Parallel effects loop for Marshall style amps

Tuco · Post by **Tuco** » Tue Sep 11, 2007 1:06 am

Larry, the problems with buzziness and weak sound turned out to be an intermitent short in the loop, caused mainly because of the temporary nature of the hookup. I am now getting good, strong signal from the amp with your loop attached.

However, the effect box that is in the loop is not responding. The "clipping" light on the effect box will flicker just for a moment, if I hit a string very hard, but that's all. Just to be sure, I've tested the effect (and the cables) through another amp's effect loop, and it works fine there.

I've checked and re-checked and re- re-checked my connections. Continuity checks out okay throughout the loop.

I've reviewed the component values. Because I'm not very fluent with the resistor codes, I thought the problem must be there. But I believe I've installed the right values.

Is it likely that the loop's send jack is bad? Is there a way to test that?

I really want to get your loop working. I would appreciate any further insight that you can provide.

novosibir · Post by **novosibir** » Tue Sep 11, 2007 7:17 am

As far as I've seen all is connected correctly, the board is supplied correctly, the values are all ok, the wiring also...

But it seems, as some of your turrets on the board aren't soldered - no solder seen inside some turrets - so I guess, that your problem is a bad contact.

Fire up your iron and complete it!

Larry

franc · Post by **franc** » Tue Sep 11, 2007 12:39 pm

I want to be able to switch between serial and parallel, just to hear the diference.
You suggested a DPDT switch. Does it need to be heavy duty at all?
Or could I use a mini switch?

novosibir · Post by **novosibir** » Tue Sep 11, 2007 2:48 pm

miniswitch is ok

franc · Post by **franc** » Wed Sep 12, 2007 6:44 am

Thanks Larry,

Looks like I am finally getting around to building it into a Plexi 50 clone.
Or rather building it ONto one.
I am having a small chassis made and a small turret board.

I am just still looking for 820k resistors (?)
and thinking about the best way to feed the wires through the top of the chassis into the small chassis.

I am thinking having a separate hole for heating.

Should I separate any other wires or can all the other wires go through one hole?
I've got B+, signal from treble and to PI and wires to and from inputs and pots.

Any ideas?

franc · Post by **franc** » Sat Sep 29, 2007 3:50 am

Me again

I was wondering how you guys run the wire from the treble pot to the Sen pot. My Send & Return are on the back of the amp, right next to the speaker outputs. Do I run the wire straight across or along the side of the chassis?
I have to get on the other side of the tubes somehow.
Does it really matter at all?

franc · Post by **franc** » Sat Sep 29, 2007 4:17 am

novosibir wrote:miniswitch is ok

Hoping someone is still reading

The switch and the rest of the circuitry are some distant apart the way I am building it. I am thinking of attaching the 220k to the DPDT, then run a wire from there to my turret board.

Good idea? Bad idea?

novosibir · Post by **novosibir** » Sat Sep 29, 2007 8:58 am

Running a long way across the chassis from the treble's wiper to the Send Level pot requires a shielded wire.

And yes, separate the heater wires! B+, ground, aso. may go to another hole.

Larry

franc · Post by **franc** » Sat Sep 29, 2007 9:22 am

Thanks Larry,

Of course, I was planning a separate hole for the heaters and one for B+
Then 4 wires from pots and jacks through 1 hole and one last hole for the wire going back to the PI input.

Might be one hole too many but it fits my layout.

I was not planning on running any ground wires, as the thing is in a chassis on top of my amp chassis and the pots will be grounded there.

If Larry is okay with it, I will post some pictures after I am done.

So I'll shield the wire coming from the Treble pot and going to the back of the amp to the Send part. Anything else that needs shielding after that?

I made a schematic of how I wanted to wire the DPDT switch and attached it.

novosibir · Post by **novosibir** » Sat Sep 29, 2007 9:35 am

franc wrote:Anything else that needs shielding after that?

Long return ways.

franc wrote:I made a schematic of how I wanted to wire the DPDT switch and attached it.

Ok!

Larry

franc · Post by **franc** » Sun Sep 30, 2007 3:38 pm

Don't know about you guys, but 820k really seems a hard value to come by.

I came up with either combining 3 270k in series (810k) or 680k and 150k (830k).

Anyone got better ideas?

Should I got metal oxide? I can get 820k 1W of those...

novosibir · Post by **novosibir** » Sun Sep 30, 2007 9:19 pm

No metal oxide in the signal path, but 1W is ok.

Larry

franc · Post by **franc** » Mon Oct 01, 2007 12:10 pm

Didn't think so about the metal oxide.

Weird that 820k is so hard to find. Looks like I'll have to go NOS. Guys sells some. Then again, these might be so far of that my composed 810k or 830k are closer anyway

donbarzini · Post by **donbarzini** » Mon Oct 01, 2007 2:45 pm

Has anyone tried this effects loop in a 12000 series with a MV (Jose or PPIMV) and 2203 mod?

Icarus · Post by **Icarus** » Tue Oct 02, 2007 4:41 am

novosibir wrote:
thinlizzy wrote:The loop is working great, I dont know how hot the signall is thats going to the effect...
Larry do you know what voltage is going to the effect??
Can't say it at the moment, because due to renovation here all my measurement writings still are buried anywhere.

But keep in mind:

Although with the Master in front of the loop section you (nearly) don't have any sound colouration, you always have to readjust the Send & Return Levels when you change the Master setting. A higher setting on the Master is resulting in a higher Send Level.

With the Master after the Loop section in front of the PI you never have to readjust the Send & Return Levels, when you change your Master setting. Although in the 2203/2204 layout at higher Gain settings then the recovery stage of the loop section more and more becomes a 'afterburner type' gain stage, the higher the setting on the Gain control, what definitely is colouring the sound away from the typical 2203/2204 sound - but many even like it.

When you try the Master after the loop section, don't forget the additional coupling cap! one .022 from the recovery stage's plate to the Master and another .022 to the PI's input.

Larry

I was just reading this , I dont know if much has changed.
Correct me if im wrong .

Are you saying if you have the FX Loop after the master Volume
You have to adjust the send and return's every time you change the
master settings ...?

That seems to be a bit of a hassle , going back to the amp to change the loop levels ?