18 watt TMB squeal & hum

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DFJB
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Re: 18 watt TMB squeal & hum

Post by DFJB »

MikeyV,

It appears you and I are on parallel paths of discovery concerning the mojotone TMB. I am also having squeal and hum issues. I would love to see some photos of your layout, especially your implementation of moving the 68K and 470K resistors to the tube sockets.

And, I absolutely agree with you. This amp is pretty darned loud. Probably too loud for my needs.

DFJB
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Re: 18 watt TMB squeal & hum

Post by MikeyV »

Yeah, I'm beginning to get the wattage/loudness thing thru my thick skull. I have amps from 7 watts, or a single 6V6 in a Tweed Princeton to 135W '79 Fender Vibrasonic Reverb, and they're all too loud, really. LOL.

Next purchase should be an attenuator.

JMP, Thanks for your help, and that further info on the MF resistors.
I think I'll order some and re-do that part. Easy enough.

I'll post pics, cell phone is dead at the moment.

Mike
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Re: 18 watt TMB squeal & hum

Post by MikeyV »

This thing is still pretty angry.

Most problems gone except for nasty loud feedback when turning up the master volume past maybe 6. It goes from silent up to about 2, then to full blast at about 3, then gets crunchier up to about 5 or 6, then feedback starts.
If I turn the guitar volume off, that feedback stops. Then the hisssss remains.

Is shielding the cable to/from the master volume pot a thing?
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Re: 18 watt TMB squeal & hum

Post by Gradysmusic »

MikeyV wrote:
Thu 01/30/20 12:04 pm


Is shielding the cable to/from the master volume pot a thing?
Yes its a thing on most high gain amps
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Re: 18 watt TMB squeal & hum

Post by zaphod_phil »

Actually all long wires carrying signal (ie not power rails) should be shielded.
If adjusting the guitar volume affects the squeal, you probably need potted pickups. Also, a loud thin hiss is what ultrasonic oscillation usually sounds like to our human ears.
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Re: 18 watt TMB squeal & hum

Post by gheorge77 »

Gradysmusic wrote:
Thu 12/23/21 10:22 am
MikeyV wrote:
Thu 01/30/20 12:04 pm


Is shielding the cable to/from the master volume pot a thing?
Yes its a thing on most higher gain amps
I know this is an old topic but another question to consider. Using shielded wire and moving the 68k and 470k to the sockets helped with noise but I still get some oscillation. My 1987 build is far quieter without any oscillations at all. The thought dawned on me why does this need a master volume if the 1987 doesn't (at least for me). It seems like the Mojotone mv is the big source of problems here.

Has anyone removed it? Seems like all I'd need to do is move the wire from the board going to the mv to the treble pot, no?
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Re: 18 watt TMB squeal & hum

Post by Bieworm »

gheorge77 wrote:
Tue 02/15/22 2:48 pm
Gradysmusic wrote:
Thu 12/23/21 10:22 am
MikeyV wrote:
Thu 01/30/20 12:04 pm


Is shielding the cable to/from the master volume pot a thing?
Yes its a thing on most high gain amps
I know this is an old topic but another question to consider. Using shielded wire and moving the 68k and 470k to the sockets helped with noise but I still get some oscillation. My 1987 build is far quieter without any oscillations at all. The thought dawned on me why does this need a master volume if the 1987 doesn't (at least for me). It seems like the Mojotone mv is the big source of problems here.

Has anyone removed it? Seems like all I'd need to do is move the wire from the board going to the mv to the treble pot, no?
Maybe you could post detailed pics of your build and the according schematic?
And you clued us by mentioning Mojotone.. that's a synonym for trouble.
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Re: 18 watt TMB squeal & hum

Post by gheorge77 »

Bieworm wrote:
Tue 02/15/22 3:54 pm
gheorge77 wrote:
Tue 02/15/22 2:48 pm
Gradysmusic wrote:
Thu 12/23/21 10:22 am


Yes its a thing on most high gain amps
I know this is an old topic but another question to consider. Using shielded wire and moving the 68k and 470k to the sockets helped with noise but I still get some oscillation. My 1987 build is far quieter without any oscillations at all. The thought dawned on me why does this need a master volume if the 1987 doesn't (at least for me). It seems like the Mojotone mv is the big source of problems here.

