SLO-CLONE Build- Preamp only

[SilverFox]

Initially I was going to build an amp based on the Fisher 500-s stereo iron. Too many problems as I didn't want to use the related output tubes. Anyway, along the path I decided instead to build the preamp section of a Soldano 30, up to the FX buffered output. My questions are: The clean and OD channels are mixed. As I have a stereo power amp I've decided to separate the two outputs with separate FX buffers and send the outputs to a mini mixer, or alternatively an effects unit, where I can EQ, then onto the PA. What are the thoughts on this?

I have a copy of the SLOCLONE Official Schematic but not sure how to upload it as a .pdf.

Silverfox.

[pdf64]

Are you sure it's really a 2 channel amp, not just a single channel with switchable clean/crunch modes, as per the SLO100?

Are you aware that guitar amps sound awful through full range flat response speakers?
Guitar speakers have a somewhat extreme EQ.
Guitar speakers / emulators are necessary for guitar amps to sound like they should.

[SilverFox]

I'm not running FRFR cabinets. I'll try to insert the .png schematics here. To me, there are two separate channels that are combined after the EQ. The OD channel may be switched on or off. Here is the schematic:

I'm having trouble uploading the schematic. I insert an address and the image does not load. I've tried pasting a copied image in and that does not work for me either.

[sluckey]

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[SilverFox]

Thanks Sluckey. I was curious as to whether you were still with us. I didn't see an attachment feature and had tried the image insert.

Thanks again.

[pdf64]

I'm not running FRFR cabinets.

You noted that you intended to use a PA, rather than a guitar power amp with guitar cab?

PA cabs aim for a full range flat response, rather than the extremely non FRFR of typical guitar speakers.

... To me, there are two separate channels that are combined after the EQ. The OD channel may be switched on or off...

From schematic provided by sluckey -
The input stage circuit around V1B is shared by both normal and OD modes.
The stage around V1A is specific to the normal mode.
The stages around V2A&B are specific to the OD mode.
The stages around V3A&B and V4A&B are shared by both channels.
The final, most significant clipping stages of the OD mode are around V3A&B.
The V3A&B stages will also fatten up the tone / cause obvious overdrive, on the normal channel too, depending on how its set.

I hope that helps?

[Snicksound]

It is correct that on the original SLO, the Normal (Clean/Crunch) channel is still active and unmuted when the Overdrive channel is active. It is also out of phase so it actually cancels out some stuff

I believe the newer versions that use relays instead of optocouplers no longer do this, but I could be wrong.

I don't own an SLO myself, but I was playing with the circuit on my prototyping setup and yeah it changes something. It's not better though, it's just different.

The original SLO's cathode follower driven loop (that is pre-EQ) is also not quite transparent even when not in use, and yet the newer SLOs have done away with this quirk and they're still SLO (there are other differences having a bigger impact like the 1nF coupling cap in OD mode, and the different voltage divider between V2a and V2b)

Point is... Don't worry too much about it. But if you want it to be as authentic as possible, yeah leave that quirk in. The downside of it is that the setting of the Normal channel switches and Gain controls will have an impact on the Overdrive channel, albeit a small one.

[SilverFox]

Thanks for the information. As is the case, I'll review it several more times. I'm just getting back into this after a 10 year break. I used to frequent Amp Garage and gained my knowledge of Train Wreck and Dumble amps.

I already screwed up the power supply and have to redesign it. I used a full wave, two diode scheme with a grounded center tap rather than a bridge so the voltage was low; Like 200 VDC at 120 AC input. Work in progress. I like to consider myself a student and that is my philosophy for the forum. So assistance will be much appreciated.

I read somewhere that the original intention of the mixing was by design. And the interaction was intentional. Is it the Marshall Plexi that has two preamps that are mixed? That's what I'm after but separation and using a five channel mixer to then send the output to an effects unit.

Yes, FRFR sounds like shit with a guitar. If I use my AX8 as the effects unit, it has the ability to set the speaker range between 20 to 20Khz. I typically set the range to 8.5Khz for the reason you are emphasizing. Beyond that, a mini mixer will allow me to EQ the FR.

The power amp I'm using is stereo. One I built based on the Dynaco ST35 using a 100 watt PT and two so called 35 watt Train Wreck OT that are likely rated for 40 or more watts. The speakers presently are from a B52 cabinet. I was running Sheffields from a Pawn Shop Amp but one of them is blown. The power amp design is clean. So all the character comes from the preamp and effects unit. It has run flawlessly over the years. That is where the preamp output will go unless and until I decide to build a SS PA or just buy a plate amp.

Present status. First I have to get the 250-0-250 Hammond 261G6 transformer to output, as I recall, 384 volts for the FX send tube. When I measured the output of the PT it was something like 390 VAC, unloaded. After I rewire the rectifier, I'll report back with the B+.

Thanks again for the information.

Silverfox.

[SilverFox]

The power supply consisting of the 250-0-250 secondary, bridge rectifier, and 22uf reservoir cap, with no load came up at: 400 VDC. The center tap is unused. I dropped the Variac down to 30 VAC to reform the cap, just in case it degraded, as they have been sitting for about eight years. I'll bring the voltage up over the next few days.

Silverfox.

[SilverFox]

How do I insert an image? I've tried and been unable to so far.

[timrobertson100]

When you reply, under the text box, click attachments and then add file. You can then optionally choose it to be inline, and it will appear like this:

IMG_1353.jpeg

Hope this helps.

[SilverFox]

Thanks. This is the schematic I'm working from. I've ordered LDR's.