Marshall 18Watt loud pop and tremolo problem.

[FranciscoPerez]

Hi!!
I recently finished a marshall 18watt clone.

Normal channel works quite good when the guitar is plugged in, but without guitar plugged, when the volume pot is turned up to almost 10, a very loud POP comes out from the speaker.
It happened twice and I hurried up to turn back the volume pot afraid of damaging the speaker, so didn't try again to turn the pot all the way up w/o guitar.

What could make this happen?

On the other hand, tremolo channel does not work at all.
It's necessary to remove the tremolo channel 12ax7 to be able to play through the normal channel, because when v3 is in, I can hear a "Ta Ta Ta Ta Ta Ta Ta Ta" sound that seems some sort of oscillation problem. It changes in volume and frequency (I mean number of "Ta" per second ) when the volume pot is turned up.

Tried different tubes in v3 without success, and rechecked the whole amp. Everything's wired well and voltages appear to be normal. Never built a tremolo channel before, so I've got no experience in this.

Any suggestions would be strongly appreciated.

EDITED:
Here you have a link to the schematic I followed.
http://www.schematicheaven.com/marshallamps/marshall_18watt_schem.pdf

Thank you,
Regards!!

[phsyconoodler]

Quote: "Everything's wired well and voltages appear to be normal"

  If that was true,it would be working normally.You have made a mistake in your wiring and you need to correct it before the amp will work properly.Try following a layout like the one at 18watt.com or Ceriatone.
 Hoffmans' Rule: "if it was wired right,it would be working right"

[FranciscoPerez]

I followed the 18watt.com layout when building the amp.

Noticed today that both channels are working good when v3 pin 2 is grounded (no tremolo effect in the trem channel),
so my mistake probably stays in the tremolo circuit.

Checked the whole circuit and did not find mistakes/bad solder joints throughout the amp :(

Do you think this problem could be caused by a given routing in the wires that go to v3? Using shielded wire is mandatory in tremolo circuits?

[phsyconoodler]

You won't find any shielded wire in the original 18 watt or the 1974x from Marshall either.Lead dress is important but it won't cause symptoms like you are describing.You still have an error that's eluding you.I've had stuff like that happen to me.A fresh perspective helps.Walk away from it for a while or turn it upside down and have another look.
  It's like playing boogle; every time you move that cube,different words appear.

[sluckey]

That particular trem circuit is very finicky. Lot's of discussion on 18watt.com about trem problems. Try totally disconnecting any wires connecting to a trem footswitch so that the only components connected to V3 pin 2 are the 2.2meg resistor and that .01µF cap. Does that help or change anything?

[FranciscoPerez]

I did not installed the footswitch yet.

With 2.2meg and 0.01uF connected to v3 pin 2 is when I get the annoying "Ta Ta Ta".
However, when I ground v3 pin 2 (2.2meg and 0.01uF still connected to v3 pin 2) the problem dissapears, but I won't get any tremolo effect when plugging the guitar in that channel.

Thank you both very much for your help and support!

[sluckey]

Put a 100pf to 500pf cap between V3-2 and ground. Does that help? Can you show us some hi rez pics, especially of V3 socket and the board area involved?

[FranciscoPerez]

Thanks Sluckey! Yes! That helped.

Seems like the footswitch wire capacitance takes part in the tremolo circuit.
I put a 100pf and it helped, and the "Ta ta ta" became a bassy "pop pop pop" that increased when turning up volume/tone/intensity/speed.
Increased the value to 500pf and it was necessary to turn knobs higher to get the same amount of noise, but still didn't solved the problem.

Increased the value of the capacitor going to v3 pin 2 to 0.022uf and that also helped in some amount.
That's what i've done so far and with the guitar plugged in, the tremolo channel works good untill I turn up the intensity pot too much, or increase the volume beyond about 4 out of 12.
In addition, an audible hum has appeared when the "pop pop pop" is not audible yet but it's about to appear if you turn the volume higher. It's something like oscillating interferences (like bad ground noise but that increases and decreases in volume intermitently).

I'll post some pictures when I come back home tonight here in Spain.

Thank you again! Seems like we're pointing the right direction :)

[phsyconoodler]

I've built a few of those and have never had any problems with the tremolo.The lead dress is important to prevent oscillations.Do not alter it from the layout or you will have issues.Don't make assumptions that because you may have mounted your tube sockets on a different angle that you can get away with running the wires any which way.The phase inverter being between V1 and V3 doesn't help either.
  Make sure all your wires are run along the chassis and none are up in the air except for heater wires.
 I like either Ceriatone's or Richies' improved tremolo layout.
   Any pictures of your build?

[FranciscoPerez]

Hello!
Just arrived home and took some pictures of the amp.
Sorry that they were taken with a compact camera without much light (it's 23:00 pm now), and they're a bit blurry.










What do you think?

[phsyconoodler]

All those mustard caps

 The wires from the tube sockets to the board are up in the air too much and they are a bit all over the place.
I'll see if I can find a picture of one to show you how they should be.Lead dress could be the issue here.

[VMS]

Hi,

what is that brown cap on the top picture? And in the same picture it looks like there is a short between the pin where the brown cap goes and the heater pin.


Also, I would wire the green heater wires like they are in this layout:

www.18watt.com/storage/18watt_layout_tremolo_improvements_b.pdf

[FranciscoPerez]

That would be great phsyconoodler!
I had some mustards arround and decided to put them in there.