Has anyone removed it? Seems like all I'd need to do is move the wire from the board going to the mv to the treble pot, no?
Maybe you could post detailed pics of your build and the according schematic?
And you clued us by mentioning Mojotone.. that's a synonym for trouble.
Not really looking for ways to decrease the oscillation. I've added shielded wire to the TMB side and honestly don't see the point of the master volume on this amp. It appears to really function to slightly reduce gain until it's dimed and just adds noise. The normal channel is dead silent even without shielded cable.

I was more curious if anyone had tried removing the master volume on this.

-Ian
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Re: 18 watt TMB squeal & hum

Post by Bieworm »

gheorge77 wrote:
Tue 02/15/22 7:41 pm
Bieworm wrote:
Tue 02/15/22 3:54 pm
gheorge77 wrote:
Tue 02/15/22 2:48 pm


I know this is an old topic but another question to consider. Using shielded wire and moving the 68k and 470k to the sockets helped with noise but I still get some oscillation. My 1987 build is far quieter without any oscillations at all. The thought dawned on me why does this need a master volume if the 1987 doesn't (at least for me). It seems like the Mojotone mv is the big source of problems here.

Has anyone removed it? Seems like all I'd need to do is move the wire from the board going to the mv to the treble pot, no?
Maybe you could post detailed pics of your build and the according schematic?
And you clued us by mentioning Mojotone.. that's a synonym for trouble.
Not really looking for ways to decrease the oscillation. I've added shielded wire to the TMB side and honestly don't see the point of the master volume on this amp. It appears to really function to slightly reduce gain until it's dimed and just adds noise. The normal channel is dead silent even without shielded cable.

I was more curious if anyone had tried removing the master volume on this.

-Ian
The general consensus is that an 18W will not do what it does best with the addition of a MV. The famous touch sensitive complex overdrive is mainly due to the saturation of the EL84 tubes. There are versions where you can get superb preamp overdrive though. The Tremolo TMB, for instance, has a pre PI mastervolume AKA 'volume' ;)
You're only compromising the gain with a regular TMB MV, and it doesn't do much on volume level either
A PPIMV is obsolete.. still no power tube overdrive then
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Re: 18 watt TMB squeal & hum

Post by JMPGuitars »

In other words, he's saying you're fine to remove the master volume. If you're not sure about the wiring without the MV, compare to a schematic in our downloads section.

Thanks,
Josh
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Re: 18 watt TMB squeal & hum

Post by gheorge77 »

Great, thanks!

I don't think I am a fan of MV on any amp to be honest. I also don't think I'm in love with this amp. I'm going to bump up the cathode bypass cap on the power tubes to 2200uF with a 180 ohm resistor and see if I prefer that.

If I were to convert this to a fixed bias amp, what should I expect? I can't seem to find a thread discussing that topic. I would love to hear anyone's experience.
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Re: 18 watt TMB squeal & hum

Post by tfrost33 »

Been lurking here a while and just became a member. Thanks! This thread in particular interests me because chalk up another Mojo TMB kit that squeals like a banshee! I did everything this thread has instructed to do except for one thing. That is moving the 68k resistor from the input jack to pin 2 of V1. At least that how I read the mojo schematic. I see other schematics are different from the mojo one. But I didn't realize that until I had already purchased the kit and built the amp.
After performing all the other things ( new ground scheme, shielded wire, touch up a few poor solder joints, etc) I still get some squeal, although not as bad as it was. I have to crank the treble, gain past 3 O'clock-ish, MV past noon-ish and that lets the banshee out!

