Rosamp SLO50 Soldano Clone Clean Channel Issue

[RoadShow]

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.

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
(Sorry, I tried to line these up with spaces or tabs, but they were removed)

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.

Rosamp schematic attached…

Thank you.

[acheld]

Hmmm.  Very complex amp, and I speak from experience having built a similar Slo100 clone early in my experience level. 

Hoffman's (and many others) first rule when getting unexpected results from a build is to pull out a fresh copy of your schematic and go through your build making sure each and every node is making the connection you have expected.  Mark your schematic.  Make sure each cap and resistor is what you expect.  Check that your VTRL5C1's are wired correctly and their resistance is in spec.    Go node by node to find a mistake if there is one.   Take your time.  Bear into it.

This is tedious, but necessary.  The odds are there will be an error. 

I would also contact Rosamp and ask their opinion.   

If it really is built to spec, there are things you can do to bring up the volume of the clean channel, but as you understand from Kuenehl's book, the key to this amp is the interaction between the stages (and I fully confess to not understanding it as well as I'd like). 

[RoadShow]

Hmmm.  Very complex amp, and I speak from experience having built a similar Slo100 clone early in my experience level. 

Hoffman's (and many others) first rule when getting unexpected results from a build is to pull out a fresh copy of your schematic and go through your build making sure each and every node is making the connection you have expected.  Mark your schematic.  Make sure each cap and resistor is what you expect.  Check that your VTRL5C1's are wired correctly and their resistance is in spec.    Go node by node to find a mistake if there is one.   Take your time.  Bear into it.

This is tedious, but necessary.  The odds are there will be an error. 

I would also contact Rosamp and ask their opinion.   

If it really is built to spec, there are things you can do to bring up the volume of the clean channel, but as you understand from Kuenehl's book, the key to this amp is the interaction between the stages (and I fully confess to not understanding it as well as I'd like).

I couldn't work on this anymore last night, I had to go to the Predators hockey game. They won! Yea!

But, I was doing thinking that the LED switches were behaving as they should, and to investigate the mechanical switch wiring.

So, I disconnected the input to S1-2 and S1-6 output and just jumpered in the resistor networks.

Huge jump in the voltage to the pot and the output at the speakers.

Although I looked over the wiring of S1 & S2 multiple times, there has to be a mistake there. So, I'll tear into that and figure it out.

Thanks for the attention and suggestions.  I'll let you know what happens.