NAD: 1x8 Champ Clone

gubble

I've been after a small fender flavoured amp for a while and found this locally.

It's a Fame (rebadged Joyo) JTA05  Sweet Baby. Which from what I understand is a clone of the Fender Champ 5F1 circuit.

This particular one has been modded with what appears to be some kind of boost switch and also a fat switch - i think it's also got a better speaker in it than came stock.

And it sounds fantastic ! I never thought a 1x8 combo could sound so full and rich and flipping huge. Sticking a reverb pedal in front of it I spent a good few hours just playing the guitar and focussing on using the guitar to alter the tone rather than knobs on an amp or a pedal.

The cleans are great but winding the volume up brings in some amazing driven tones - especially with the two mystery switches turned on.

Now if only it came in tweed tolex and said fender on it............

Alex2678

Nice, looked at one of those a while ago but they were out of stock everywhere so ended up going a different route. Congratulations 

gubble

Took the back panel off to have a look what the two mystery switches.

One of which seems to to switch R7 in and out, the other adds or removes something (maybe a capaictor?) to C7:



As I've not really got any electronics knowledge could anyone tell me what this means and what they could possibly do?

hollywoodrox

gubble said:

Took the back panel off to have a look what the two mystery switches.

One of which seems to to switch R7 in and out, the other adds or removes something (maybe a capaictor?) to C7:



As I've not really got any electronics knowledge could anyone tell me what this means and what they could possibly do?

ICBM will know I bet 

thermionic

I’ll make a wild guess that R7 is the negative feedback resistor.

Alex2678

Having had a quick google the c7 cap looks to be a switchable cathode bypass cap, engaged it should add gain. 

The wires connected to either side of what you’ve said is r7 (r6 on another photo of the pcb I’ve seen) doesn’t look to be switching it out, because both sides of the resistor look like they’re still connected, is there no cap or anything connected to those wires near the switch?

DartmoorHedgehog

Alex2678 said:

The wires connected to either side of what you’ve said is r7 (r6 on another photo of the pcb I’ve seen) doesn’t look to be switching it out, because both sides of the resistor look like they’re still connected, 

If the switch is just connected in parallel with the resistor then with the switch off it's just as normal, and with the switch on the resistor is shorted out, as if it was replaced with a jumper wire rather than physically removed.

Alex2678

DartmoorHedgehog said:

If the switch is just connected in parallel with the resistor then with the switch off it's just as normal, and with the switch on the resistor is shorted out, as if it was replaced with a jumper wire rather than physically removed.

Sorry didn’t phrase that right, I thought it was being suggested that it was a switch to disconnect the nfb, assuming it was the nfb resistor, and this just bypasses that resistor 

DartmoorHedgehog

@Alex2678 ;
Yes, sorry - I misunderstood what you were getting at there.

gubble

Alex2678 said:

Having had a quick google the c7 cap looks to be a switchable cathode bypass cap, engaged it should add gain. 

The wires connected to either side of what you’ve said is r7 (r6 on another photo of the pcb I’ve seen) doesn’t look to be switching it out, because both sides of the resistor look like they’re still connected, is there no cap or anything connected to those wires near the switch?

The C7 switch certainly adds a bit more gain, I think the switch connected somehow to R7 (or R6) does something similar - it's certainly the negative feedback resistor mod (I don't know what that means).

What i do know is with both switches engaged the amp some awesome !

Sticking a Gretsch and a reverb pedal in front of it makes me very happy and want to play guitar for hours.

Alex2678

I don’t think that’s the nfb resistor, I think it’s more likely to be the second cathode resistor