Idea for a dedicated Rhodes preamp, need help !

[PermO]

Found a cheap replacement for the rather expensive Elma rotary switch;

Looks like it's about the same size, provides 8 gain steps.

https://nl.aliexpress.com/item/4000...il_item.3.4c916d76q9tXOK&gatewayAdapt=glo2nld
I ordered 10 pieces, working on a PCB for the battery powered DI version.

 

[abbey road d enfer]

These are not low-level switches, they will almost certainly eventually become scratchy, compared to gold flash contacts.

 

[PermO]

At 1% of the cost of the Elma switches,I'm taking my chances with this one, they might not be so bad.

I've been using cheap Lorlin switches for years without any problems.

 

[abbey road d enfer]

I agree. You don't take much risks in the end.

 

[Walter66]

In life, for every good product there is at least one offer for cheaper price and lower quality.
You hit the jackpot, if your after the lowest quality possible.
Good luck with those "quality components" LOL

 

[Graham Nystrom]

FYI Alpha Taiwan has some very nice rotary switches on Mouser. One is a very solid metal 2 pole 5 position 2 deck switch for like $6, and there are some plastic ones that look more like the one you found on AliBaba. Everything I have ordered from AB has been...problematicly low quality like my friend Walter here said. Good luck.

 

[PermO]

So I started to learn Easyeda and picked the "DI box" version as my first project.
I have swapped the IC's for SOIC versions on the pcb as the DIP8 versions are getting hard to get.
This is my first attempt at a pcb, and so far I have my schematic and layout, have not started tracing yet.



Any comments on schematic or layout are welcome, I've never done this before.

I went for trough hole components so the gain structure / input impedance / FX output impedance are flexible.

And this is how all of it will fit on a 6,5cm x 4,5cm board so it will fit a Hammond box including the batteries.

How did I do so far ?



Cheers !

 

[ccaudle]

Pretty decent. Your power supply 0V is not connected to the rest of the circuitry 0V, it has a different name.
If you look at the ratsnest the node which connects all the capacitors together just ends at the last pair of capacitors, it is named GNDB on the schematic, and the rest of the circuitry 0V node is named GND.

You are also inviting noise problem carrying pin 1 from the XLR all the way to the PCB, and also having one corner of the PCB connected to chassis. Pin 1 of the XLR connector should connect directly to the chassis, not to the PCB.

 

[Whoops]

In life, for every good product there is at least one offer for cheaper price and lower quality.
You hit the jackpot, if your after the lowest quality possible.
Good luck with those "quality components" LOL

It depends on the usage, how many turns will happen in 1 year.
If it's a switch that you are not using everyday, and maybe only once a month you have to change the setting, then probably a cheaper one will fit the bill.

If it's a switch that you are changing many times everyday, then you need something expensive.

Anyway this is not medical equipment, no one dies if the switch fails...

 

[PermO]

Thanks for this !

I purpously renamed the 0V to separate the audio ground from the rest till I figure my groundscheme.

I will remove pin 1 from the PCB.
There's an unbalanced instrument input (source in general is floating) and an unbalanced FX or reamp output that share the same groundpin on the PCB.

Should this pin remain or should these grounds also be tied to chassis / Pin 1 ?

 

[PermO]

Schematic and layout updated;


Yes that seems to clean up some nodes...

 

[PermO]

So I just ran the autorouter, somehow it won't work for me at night, probably due to too much traffic on the server.
But it worked fine this morning.
117 connections, 0 fails, 1 via;

That doesn't look too bad to me ?

How would you normally approach this ? Click the order button ? or would you start editting stuff ?


Question ?
This morning I was thinking (just a thought), what would it take to turn this into a mic pre ?
My initial guess is... just a transformer and a XLR input ? (if we forget about phantom power)

 

[rock soderstrom]

How would you normally approach this ? Click the order button ? or would you start editting stuff

Rather the latter, there is always something to optimize.

Maybe I'm getting too old, but I find the traces and many soldering pads too small. I would rather work with vias to make soldering more comfortable, if necessary.

EasyEDA is pretty easy to learn, isn't it? I was surprised how quickly you could get good results as a beginner.

 

[rock soderstrom]

Maybe I'm getting too old, but I find the traces and many soldering pads too small. I would rather work with vias to make soldering more comfortable, if necessary.

... to be a little more specific. In my opinion, the large film capacitors have solder pads that are too small; the ratio between the wire thickness of the component and the size of the solder pad is unfavorable.

The mechanical attachment and solderability suffer as a result. I would also check all drill holes to see if the diameter matches your components.

I've already had component footprints where they were much too small, that's a problem later...

Personally, I wouldn't run any traces through the footprints of the SMT semiconductors, as this can quickly lead to unwanted bridges when hand soldering.

Just some examples...

 

[PermO]

Easyeda is the first PCB design software that does not drive me borderline crazy, I just sarted doing this a week ago.

I actaully start to like it now, only the component selection is a bit bordersome

I'll be doing a bit of redesign as I found a way to sort of mimic a guitar pickup impedance for the FX output running it trough a winding of a small mouser transformer followed by a guitar type "tonestack" ...

 

[rock soderstrom]

On closer inspection you can see that the autorooter has not done a good job, there are many places that make little or no sense.

Here, for example, what is the idea behind this?

 

[PermO]

Yes my plan is to use the autorouter as a basis and draw the routing myself, I;ve allready noticed some weird stuff going on caused by mislabeling of some nets.

 

[PermO]

Yes I've fixed that bit in the upper right corner, it was caused by some mislabeled nets, net 1 instead of net_1

 

[rock soderstrom]

Easyeda is the first PCB design software that does not drive me borderline crazy, I just sarted doing this a week ago.

I actaully start to like it now, only the component selection is a bit bordersome

I felt the same way...I was amazed at how quickly I got into the game. My main criticism is the component handling in the transition from the schematic to the PCB design.

 

[rock soderstrom]

Yes I've fixed that bit in the upper right corner, it was caused by some mislabeled nets, net 1 instead of net_1

Okay, the autorouter is unguilty!