Vox Cambridge V30 Send Return Project, Help Please

[fair.child]

Hey folks,

Now, I have my USED Cambridge amp V30 twin reverb here. I have a question with my related project here,

1) How do I put send and return to this amp ?
2) Is it possible to do that ? Literally, I need this function to grab advantage from the VOX power amp and connect that with Axe Fractal II

Okay these are the basics question to start with. I have some thoughts regarding my project, and indeed, it's good to have a thought before start to post something here. Here are my quick views;

1) I've found the right schematic and it seems match with my vox amp

http://music-electronics-forum.com/attachments/5429d1242749475-cambr-schema.jpg

2) Here are some gut shots inside of my amp


IMG_0816 by DIY Parts + PCB Center, on Flickr

I believe I need to do some work here, because TDA2050 is a power op amp IC


IMG_0822 by DIY Parts + PCB Center, on Flickr


IMG_0820 by DIY Parts + PCB Center, on Flickr

Final Shot


IMG_0813 by DIY Parts + PCB Center, on Flickr


Indeed, it's working amp and good amp, it has reverb, clean and crispy overdrive, however, I just need the power amp selection to run the send and return without any colored sound. I intend to re-solder the TDA2050 and make the connection to Power amp input and Power amp out, which this what I'm confusing about. And yes, I've already read the TDA2050 data sheet, but I still confuse what is the difference between non inverting input and input, which one that should I solder to obtain the real uncolored sound to my amp ? and I ensure that TDA2050 pin 4 is the output and it means that the return, doesn't it ? well if I'm wrong, please kindly correct me

Implied with my two questions above, I need to know what should I do if I want to make send / return (effects loop) with this amp

Any suggestions and thoughts are welcome here, please help me

Thank you
Cheers all

[R.G.]

1) How do I put send and return to this amp ?
2) Is it possible to do that ? Literally, I need this function to grab advantage from the VOX power amp and connect that with Axe Fractal II

It's possible. There are several methods.

...I just need the power amp selection to run the send and return without any colored sound. I intend to re-solder the TDA2050 and make the connection to Power amp input and Power amp out, which this what I'm confusing about. And yes, I've already read the TDA2050 data sheet, but I still confuse what is the difference between non inverting input and input, which one that should I solder to obtain the real uncolored sound to my amp ? and I ensure that TDA2050 pin 4 is the output and it means that the return, doesn't it ?

I thought I knew what you wanted, but correct me if I'm wrong.  Do you want to effectively not use the preamp and effects on this amp at all, and insert some other thing (Axe Fractal??) as what the signal comes through to let the 2050 power amp still work the speaker in this amp?

If so, you cut the connection between R47 and point C, and insert a send/receive jack pair there. I personally would also put in a protection network to keep the outside world from possibly destroying the power amp input on pin *1*.  The protection network will be a 1M to ground, a series 10uF NP capacitor from the return jack in series with a 1K resistor, and I would add a four-diode shunt clipper to keep big voltages which are accidentally hooked in from damaging the power amp chip - or worse yet, the speakers.

[fair.child]

1) How do I put send and return to this amp ?
2) Is it possible to do that ? Literally, I need this function to grab advantage from the VOX power amp and connect that with Axe Fractal II

It's possible. There are several methods.

...I just need the power amp selection to run the send and return without any colored sound. I intend to re-solder the TDA2050 and make the connection to Power amp input and Power amp out, which this what I'm confusing about. And yes, I've already read the TDA2050 data sheet, but I still confuse what is the difference between non inverting input and input, which one that should I solder to obtain the real uncolored sound to my amp ? and I ensure that TDA2050 pin 4 is the output and it means that the return, doesn't it ?

I thought I knew what you wanted, but correct me if I'm wrong.  Do you want to effectively not use the preamp and effects on this amp at all, and insert some other thing (Axe Fractal??) as what the signal comes through to let the 2050 power amp still work the speaker in this amp?

If so, you cut the connection between R47 and point C, and insert a send/receive jack pair there. I personally would also put in a protection network to keep the outside world from possibly destroying the power amp input on pin *1*.  The protection network will be a 1M to ground, a series 10uF NP capacitor from the return jack in series with a 1K resistor, and I would add a four-diode shunt clipper to keep big voltages which are accidentally hooked in from damaging the power amp chip - or worse yet, the speakers.

Hey Great R.G

thank you for your response, I really appreciate that, instead I was trying to make a move solder my thoughts.

