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Messages - Tassieviking

#46
G'day and welcome to the forum.
In my opinion the Drive-55 will not have enough output to drive the power amplifier properly, you will still need a pre-amplifier as well.
You can incorporate the Drive-55 in it like a dirty channel but it wount have enough gain by itself. (In my opinion)

PedalPCB have a lot of Preamp pedals and many of them will most likely drive that amp.

There is the Honey Amp project designed by people on this site (Thanks JoeCool) that is a great starter amp, and you can use the Drive-55 pedal with it as well.
Just look at the top right of the page for the link to the shop.

BAJAMAN on the FSB forum designed many preamps that sound like nice amps for stompboxes, and there are vero board layouts for them as well.They should be able to drive the amp.
https://www.freestompboxes.org

Aion effects have the Sunn Beta and the Lab Series L5 which are nice.https://aionfx.com/projects/

The Preamp pedals are usually able to plug into the return jack on a normal guitar amp and totally bypassing the preamp stage in the guitar amp itself, basically making it a different guitar amplifier.
Hope I make sense, audio circuits are not my area neither, I am a retired electrician myself but I have extensive electronic experience in industry.DC drives,AC drives PLC interfacing etc on machinery that had up to a hundred motors and pneumatic and hydraulics all tied together.
#47
The Newcomer's Forum / Re: Carvin sx amp build
December 09, 2023, 11:48:16 AM
The 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
#48
That is one of the better pictures I have seen of the track side of a PCB, it really helps to see the shadow of the components through the board.
I often use a torch to shine through the board when I take the photo.
Would you be able to take some good clear shots of the component side, it helps to see where the tracks go to.

Perhaps you can open your 150 amp and see if the same link is on the bottom of that PCB ?
It seems to be the same amp basically and the PCB seems to be the same type.
If you do that then you might as well take the photos of that amp.
#49
The Newcomer's Forum / Re: Carvin sx amp build
December 09, 2023, 10:25:47 AM
I think you would have to make your own PCB board for that, my favorite FREE program is KiCad as it has no restrictions at all on what you can do with it.

You can get the PCB made from many different places and they are not that expensive if you shop around.

The first problem will be to work out all the components in the schematic like I mentioned above, if you could open your amp up and find Q21 and Q22 and see what they are would be a good start.

I can't find any values for P1 which is a dual gang pot, see if you can see a number on it in your amp please.

If you take the lid off and take some good photos of the PCB top and bottom it would be a great help so we can work this out with you, especially if the components are easy to read.
#50
Thanks for the Reverb Tank info, I am definitely putting this amp on my to-do build list.
If you have the lid of the amp you could measure the voltage across the 12v Zener diode, I think it's the one behind the big resistor so it might be a bit tight to get at.
You can also tap some components in that area with a plastic or wood chopstick to try to make the LED's flicker on, it is an easy way to look for bad connections.
Make sure the chopstick is plastic or wood only and it should be safe, plastic is the preferred type of course.
#51
The Newcomer's Forum / Re: Carvin sx amp build
December 05, 2023, 06:57:33 AM
Do you have a SX-50 still ?
I am wondering as we will have to identify some transistors (FET's) as they don't seem to be marked on the schematic.
Q21 and Q22 are most likely JFET's in a TO-92 casing so we need to identify them.
The LED's D1, D3 and D5 are most likely red, but best to make sure, they should be on the PCB as well.
#52
The Newcomer's Forum / Re: Carvin sx amp build
December 03, 2023, 10:17:37 PM
I was looking at the schematics as well and we really need to know what model we are talking about, there are differences between the different size amps.
We might also need help identifying some of the components as they might not be marked the schematic.
I was pleasantly surprised when I found  the schematics on Carvins website.
https://carvinaudio.com/pages/guitar-amp-schematics
#53
Would you be able to check the reverb tank for the model ?
I might build myself one of these and the reverb tank information is not on the schematic.
If you could provide all information you can see on the tank I should be able to work it out.
Thanks
Mick
#54
I use KiCad to make schematics, I use it mainly to make up PCB's for stomp boxes and amps i want to build for myself. It is freeware so it costs nothing and is really good and easy to use.

