Installing a Zero Loss Fx Loop on a Soldano Hot Rod 50

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Installing a Zero Loss Fx Loop on a Soldano Hot Rod 50

Post by Oliviervgirard » Sat Aug 06, 2022 2:01 pm

I've seen no or very few comments on that amp so I had to pretty much figure it out.

I hope it will help someone, it may work on a SLO but I only have experience with a Hot Rod.

1. Remove all tubes.

2. Discharge the filter caps, take a wire and attach it to the chassis ground. Use a 1 watt 100 ohms resistor and attach it to the other end of the wire. use shrink tube or tape and isolate the resistor. Don't touch the resistor metal parts! With the resistor exposed leg, touch the positive side of the filter caps (the 4 big ones close to each other).

3. Desolder the stock loop cable. Remove the Send/Return pcb on the back.

4. VERY IMPORTANT! Desolder the 4.7k resistor on the original loop pcb. Solder it across the "S" and the "G" pads on the main pcb. The loop will now be Post-Eq and Pre-Master.

5. Remove the main pcb from the chassis. Uncrew all front knobs and input jacks. Desolder the cable that come from the standbby switch. Unscrew all screws that hold the pcb to the chassis.

6. Locate the trace that tie the Treble wiper (centre lug) and the Master pot. About 1 inch long. Cut that trace with a dremel or something. Go slow, break that connection without destroying the pcb underneath.

7. Reinstall the pcb. Put all screws, pot and jack nuts back. Resolder the standby switch wire.

8. The loop module won't fit with the original wholes, you need to desolder the right jack (when viewed form the front) on the ZL loop board and reconnect it with flying leads.

9. I you want to keep the Slave Out volume knob, you will need to desolder it, reposition the board and reconnect it with wires to the pcb. If you don't care, you can disconnect and remove the whole pcb or simply replace the pot by fixed 2w resistors. Might be a good spot to install the bypass switch or a footswitch input.

10. Install the ground lug. I used the transformer screw right below the return hole. Make sure remove the paint and have good contact with the chassis before installing the lug and the nut back. You will connect the ground of the board and the shield of the signal wires there.

11. I used the highest value resistor that come with the loop kit. I connected it the the closest 15k resistor's leg to get 400v to the board. I read 305v on the board test resistor (check manual).

12. Rest of the installating is pretty straight farward. Look a the loop manual. I left all resistors stock and lost about 15v on 400v. No impact on the performance, at least none that 0.5 more gain can't fix.

13. Use tie wraps to secure the signal cables that goes to the loop. Check 1/4" cable clamps to use to secure the loop resistor power tap and whatever else. These are my new favorite things.

14. I've used hot glue to insulate the Slave knob and the Ground screw from the loop board. Just to be shure.

It works perfectly, 110% transparent and no level calibration was needed. What an absolute must for this amp!

If you have question or comments feel free to add something!

ps: I can't figure out how to post pictures, I'll have a look a it later

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Re: Installing a Zero Loss Fx Loop on a Soldano Hot Rod 50

Post by danman » Sat Aug 06, 2022 7:08 pm

Nice write up...happy to see that you got it figured out and working well! It's sad that the forum has gotten so slow these days. It would be nice to see it jumping like it was ten years ago!

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