I've already tried my first move to solder first ping of TDA2050 and fourth pin also the third pin for the ground, and as result, no sound, dead amp, okay, I chose to put back and decided to keep the amp as the original though, it worked out

hmm, about cut connection between R47 and point C, how should I do with that ? cut the PCB trace or re-solder the component ? and about effectively not use the preamp section and effects on this amps, yes correct, we have the thought here, and again indeed I wanted to use just the power amp section of this amp. Furthermore, I just wanted to use both functions of the amp (Vox amp and send return (effects loop)), which  it lets the 2050 power amp to loud up the speaker. Yes, again your thought is perfectly right!!!

the protection would be like


tip by DIY Parts + PCB Center, on Flickr

Please correct me R.G if I'm wrong, then I need to know what should I do with the main board and Power amp board (in this case, means TDA2050)

Thank you R.G

Cheers

[R.G.]

What I had in mind was this:


I also showed a note about the use of zeners in these amps to get the low voltages from. It's a failure prone way to do it. I recommend changing those out for three terminal regulators, although with you not using the preamp, it may not matter. The first jack after the preamp is the send, the one closest to the power amp is the return. The jacks are mono with tip shunts. The shunts are wires so that when nothing is plugged in, signal flows through them to the power amp like before.

[fair.child]

What I had in mind was this:


I also showed a note about the use of zeners in these amps to get the low voltages from. It's a failure prone way to do it. I recommend changing those out for three terminal regulators, although with you not using the preamp, it may not matter. The first jack after the preamp is the send, the one closest to the power amp is the return. The jacks are mono with tip shunts. The shunts are wires so that when nothing is plugged in, signal flows through them to the power amp like before.

Sweet!!!! Love that R.G

I have few question here, regarding your last post
1) What kind of zener that should I use ?
2) Is it okay if I change the terminal regulator to 7805 or do you have any recommendation for the regulator ?
3) I think about master volume ? Do I need to re-solder the master volume for this amp ?

In sum, I have two options actually, I wanted to make this have a send and return (effects loop), also I wanted to make it to regular vox preamp which means in future if I forget to bring my fractal then I still can use my vox amp as regular Cambridge V30 twin reverb. To make this real, I need to emphasize again, that I need to make effects loop without losing my original vox preamp. Based on your schem, I need to cut connection between R47 and C, and it means that I would not be able again to use my vox preamp section and I can only use only the power amp section, for this case, should I use SPDT switch to make it more reliable ?

Thank you RG

[R.G.]

1) What kind of zener that should I use ?

I was recommending removing the zener diodes that are already there. Actually, that is an advanced thing, and I recommend you don't mess with the power supply until you get everything else running correctly. Then see if you want to that that. It's a fair amount of work and I did not draw in the circuits to do it.

2) Is it okay if I change the terminal regulator to 7805 or do you have any recommendation for the regulator ?

No, probably not. As I said, don't mess with this until you get everything else done - and probably when you have more soldering skills.

The 7800 and 7900 series of regulators have the last two numbers as their voltage. 7805 is a 5V regulator, and won't do what you want, even if it works OK.

The 7800 series is positive voltage, so the 7815 is +15V and the 7809 is +9V. The 7900 series is negative voltage regulators; 7915 is -15V and 7909 is -9V. The pinouts are different from 7800 series to 7900 series.

3) I think about master volume ? Do I need to re-solder the master volume for this amp ?

I didn't notice a master volume on it, but then I didn't look through the preamp circuits in any detail. Do you need a master volume?

In sum, I have two options actually, I wanted to make this have a send and return (effects loop), also I wanted to make it to regular vox preamp which means in future if I forget to bring my fractal then I still can use my vox amp as regular Cambridge V30 twin reverb.

That's what this circuit does. If you plug an external effect into the send/receive loop, you get the Vox preamp through the effect loop. If you use your Fractal (?) then you just plug the outboard unit into the receive jack. This disconnects the internal Vox preamp and now the Fractal uses only the power amp and speakers.

To make this real, I need to emphasize again, that I need to make effects loop without losing my original vox preamp. Based on your schem, I need to cut connection between R47 and C, and it means that I would not be able again to use my vox preamp section and I can only use only the power amp section, for this case, should I use SPDT switch to make it more reliable ?

The switching in the tip shunts in the jacks do the switching for you when you plug in a cord. I believe it already does what you want. This is the most common way for amps to plug in effects loops. Your Vox preamp still works as long as neither the send nor receive jack is plugged into - and as long as the internal switch contact doesn't get dirty, but that's another and different problem.

