I guess one could mix concrete with a food blender but there are better ways.
Bridging small chip amps is counter productive,
If you want more power ,,Get a bigger Chip that is designed for higher power,
LM3886 are cheap.
Phil.

Quote from: Endeo on February 07, 2024, 03:03:47 PMCan anyone confirm if the output of the voltage divider is a recording out or something? (marked headphone/rec out? on the schematic)

Yes as it has a Preout then the other is likely a head phone.
Phil.

As the amp is working it's unlikely the hiss is failing transistors.
A fair bet those older circuits were noisy by design.
 I just found this schematic Sears 40 XL;
https://www.ssguitar.com/index.php?topic=4127.30  (post 38)

If that is your Schematic I can tell the circuit will be prone to Hiss as there is no inter-stage volume. The Volumes are before the first stage (passive) and wired backwards so even with the volume control off the rest of the circuit is wide open. = Hiss
So even if you replaced Everything that design will always be prone to hiss.
Phil.

Hi Maddus,
          Good on you for having a crack at this 
but sorry but I doubt it's correct.

You will have to go over this quite a few times to get it right.
My advice is use paper and pencil as you may well end up having to draw it out many times.

Use Nodes to label each wire, then count how many components connect to each node or wire.

I started out doing this well over 30 years ago, no internet just some books and a few schematics. I used to end up with a bin full of scrap paper before I got it right.

Also check pinouts on the active components,wrong pinout on transistors is a common mistake.
Oh ed1; if you can up load some pics of both sides of the PCB we maybe able to help you verify the drawing.

Phil.

Most headphones will work some better than others. R34 reduces the volume for headphone out.
Obviously use common sense and turn the volume down if the level is higher than needed.
Yes you can use Headphone output to record but both channels will be mono. Suck it and see.

R31 & R32 forms a 10/1 divider for Preout which should have been labeled "Direct Out".
Whether you take a signal from R24 Post Gain or from Direct Out will make little difference as the TDA2040 will simply reproduce what is at its input.(give or take an electron)

As for FX;
Q, How do you intend to use an FX Loop?
In such a simple circuit there is little benefit.
In all my years of playing I've found they cause more problems than they solve. just put your FX in front.
Although they do come in handy when trying to fault find a circuit.

As for Mods;
If it was mine I would raise the value of R20 (220k) up to 1Meg it will likely make the tone controls more effective. Although it will make that more sensitive and at high volume it may introduce a bit more hiss. suck an see

I often use 2Meg in the type of tone circuit.
Phil.

Obviously a very early design tank, maybe not double sprung.
If you notice most fender amps have the internal spring assy connected to the outer case via springs but then the whole unit is also slipped into a soft bag to reduce any tendency to feedback.
But if the other tanks works better then easy fix.

Those of us who are old enough to remember how hard it was to stop vinyl record players from feedback at high volumes in disco teks, we found many inventive ways to stop that problem.

I built a few DJ rigs for DJs and some turntables were harder than other to fix.
Phil.

without a schematic it's hard to know but I'd guess the preamp section is causing the harsh distortion, not so much the power stage but it is a budget amp design and high chance there was little to no R&D before it went on sale.
Phil.

You obviously have continuity on both ends of the tank so either the cable is open or shorted, or the drive circuit is dead.
The drive circuit has just 2 transistors so it should not be hard to find replacements.
Phil.

Just a note on Digi Amps and SMode supplies.
Ok they are cheap, light weight, and so so convenient.
But keep in mind, Unlike Smode supplies Iron and Copper Transformers have an indefinite life span, if used within spec.
Jezzus Not even god could make a more bullet proof design.

 I doubt that in 50 years from now that these SMPS circuits will still be running as they are far more complex and hence far more prone to failure.
Notice how many Dead computer Power boxes fill bins in repair shops.

Now I'm not up to speed on Digi amps but the few I've had the displeasure of working with leaves me thinking that it's hard to beat a basic old school transistor poweramps.
Well designed unit go for years without issue. Of course Can caps dry out eventually but simple to replace.
with most things now surface mounted and hard to work with it's a throw away item. But by then you find out OH sorry they don't make them anymore.
 and you are left with land fill.  

If it interests you Rod Elliot has a ton of info on Amp design, a lot of which is aimed at muso gear.
Start here;https://www.sound-au.com/

I have found him to be very helpful while trying to build Analog Power Amps.
Phil.

You may have a dry or cracked joint somewhere. Get a wooden skewer stick and start gently probing and prodding around the PCB, large components are more prone to cracked solder pads.
Phil.

You might be wise to build a limiter before you power up next time as it will save you blowing transistors. All info needed can be found here;
https://www.ssguitar.com/index.php?topic=2093.0
Phil.

Hello and welcome,
Yes you can use a HiFi amp for guitar, some will work better than others.
If you have a line input then try it. Even CD input may work.
Of course obviously you use a guitar speaker NOT hifi speakers.

