I think I was going to put it in a 2U rack case originally, but I think it would be better in something like a Hammond 1441-33 case (17x4x10).

You also have to consider what Power amplifier you are going to use with the pre-amp, that will determine the transformer you need.

If you are looking for the font for the writing on the front panel (c-mos) I think the font "FontsFree-Net-bitwise.ttf" comes close.

here are some pics of a front panel PCB I was working on, I sometimes use a PCB as a fascia on my home jobs.
I have made the front for Lead and the back for Bass, on the Bass I labeled the reverb pot as comp as I was going to add a 1 knob compressor to it separately and place a pot in the reverb position.

Great,
If you have problems finding the B1M dual gang pots you can get them from Tayda, that's where I get most of my parts from
https://www.taydaelectronics.com/pb-1m-ohm-linear-dual-taper-potentiometer-pc-mount-round-shaft-l.html

I have read that changing the level and master pots to A100k instead of B100k makes it easier to control the volume, also one of the tone pots can be improved by going to C100k, but I can't remember which one right now.(Treble ?)
I also changed the values of the resistors in the foot pedal circuit to higher values and 1/4 watt but I haven't proven that yet except on a breadboard.

The Sunn Beta has a strange plug for the foot pedal, I was going to use a 4 pin GX12 or GX16, but any 4 pin plug will do.
https://www.taydaelectronics.com/connectors-sockets/midi-connectors/4-pins-male-circular-connector-12mm-gx12.html
https://www.taydaelectronics.com/connectors-sockets/midi-connectors/4-pins-male-circular-connector-gx16.html
Cheers
Mick

Silicon Chip magazine tested several cheap modules and felt that the two they picked would actually pass Australian safety standards, and the components ratings were up for the job.
They did recommend that the speakers should be 4ohm or above which de-rates the setup to approximately 500 watts @ 4ohms and not the advertised 1000 watts @ 2 ohms.

Here are the links to the amp and power supply provided by the magazine:
https://www.ebay.com.au/itm/114672525935?var=414836775679
https://www.ebay.com.au/itm/163230622080
https://www.aliexpress.com/item/32873549833.html
https://www.aliexpress.com/item/1005003208947027.html
https://www.aliexpress.com/item/32917489810.html

https://www.siliconchip.com.au/Issue/2023/April/500W+Class-D+Mono+Amplifier

They stuck them in a metal case 304mm wide (12") x 279mm deep (11") and 88mm high (3.5") along with an 80mm quiet fan.

I thought it would make for a nice Bass amp for home, I would just make a pre-amp PCB that sits against the front panel, pots mounted on the PCB.

Maybe a Lab Series L4 or a Sunn Beta Bass, there are lots of bass amps that are solid state.

I think it would fit nicely in a Hammond 1444-12103 aluminium case (12x10x3)
or a Hammond 1444-12123 case (12x12x3)

I don't need it but it would be fun making it anyway, my daughter could use a louder Bass amp for home.

G'day all.
I am thinking of trying out  some of the high power "D" amp modules that are everywhere.
Silicon Chip magazine had a story on some modules they tried out, a 1000 watt amp and 1000 watt power supply that they called a 500 watt amp put together.
I might try this out with a Bass preamp I am making.

The problem is that the power supply has only got +- 70v rails, and a single +15v output also.
I guess the easy option would be to convert the +15v to -15v with a LT1054 or similar but it would be a bit less then -15v at the output.

Since I would be dropping from 70 volts to 15 volts at an unknown current I don't really want to use a dropping resistor, not even going into a 7815 regulator.

The 7815 and 7915 can go up to 35 volts max so they are out.

This would be a common problem with any design requiring more then +-35 volts going to the power amplifier PCB, most pre-amps will want a nice +-15 volt supply.

Does anyone have a good solution ?
Maybe a Zener diode with a low loss mosfet or transistor to do the dropping ?
I would love to hear what methods others have used in the past.
Thanks
Michael

Welcome Saturated, yeah I know , a bit late but I am always a bit slow.

If you are new to soldering then the best thing you can do is get a soldering iron with a temperature control and some small tips.
I use a 50 watt iron with a digital temperature display, 50 watt lets it keep the heat better then a smaller iron.

Never buy solder cheap online, you will just produce *s!!t* solder joints that might not make a connection.

