COMPLETE Soldano SLO Overdrive

[Hexjibber]

This sounds great and I am total SLO fanboy so would love to see what's going on here. I realise there are some other SLO type projects out there, that recent tube based GTO project for one but apart from that this is the first time I've seen one actually from Soldano themselves. Some of the YT demos sound pretty sweet.

 

[CR0SSBL4DE]

Why add complexity to the circuit? Does it sound ok without cold clipper simulation? Probably, because there are a lot of oohs and aahs. Is it selling well? Well, rather... and it has the Soldano logo

Yeah. Probably more of a marketing move, that an actual attempt to replicate the original SLO preamp tone.
The Soldano SLO was revolutionary because of the tone coming from the cold clipper stage. Before that, the only similar thing was the JCM800, that had a 10k cathode resistor in the 2nd stage. Soldano added it as an extra stage and took the value to 39K. Then mesa replicated this on the mesa rectifier.

 

[Rock'n me]

Maybe they didn't want first and second stage in a single IC (crosstalk?)?

But, why don't Robert uses two TL071?

 

[temol]

With TL072 you have one opamp on the left side, second opamp on the right side. With tl071 you have input from the left, output from the right.

 

[Robert]

But, why don't Robert uses two TL071?

A few reasons, in no particular order.

1) That's what the original used
2) I (maybe foolishly) assume that dual opamps are more common than single
3) I (again, maybe foolishly) assume that there are more options for cork-sniffer / opamp-rollers in dual format
4) What temol said
5) That's what the original used

 

[temol]

 

[Erik S]

Of course it is not nice that Robert isn't offering a discount again now.

Should have waited three days.

 

[Giorfida]

Should have waited three days.

And risk it selling out?! Nonsense! Lol

 

[drgonzo1969]

Last one to the build reports is a rotten egg.....

 

[temol]

It's on a breadboard now. My layout is a bit unstable with gain cranked. The oscillation is present all the time (visible on a scope) but squealing appears with gain set past noon. I suppose good pcb layout is a key here. Signal levels reaching the tone stack are up to 20V p-p.

 

[Robert]

I suppose good pcb layout is a key here.

Critical, this is what took so long to finish the PCB.

I ended up with a 4-layer PCB with plenty of isolation between traces as well as internal shielding via the ground planes.

 

[temol]

Just like the original pcb.. many, many vias...
Am I naive hoping for a quiet, single sided smd board?

 

[Giorfida]

A few reasons, in no particular order.

1) That's what the original used
2) I (maybe foolishly) assume that dual opamps are more common than single
3) I (again, maybe foolishly) assume that there are more options for cork-sniffer / opamp-rollers in dual format
4) What temol said
5) That's what the original used

Insomnia sucks!
That said, my mind went a million places and remembered that the SLO pedal was supposed to be the SLO mini preamp section in a pedal.
As such, the mini had switchable crunch/oD settings as well as an fx loop. So it makes me think:
1. the “unused” opamp halves were used as power amp drivers, the switchable preamp voice, fx loop buffers or some other feature in the mini head, and they simply copied and paste the preamp section as the pedal schematics, and generated the layout Or
2. Scale of production: difference in cost between a TL072 and TL062 are essentially negligible at equal quantities, but as quantity increase, price goes down, so it’s likely cheaper for them to buy the TL072 in quantitative for both the pedal and the head vs dedicated chips for both.
Still doesn’t explain why separate chips vs just using both halves of one… unless it was harder to make a stable board w/o using 2

 

[Robert]

Am I naive hoping for a quiet, single sided smd board?

Maybe not, you'll have a bit more room to spread out with SMD.

Still doesn’t explain why separate chips vs just using both halves of one… unless it was harder to make a stable board w/o using 2

My guess is that it was probably for stability. As temol has noticed, this circuit has a lot of gain.

 

[Giorfida]

Maybe not, you'll have a bit more room to spread out with SMD.



My guess is that it was probably for stability. As temol has noticed, this circuit has a lot of gain.

I can only imagine the instability! I have a Plimsoul works like here with a decent amount of gain, and if the settings are right and something causes squeal (unpotted pickups etc), it will pick up on that and start oscillating itself. Even the tried and true Rat can go to the stratosphere with bad lead dress or the board layout. So something copping a high gain amp I’d expect to be a bit touch

 

[music6000]

Critical, this is what took so long to finish the PCB.

I ended up with a 4-layer PCB with plenty of isolation between traces as well as internal shielding via the ground planes.

How much does the PCB end up being thicker than a standard PCB?

View attachment 66873

I was going to say earlier " That's going to Oscillate'', Robert had that on the first 2 prototypes!.
I did report this in earlier discussions when Members were asking ''where is it".
& Robert replied with the 4 layer deal.

 

[Robert]

How much does the PCB end up being thicker than a standard PCB?

I haven't measured them but it's still a 1.6mm PCB so should be pretty much the same.

They do seem slightly heavier than normal because of the added copper.

 

[temol]

I think many of us assumed that if it was signed by M. Soldano, it must be super faithful to the original down to the smallest detail. Yeah...
Playing with LSO in ltspice right now. Signal envelope - symmetrical clipping, with hard exit from restriction, like from ordinary distortion pedals.
Zero dynamics - no shift of the bias point, fixed duty cycle. Square signal (last opamp) even with 50mV p-p input and low gain setting.

Some examples below.
50mV p-p input signal, gain pot setting 0.1 (range from 0 to 1). Output of the last op-amp.



Output of the tone stack - pedal and tube preamp.



Output from the cathode follower (tube preamp)



Input signal 250mV p-p, gain maxed. Second stage out, third stage out, treble out, last stage out.


I have no complaints about the sound, it's great. But what you see in the simulation is a bit disappointing.

 

[Bucksears]

I think many of us assumed that if it was signed by M. Soldano, it must be super faithful to the original down to the smallest detail. Yeah...
Playing with LSO in ltspice right now. Signal envelope - symmetrical clipping, with hard exit from restriction, like from ordinary distortion pedals.
Zero dynamics - no shift of the bias point, fixed duty cycle. Square signal (last opamp) even with 50mV p-p input and low gain setting.

Some examples below.
50mV p-p input signal, gain pot setting 0.1 (range from 0 to 1). Output of the last op-amp.
View attachment 66945 View attachment 66946


Output of the tone stack - pedal and tube preamp.
View attachment 66947 View attachment 66948


Output from the cathode follower (tube preamp)
View attachment 66949 View attachment 66950


Input signal 250mV p-p, gain maxed. Second stage out, third stage out, treble out, last stage out.
View attachment 66951 View attachment 66952

I have no complaints about the sound, it's great. But what you see in the simulation is a bit disappointing.

Thx for this.
No offense and just speaking for myself, yeah, I'm not expecting it to replace a 100W SLO or be fooled that I'm nailing that sound out of a pedal. But if it gets a good amount of the FLAVOR (in the same way a Marvel Drive or Guv'nor attempts to do Marshall tones), I'm ok with it.

I'd be curious to see your comparison against the Synergy SLO module, which I'd imagine might be somewhere in-between.

 

[music6000]

I haven't measured them but it's still a 1.6mm PCB so should be pretty much the same.

They do seem slightly heavier than normal because of the added copper.

I summize the cost of the PCB doubles in price?

 

[Robert]

I summize the cost of the PCB doubles in price?

It depends on the quantity. There's an increase but it's not quite double.