I know the basics of audio circuits but nowhere near as much as many others on this forum, I'm just a retired electrician so I know more about industrial electronics.
cheers
Mick
#55
I redrew the schematic around the channel swiching so you can see it all in one place.
I included the red wire so i put 2 connectors in the circuit.
It might be easier to follow from the switches to +58v
#56
That is a very common relay so most mayor electronic companies have them.
Mouser, RS-Electronics, Element-14, Digikey, etc. just google G5V-1 relay.
If it was the relay not working then the LED's should still work.
I still think you are loosing power somewhere between the 58V (B)and the earth end of the 2k2 resistor.
If I am correct that the LED's are swapped on the schematic and terminal X has to be connected to earth for the overdrive to be on then the problem would be between the 58V and the grounding on the treble pot switch or the foot switch jack.

Are you using the treble pot or the foot switch to select the overdrive channel ?

If you are using the treble pot then try the foot switch instead and see what happens.
If you do not have a foot switch then insert a normal mono plug into the footswitch jack as this should work as well. (guitar lead will do)

Try the opposite of what you have been using to try to eliminate the fault.

It might be a bad part or component, but more likely a solder joint that has gone bad over time from vibrations.
#57
That 5W resistor must be original if both have it I guess.
I had a quick look at the PCB track picture I found on SSGuitar, I painted in the relay and resistor to see how it was set out.
I think the small relay might be similar to an Omron G5V-1 relay.

You cannot view this attachment.
#58
The picture was in post #4, I had to open it in a new window and then download it before I could see it.
It is the resistor standing up near the front panel, it is circled in blue.
I think it is 1k5 5 watt, it is marked "1k5 ohms 5% CW5"
He has re-posted the picture in post #8
I think the small square blue thing behind it is the relay for the  channel switching.

There is a chance that with the resistor standing up like that the solder could develop cracks and cause a bad contact just from the vibrations from the speaker also.

The link I posted in post #8 shows a much smaller component so I wonder if that big resistor is not original, it makes no sense to mount a large resistor standing up like that. Too much weight relying on the solder to support it, it's bound to suffer from mechanical failures with time.
Plus the schematic says 1 watt and that looks like a 5 watt resistor to me.

If you use a torch to light up under the PCB you can sometimes see the copper tracks from the top, see what it connects to.
The link in post #8 shows a partial picture of the tracks as well.

Cheers
Mick


#59
If I have the facts right, the following happens:
1.Distortion channel stops working but amplifier still works but only on the normal channel.
2. When this happens both the normal and distortion LED's go out.

When you want to use the distortion channel you have to pull the Treble knob out, or use the foot switch.
The relay operates and switches the amp to the distortion channel, the relay determines the channel that is used.
power is lost to both the LED's and the relay when fault appears, pointing to the 1k5 1w resistor to me.

I would suspect that the power to the relay goes out, possibly a bad solder joint or a faulty 1k5 1W resistor that goes to the relay from the +58v rail.

It is strange that you are worried about that power resistor that is also 1k5 that is dropping all that powder, there are only 2x 1k5 resistors on that schematic that I can see and they should be 1 watt.

In a previous post the same component was questioned.
https://www.ssguitar.com/index.php?topic=4596.msg36810#msg36810

I think you should try to trace where the 1k5 resistor is that feeds the relay, and then replace it. also re-flow all the solder joints in that part of the circuit.

If you take the PCB out and take some photos of the bottom tracks and the top of the PCB we might be able to help you trace it better.
Inspect the solder joints with a jewelers loupe or strong magnifying glass and you might see the problem.
I have 3 jewelers loupes I use for that job, 10x, 20x, 30x magnification I got from E-bay for dirt cheap. Best buy I ever did.

Edit: I think the red and green LED might be swapped around in the schematic as well.
Cheers
Mick
#60
I would guess that the sound you are hearing is not very loud ?
You most likely are generating the sound with Q205, and possibly Q208.
It would not be very loud because it goes through the 100 ohm resistors to the output.

At a wild guess I would say that Q208 is bad and its driving the TIP42 fully on.
With the 0R5 resistors removed and amp on, do you have any DC output to the speaker ?
Disconnect the speaker and measure the output again, it should be very close to 0 volts if everything is ok.

Are the +32 and -32 volt rails ok ?
I presume the TIP transistors have good insulators behind them, check with a meter.

Without the resistors in the amp the TIP transistors are not doing anything and the amp would not be working very well at all.
A 25 watt acoustic amp would be fairly loud.