Princeton / adding loop Complete

[Ed_Chambley]

I took out my chassis and drilled holes for a loop installed jacks.  Hooked up test speaker and checked amp.  I got a squeal.  Changed tubes.  No luck.  Checked plate voltages with tubes pulled.  I was 417, now 480.

Checked the PT and reds are 350-0-350vac.  Centertapped.

It is a 660vac  Bias supply 54 vac.  Heater 5.2.  

B+ 480vdc and grids about the same. Changed rectifier tube a couple of time. 5u4gb.
The PT is a 660.  Wall voltage is 121.

Anyone have any idea?

[phsyconoodler]

Phase issue.Same as when you have the plate wires switched on an amp with negative feedback.
 Where do you have the effects loop wired into?

With the tubes pulled it's normal for the unloaded voltage to be higher.Totally ok there.

 Squeals are indicative of phase,oscillations and such wonderful hard to find issues.Obviously the changes are the loop and how it's wired into your amp.
 

[Ed_Chambley]

The loop is not wired.  Just grounded.  I did not want to wire it until I figured out the best lead dress for it.  I just drilled holes and installed the jacks.

I not change anything in the circuit.  I have attached what I was going to use.

I can check the loaded voltages.

[phsyconoodler]

Ok,so you haven't wired in the effects loop and you are getting a squeal.Was the amp ok before you installed the jacks?If so,you may have put the ground for the loop somewhere other than actual ground.Like maybe the tip of the output jack?
 I am assuming the amp was ok before you installed the loop jacks.Is that correct?

[Ed_Chambley]

It solved the problem moving the ground to the bus wire on the pots.  I am installing the loop on the front of the amp.  No room on the back.  Back to normal voltages.  Wow, I had no idea grounding the loop on the chassis could cause this.

Now for the lead dress.  Think it would be best to use shielded since I will have a fairly long run of wire?.

[Willabe]

Think it would be best to use shielded since I will have a fairly long run of wire?

I'd say yes on the return. Might not need it on the send even if it's a passive loop and you put the coupling cap right on the send jack. Probably won't need it on the send if it's a CF buffered (low impedance) loop.

Also from your schemo, I think I'd move the verb return to the loop return. The way it is now any FX you put in the loop will be fed verb and than the verb will be flanged/chorused/delayed, instead of the FX sound being washed in verb.

OR make the verb and loop parallel instead of series.

  
                     Brad    

[Ed_Chambley]

Think it would be best to use shielded since I will have a fairly long run of wire?

I'd say yes on the return. Might not need it on the send even if it's a passive loop and you put the coupling cap right on the send jack. Probably won't need it on the send if it's a CF buffered (low impedance) loop.

Also from your schemo, I think I'd move the verb return to the loop return. The way it is now any FX you put in the loop will be fed verb and than the verb will be flanged/chorused/delayed, instead of the FX sound being washed in verb.

OR make the verb and loop parallel instead of series.



  
                     Brad    

I do not know what you mean by making the verb and loop parallel?  I get returning the verb to the return, but do you think there would be much difference?  Your statement "washed in  verb".   If they are returned at the same place how will that change any modulation effect from still being washed in verb?  I am planning to experiment, but I have an underboard wire that it looks as the loop will replace.

First PDF is not correct.

[Willabe]

Hi Ed,

I get returning the verb to the return, but do you think there would be much difference?

Yes. Most, if not always, reverb is the last Fx in a pedal board string, not the 1'st. If you where running pedals into the front end of an AB763 with built in reverb, it would automatically put the reverb last.

Do you want verb on the flanged guitar signal or do you want to flange the reverberated guitar signal? I think the 2 would sound pretty different.

Your statement "washed in verb". If they are returned at the same place how will that change any modulation effect from still being washed in verb?

It won't. But that's my point. Now the verb is after not before any Fx. Depending how you do it they might be in series or in parallel, but the verb won't come before any Fx.

I do not know what you mean by making the verb and loop parallel?

You split the feed signal into a Y from the preamp to the Fx loop and the verb. Then you mix the 2 returns back together. So the Fx loop is parallel to the verb loop. When their mixed back together any effect run through the Fx loop will get washed in verb. You can mix Fx like this in the recording studios.

On a Fender BF- SR/DR/TR.... the dry signal is in parallel with the reverb (loop) signal.

Now that I think about it, from your schemo, if you move the reverbs return to the Fx loops return, they would be in parallel.

