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Carvin sx amp build

Started by smsuryan, December 02, 2023, 09:46:59 PM

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smsuryan

 I've owned 2 solid-state carvin sx amps, the overdrive sounds great turned to 7 or 8 with the blues switch turned on.  The clean channel I don't really use too much. I would like to make a similar amp with one channel and lessen the overdrive to that "sweet spot". I used to have a job soldering circuit boards for a living years earlier. I think it would be a fun and challenging project.  I'm sure there's a lot to learn, I've looked at the several schematics for that amp and it's just pages and pages so I'm not sure which one (or more) to reference.  I don't want to launch the space shuttle, just make a decent one channel amp (head), and a solid state is even more satisfying since most amps are tube.  Any advice, references, etc.  I'd appreciate.  I'm not in a giant hurry or anything.  I'd like to do this slowly, carefully, and accurately. 

phatt

Can I suggest you mention the model and maybe a link to Schematic might help.
If you have the Amp open, take some gut shot pics of the internals would be helpful.
Phil. ;) 

smsuryan

Quote from: phatt on December 03, 2023, 05:31:48 PMCan I suggest you mention the model and maybe a link to Schematic might help.
If you have the Amp open, take some gut shot pics of the internals would be helpful.
Phil. ;) 
https://cdn.shopify.com/s/files/1/0476/5297/files/sx-schematics-all.pdf?2270

It's a lot to sift through, not sure how to distinguish where the "blues button" is located and omit the clean channel.  It's been awhile since I've read one of these.  Haven't opened up the amp yet. 

Tassieviking

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
There are no stupid questions.
There are only stupid mistakes.

smsuryan

Quote from: Tassieviking on December 03, 2023, 10:17:37 PMI 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

It's the sx50 model..the smallest one.  Might not be much different than the 100 model?

g1

#5
Quote from: Tassieviking on December 03, 2023, 10:17:37 PMhttps://carvinaudio.com/pages/guitar-amp-schematics
Excellent.  From the SX package on that page, the SX50 is pg.14 and 15 of the pdf.

Quote from: smsuryan on December 03, 2023, 08:50:50 PMnot sure how to distinguish where the "blues button" is located and omit the clean channel. 
The blues button puts back the 500Hz that is notched out for metal and hard rock tones.  It is only on ch.1.
It is shown as S1A and S1B around IC's A3A and A8A.
Around Vol.3 pot (which should be labelled Vol.2?) you can see the 500HZ notch circuit with no defeat switch.

smsuryan

Quote from: g1 on December 04, 2023, 12:32:28 PM
Quote from: Tassieviking on December 03, 2023, 10:17:37 PMhttps://carvinaudio.com/pages/guitar-amp-schematics
Excellent.  From the SX package on that page, the SX50 is pg.14 and 15 of the pdf.

Quote from: smsuryan on December 03, 2023, 08:50:50 PMnot sure how to distinguish where the "blues button" is located and omit the clean channel. 
The blues button puts back the 500Hz that is notched out for metal and hard rock tones.  It is only on ch.1.
It is shown as S1A and S1B around IC's A3A and A8A.
Around Vol.3 pot (which should be labelled Vol.2?) you can see the 500HZ notch circuit with no defeat switch.

Wow! Thanks for your help! I'll check that out!

Tassieviking

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.
There are no stupid questions.
There are only stupid mistakes.

smsuryan

Quote from: Tassieviking on December 05, 2023, 06:57:33 AMDo 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.

Yes I still have it, play through it daily.  What sources are available to buy PCB boards?

Tassieviking

#9
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.
There are no stupid questions.
There are only stupid mistakes.

Tassieviking

#10
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
There are no stupid questions.
There are only stupid mistakes.

phatt

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 8)  8)  8)
Phil.

smsuryan

Quote from: phatt on December 27, 2023, 06:53:24 AM
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 8)  8)  8)
Phil.

How much more involved would it be to build a small amp rather than the pedal?  I've never built an amp from the ground up.

phatt

 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.

smsuryan

Quote from: phatt on December 28, 2023, 07:09:46 AMI 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.

Thanks for the advice! I've started building my own guitars years ago because it's less expensive than a custom shop and wanted to carry that spirit over to amp building, without the expense and replacement of tubes.  Lots of great solid states now... I'll try to make a pedal first, I'll let you know how it goes.  This site is a great resource! Thanks guys!