Soldano SLO50 build

[Lothy]

Greetings,

I know, there is a dedicated Soldano board, but if someone uses the search function here, I want to give him/her the opportunity to to find solutions to some problems I stumbled uppon.
First of all, I don't wanted the regular Soldano look for the amp. I'm a big fan of Dumble style amps and so I decided to layout the chassis in the way we all know and love. Here is, how it looks:

IMG_20220110_205256.jpg

In the original layout, the preamp tubes are at the front, close to the pots. I was a bit concerned about the long cable runs, especially for the tone stack, but that was no problem at all.

The build was very straight forward, I used a PCB I found on Ebay and for the Powerboard a design from the German TubeTown forum, which has the DC-heater supply integrated.
To keep hum down, DC heater, for at least the first 2 preamp tubes and isolated jacks are crutial. And there was my first mistake, or not, as we'll see. I used an isolated jack for the footswitch connection as well. When I turned it on the first time, everything seems to work. But there was a terrible hum in the clean channel. Double checked the schematic and found 2 missing parts, but nothing what can cause the hum.

The next day, I realized, that the ground reference for the switching power supply runs over a non isolated jack. No problem, just clip an a lead to the chassis and - boom, the small rectifier has bitten the dust in smoke. No more switching, but the hum was gone. After sacrificing another rectifier, I needed to find out what was wrong. After one or two days of moaning and weeping I found out, that I connected the center tap of the second heater winding to ground. What a bummer and what a dumb moron I am...

After solving that, the amp was dead quiet and works perfect. I have a short demo here, but that was before the fix:



Next problem was the fx-loop. Some of my reverb and delay pedals tend to distort. Also in the OD channel delay and reverb are very dull and allmost not present. Fortunately there was a fix with an additional cathod resistor (R50) before the loop and a cathod bypass cap (C13) in the recovery stage:

slo_fxloopmod.PNG

All in all, this amp sound great. And I can imagine the power supply and power amp configuration could be a very healthy part of a Dumble build.

I still waiting for a proper headshell. I let you know how it looks, when it arrives.

Here is everything you need, if you want to build one like this, including the files for the faceplate, which took me a lot of time to create.

https://drive.google.com/open?id=12wsV4 ... p=drive_fs

Hope this all helps.

Cheers
Gerhard

[professormudd]

Sounds great!

[bepone]

excellent! i had also several builds of SLO, one even point to point.. also had in hand HR50 orig.. with soldano it is not possible to have bad tones

which output transformer is? by colors.. looks like they are from tube town ?

[Ten Over]

The effects loop mod radically changes the gain at the grid of V4A, thereby changing the sound of the amp. Here is a design that doesn't change the gain.

FX LP Dual CF 6.png

[Lothy]

excellent! i had also several builds of SLO, one even point to point.. also had in hand HR50 orig.. with soldano it is not possible to have bad tones

which output transformer is? by colors.. looks like they are from tube town ?

I've seen a very pretty PTP build in the SloClone forum. Is that yours?

Yes, all the parts are from Tube Town.

@Ten Over
I haven't realized a big change in tone. But I haven't done an A-B comparison.
But the delays are slightly to dull for my taste. Does the 22u help me out with this?

Cheers
Gerhard

[bepone]

I've seen a very pretty PTP build in the SloClone forum. Is that yours?

Yes, all the parts are from Tube Town.

yes i have published something there years ago it was the test for the p2p if can handle high gain, without any problem! sound was really good and noise low.

But the delays are slightly to dull for my taste.

problem here is the 100k resistor coming from the cathode to the 1k (in your schema), this is forming RC low pass filter with the cabling and your delay in fx loop. so or you make another buffer (simple FET follower) for the delay and effects which will be in the pedal chain, or you can play with this 100k..
add in parallel 50pF, 100pF, 220pF, 470pF.. see what you will like..this roll of heighs is working with your tone, keeping it more smooth, not harsh, which is good, but i assume that you want that "wet effect"of OD+delay which is +level up in the tone

[Ten Over]

But the delays are slightly to dull for my taste. Does the 22u help me out with this?

The bypass capacitor on V4B?

[Ten Over]

problem here is the 100k resistor coming from the cathode to the 1k (in your schema), this is forming RC low pass filter with the cabling and your delay in fx loop. so or you make another buffer (simple FET follower) for the delay and effects which will be in the pedal chain, or you can play with this 100k..
add in parallel 50pF, 100pF, 220pF, 470pF.. see what you will like..this roll of heighs is working with your tone, keeping it more smooth, not harsh, which is good, but i assume that you want that "wet effect"of OD+delay which is +level up in the tone

The output impedance at the FX Send jack with the 1k resistor installed is:
Ro = (100k + 488) || (2.2k || 1k) = 100,488 || 687.5 = 683
The capacitance of 15 meters of cable @ 105pF / meter = 1.575nF
The corner frequency = 1 / (2*pi*1.575nF*683) = 148kHz

There is no RC low pass filter problem here.

[Lothy]

But the delays are slightly to dull for my taste. Does the 22u help me out with this?

The bypass capacitor on V4B?