                      
                               Brad      

[Ed_Chambley]

Ok, you convinced me.  I am having trouble.  I attempted too many mods this weekend.  All went well except this one.  I got the schemo from Tubenit.   The only difference in this one and the fender schemo V3a and V3b are swapped.  No difference than the numbers.

I attached it.

It looks as simple as removing the wire from the tube, V3a pin 2 and running it through the loop and back to pin 2.  This is idea anyway as I see it.  No other added parts other than 2 grounding inputs.  Should make a simple passive loop.  I haven't gotten any further than simply putting jumper wires to check it.  Didn't work, but it is the next thing I plan to complete so I wanted to make sure I was reading it correctly?

Will the Reverb pot have any effect on the loop?

Jumper wires caused noise and oscillation, so I called it quits till I understand it better.

[Willabe]

I got the schemo from Tubenit.

Can you post it as an Sch?

Will the Reverb pot have any effect on the loop?

I don't think so.   


                       Brad     

[sluckey]

The jack is wired wrong in the schematic. The input signal connects to the tip (outer lug) of a jack. The output signal connects to the tip of the other jack. The switch (middle lug) of one jack connects to the switch of the other jack. At least that's how it is with switchcraft jacks.

[Ed_Chambley]

I got the schemo from Tubenit.

Can you post it as an Sch?

Will the Reverb pot have any effect on the loop?

I don't think so.    


                       Brad      

Here is the .sch in case you still want it.  I think Slucky's post will take care of it.

Brad, my reverb returns at in 7 of the PI, so what you are suggesting is simply connect this to the return on the loop and connect the loop to pin 7 and this will parallel the reverb?

I know these questions seem like simpleton, but I have never installed a passive loop, or any loop in a fender.  New territory and this amp is really nice.  Just want to get it right.

The reason I asked about the reverb pot is I have seen people use the reverb in and out for a loop by using RCA to 1/4 inch.  I have never done it cause I never thought it was a good idea.  Remember the Ice Cube From the 70's?  Those things you plug into the reverb send and return.  I still got 2 of those things.  One just makes a terrible overdrive and the other one has a slider to allow you to mix in reverb.  They are really nasty sounding, but they act as some sort of clipping and this clipping is controlled by the reverb pot.  I don't know what they really are, but I think it is just a resistor in molded plastic.

[Ed_Chambley]

The jack is wired wrong in the schematic. The input signal connects to the tip (outer lug) of a jack. The output signal connects to the tip of the other jack. The switch (middle lug) of one jack connects to the switch of the other jack. At least that's how it is with switchcraft jacks.

Thanks Steve.  This is it, I think.  I will check.

[Willabe]

All you'll be doing is putting the Fx loop into the dry signal, ie, in series with the dry signal. Because the dry signal is already in parallel with the verb (wet) signal, now the 2 loops are in parallel.

If the Fx loop doesn't have enough drive into the send, you might have to play with the 3.3M R. Maybe, say a 2.2M R in series with a 1M pot wired as a rheostat, to use as a send volume?

Like this.


            Brad    

[Willabe]

Here's a 2'nd send volume option.

Option #2 gives more signal to the send jack. When you plug into the Fx loop jacks you take the 3.3M R/10Pf C out of the loop. Now you have a 1M volume pot. If you don't have anything into the Fx jacks and turn the 1M pot all the way up your back to the stock 3.3M R/10Pf C.  

I don't know if either of these are even needed. I think they would both work. I think it will depend on what kind of Fx your going to use, stomp boxes or line level type.  


                    Brad    

[Ed_Chambley]

Thanks Brad.  Stomp box.  I already have a 1meg pot installed next to the loop jacks.  I was planning on using it to replace the 1 meg resistor in the trem, but it is really not necessary.  If I need it it is there.

I hate underboard wires.  The reverb return is underboard.  I can get it out tho.  I read a post where Bnwitt said he was not going to use them anymore on turrets.  I have thought the same thing many times.

Thanks for your explanation and drawings.  The brain clicked.

[Willabe]

The brain clicked.

Good, always glad to try to give back here.        Most times it's easier for me to draw it than to write it. Looking forward to hear how it turns out.

I read a post where Bnwit said he was not going to use them anymore on turrets.  I have thought the same thing many times.