You can use an SPDT switch if you like, but then you have to find a place to mount the switch as well as the send-receive jacks. It will also confuse things if both the jacks and a switch set whether the inboard preamp works.

Another thing you can do is to not cut the connection between R47 and point C. This makes whatever is plugged into the receive jack be mixed into the power amp with whatever the Vox preamp is doing. You can mute the Vox preamp by turning the volume down on it. However, the send jack can't be used the same way if you do this, and should be left off.

[fair.child]

1) What kind of zener that should I use ?

I was recommending removing the zener diodes that are already there. Actually, that is an advanced thing, and I recommend you don't mess with the power supply until you get everything else running correctly. Then see if you want to that that. It's a fair amount of work and I did not draw in the circuits to do it.

2) Is it okay if I change the terminal regulator to 7805 or do you have any recommendation for the regulator ?

No, probably not. As I said, don't mess with this until you get everything else done - and probably when you have more soldering skills.

The 7800 and 7900 series of regulators have the last two numbers as their voltage. 7805 is a 5V regulator, and won't do what you want, even if it works OK.

The 7800 series is positive voltage, so the 7815 is +15V and the 7809 is +9V. The 7900 series is negative voltage regulators; 7915 is -15V and 7909 is -9V. The pinouts are different from 7800 series to 7900 series.

3) I think about master volume ? Do I need to re-solder the master volume for this amp ?

I didn't notice a master volume on it, but then I didn't look through the preamp circuits in any detail. Do you need a master volume?

In sum, I have two options actually, I wanted to make this have a send and return (effects loop), also I wanted to make it to regular vox preamp which means in future if I forget to bring my fractal then I still can use my vox amp as regular Cambridge V30 twin reverb.

That's what this circuit does. If you plug an external effect into the send/receive loop, you get the Vox preamp through the effect loop. If you use your Fractal (?) then you just plug the outboard unit into the receive jack. This disconnects the internal Vox preamp and now the Fractal uses only the power amp and speakers.

To make this real, I need to emphasize again, that I need to make effects loop without losing my original vox preamp. Based on your schem, I need to cut connection between R47 and C, and it means that I would not be able again to use my vox preamp section and I can only use only the power amp section, for this case, should I use SPDT switch to make it more reliable ?

The switching in the tip shunts in the jacks do the switching for you when you plug in a cord. I believe it already does what you want. This is the most common way for amps to plug in effects loops. Your Vox preamp still works as long as neither the send nor receive jack is plugged into - and as long as the internal switch contact doesn't get dirty, but that's another and different problem.

You can use an SPDT switch if you like, but then you have to find a place to mount the switch as well as the send-receive jacks. It will also confuse things if both the jacks and a switch set whether the inboard preamp works.

Another thing you can do is to not cut the connection between R47 and point C. This makes whatever is plugged into the receive jack be mixed into the power amp with whatever the Vox preamp is doing. You can mute the Vox preamp by turning the volume down on it. However, the send jack can't be used the same way if you do this, and should be left off.

nice stuff and blunt answer R.G, again, I really appreciate your time to help me figure how to deal with this amp.

however, I have several thoughts here;

1) About the condition, yes, I've noticed that you already given the zender diodes or regular 1N4xxx diodes for the schematic. My question, what are the type of diodes that should I use for it ?, the one, it is near with 1K resistor.

2) Actually the only thing that I need is the power amp, it means return jack, I won't use send as my effects loop for now, but in the future probably I will use that, so I think this project will be a good investment to play with a lot of rig, such as stompboxes and other amplifier, (marshall, boogie, HK, etc) but right now I just need that to plugged that with my fractal system so I can use just the power amp section only to run that.

3) Okay lets say that I did your schem, and cut the connection between R47 and C, so what will happend to my amp ?
am I going to not be able use my vox preamp or what if I just make another solder joint from R47 point to build effects loop, without cutting the R47 ?

4) Grounding system, do I need to put the grounds into one point or I can make that into other ground points  ?

5) How do I put the master volume ? what do you think ? do I need to put the master volume for the effects loop  ?


Cheers, and thank you RG

[fair.child]

Finally I've got it worked out with me !! Thanks a lot RG


IMG_0893 by DIY Parts + PCB Center, on Flickr


IMG_0867 by DIY Parts + PCB Center, on Flickr