I use a 1mm solder tip and good solder that is 0.5mm thick, 0.8mm is ok as well.

I use a magnifying loupe  10x or 20x to check all my solder joints, its amazing how much you will miss if you don't check them properly.

I have been building stuff since I was a young smart-arse way back, my first serious project was a 16 channel mixer desk (ETI I think) around the mid 70's, along with 2 x 100 watt amplifiers that a friend used as a mobile disco.

Once you start building your own stuff you never stop, and why would you when you can make your own amps and pedals cheaper then what you can buy them for.

Shop around for parts as you can get some stuff a lot cheaper if you do, I buy a lot of stuff from Tayda because the price is good.

Cheers
Michael

Sounds good, I would love to see some pictures of it.
It sounds like you made yours the same size as the original.
Did you make a copy of the power amp as well, or just the pre amp

I have no idea where I got the idea that one of the pots was a G50k taper but that's what I thought it was, most likely confusing this with a post on another forum.
A25k pots with a push pull switch should not be hard to source, the pots on the pictures reminds me of an old type of Noble pots from the 80's.
The Noble pots were a bit "chunky" around the shaft base where the thread starts.

I don't know where "gastric" lives but if in the states then these guys have a switched pot that could be made to fit : https://www.bestbassgear.com/alpha-25k-volume-potentiometer-audio-taper-push-pull-6mm-solid-shaft.htm

You would have to solder some stiff wire on the pot lugs to poke through the PCB,just some leads cut of some 1N4004 diodes would be good enough.
Standard A25k pots are easy to source, I get mine from Tayda mainly and I find them good.
Check Ebay for "A25k push pull"

I would be 99% sure that the pots are standard 16mm with 5mm leg spacing, but they might 5.08mm as well.

I personally would remove the PCB and then mount it from the outside of the case by tightening all the pot nuts before soldering the new pots in, that way the pots are aligned before the solder locks them in position. You really want the pots tight against the panel before soldering, if you solder them first and then tighten up the pots you could put strain on the pots and solder joints.

I think it might be best if you remove the bad pots and clean the solder up with solder wick so you can get an accurate measurement of the hole spacing on the PCB.
I have not come across any 16mm or 5/8" pots with 4mm leg spacing before, but I have seen where someone has squashed the outer legs inward so the pots didn't fall out before they soldered them in place.(Not good practice)

I think you would most likely be able to fit a new pot with 5mm spacing in with no problem.
That looks like a single sided PCB with copper tracks on the bottom only, it should be easy to make the holes a bit larger to make them fit if you needed to.

The switched pot will be the hardest to get, I can't see if there is any brand on them at all, sometimes its a symbol stamped into the metal on the back of the pot.

It might be possible to dismantle the switched pot and just replace the disc with the carbon track taken from another brand new pot without a switch.


Here are the standard sizes for Alpha pots for reference, but it will differ with brands.

If you are not very used to reading schematics or looking at PCB overlays, especially larger ones where the tracks are very close it might be a good idea to print the layout on paper and use highlighter pens to mark out ground, +9v, -9v or any part of the circuit you are tracing.

Use your computer to crop and print the area you are working on, or maybe go to a library or somewhere and print it out at A3 size.

I always use the earth from a nearby component, in the Peavey that would be the part I coloured green, the minus side of C58 should be ok.
On a PCB with so many links you might have a bad solder joint where you might loose the earth signal going to the part you are testing.
Very often the centre tap of the transformer is connected to the earth, or 0V.
That would be the red/yellow wire from the transformer in this case.

Once you mark out the power rails and the traces you are following it becomes easier to follow the the layout.
You cannot view this attachment.

Tayda has W50k pots but the wrong type of legs, nothing a side cutter cant fix followed by some copper strands out of some 4mm building wire.
Or just use the legs from some 4004 diodes and solder them on the pot.

At least I think W taper is the same as G taper, but if you want that center detent(click) you will have a harder time finding it.

Are you thinking Deoxit Phil ?
I used WD-40 in industrial situations, especially if there was acid in the air, but that is frowned upon in amplifiers by many people.

I think Deoxit does not wash away the special lube in pots or something like that while WD-40 and Electraclean type products might, there used to be a "Lectraclean" that used to melt most plastics on contact, nasty stuff if you are not careful.

