Completely Out of My Depth - Modulus 50w 69 Build

[LyseFar]

It also didnt come with an impedence selector switch so I was advised to wire it similar to the 'DF Mrs 50 Layout' (Attached).

So in essence all I am doing is wiring up all the wires from the OT to all the switches and that one signle wire gets wired to the presence POT on the first lug. Have I understood this correctly?

Yeah. Normally a purple wire (negative feedback) from one of the speaker outs 4,8,or 16 ohms.. remember a resistor between.... 100k or something.
I guess you hardwire those without any impedance switch. That will work fine. Just remember to put the right labels on your different speaker outputs so you get the impedeance matching right...
I can see that the negative feedback wire on the "Fried ..." thing is green from the 8ohm tap - and purple on the "Small box 50 layout".

 

[PelliX]

It also didnt come with an impedence selector switch so I was advised to wire it similar to the 'DF Mrs 50 Layout' (Attached).

Right, ok.

So in essence all I am doing is wiring up all the wires from the OT to all the switches and that one signle wire gets wired to the presence POT on the first lug. Have I understood this correctly?

The Presence control (sorry if I'm preaching to the choir, etc) is the negative feedback. More Presence = less negative feedback. Negative feedback is the *secondary* side of the *output* transformer feeding back into the amp's circuit. The black wire you're pointing at comes from the *power* transformer, no?

I agree with @LyseFar that it should be grey, but that should be the center tap for the HT winding, yes.

RE: soldering iron. OK, those aren't the best in my experience, but they generally work well enough. Probably you just want a little practice dealing with lugs and stuff. A lug or any metallic body will act as a heatsink and thus require a little more from the iron when you solder to it.

RE: pilot light, it's hard to make out. There's a chance that diode on the end of the wire pops right back in but I really can't see that.

 

[BlueX]

Sorry this black wire coming out the transformer

Jumping in again, hope I don't confuse.

You can determine what the black wire is. Measure resistance between this black wire and each of the red wires nearby, and report here. The results will tell you if the black is the Centre Tap (CT) to those red PT secondaries (which it probably is).

 

[BlueX]

It also didnt come with an impedence selector switch so I was advised to wire it similar to the 'DF Mrs 50 Layout' (Attached).

Maybe you should get an impedance selector. Doesn't cost much and the amp will be much more useful in the future.

 

[kingfredward]

So done some more tidying up it looks way better than the first image I sent



Everything seems to suggest that black transformer wire is the grounding one. When I compared to other people’s builds that what they did

Also not convinced buying an impedance selector by this point considering the fact it would cost me £45 and then the faff of trying to cut a whole in the plexi to fit it. Unless it’s easier?



Reference the diode on the indicator light if I push it in it just slides straight out again so worried I need to buy a new one

 

[PelliX]

Also not convinced buying an impedance selector by this point considering the fact it would cost me £45 and then the faff of trying to cut a whole in the plexi to fit it. Unless it’s easier?

45 quid seems excessive, but I'd agree that you don't really need it per se. Sounds like your best bet is indeed getting a replacement pilot light unless there's some way of accessing the inside without destroying it.

 

[Pete Farrington]

Also yes I do have a temp dial View attachment 157691
I found above 300 it’s impossible to clean and solders horribly

The photos don't help much as can't see any make / model etc details of the soldering iron.
I suspect that the needle point tip would need a lot of oomph behind it to transfer heat to the joint being worked on without it cooling down excessively.
I find a more substantial chisel type tip is better for amp work.

Chinesium solder may be crap, best to buy branded stuff from manufacturer accredited vendors.

 

[BlueX]

Also not convinced buying an impedance selector by this point considering the fact it would cost me £45 and then the faff of trying to cut a whole in the plexi to fit it. Unless it’s easier?

With those speaker outs a selector doesn't make that much sense.

Seems like your kit is a mix of '69 Small Box and Deep Fried Marshbar.

 

[Pete Farrington]

First the kit seems to advocate a transformer securing point for the earth bond point

What document are you using? The Modulus layout looks good in that regard, with a dedicated fastener for the chsssis safety earth.

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[kingfredward]

The above layout is what I have been using

Been working abit more on the turret board

Not sure what wire to use on the back so used old wire that camp with my pedal kit should this be fine?

 

[Pete Farrington]

Recently I've seen a lot of Modulous schematics that range from a little misleading to downright incorrect. I have nothing against Micheal and co, but for those just starting on these projects, it would help to provide accurate instructions/schematics to get that stuff right.

Modulus fanboy here
I don't claim the Modulus layout drawings are perfect but at least they show the chassis safety earth with a dedicated fastener and the mains fuse wiring is good. So many reputable sites completely feck that stuff up, eg see link below.
And getting electrical safety right with DIY mains equipment is kinda crucial, right?

First amp build - the good, the bad, and the ugly

And now, a few thoughts on the kit itself... As mentioned, I used a Mojotone kit for this. It's this one. The parts seem like decent quality, though they are all Mojotone-branded, so who knows where they come from. None of them seemed obviously flimsy or cheap, and I like the way the amp...

www.thegearpage.net

 

[BlueX]

Not sure what wire to use on the back so used old wire that camp with my pedal kit should this be fine?

The yellow "snake" in the middle carries high voltage. I would use a wire where I know the insulation has proper voltage rating.

The long purple is in the layout, but might not be a great idea. Seems to introduce a ground loop.

 

[Pete Farrington]

Not sure what wire to use on the back

For new builders especially, wherever feasible, I think it's best to put link wiring on top of the board.
There must be a gazillion threads on amp building forums where it transpiresd that the builders inadvertently ran a link wire to the wrong terminal / soldered it badly / missed it out entirely.

 

[purpleplexi]

I've considered a couple of modulus amps - tay bridge disaster and deep fried marshbar get my attention. I've told myself that I can do the build myself but in reality I really should just pay modulus to do it for me. If they ever get the dumble clone ready I will prob go for it.

 

[kingfredward]

Thanks everyone for your help

Right I retained the purple wire reckon it will be enough to retain the ground?

Redid the orange wire to something sturdier



I also got the yellow caps arrive so been working on adding a few more lines to the board and redid some of the solder joints



Ordered a new indicator light too

Thanks everyone feel like I am getting some where now

 

[PelliX]

Thanks everyone feel like I am getting some where now

Looks like it

Right I retained the purple wire reckon it will be enough to retain the ground?

As @BlueX suggested, that purple wire may be redundant ground. As it's on the underside of the board, it will be hard to access once assembled. Perhaps take heed of Pete's advice on running it on top of the board just in case.

Another little thing - and I don't want to be pedantic - is that when you mount capacitors, it's appreciated to have the values facing upwards. That makes it easy on yourself and anyone else in the future servicing the amp.

 

[kingfredward]

Hi all here are some updates!
As per the suggestion it’s now wired to the top



I also reworked the back and got rid of that crappy thin purple wire and replaced with with the thicker stuff


Also routed the other wires around the top too


Further I have added more to the board but ran out of fun (too much huffing lead) and a missing 10k cap means I decided to leave it on pause unless it’s this haha?



I suppose we are getting a little bit closer every day

Thanks all for your help once again. Like always feedback is appreciated

Ps I took your advice and now they are facing up