I've used some turrets now a few times and have mixed feelings about them at this point. I really like them for some things. Like for using the small modern E-caps and for parts in a circuit where you have too many wires/leads to fit into an eyelet. With grounds for a galactic wired ground node it works great, per KOC/Merlin. With Doug's ground system you don't end up with too many ground wires/leads at 1 spot, because it's a ground buss. And it's been proven here many times to work great. Also you can take a more 3-D wiring approach with them. You can run parts on top in the turrets holes and wires/leads down below wrapped around the turret.

If you have an amps circuit proven and don't need any tweaking I think they would be fine too. But at this point, with limited experience using them, I find eyelets way easier to redo. I plan to still use both on the same board for different needs but only use turrets where I need to.


                         Brad        

  

[Ed_Chambley]

It is in and working great.  Tried a couple of different arrangements.  Ended up using a combination of the suggestions.  Once my brain clicked it was simple.  Tried it with a send and not.  Not any noticeable difference in the the effect level since my pedals have levels on them.

I did check out what Willabe meant by washed in reverb, and I get it now.  With delay the reverb overpowers the delay and you get a very space trippy sound.  Since I had underboard return I just disconnected that part of the circuit and put another 3m3/10pf resistor across the loop.  Plenty of signal.  Kept all the original circuit parts intact, just not connected.  Worked out great.

Just used single strand teflon wire and the amp is still quite.  No, nada bit of additional noise.

Very nice, thank you very much for the assistance.  Now onto the last thing.  Put the chassis back in the cab and draw nice faceplate.

[Willabe]

So, did you move the verbs return to the Fx loops return?      :don't know:

I'm glad you got it working and you like it but I don't understand what you did.

It is in and working great.  Tried a couple of different arrangements.  Ended up using a combination of the suggestions.  
and put another 3m3/10pf resistor across the loop.

So you wired it like in option #2 but without a volume pot on the send?

I did check out what Willabe meant by washed in reverb, and I get it now.  With delay the reverb overpowers the delay and you get a very space trippy sound.

That's not really what I meant. By "washed" I meant, on top of or covered with, not over powered by or drowning in it. If the delay is over powered by the verb, then you need to turn down the verb to balance the 2 better. I'm not finding the right words to describe it better to you, sorry Ed.    

Or, the delay pedal doesn't have enough output signal to give to the return jack to keep up with the verbs signal strength?
                        

                                             Brad      

[Ed_Chambley]

So, did you move the verbs return to the Fx loops return?      :don't know:

I'm glad you got it working and you like it but I don't understand what you did.

It is in and working great.  Tried a couple of different arrangements.  Ended up using a combination of the suggestions.  
and put another 3m3/10pf resistor across the loop.

So you wired it like in option #2 but without a volume pot on the send?

I did check out what Willabe meant by washed in reverb, and I get it now.  With delay the reverb overpowers the delay and you get a very space trippy sound.

That's not really what I meant. By "washed" I meant, on top of or covered with, not over powered by or drowning in it. If the delay is over powered by the verb, then you need to turn down the verb to balance the 2 better. I'm not finding the right words to describe it better to you, sorry Ed.    

Or, the delay pedal doesn't have enough output signal to give to the return jack to keep up with the verbs signal strength?
                        

                                             Brad      

I used #2 without a send.  Actually I did #2 with a send also.  It just worked without the send.  Yes, I did return the reverb to the return loop.  Did it first without to see what it sounded like, trippy may not be the correct word. then changed the reverb to the return.

The result of using delay, which is what I was mainly looking to loop, is the delay is much more pronounced.  Seems clear between slapback even if you have some reverb.

I plan to check out some other effects in to see what sounds like.  I think the will be nice as well.

[Willabe]

I used #2 without a send.  Actually I did #2 with a send also.  It just worked without the send.

Tried it with a send and not.  Not any noticeable difference in the the effect level since my pedals have levels on them.
Plenty of signal.

 

Send jack or send volume pot?

A guitar Fx pedal input is set up to see the small output signal from the guitars PUP's. It doesn't need a preamp level/line level signal in front of it. That's why I suggested that you might need a volume pot to cut down the signal going from the send jack to the pedals input. The 2.2M R + 1m (trim) pot (option #1) instead of the 3.3M R before the send jack was to give a line level rack mount Fx a little more signal if needed. Option #2 was to move all of the 3.3M resistance out of the signal path to the send jack if a line level rack mount Fx needed even more signal. But if it's not overloading the pedals input, that's great.  