One can of Deoxit will last most people a lifetime at home if you only use it for pots.

If a component is faulty it might be shorted out, then it can absorb a lot of power and go up in a puff of magic smoke.
With a 12v car or boat battery connected to it it can pull enough amps to make it burn up and even catch fire, even the leads can melt if they are not big enough.

If you place a resistor between the battery and component the maximum amps it can draw is calculated by I= E/R, or amps = voltage divided by resistance. That is the most amps you are allowing to pass through the circuit in case the component is faulty.

If you used a 6 ohm resistor between the battery and component the maximum amps will be I=12(volt)/6(ohm) which is 2 amps.

Of course the resistor needs to be able to survive the amps you pass through it, in case it is a shorted component it will be 12v and 2 amps. Power=volts x amps = 24 watts, I doubt you have a 24watt or bigger resistor laying around.

Another easy way to limit the amps is to use a light bulb instead of a resistor, in this case you would use a 12v globe from a car maybe.
I would use a small wattage light bulb to start with, something like a 4 watt tail light bulb would be fine, if the component is good there will be hardly any current used so the bulb will not light up and you would get 8 volts between pin 2 and 3 on the 7808 regulator.
If the regulator is faulty then the ligh bulb lights up if the 7808 is shorted out, or if it has gone open circuit then nothing will happen as there will be no way for the power to go through the regulator.

If you make a triangle over the formulas and then cover the one you want to work out it shows how to do it, I better explain better.

   V         V         
I          I
   P ,       R ,   

I=V/P,  V=I x P,  P=I x V,      I=V/R,  V= I x R,  R=I x V

The light bulb is there to protect not so much the 7808 you are testing but the battery and the wires you are using to test the 7808 with, and it also stops you from breathing in too much smoke.

The hot glue was used to keep the components steady and safe from vibrating too much, if you wiggle and bend the component leads too much they will break.

Large capacitors used to be glued down a lot because with their weight, and if someone playing a 100 watt combo amp at full blast there will be some vibrations if you are doing it right. Also Amp heads often get placed on top of the speaker cab as well.
Imagine a 400 watt Bass amp speaker at full blast, sit on top and you will sing in a natural vibrato.

Cheers
Michael

The footprint on the PCB looks like a standard size pot, PCB mount straight legs.
It appears that they are 16mm with legs 5mm apart from the PCB picture in the service manual.
You really need to get some pictures and measurements to get the right one.
Is the thread length standard, what type of shaft do they have etc.

Something like this might fit for gain: https://www.digikey.com.au/en/products/detail/bourns-inc/PDB183-GTR03-253A2/4699138

You cannot view this attachment.

Have you checked the power amp to see what filters are built in ?
I'm sure there are LPF's and HPF's in there somewhere, possibly to protect the speaker they used specifically in that amp combo.

The return jack on the 5215 does not go straight to the power-amp as well, it goes back to the pre-amp PCB where it goes through the effects amp and then the output amp stage, and then onto the power-amp PCB.

There are a lot of areas where you can loose and alter the signal between the return jack and the speaker, I would concentrate on other areas before looking at the feedback circuit on the power-amp.

Perhaps you could lift the wire marked 'E' and use that to send/return to another amp just to hear the difference compared to the send/return jacks.

Its just more experimenting and more fun
Mick
You cannot view this attachment.

If you want to do as much testing as possible there are a few more tests you can do, the fact that you have 0.646v across C58 at the moment could indicate there is a shorted track or component somewhere in the circuit.
It might also be that the 7808 regulator is stuffed but CR24 is lifting the voltage to 0.646v.

I would short CR24 and remeasure the voltage across C58 to see if it changed.
 
I would remove the links I put an X on in the picture in post 21.
Lift one link at a time and then measure the voltage across C58 to see if it made any change, if you lift a link and the voltage goes up to 8-9v then there is a short somewhere that that links goes to.

There is a small chance that C58 has failed big time and is shorting out, but you can usually see if there is something wrong with a cap and they don't usually short out.

You can remove the 3 links and lift a leg on C58 and then measure the voltage on leg 3 of the 7808 regulator to make sure it is the regulator.
You would measure from leg 3 to ground.

I still think Phil is right and the 7808 needs replacing, but doing more tests can not hurt, all you can do is gain more experience.(and have more fun doing it).
Mick