Anyway I am having trouble wrapping my head around rewiring the input jack for the tmb channel and moving the 68k resistor to the tube socket. Mostly just how to wire the jack after moving the resistor. I think the resistor is pretty straight forward.

looking at other schematics it seems pretty simple, but can the schematics be intertwined? For instance the Valvestorm Scheme (if I am reading it correctly?) has it going to pin 7 of V1.... Could I just wire it the valvestorm way except land it on pin 2 (where it currently resides)

Other than that, I do say the amp sounds great up to the point it starts to squeal, then it still sounds good, but it just squeals! And the normal channel is spectacular!

Thanks everyone!

Tony
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Re: 18 watt TMB squeal & hum

Post by Bieworm »

tfrost33 wrote:
Fri 02/18/22 2:23 pm
Been lurking here a while and just became a member. Thanks! This thread in particular interests me because chalk up another Mojo TMB kit that squeals like a banshee! I did everything this thread has instructed to do except for one thing. That is moving the 68k resistor from the input jack to pin 2 of V1. At least that how I read the mojo schematic. I see other schematics are different from the mojo one. But I didn't realize that until I had already purchased the kit and built the amp.
After performing all the other things ( new ground scheme, shielded wire, touch up a few poor solder joints, etc) I still get some squeal, although not as bad as it was. I have to crank the treble, gain past 3 O'clock-ish, MV past noon-ish and that lets the banshee out!

Anyway I am having trouble wrapping my head around rewiring the input jack for the tmb channel and moving the 68k resistor to the tube socket. Mostly just how to wire the jack after moving the resistor. I think the resistor is pretty straight forward.

looking at other schematics it seems pretty simple, but can the schematics be intertwined? For instance the Valvestorm Scheme (if I am reading it correctly?) has it going to pin 7 of V1.... Could I just wire it the valvestorm way except land it on pin 2 (where it currently resides)

Other than that, I do say the amp sounds great up to the point it starts to squeal, then it still sounds good, but it just squeals! And the normal channel is spectacular!

Thanks everyone!

Tony
Hey Tony! Welcome to the forum.
For the correct wiring of the input jacks you can go to the Downloads area and take any layout from Josh. Look for 18W modern classic .. that one will correspond largely with what you need.
Maybe the oscillation is from something else in the circuit. If you can post detailed Hi res pics of the build we can have a look under the hood 👍

Grtz Bjorn
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Re: 18 watt TMB squeal & hum

Post by tfrost33 »

Bieworm wrote:
Sat 02/19/22 3:38 am
tfrost33 wrote:
Fri 02/18/22 2:23 pm
Been lurking here a while and just became a member. Thanks! This thread in particular interests me because chalk up another Mojo TMB kit that squeals like a banshee! I did everything this thread has instructed to do except for one thing. That is moving the 68k resistor from the input jack to pin 2 of V1. At least that how I read the mojo schematic. I see other schematics are different from the mojo one. But I didn't realize that until I had already purchased the kit and built the amp.
After performing all the other things ( new ground scheme, shielded wire, touch up a few poor solder joints, etc) I still get some squeal, although not as bad as it was. I have to crank the treble, gain past 3 O'clock-ish, MV past noon-ish and that lets the banshee out!

Anyway I am having trouble wrapping my head around rewiring the input jack for the tmb channel and moving the 68k resistor to the tube socket. Mostly just how to wire the jack after moving the resistor. I think the resistor is pretty straight forward.

looking at other schematics it seems pretty simple, but can the schematics be intertwined? For instance the Valvestorm Scheme (if I am reading it correctly?) has it going to pin 7 of V1.... Could I just wire it the valvestorm way except land it on pin 2 (where it currently resides)

Other than that, I do say the amp sounds great up to the point it starts to squeal, then it still sounds good, but it just squeals! And the normal channel is spectacular!

Thanks everyone!

Tony
Hey Tony! Welcome to the forum.
For the correct wiring of the input jacks you can go to the Downloads area and take any layout from Josh. Look for 18W modern classic .. that one will correspond largely with what you need.
Maybe the oscillation is from something else in the circuit. If you can post detailed Hi res pics of the build we can have a look under the hood 👍

Grtz Bjorn
THANK YOU!!!

