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Messages - Tassieviking

#1
Great explanation Phil, helped me understand it better.
Thanks.
Michael
#2
If you want something that slips into that chassis, start looking around for another Peavey,
You like the sound of the amp so just get another one,

If you get the same amp you can start looking up some electronic lessons on the web, and then start taking measurements on both amps and slowly trace the fault yourself.
You might slowly learn more and more, get the amp fixed eventually.

I bet you would start building your own stomp boxes in no time.
I saw a Peavey Special 130 go for $65 at an auction where I live 2 weeks ago.
Keep looking till you find what you want.
Just don't throw it out, someone else would love to have a go at repairing it.
#3
A quick drawing of how most pre-out signals go into poweramp-in jacks, but not always on every amp.You cannot view this attachment.  You cannot view this attachment.
This is the switch that plays up when you lose signal to the power-amp with no jacks inserted, I like to get a small strip of normal printer paper and put a drop of WD40 or contact cleaner on the paper, put between the contacts and run paper up/down to clean the switch contacts.
There is no need to spray lots of anything in there, the paper will rub the dirt away, simple.
#4
The coupling caps are C41 and C42, they are in parallel to form one capacitor of 0.2 uF
Measure the DC output of the power amp with black probe on gray wire and red probe on yellow wire going to the speaker jacks on the back panel.

IF YOU HAVE DC ON THE SPEAKER JACK, MAKE SURE YOU DO NOT PLUG THE SPEAKER IN.
DC on a speaker can cook the speaker coil, not a good thing at all.
Maybe isolate the power amp from the pre-amp, put a plug into the FXreturn jack, even plug the speaker into the FXreturn as this isolates the power amp from the pre-amp and it makes sure there is no input on the power amp.

Also, running a lead from the FXsend to the FXreturn does nothing, there is no buffer or anything else that magically appears.
If you trace the wires you will see that the fxsend is wired directly to the fxreturn socket, when you plug into the fxreturn this link is broken by the switch in the fxreturn jack.
#5
Have you got +16V and -16V on the board ? Check all fuses if not.
Measure voltage across C61, C62 for 16V dc   (+C61 to -C62 = 32V dc)
Measure voltage across C55, C56 for 42V dc   (+C55 to -C56 = 84V dc)
What is the DC voltage on the speaker output ? is it + or - voltage ?
A few mV on the speaker output is ok, 40V is very bad.

Here is the schematic for you to check with.
Output transistors are Q7, Q8, Q11, Q12
You cannot view this attachment. 
#6
Amplifier Discussion / Re: Lab Series L4 Bass Preamp
September 05, 2022, 01:02:41 PM
I should also include the original schematics I started with I guess.
Also the OTA's datasheets.

I would love to make up a PCB for a full preamp and use a class-D power amp with it.
And also a Pre-amp pedal.

Has anyone else ever noticed that the TPA3116D2 Bridged 100W amplifier module with XH-M542 written on the bottom fits easily into a 125B pedal enclosure with plenty of room for 2 jack sockets and a power socket at the top end. (2-4 ohm in bridged mode)

Run it on a 4.5V wall wart for approx 5W output to 24V for 70Watt output at 1% THD
Advertised as 100W output or 120W on most E-bay stores, but distortion is 10% THD.
Google TPA3116D2 or XH-M542 amp and you will see the one I am talking about.

Rock up to practice with 2 pedals and a speaker cab and blow them away ?
 Most of us can grab an old laptop power supply from somewhere to power it,

Anyhow, here are the rest of the schematics :-
#7
Amplifier Discussion / Lab Series L4 Bass Preamp
September 05, 2022, 12:19:54 PM
G'day guys and gals
I have been wanting to make a Lab Series Pedal for a while, recently I was talking to a young dude who plays Bass in "June And The Desert Flames".
While I was talking to him I realized he does not have a lot of gear and I can easily build some Pre-Amp pedals and some effect pedals for him fairly easy.
I have some PCB's for Sunn Beta pedals, Chunk System Brown Dog/ Agent 00Funk, etc at home.
I also thought it might be a good time to get into a Lab Systems PCB, the L4 Bass is simpler then the L5-L11 pedals so its a good starting point for me.

