Valve Special DSP bypass

[mpoirier]

Hi,

 

I am ready to try the famous DSP bypass surgery on my Valve Special.

 

I read tons of messages about it but I was not able to find clear instructions about how to do it ?

 

Posts from people who actually attempted to do it say that they had to do something else for it to work. Some event mention the DSP is still working !?!

 

Please ! Please ! Please ! Can someone explain in detail the supposedly simple procedure here ?

 

I would really like to use my amp to the fullest...

 

Thanks for your time !!!

 

Michel

[pickpicker]

this mod is not very hard to do.

 

after remove the chasing.

 

1. connect a wire from VR2 Treble Pot (top right) to C6, as shown below:

 

2. remove the built in dsp board, located at top right as shown below:

 

here's the removed dsp board:

 

 

that's it. good luck!

[mpoirier]

this mod is not very hard to do.

 

after remove the chasing.

 

1. connect a wire from VR2 Treble Pot (top right) to C6' date=' as shown below:

http://i298.photobucket.com/albums/mm265/durianpicker/100_5106.jpg

 

2. remove the built in dsp board, located at top right as shown below:

http://i298.photobucket.com/albums/mm265/durianpicker/100_5038.jpg

 

here's the removed dsp board:

http://i298.photobucket.com/albums/mm265/durianpicker/100_5242.jpg

 

that's it. good luck!

 

[/quote']

 

 

Hello !

 

Thank very much you for your reply.

 

It does look simple... However...

 

One quick question, from the picture your showing a red wire from C6 to "Master Volume" (top right) not "Treble" control.

 

Now I am confused. The "Valve Special" schematic shows this as being already wired like this ?!?

 

http://www.sewatt.com/files/sewatt/sewatt/files/epiphone_valve_special_schematic.pdf

 

I also removed the DSP board and the amp still plays just like usual. Is this weird ?

 

Thanks for your help !

 

Michel

[mpoirier]

Hi,

 

I found out what was confusing about the instructions for the DSP bypass. It seems the Valve Special schematic floating around everywhere does not match my amp version ( VER050305 ) and yours probably... It shows the Master Volume "after" the DSP circuit.

 

Looking closely at my board, it appears to me that the Master Volume is "before" the DSP circuit. That is why your mod works as expected.

 

I modified my amp as you explained but with minor difference and it works fine.

 

To make sure the DSP circuit is completely out of the loop, I lifted one leg of C13 and JP52 as shown in the pictures below:

 

 

 

I cannot say the difference is day and night but the tone stack now seems to have quite more effect on the output.

 

I found another schematic image ( poor quality ) with the correct configuration for my board. This is different from the PDF schematic.

 

 

Thanks !

[pickpicker]

yes,

my first pic is for the second schematic you sent. If that's not working, most probably your amp is referred to the first

schematic which you need to connect wire from Master Vol pot to Treble pot (slightly longer).

 

sorry for my misleading instruction on the 1st post. It should be written as '1. connect a wire from Master vol pot (top right) to C6, as shown below:"

 

thanks.

[zatoichi]

Hey, mpoirier - can you ask the guy on the Kramer board what he thinks of the DSP board since replacing the op-amp chips?

 

Thanks!

[mpoirier]

He, he, will do...

 

I will also take some more pictures of the mods I am making for this forum.

 

But these things take a very long time !

 

Michel

[zatoichi]

If I were in THAT big a hurry, I'd be knee-deep in trying to figure out what I'd already screwed up...Time is a precious commodity - use it wisely!

[zatoichi]

I modified my amp as you explained but with minor difference and it works fine.

 

To make sure the DSP circuit is completely out of the loop' date=' I lifted one leg of C13 and JP52 as shown in the pictures below:

 

[img']http://lh5.ggpht.com/michel.poirier.at.videotron.ca/SN_nHR4090I/AAAAAAAAABs/P4iFgcnWSHo/IMG_4150A.jpg[/img]

 

I found another schematic image ( poor quality ) with the correct configuration for my board. This is different from the PDF schematic.

Your post fills me w/ questions!

 

What was different about your mod from what pickpicker described?

 

Is there any chance of seeing the pics of you lifting C13 & JP52? On mine, C13 is THE FURTHEST POINT from everything else...

 

I appreciate you posting that pic of the "new" schematic (050305), but can't make the text resolve - any other way of making the original available?

 

Thanks!

[cGil]

Post the schematic on SEwatt, and I'll see that it gets in the FAQ next to the older version.

 

Gil...

[mpoirier]

Unfortunately, that's all I have guys.

 

It is a little different from what pickpicker did by lifting the jumber and cap leg. Otherwise, it seems to me that you would have the DSP circuit in parallel instead of bypass... (?)

 

I setup a new sites for pictures, I hope this time the pictures are visible for everyone.

 

I am still waiting for a parts list to finish the modification.

 

I can't wait to get this done too !

 

Michel

[zatoichi]

My PCB seems to match yours (VER050305) - have not found a schematic that describes this one. I like the fact that your method does not require removing the PCB from the chassis - I'm surprised to hear you say it didn't make that big of a difference: can you describe the change? Gil, does this sound like his method actually works?

 

One of the strangest things about all this is that the DSP is SO simple to bypass - but there seem to be problems associated w/ every method I've been able to find (loss of bottom seems to be the nr.1) 'Course, the fact that there are at least 2 PCB versions & only 1 actually-legible schematic could be a major source of problems, right there

[mpoirier]

The source of the JPG file I have:

 

http://www.blueguitar.org/new/schem/electar/Epiphone_Valve_Special.JPG

 

In the JPG file, the middle leg of VR6 (Master Volume) is hardwired to C13.

 

The source of the PDF file is:

 

http://www.ppwatt.com/files/ppwatt/ppwatt/files/epiphone_valve_special_schematic.pdf

 

In the PDF file is that the middle leg of VR6 (Master Volume) is already hardwired to C6.

 

 

My board (VER050305) matches the schematic in the JPG file, here's what I did:

 

Lifted the C13 leg connected to middle leg of VR6.

 

Lifted one leg of JP52, the other leg is hardwired to C6, it was just easier to apply solder this way.

 

Lifting those 2 removes the DSP from the circuit.

 

Finally I connected middle leg of VR6 to JP52.

 

 

Michel

[zatoichi]

no loss of bass? no increase in gain/presence/etc?

 

I've just found a source for TI RC4558P opamps (only 40¢ ea), so I believe I'll try replacing the TL072's before I go carving up traces.

 

So, does it matter which leg you pull up? Which leg you solder the jumper to?

[mpoirier]

no loss of bass? no increase in gain/presence/etc?

 

I've just found a source for TI RC4558P opamps (only 40¢ ea)' date=' so I believe I'll try replacing the TL072's before I go carving up traces.

 

So, does it matter which leg you pull up? Which leg you solder the jumper to?[/quote']

 

I noticed a better effect of the tone stack but not that much. Maybe my ears are not discrimating enough...

 

That is why I want to continue with the other mods as described on the Kramer guitar site as soon as possible. But I don't know what are the replacement parts I should buy...

 

It is VERY important to lift the proper leg of the component and connect the proper connection points on the board !

 

But I did not have to carve any trace on the board... Now you got me wondering if I should... :(