Yes, I did return the reverb to the return loop.  Did it first without to see what it sounded like, trippy may not be the correct word. then changed the reverb to the return.

The result of using delay, which is what I was mainly looking to loop, is the delay is much more pronounced.  Seems clear between slapback even if you have some reverb.

So it did make a difference, the delay sounded "trippy" when it was after the verb? But sounded more pronounced/clear when it was before the verb?



                              Brad    

[Ed_Chambley]

I added a send volume and changed the resistor to 2m2 which changed the line level.  Worked well, but I was only looking for something simple as I won't ever be using this amp with a processor or multi effects units.  I have another setup for this.  I love the tremolo on this amp and I want to be able to use the pot in place of the 1 meg resistor.

The difference in returning the verb to the return is not quite like having reverb pedal at the end of a pedal chain, but I understand why you described it this way.  It retains more definition, some call it articulation.  I have only tried 2 delay pedals, a carbon copy and wampler faux tape echo and both worked nice.  My main setup is a Compressor to Rc booster and delay of some sort.  When the delay was in the pedal chain the Princeton would get mushy and lose spank and keep me from making it have the cluckin' chicken sound.  This solved the issue.

It was so much easier to put new resistor and cap across the loop since I was putting the loop on the front of the chassis.

[Willabe]

The difference in returning the verb to the return is not quite like having reverb pedal at the end of a pedal chain, but I understand why you described it this way. It retains more definition, some call it articulation.

When the delay was in the pedal chain the Princeton would get mushy and lose spank and keep me from making it have the cluckin' chicken sound.  This solved the issue.

Ok, thanks Ed. I think I get what your saying now. Good to know.

IIRC, Tubenit found about the same thing when he put in a passive Fx loop for his delay pedal.

Some pedals don't like to be before/after some other pedals, impedance issues? So I wonder if by putting your delay in the loop instead of in the pedal chain it's getting around that issue? Or if it's got to do with now being after the tone stack and the way your setting it for the tone you need?      



                              Brad           

[Ed_Chambley]

Some pedals don't like to be before/after some other pedals, impedance issues? So I wonder if by putting your delay in the loop instead of in the pedal chain it's getting around that issue? Or if it's got to do with now being after the tone stack and the way your setting it for the tone you need?      



                              Brad           
[/quote]
There is a slight impedance increase, but it is not very much.  I assume this only as I did not test impedance.  My assumption comes from simply the level on the pedal.  Running it into the front and keeping the input level on the pedal the same and then plugging it into the loop you will get an increase in overall delay.  Not much tho.  The coolest thing is it will fool you using delay.  If you have reverb set low it sounds like you turned it off.  I thought it was turning it off, but when I increased the reverb it became very apparent.  It will still be dripping wet if you want it although I do have a full size 3 spring tank with a dwell.

I have put loops in all my MV marshall type amps for chorus mixing for the 80's rock lead sounds, but this loop acts different.  It is really good at keeping the Fender sound.  It doesn't change the tone which I think is because of the effect insertion.  This is great for delay.  I have a Homebrew Analog Chorus I am interested in seeing how it acts.  The pedal is strange and has huge touch sensitivity.  Playing chords with a light touch it makes a wonderful 3d sound.  Hit a power chord hard and the thing will distort.  Sounds weird, but it is really cool.

It is just simple and works well, there is just no other way to say it.  Princeton amps breakup so easily it is very easy to get a mushy flabby sound especially since I have 2, 10's which are 15 watts and very inefficient.  With delay in the front it is worse.  I have some other speakers I am going to test with it.  It sounds better plugged into a couple of other cabinets I have.

I think going around the tone stack is key.  Thinking about the difference in what I hear.  I don't have to fight with the knobs on everything.  Last night I simply set the amp to a tone I was pleased with.  Stomped the delay and nothing really changed except I had a slapback.  With the wampler echo it sounded the same, with the carbon copy the delay had some coloration and the repeats distort a little.  That is what the Carbon Copy does anyway.

[Ed_Chambley]

Well I put 2 Celestion Gold 10's in and tried every modulation pedal I have.  They all worked great.  I even tried a compressor in it and that was useable.  Installed a homemade pedal supply wiring it to the inside and installed a boss style jack which will keep batteries away.  Did wire the 1 meg pot to replace the 1 meg resistor in the tremolo.  Very nice.  Put it back together and stuck a fork in it.

Thanks for the help guys, it is great little amp.