The brown cap is a mica capacitor from RadioSpares. I got some of them from ebay really cheap. Marshall used those in plexi amps in the 60's.

I can't see the short between the pins you mentioned VMS.

[FranciscoPerez]

The 560pf is what sluckey suggested to solve my problem.
As far I am concerned, including that capacitor replaces the capacitance of the footswitch wire. Note that my amp has not a footswitch installed yet, so you must "fool" the circuit adding that capacitor.

I might be wrong though, sluckey would know the reason for sure.

I can't tell what pin, or valve,  you have that attached to

I'm afraid I don't understand what you mean. v3 in my amp is a miniwatt ecc83 valve made in Holland, and pin 1 on v3 has a 0.047 cap going to ground, as you mentioned.
 
Thank you for your suggestions!!
Do not hesistate to critique, it's the best way for me to solve the problem. I will route the wires again so they're close to the chassis.

[FranciscoPerez]

In my opinion it's not a patch, but a substitution.
If you do not have the footswitch installed you should put that cap in order to replace the footswitch's wire capacitance that would be present otherwise.

[VMS]

I can't see the short between the pins you mentioned VMS.

Yeah, I'm probably seeing things, but this is the place where I see the short:

[FranciscoPerez]

You're right! It looks like shorted but it's because of the perspective view of the picture shot.

There are no shorts between pins, they are well separated from each other. I should have taken the pictures in a different angle, so it was shown more clearly.

Thanks for pointing this out anyway!! These could have been shorted and maybe I wouldn't have realised.

[sluckey]

Here are a couple 'patches' I did to get rid of the tremolo tick-tick in my amp. There's also a 'patch' for the normal channel that I borrowed from Ceriatone. (Focus on the schematic)

http://home.comcast.net/~seluckey/amps/18w/18w.pdf

I've seen plenty of trem related problems with this amp. And some were beautiful workmanship. That trem circuit sounds great, but it was built 'on the edge' of stability. I don't think enough planning went into the design of that amp. And who ever thought it was a good idea to sandwich the PI between the two preamp tubes? The design only makes sense to me when I consider that the amp was the bottom of the Marshall line when it was originally built.

[FranciscoPerez]

Thanks Sluckey  ,

I'll try all things you all told me when I come home from work and let you know the results.
The boss is staring at me in a way that scares me 

[phsyconoodler]

I think bosses get together and come up with looks that freak out their employees on purpose.
  I don't know! Mine has this look when I'm down on the guitar floor on a break when he thinks I should be soldering SVT's or something!

[FranciscoPerez]

I finally added Cx = 270pf and Cy = 100pf without any improvement. (I did not have 33pf nor 220pf around )
Also added Rx but did not either solve the problem   

Tomorrow I'll remove all wires to the preamp tubes and rewire them in a more convenient way.
Did you find some pictures of yours phsyconoodler? Seeing a real amp correct wired would help me a lot!!
Any more suggestions?

Thank you all!

[phsyconoodler]

I can't find any of my old pictures since my computer crashed but a look at Richies layout will tell you a lot.The wires run the way they should.I can't really see where your wire go,the pictures you have center around the one tube socket which is really not that bad.The soldering looks good,but the lead dress may be the problem.A picture that shows more of the lead dress in that area would be cool.
 

[drew]

Francisco, are you a member of 18watt.com?  There are a lot of photos, and many threads devoted to trem problems (search for "motorboating") over there. 

The "Richie's Improved Tremolo" layout calls for shielded cable for the V3-1 and V3-6 connections; you might want to give that a try before you tear all the wiring out.

[phsyconoodler]

Now THAT's good lead dress!
  See how the wire hug the chassis and the spacing?

[drew]

Ampcabinets' amp also uses those three ceramic disc caps for the trem where the originals did, which some people on 18watt.com suggest does matter.  Changing the three mustards out for ceramics might be something else to try.

[sluckey]

don't get in an uproar about the word patch.

Uproar? I just used quotes because you did. No offense received here.

[FranciscoPerez]

Hi!

I shielded v3 pins 1 and 6 wires and input wires of the normal channel without any improvement.
Also changed the three caps to ceramics as you suggested Drew, but it did not help either.
Finally decided to tear all the wires apart and today I'll completely rewire the board following Ritchie's improved tremolo layout. In case that this is not enough, I'll give a try again to the fixes Sluckey suggested.

I'm a member of the 18watt.com website but had no looked arround its forum. Now I see there are lots of people having the same problem!

Hope that all this will fix the problem!!
I'll let you know ;)
Thank you very much you all!!!

[FranciscoPerez]

Hi again!
Still got that heartbeat sound!  

I completely rewired the preamp section following ritchies' improved layout and the problem improved a lot.
However, still got the heartbeat sound when turning the volume knob higher than 6/12 when intensity and speed are turned all the way up.

That done, the amp sounds quieter than before and the tremolo channel can be played well if you don't turn intensity and speed too high.

Now I'll try sluckey's suggestions to check if it gets better. (Already added that 120ohm resistor in the norm. ch.)

I would be happy to post again some pictures of the preamp sockets when I come home .
Please, let me know if you see something strange!

Thanks!!!

[FranciscoPerez]

Here they are!!
Look forward to hearing your opinion!

Thank you very much you all!!