I have tried to change the CA3094 and CA3080 IC's to one LM13700 IC, but I am not that good on theory, I gave up working as an electrician 15 years ago because of all the narcotic pain killers I have to take every day.

Could some of the really great people who post here check my changes please and see if it is feasible to replace the 2 IC's with one LM13700 please.

I have read through lots of posts on this type of modification on the net and did the best I can, my brain is too forgetful to try working it out or trying to simulate it.
If someone knows how much the +- 15V rails use would also be great, I would love to power it from a LT1054 or similar on 9V supply.

Thank,
Michael

#8
Amplifier Discussion / Re: 12w Marshall
September 05, 2022, 10:51:44 AM
If you want to see the pictures larger, right click on the small picture and select open in new window, this makes the picture really large.
#9
Amplifier Discussion / Re: 12w Marshall
September 05, 2022, 10:49:37 AM
I have finally gotten back home a week ago and had some time to  work on this PCB, I can't guarantee it's correct but I will order some PCB's for myself later this year to test.

I decided to squeeze in a 9V regulator for pedals as its a smaller amp and is good for practice and learning on, and it cant hurt to be able to run a pedal or two from the amp.

I have made the Gerber files for JLCPCB to make the boards, but feel free to use the project any way you want.
I am going to use the KiCad schematic to make a pedal eventually as well, without the reverb circuit (unless I can get the correct mini spring pan).
#10
I can think of one more thing you can try, increase the taper of the pot.
place a resistor between pin 1 and pin 2 of the pot and the audio taper curve will increase.
The taper effect will be more pronounced at low volumes, you can buy audio pots with different taper curves, but the easiest way is just add the resistor.
You can read more here :http://www.geofex.com/article_folders/potsecrets/potscret.htm
It would give you even more control at low volumes.
#11
You cannot view this attachment.

All I have on small Orange amps

Also this thread on DIY stompboxes :  https://www.diystompboxes.com/smfforum/index.php?topic=87122.0

This video shows a schematic as well : https://www.youtube.com/watch?v=7WM6HoQmDgU
#12
Scoobynuts, please take note of the fp before the 130 on the resistor.
This might mean the resistor should be fireproof, if it fries again it will not go up in flames as long as you use a fireproof resistor.
I could be wrong, but would you chance it. Some of the more knowledgeable people here might pipe in and I and others might learn something important if they know what it stands for. :)
If it might get hot, make sure you leave some space under the resistor for airflow, also makes the PCB less hot.
#13
Amplifier Discussion / 12w Marshall
July 22, 2022, 01:39:40 PM
I started to looking into building a 12 watt Marshall by mixing all the 12watt Preamp circuits I found, and also mixing the 12 watt and a 30 watt amp circuit in Marshall amps so I could make any one of the 12 watt amps with 12 to 30 watts output on the same PCB. You just had to pick the right components to make the version you wanted.
Some 12 watt amps had a Bias pot and some did not. Mk1 preamp has diode clipping and the later ones dont, etc.

I got derailed when my dad got sick, traveled from Tassie to northern NSW (Australia) and spent 4 weeks with him. Had to go back to Tassie for medical reasons and be with my family for a week, then back as dad passed away as soon as I left, stayed 5 weeks then back home for Doctor visit and now I am going back up to pack what I want to keep and sell the rest, sell houses, cars,  etc.
I am going to sort all my stuff nice and neat when I get a chance because its hell trying to go through your parents stuff when they are both gone and everything is all over the place.

Anyway, this is as far as I got on a 12 watt amp before the wheels fell off.
I was going to post the KiCad files  of the PCB when I finished and still might when or if I get back to it. I put a jumper on the board if reverb is not wanted, and a place for effects to be inserted which can be bridged if not wanted.
I made the PCB so TO3 transistors had to be wired in or TO247 can be used on PCB.


#14
I have seen at least 3 different Marshall 12 watt amp schematics, one has what looks like clipping diodes.
And then there are the 12 watt Reverb models as well to consider.
#15
Thanks guys for the answers, I think I will not keep the Electrolytic caps since I don't know the age of them.
Better be safe then sorry.