Yes. I have a 1u there. But propablely not. I figured out, I have to use a different approach to dial in my Delay as I do it with my Dumble clone.
The loop is in front of the tone stack and a muddy analog delay is not what you want there. I use the studio setting on my Volante, and it works pretty good.

Cheers
Gerhard

[bepone]

problem here is the 100k resistor coming from the cathode to the 1k (in your schema), this is forming RC low pass filter with the cabling and your delay in fx loop. so or you make another buffer (simple FET follower) for the delay and effects which will be in the pedal chain, or you can play with this 100k..
add in parallel 50pF, 100pF, 220pF, 470pF.. see what you will like..this roll of heighs is working with your tone, keeping it more smooth, not harsh, which is good, but i assume that you want that "wet effect"of OD+delay which is +level up in the tone

The output impedance at the FX Send jack with the 1k resistor installed is:
Ro = (100k + 488) || (2.2k || 1k) = 100,488 || 687.5 = 683
The capacitance of 15 meters of cable @ 105pF / meter = 1.575nF
The corner frequency = 1 / (2*pi*1.575nF*683) = 148kHz

There is no RC low pass filter problem here.

thx,
i completely ignored that for AC analysis 100k coming from cathode (+ cca 600 ohm internally) is in parallel with the load/ because Ub+ and gnd are the same

[Lothy]

The effects loop mod radically changes the gain at the grid of V4A, thereby changing the sound of the amp. Here is a design that doesn't change the gain.
FX LP Dual CF 6.png

Hello Ten Over,
if it is no problem, could you please explain, why there is a 2,2u cap instead of a 1u?
Sorry, if this is a silly question..

Cheers
Gerhard

[Ten Over]

if it is no problem, could you please explain, why there is a 2,2u cap instead of a 1u?

Corner Frequency = fc = 15Hz
Input Impedance of FX Device = 20K = Worst Case
Zo = Output Impedance from CF Driver
C = 1 / [2*pi*(Zo + 1,2k + Ri)*fc]
Zo = 3,3k || 100,5k = 3,2k
Ri = 750 || 20K = 720
C = 1 / [6.28*(3,2k + 1,2k + 0,72k)*15] = 0,0000021F
0,0000021F rounds-up to 2,2uF

[Lothy]

Corner Frequency = fc = 15Hz
Input Impedance of FX Device = 20K = Worst Case
Zo = Output Impedance from CF Driver
C = 1 / [2*pi*(Zo + 1,2k + Ri)*fc]
Zo = 3,3k || 100,5k = 3,2k
Ri = 750 || 20K = 720
C = 1 / [6.28*(3,2k + 1,2k + 0,72k)*15] = 0,0000021F
0,0000021F rounds-up to 2,2uF

Thank you.
I will give it a try, when parts arrive.
In the current configuration with the 1k over 2,2k R24/1uF C13 the output of the CF is still too hot for any delay device I have (e.g. Strymon Volante). I still get distortion on the input. Will your mod fix this problem? Or should I accept this fx loop design is not made for this kind of application? The spillover effect does not concern me too much, but distortion on the dry path drives me nuts...

Thank you so much.

Gerhard

[Lothy]

if it is no problem, could you please explain, why there is a 2,2u cap instead of a 1u?

Corner Frequency = fc = 15Hz
Input Impedance of FX Device = 20K = Worst Case
Zo = Output Impedance from CF Driver
C = 1 / [2*pi*(Zo + 1,2k + Ri)*fc]
Zo = 3,3k || 100,5k = 3,2k
Ri = 750 || 20K = 720
C = 1 / [6.28*(3,2k + 1,2k + 0,72k)*15] = 0,0000021F
0,0000021F rounds-up to 2,2uF

@Ten Over,
ok, it's done and it works like a charm. Thank you very much!
Gerhard

[syscokid]

The effects loop mod radically changes the gain at the grid of V4A, thereby changing the sound of the amp. Here is a design that doesn't change the gain.
FX LP Dual CF 6.png

Stumbled onto this thread while looking for more info on the SLO fx loop. Your schematic is very interesting, and I'm trying to understand what is happening.

In the stock SLO schematic the CF voltage of V3a is 202v. The voltage divider (100k/2.2k) reduces the voltage to 4.3v. Therefore, 4.3v travels into the Send, then into the Return, and finally, 4.3v into the grid of V4b. This setup creates a +4dB that's useful for rack effects. Correct?

The "standard" SLO loop mod adds a 1k in parallel with the 2.2k to create a 688 ohm divider for a voltage reduction down to 1.4v, instead of the stock 4.3v. Correct?

The "new & improved" D Tinnopher schematic changes the voltage divider resistor to 3.3k, and now the reduced voltage is 6.5v that goes directly to the Return and into the grid of V4b. But there's a second voltage divider (1.2k/750R) that has been added to create 2.5v directly to the Send. Send and Return/Grid are receiving two different voltages. Correct?

Whether my assumptions and calculations are correct, or not, have you or anybody else, actually implemented this mod? I can't really tell if Lothy's response is a thorough implementation of your schematic mod...

Greg