I will see what I can do as far as posting some pics, I think you may all enjoy the cabinets that I build? However, your guidance was the final nail in the coffin. No more squeal! I wired the MV (High Gain Channel) input as per Josh's diagram. I can't thank this forum enough!

Just for the record I performed everything this thread provided and a little extra. I am not sure if it made a difference or not, but I went through the tedious process using shielded cable on the Treble/Gain/and Master pots. Then moved the said resistors to the tubes. Previous to that I had touched up a couple questionable solder joints, but that didn't really seems to make a difference. I also re-did the ground scheme per Josh's grounding...

In order of operations:

1: re-touch some solder joints (little to no change)

2: redo the ground scheme (made a difference but still had squeal after turning the T/G/MV pots up past 2 oclickish)

3: Moved normal channel resistors to tubes (not relevant but I did it anyway) No help here with squeal on the other channel

4: Rewired the T/G/MV pots with shielded cable and moved the 470 resistor to the tube ( major help!) Could turn everything up to about 9 oclock before the squeal started

5: moved the input resistor (68k for Pin 2 at V1) rewired the input jack per Josh's scheme and used shielded cable here as well. Now I can crank all knobs with no squeal, but MAN can I get me some on demand feedback ;)

Put the amp through its paces today and it sounds absolutely incredible. If I were to do this again, and I just might, I would definitely not get another Mojo kit... This is the 12th amp I have built now and this is the first time I have had an issue (except for a minor standby switch issue with a Metro JTM45 kit I did geez back in 2005-ish already)

Anyway, hope these details can help someone else in the future... Oh and one last thing, once I get some pics posted I know about the overheated resistor at the cap can and its been changed!

Thank you again everyone! Now I have a lot reading to catch up on here at this amazing 18 watt site!!!

Thanks

Tony
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Re: 18 watt TMB squeal & hum

Post by tfrost33 »

ALRIGHTY, Just did a photo shoot (with the iPhone of course) I am not a pro photographer.

Anyway, I have been building all my own amps, cabs and all since 2005. I experimented with Speaker Cab sizes and found what I think is a secret sauce to my amps, I oversize them quite a bit compared to "stock" Marshall and Fender amplifiers. Without getting too long winded, I feel like I have come up with a really good recipe for tone... Anyway, as promised, here are some pics of the new 18 Watt TMB.

Again, thank you everyone for this fine forum! It helped immensely! This amp sounds great!

Tony
Cover Photo 2.jpg
REDBONE.jpg
HEAD CLOSE UP.jpg
Internals.jpg
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Re: 18 watt TMB squeal & hum

Post by JMPGuitars »

Cool style!

I also like oversized cabs. To the point that I prefer a detuned 2x12 cab to anything else (detuned = 2x12 cab with only 1 speaker in it).

Thanks,
Josh
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Re: 18 watt TMB squeal & hum

Post by Bieworm »

I'm building a 2x12 cab with vertical setup.
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Re: 18 watt TMB squeal & hum

Post by rockon1 »

First post here. Ive got a noise problem with the trrem channel on my Mojotone revision 5 18watt tbm.From a post at TGP-
Now this morning I'm looking at the trem channel. Gone over the wiring.As soon as I connect the 4.7nf to the tone pot to ground I loose the all sound ?they should have used different colored wires from the volume pot to the board I think cause two gray ones are easy to mix up imo- thats if they correct in the first place... Im using a 4.7nf 600volt rated orange drop cap in place of the original as its tests open- unless I need the original type...

Edit-Im not sure if this a clue but at one point it the trem side worked- Thats when I discovered the volume wires(gray in the layout pic) going to the board were wrong(crossed up) and corrected them. I just put them back and voila-humming in both channels but volume. The trem works also...

