inverter. The full schematic loses a lot of readability when screenshot.


Thank you.
 

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Have you tried jumping R17 with alligator clips if it brings Clean vol up? I’d start from there if there’s no cold solder spots or other problems you catch visually or with DMM.

If jumping R17 works, maybe change Clean side switching circuit same as in OD side.

IMG_7761.jpeg
Edit. hold your horses and do next thing first!

IMG_7762.jpeg
Okay, seems like Rob’s schematic has same 2.2M attentuator after clean channel too, but maybe that leads somewhere? 2.2M attentuates approx 87% signal strength SO maybe you have just really weak or faulty tube in V1 spot?

Best tube amp troubleshooting trick ever; TRY ANOTHER TUBE!

All brand new tubes aren’t always good or strong enough tubes.
 
Last edited:
i’ve built the 100W version of this.

selecting the crunch mode (from clean) in the ‘normal channel’ should result in a large output volume increase.

if that’s not happening, i’d suggest carefully reviewing the wiring around the toggle switches, for a start.

the amp shouldn’t need mods to make it operate properly.

having said that, it appears to be normal to require the master volume on the clean/normal channel to be turned up a lot more than the OD/lead channel master volume for balanced output.
(assuming you’re running the clean channel ‘clean’. cos if you blast it with a loud fuzz/distortion, well that’s another story)
 
Thanks for all the input. I’ve tried the suggestion, thanks, but they didn’t quite pan out. One of the first things I did was swap tubes. Yes, crunch is a boost. Not using pedals at this point. I'm trying to boost the clean as it's sooo much lower than the crunch and especially the OD. Note my settings above.

I decided to put a scope on everything and see what’s what. I put a tone generator with a 500Hz @ 64 mV at the input. You can follow the signal through the front end and see the results in the attached pic, all voltages are p-p.

Just some note clarifications:
CL = Clean Channel
CR = Crunch
OD = Overdrive
VR2-3 is the input to the pot
VR2-2 is the pot wiper arm
VR2-2 @ 3 is the pot with the wiper arm set at 3

I pulled R7 39k from ground and made measurements with 56k & 100k resistors added in series to lessen the attenuation in Clean mode. You can see the increases for each before and after V1A. I got better volume without making it dirty.

Jumpering out R17 2M2 made a big difference by changing that attenuation circuit. However, it was close to crunch. I played with values down to 330k. This maintained the clean strumming at the bench.

I felt the OD circuit was way way too much for me, so I put a 220k in parallel with R13 1M dropping the input to V2B from 68% of the signal to 28%. I like it a lot better.

I tried dropping the V1A cathode resistor R16 2k2 to 1k8 to boost the V1A gain. Jumpering a 10k across it made it a 1k8, but the gain only went from 20 to 23. Tried a cap across it to.

So, I’m settling in on these changes:
  • Parallel R17 2M2 with 330k to make it 287k
  • Add 100k in series with R7 making it 139k.
Thoughts?
 

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