If the signal distorts early then the incoming signal will need to be reduced.

The older the hifi the more basic the design which may well work better for guitar.
The Digital Pwr amp designs used now may not work as well but suck it and see.

Just keep in mind that the tone controls on hifi gear are not ideal for guitar, again try it let your ears make the judgement.
Midrange for guitar is around 400hZ while hifi is centered around 1khZ.
Phil.

 I don't wish to dampen your enthusiasm but but you may eventually be defeated.
There is just so many nightmares waiting for you.

My advice would be to go buy a bread board and parts needed to run a 30 volt split rail supply and start experimenting.

You will spend many months getting the preamp to work.

Then you will have to learn how to use a cad program to make the preamp PCB, another few months will go by.
at that point your best bet is to purchase a poweramp kit.

Meantime you will then need to consider a case to mount it all.
Oh did I mention that layout of PCB can be a nightmare if you don't understand that sensitive sections will pick up hum from bad design as well you will need to learn how to NOT create ground loops a common issue when designing sensitive audio circuits.

AND heaps of other gotcha's that better minds on this forum will tell you about.


If it interests you,
My rig consists of a pedal board, most of which is my own designs and my main amp is nothing more than an old SS Keyboard amp.
I just posted an mp3 composition I wrote on here last week.
It will give you some idea of what can be achieved with average gear.
https://www.ssguitar.com/index.php?topic=5309.msg41595;topicseen#new.
But keep in mind I've been doing this for over 30 years so I have learned a lot about how to get things to work together to get the Sound/Feel/dynamics to come together.

40 odd years back I was in your situation faced with a similar dilemma so I have a fairly good idea of what is ahead for you,,So I wish you luck.
Be aware DIY is rather addictive.
Phil.

Quote from: Tassieviking on December 09, 2023, 11:48:16 AMThe SX300 preamp on page 25 in the manual has a very similar input circuit as the SX50, the SX3000 uses 2N5457 fet's so I think we can say that Q21, Q22 are 2N5457 FET's

This might make a nice pedal from the overdrive channel, 2 FET's and 4 dual OP amps is all, 5 pots and 1 switch as well

That would be the best advice for something that would otherwise exceed the cost of trying to build a whole amp from scratch    
Phil.

Quote from: Tassieviking on December 21, 2023, 10:29:13 AM

Quote from: phatt on December 20, 2023, 03:00:47 AMthe rest was me learning how NOT to waste time building land fill.

Have you figured out Phil ?
No more landfill ?
Please tell me the secret, I have been doing it since the mid 1970's and I am still working on landfill all the time.

Yep tiss easy to just dive in and build stuff but I think most of us fail to realise that it may have worked for the bloke on utube but we forget that while his guitar/amp setup might sound good,,, our setup will likely not reproduce the same results.
There are just way too many variables so you are just shooting arrows into the air and missing every time because you have no full knowledge of the target.

So I always BBoard test ideas first through as many amps & speakers as I have.(even head phones)
While it's all on the BB I also simulate it as well.
This is where you can clearly see just how each section is winning or loosing the magic.
You might find one section is hard clipping too early.
You can also tell where there is too much, to little bass or treble.
You then adjust the test circuit until you get a good balance.

If you put in the time for the R&D then you build far less land fill.

Same goes no matter if it's Pedals, SS Amps or Valve Amps.

I recently modded a small Mesa amp.
The balance between the 2 channels was unusable.
Again I could have wasted hours or dayze changing component values and guessing.
Just by using a simple sim of the preamp stages it only took 2 days to work out how to tweak the circuit to bring the 2 channels closer to a usable balance of drive and tone shaping.

I have built many circuits in my garage that I thought sounded great only to find that on stage they just turned in to crud.

I think my brain has trained itself over the years to pick tone and harmonics.

A bit of trivia;
Some years back I was watching as SBS doco on the study of music where they had 20 or so Conservatorium students in a massive cathedral in Europe. (Names escape me)
The Cathedral housed one of the largest pipe organs on the planet. wow
A blind test was setup for the students where they had to pick the REAL Organ from a Digital Organ which had been setup in the same cathedral.
The samples for the Digital organ were taken from that very same organ.

The same organist played the same piece on both the real and digital organs

Before the second piece had finished I picked the real one.
My Wife was struck by my ability,,, she asked how on earth could you tell?

I said that was easy to pick because the digital organ had far more bandwidth,, the real organ does not have all those hi freq artifacts.
(I may have had a slight advantage because I've heard a few big pipe organs in my youth)

This is why I keep trying to tell guitar players that they will never sound like the old amps because most gear now has way too much bandwidth.
Those old famous Valve amps had very limited bandwidth.
So modern gear including a lot of fancy pants Valve rigs suffer because of that very same issue.
hope it helps folks who are chasing the many secrets of amplification of musical gear.
Phil.