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Messages - Tassieviking

#31
Eliott from ESP has a good article on "Care and Feeding of Spring Reverb Tanks",
https://sound-au.com/articles/reverb.htm
At the bottom of the page he has a list of part numbering of reverb tanks, Table 4.
In the table he lists the bobbin colour that match the impedance for that coil.
So if you have say a red bobbin its a F type coil with an impedance of 1475 Ohm.
I don't know if this is always the case, especially with older tanks but it might help.
#32
This might help a little bit:
#33
In my opinion, and it is only my opinion based on my understanding.
If you ignore the LED's,R13 and C9 would be a low pass filter, the LED's will clip the signal when it reaches the voltage to make the LED's conduct.
Look at the LED's while using the amp, full gain and the switch on overdrive and if the LED's light up its working as a clipper.
Q1 changes the gain of the op-amp, it puts R5 in parallel with R6.
If you want more clean head-room, you could add a germanium diode in series with each LED.
That would slightly increase the clipping voltage.
You could try different led's or different diodes in series with the led's to experiment until you are happy with the sound.
I think removing the LED's might not be a good idea, too much signal might get through.

Which amp model do you have ?
It appears that there might be 2 models using that circuit, the watts available depends on which power transformer is used.
#34
This is circuit as I traced it from the pictures, very similar to the online circuit for the 5205 with a few small differences.

The C12 in parallel with R17 is actually C16

The tone controls are connected slightly different

The power rails on mine are 24 Volts, ignore this as its approx 21 Volts.
KiCad only has 15 Volt or 24 Volt symbols and I haven't made any 21 volt ones yet

Your Bridge rectifier is different number then Marshall drawing, but both are 1.5 Amp.

That's all the differences I found from the original schematic.

Michael
#35
The Newcomer's Forum / Re: Modding a Frontman 15
March 30, 2022, 02:27:57 AM
Quote from: Chorch Cluni on March 29, 2022, 06:39:13 PMIt's a gift from my mum, so, you know... sentimental value, I guess.

Well...a gift from mum changes things, mod it is.
Yes, add the reverb circuit to the PCB, while you are doing this you should add IC sockets to all the op amps.
Swapping op-amps will be easier, and sometimes this will change the tone or the distortion.
There are a lot of mod pages out there for the Frontman 15 if you google it.

The best mod is usually changing the speaker, also try using it with the back cover off, partly closed etc.
I have read that someone had great sucsess with a MOD speaker and 2 planks across the back, leaving a gap in the middle.
Is it possible to fit a larger speaker ? If you can go up a size it might be more efficient/higher dBA as well as nicer sounding.( you still need room for a reverb tank )
I don't know the amp at all, but if you can locate the caps in the filters maybe stick some sockets in so you can swap the caps till you find a better tone.
I mean low pass and high pass filters.
You could do the same with the resistors in the gain circuits, sockets and try till you are happy with the results.
Here is the service manual url: https://elektrotanya.com/fender_frontman-15_frontman-15r_sm.pdf/download.html
You cannot view this attachment.

The reverb tank might be harder to work out, Insulated input and earthed output, but the model number might be harder to work out exactly. The numbers people are floating around don't match what the DC resistance indicates exactly.
Fender Part No: 041397  Reverb Spring 1BB2E4A Reverb Pan
Someone measured the DC resistance as Input 28 ohms DC, and Output 229 ohms DC
That would indicate to me the input could be B or C, output B
If you mount the tank on the floor below the speaker go for a 8BB2C1B (8CB2C1B ?)Tank

A lot of people ask what mods they should do, not many answers as it depends on what you want yourself, nobody knows this.
If you ask specific questions like how to get more Bass, less treble etc. you are more likely to get more answers. People smarter than me know just what to do to to change high/low cut filters, increase/reduce gain and all that stuff.
Good luck and happy modding
#36
The Newcomer's Forum / Re: Modding a Frontman 15
March 29, 2022, 04:54:36 AM
That power chip (TDA2050) can drive a 4 ohm load, so you could theoretically run another 8 ohm speaker in parallel with the inbuilt speaker.
You will most probably find out the hard way that your power transformer will not be large enough, you can tell by the smoke pouring out of the amp.
If you did not melt the transformer you might blow some tracks up on the PCB if they are not large enough for the extra current if running 4 ohm loads.

But why would you even consider using the internal speaker which you said is crap, if you have a good sounding speaker cab you can plug it into ?
Why would you want to add the crap sound with a nice sound ?
(Unless you are using it to scare the crows of your veggie garden) ;)
 Just get a nice external speaker cab, or replace the internal one with something good.

I would get a nice speaker cab, one you would want to keep for your next great sounding amp, build your gear up with quality one step at a time.

The price you might spend to install the internal reverb might be better spent on a nice reverb pedal, especially if you can make it yourself.
#37
Here are my KiCad files for the Marshall 5010 PCB78-2

The heatsink I would use would be :https://au.element14.com/aavid-boyd/505403b00000g/heat-sink/dp/1313918?st=heatsink%20to-3
Or just make one out of aluminium yourself
The Schematic does not match the board files in KiCad as I changed it slightly to make the PCB, I removed the transformer, switch etc.
I think it is the best I can do for now.
 I might make a smaller PCB in the future with the Jack sockets off the PCB, and add an effects loop and maybe reverb as well.
I will not be making this PCB myself but it is fairly close to the original.
The strange capacitors are a mixed footprint so you can use Tantalum, Electrolytic or WIMA box type for the 2,2 uF caps.
The PCB will accept Alpha 24mm pots like the original, or Alpha 16mm pots (The holes will be lower on the front panel with 16mm pots.
Michael
#38
That is....sparkly
Those are very big glitter
I think I will use an aluminium panel and plain old gold spray paint can when I make my Marshall front panel.

