Lay outs for effect loop (pre amp out - power amp in)TWIN STYLE AB763

[tedsorvino1]

Hi there.
I'm looking for some appropriate documentation (a Lay out would be more prefferable to a schematic) for adding an effect loop (pre amp out - power amp in) to my Twin Style AB763 amp.
Either passive, or active. Whatever works better.
Thank you in advance.

[tubenit]

https://store.metropoulos.net/products/zero-loss-fx-loop-kit

ARCHIVES:        http://el34world.com/Forum/index.php?topic=10208.0

[tedsorvino1]

Thank you TUBENIT. Really helpful to understand that it can be done and approximatelly how it works.
But I can't find any exact relevant documentation which loop is the most appropriate for an AB763 - Twin style, and where in the circuit it should be placed. I mean the exact location (a lay out would be helpful).

[tubenit]

I don't think there is a "best FX loop" for AB763.  There are plenty that will work quite well.  Individuals will have their own preference about which one they think is best.  Typically the loop is inserted prior to the LTPI in the signal chain after the preamp tubes.  Very simple.

You can simply do a passive FX loop if you want with two stereo jacks (send and receive) prior to the LTPI. 

I don't know of a layout for a Twin AB763 with an FX loop?   Having said that,  there is ALOT of information on this forum and on the internet about install FX loops in an amp.   

It should be noted that the Metro Loop has fantastic documentation on how to install one. PLEASE read that information as I think it will answer many of your questions.  Since it is built on a layout board already, you don't need to have a AB763 layout board incorporating the FX loop.

With respect, Tubenit

[tedsorvino1]

Thanks again.
The METRO board is slightly expensive for what it is IMHO. I don't doubt their expertise. I will read their documentation again.
On the other hand the new schematic you ve sent me shows a tube involved in the fx loop.  It goes just after pre amp (vibrato or normal channel in my case---around two resistors I think) and just before phase inverter, I guess.  But I seriously doubt it that there is space for another or two more tubes in there.

[tubenit]

You can do a passive effects loop.  There are numerous delay pedals for example that work fine in a passive loop among ones that worked for me were the Carbon Copy,  Moen Pretty Dolly and Boss Delay

You will have to experiment with what value pot.  Maybe a 50ka (or somewhere between 25ka and 100ka) would work?  You could also use a resistor to instead of the pot.

With respect, Tubenit

[2deaf]

What exactly is your Twin style ab763?  Two channels?  Vibrato?  Master volume?  Actual Fender Twin?  Kit?

[tedsorvino1]

I would also like to be able to use the Power Amp section with a different pre amp and the Pre Amp section on its own. Is this possible with a passive loop Tubenit?

Hi 2deaf. It's an old  70s Italian silverface Twin copy modified as a Blackface Twin AB763. No Master. 2 channels Vibrato - Normal. Diode bridge rectifier. Opto tremolo.  Normal channel modified with Mosfet after the pre amp tube 1 for a more Marshall tone. The power section is powered by 2 KT66.

[tubenit]

I have run preamps of one amp into the power section of an amp that has passive effects loop.  And I have done the same thing with an amp with active effects loop.

I can NOT reassure you this will work for you, but it worked fine for me and I was happy with it.  Here is a soundclick demonstrating that:
https://www.soundclick.com/html5/v3/player.cfm?type=single&songid=9488477&q=hi&newref=1

With respect, Tubenit

[2deaf]

Hi 2deaf. It's an old  70s Italian silverface Twin copy modified as a Blackface Twin AB763. No Master. 2 channels Vibrato - Normal. Diode bridge rectifier. Opto tremolo.  Normal channel modified with Mosfet after the pre amp tube 1 for a more Marshall tone. The power section is powered by 2 KT66.

So the two channels probably mix together with two resistors right at the input capacitor for the PI.  If so, you would break the signal where these resistors connect to the PI capacitor.

There is a problem with a passive loop at that point.  The PI will be driven by the output from an effects device and most of them don't put out enough signal to fully drive the PI.  Most active effects loop kits boost the signal going back into the PI to overcome this problem.

 

[tedsorvino1]

Thanks guys for the info, but without an appropriate layout or schematic  and the exact connections (either of a passive or active loop) for the particular circuit (two channel AB763) I can't afford to risk something that may not work.

[tubenit]

Thanks guys for the info, but without an appropriate layout or schematic  and the exact connections (either of a passive or active loop) for the particular circuit (two channel AB763) I can't afford to risk something that may not work.

Looks like you've made a good decision for yourself that I fully support. 

Having said that, I'd like to point out a few things:

1)  You never provided us a schematic or layout of your specific amp. Nor did you even
     provide photos.  And per your reply #7,  it's not a true Twin AB763.

2)  I suspect the Metro Loop would work fine for you, but you vetoed that saying "it's slightly expensive". Your reply #4  I
     view the cost was remarkably inexpensive.

     The Metro Loop had very detailed instruction and the layout was not an issue since they did that for you. 

3)   Then you vetoed using a tube active effects loop in Reply #4  saying that "I seriously doubt it that there is space for
      another or two more tubes
      in there"   (There is only one tube used for active FX loop)

4)  Finally we go down to simply installing and wiring two jacks up for a passive FX loop.  We provided both a schematic
     and explanation of the simplicity of that & you respond " you can't afford to take the risk".  It involved one pot and two
     jacks. Pretty simple.

5)  It should be pointed out that Reply #8 in the Archives on active FX loops provided both a layout and a schematic. 
     However,  since you haven't provided a schematic, layout or photo of your specific amp, we were not
     able to help you any further.