This is a test panel I sprayed with the cheapest satin gold paint I could get at the hardware store
#39
It is not a reverb board, it is an echo board.
I would place it after the Uno preamp circuit, you can also try it om the wiper of the treble pot as this is a common place for a volume pot. Just experiment.
I don't think it would work very well as a reverb, but I would be curious if you could mount 3 of them in parallel and set slightly different times, what it would sound like.
Like Joecool85 said, a Belton Brick is 3 PT2399 units running together set at different time intervals.
You should also look up The "Valve Wizard Equinox 2" project, just google it.

Please let know how it works

#40
Sound like your back is the opposite to mine, my vertebrae between my shoulder blades have fused together to one solid lump of bone, and it tries to do that all over the place.
Soft connective tissue like ligaments and tendons start turning into bone, if my hole spine fuses and I fall it will snap.
To be honest I hate taking oxy, but I use it practically every day when I go to bed.
I never get a buzz from the oxy, not even when they fed me 32 tablets in 20 hours in hospital. If it is really needed for pain it does not give you a high, or maybe the pain was just so bad I didn't notice.

I have nearly finished the PCB now, just tidying up, then I will post it here for others to use if they want to.
I will make a different one later a lot smaller, with the sockets off the PCB, and maybe add an effects loop and reverb on the PCB.

But before I make this one smaller I will make one up for the Marshall 12 watt reverb
with an effects loop, I will combine all the 12 watt circuits I can find and add them all on one PCB, then just add the components you need for the one you want to build.
I will also make the power amp a mix of the 12 watt and the 30 watt one, again just use the right components for what you want.

Jimiphoton, you wouldn't have the measurements for the 12 watt amp would you ?
I would be after the spacing of the pots and pots to jacks.

Chers
Michael
#41
It sounds like you need to convince someone to make a Paramix with a reverb circuit built into it, that might be a nice board that can be added to any amp.
I find measuring inches with a metric ruler hard too, always never on the line.
I find a small plastic ruler best that you can see through when I measure PCB's.

I found a nice Inches to mm guide online I downloaded.
#42
Thank you so much for that phatt.
Its joining the build list, might even get nudged towards the top of the list.
:dbtu:
#43
Looking at the circuit again, I would definitely go for the Log pot first, that would give you more control over the volume at lower level.
Another option is to put a resistor in series with the pot, but then you cant turn it up to full any more.
I presume it is a 24mm Alpha Taiwan potentiometer you have in there (RV24AF-22 model) since it is a Marshall.

The very last option if it were my amp, I would get a 16mm pot (log A4k7) with a push pull switch on it, and wire that in.
Wire it so if you pull the switch out you put a resistor in series with the pot, when pushed in it is like it is now.
Being 16mm you would have to run short wires to the PCB as the pot won't reach the PCB.
If the pot is too close just turn it sideways so the terminals point sideways.
I don't know if the capacitor C31 will be in the way for this.
#44
If you have a copy of where you drilled the holes on the chassis I would love to see it, that would confirm the PCB measurements.
If you can measure the PCB from the left side (Input side) to the center of the sockets and center of the pots (pin 2 wiper),
that would make it easier for me to understand.
Sometimes I don't think too clearly, I'm only 61 but have constant chronic pain and have trouble sleeping.
Shitty bone disease as well as arthritis everywhere, at least my doctor gives me drugs I only dreamed of when I was younger. ;)

I get my PCB's from JLCPCB, I just checked and 5 PCB's for this amp would cost me $18 plus shipping ($ 13 to $27 to Australia)
5 PCB's to the US would be $18US for the 5 PCB's and shipping $24US  DHL, $23US FedEx, $11 Airmail.
I think that is fairly good for 5 large PCB's (JLCPCB only do 5 PCB's minimum)
#45
I am a bit wary as well on any stress put on solder points, like pushing plugs in /out.
If I use a jack on a PCB it will always be a stereo switching jack socket with 6 pins for the most strength.
I made up draft 5 of the schematic, we will se how we go this time.
pinkjimiphoton, I am not sure what you meant with the measurements on the Jack Sockets.
I think you left a message on the DIYstompboxes forum that the measurements were to a pin and not the center of the socket.
I am posting a picture with measurements, If you could write on the picture and return it I can get that fixed up as well.
I have the PCB nearly finished apart from moving the Jack Sockets to the final place.
The strange footprint for the Tantalum caps is one I made up when I did the Sunn Beta board for myself.
Its so I could use Electrolytics, Tantalum, WIMA Box caps where the 2uF electrolytics were on the original PCB.

One more thing, the hole for the spacer between the heatsinks, do we want that in the same location as the original ?
I would need the measurements for that as well.
The only tracks on the top of the PCB are on the TO-3 transistor, the original did not have any, they relied on the power going through the screws.
There are also tracks on the fuse holders on the top, but they can be on the bottom, it's just the way I made the footprints.
You can make it a one sided board if someone wants to etch one, just leave out the tracks between the screws on the TO-3's like Marshall did.