I don't care whether you have an active FX or not.  I personally would not want one on a Twin AB763 and would be happy with reverb and tremolo.

In summary, you vetoed:

- a compact PCB board that is inexpensive, well documented and has great reviews
- using a tube for FX
- simply passive FX that has a schematic and explanation "only" (because you never provided a schematic, layout or photo
  of your amp)

 

In the future, when and if you ask help on "your" amp, please provide a schematic and layout of your amp.  The forum members can't provide you a schematic or layout of your amp since it's not truly a  Twin AB763 and you did not give us a schematic, layout or photos to work with.

I say the above respectfully and in good will towards you.  Tubenit

 

[pdf64]

I don't understand what benefit folks perceive with adding an FX loop to a non master volume amp 

[tubenit]

I don't understand what benefit folks perceive with adding an FX loop to a non master volume amp 

I installed one in my Tweed BluezMeister and the FX  level was used as the "master volume".  There was no pre LTPI master volume nor PPIMV. 

With respect, Tubenit

[tedsorvino1]

I totally understand what you 're saying Tubenit. And there is no misunderstanding
I just thought that there may be a standard loop mod for a Twin style amp (even if it's not necessary). And I thought it may be quite simple. It may be, but it's not so obvious to me, since it's not applied on the particular AB 763 schematic - layout.
And yes the Metro one may be a good solution, after all (for me it's quite expensive, since there is international postage and a probable duty tax,  involved)
But thank you anyways for the help.

[2deaf]

Tube-Town in Germany has a "Seriel FX-Loop LND150" kit for 29,90 EUR plus shipping.

[pdf64]

I don't understand what benefit folks perceive with adding an FX loop to a non master volume amp 

I installed one in my Tweed BluezMeister and the FX  level was used as the "master volume".  There was no pre LTPI master volume nor PPIMV. 

With respect, Tubenit

So the 'fx level' control sits after the preamp and affects the signal level? That would seem to be a master volume type amp then.

From http://carlscustomamps.com/master-volumes-and-their-uses/

What is a master volume?

A master volume basically allows the user to turn up the pre-amp section while controlling the signal going to the power amp controlling the overall volume of the amp.  In a non-master volume amp this control does not exist.

Your amp, you choose the control labels, but if your 'fx send' looks and functions like a master volume, it then seems incorrect to think of  the amp as 'non master volume', just because a control that acts as master volume has been labelled otherwise.

Sorry if I've misunderstood something

[sluckey]

This is a simple task to add a preamp out and power amp in to any AB763 twin reverb amp. All you need is two Switchraft 12A phone jacks. Cost under $6. Look at page 2 of this pdf to see how to connect them between the preamps and phase inverter input cap. This particular drawing shows a master volume but the standard AB763 will just have two 220K mixing resistors.

     http://www.sluckeyamps.com/misc/76_Amp_Project.pdf

If what I said above doesn't make sense to you, or you can't read a schematic, then just use google to find a "paint by numbers" drawing that shows exactly where to put every wire. This is not hard to do but it will require a little bit of effort on your part.

[tedsorvino1]

Thank you Sluckey. It's pretty obvious where it goes and I will do my further research, 2 deaf I will definitelly check with tube town.

[SILVERGUN]

I don't understand what benefit folks perceive with adding an FX loop to a non master volume amp 

I installed one in my Tweed BluezMeister and the FX  level was used as the "master volume".  There was no pre LTPI master volume nor PPIMV. 

With respect, Tubenit

So the 'fx level' control sits after the preamp and affects the signal level? That would seem to be a master volume type amp then.

From http://carlscustomamps.com/master-volumes-and-their-uses/

What is a master volume?

A master volume basically allows the user to turn up the pre-amp section while controlling the signal going to the power amp controlling the overall volume of the amp.  In a non-master volume amp this control does not exist.

Your amp, you choose the control labels, but if your 'fx send' looks and functions like a master volume, it then seems incorrect to think of  the amp as 'non master volume', just because a control that acts as master volume has been labelled otherwise.

Sorry if I've misunderstood something

He was referring to the FX Return control as a Master because of it's placement in the circuit.

I think the misunderstanding is just that tubenit was responding to your statement:
"I don't understand what benefit folks perceive with adding an FX loop to a non master volume amp"
He provided an example of a perceived benefit to someone adding an FX loop to a non-master volume amp.
That, in his case, the addition of the FX loop brought a master volume control into the circuit and that could be seen by some as "beneficial".
Respectfully,
SG

[jojokeo]

I don't understand what benefit folks perceive with adding an FX loop to a non master volume amp 

I installed one in my Tweed BluezMeister and the FX  level was used as the "master volume".  There was no pre LTPI master volume nor PPIMV. 

With respect, Tubenit

So the 'fx level' control sits after the preamp and affects the signal level? That would seem to be a master volume type amp then.

From http://carlscustomamps.com/master-volumes-and-their-uses/

What is a master volume?

A master volume basically allows the user to turn up the pre-amp section while controlling the signal going to the power amp controlling the overall volume of the amp.  In a non-master volume amp this control does not exist.

Your amp, you choose the control labels, but if your 'fx send' looks and functions like a master volume, it then seems incorrect to think of  the amp as 'non master volume', just because a control that acts as master volume has been labelled otherwise.

Sorry if I've misunderstood something

Ugh... beware of people that perform inferior work and provide inferior information...

[jojokeo]

What a bunch of wasted time and thread space over simple send/return help that won't be heeded (and was provided from the very beginning)... excuses excuses... You can lead a horse to water but...