I Know the wiring is a mess but to the best of my knowledge I think its correct.BTW that 500pf looks like its touching the middle tab on the volume pot but thats an illusion caused angle of view. TIA Bob

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Image
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Re: 18 watt TMB squeal & hum

Post by Bieworm »

rockon1 wrote:
Sun 02/27/22 5:26 pm
First post here. Ive got a noise problem with the trrem channel on my Mojotone revision 5 18watt tbm.From a post at TGP-
Now this morning I'm looking at the trem channel. Gone over the wiring.As soon as I connect the 4.7nf to the tone pot to ground I loose the all sound ?they should have used different colored wires from the volume pot to the board I think cause two gray ones are easy to mix up imo- thats if they correct in the first place... Im using a 4.7nf 600volt rated orange drop cap in place of the original as its tests open- unless I need the original type...

Edit-Im not sure if this a clue but at one point it the trem side worked- Thats when I discovered the volume wires(gray in the layout pic) going to the board were wrong(crossed up) and corrected them. I just put them back and voila-humming in both channels but volume. The trem works also...

I Know the wiring is a mess but to the best of my knowledge I think its correct.BTW that 500pf looks like its touching the middle tab on the volume pot but thats an illusion caused angle of view. TIA Bob

Image

Image
Hi there!! Welcome to 18Watt!! This is not a TMB, but an 18W classic.. just for the record :D
ok, there's no easy way to say this..
I don't know what others will say about your build, but that is really a messy and DANGEROUS build. Do you have experience with building amps? It doesn't mean when everything is connected to the right connection that you'll have a successful build.
My advice is:

1. read the docs on modern grounding schemes and soldering technique
viewtopic.php?f=4&t=25372

2. throw away the MOJO docs.. they're a disaster! use these:
viewtopic.php?t=25606

3. prepare for desoldering the entire thing and do it over the right way, we'll guide you.

Note that it's a really great amp when done properly! But you have very bad component placement, burnt wiring, bad grounding layout,... yes, it's really dangerous in general.
If you follow our advice you'll end up with a great and noisefree amp, I promise!
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Re: 18 watt TMB squeal & hum

Post by rockon1 »

Bieworm wrote:
Mon 02/28/22 2:31 am
rockon1 wrote:
Sun 02/27/22 5:26 pm
First post here. Ive got a noise problem with the trrem channel on my Mojotone revision 5 18watt tbm.From a post at TGP-
Now this morning I'm looking at the trem channel. Gone over the wiring.As soon as I connect the 4.7nf to the tone pot to ground I loose the all sound ?they should have used different colored wires from the volume pot to the board I think cause two gray ones are easy to mix up imo- thats if they correct in the first place... Im using a 4.7nf 600volt rated orange drop cap in place of the original as its tests open- unless I need the original type...

Edit-Im not sure if this a clue but at one point it the trem side worked- Thats when I discovered the volume wires(gray in the layout pic) going to the board were wrong(crossed up) and corrected them. I just put them back and voila-humming in both channels but volume. The trem works also...

I Know the wiring is a mess but to the best of my knowledge I think its correct.BTW that 500pf looks like its touching the middle tab on the volume pot but thats an illusion caused angle of view. TIA Bob

Image

Image
Hi there!! Welcome to 18Watt!! This is not a TMB, but an 18W classic.. just for the record :D
ok, there's no easy way to say this..
I don't know what others will say about your build, but that is really a messy and DANGEROUS build. Do you have experience with building amps? It doesn't mean when everything is connected to the right connection that you'll have a successful build.
My advice is:

1. read the docs on modern grounding schemes and soldering technique
viewtopic.php?f=4&t=25372

2. throw away the MOJO docs.. they're a disaster! use these:
viewtopic.php?t=25606

3. prepare for desoldering the entire thing and do it over the right way, we'll guide you.

Note that it's a really great amp when done properly! But you have very bad component placement, burnt wiring, bad grounding layout,... yes, it's really dangerous in general.
If you follow our advice you'll end up with a great and noisefree amp, I promise!
Thanks!Yeah I know-its messy...I figure I'll clean it up after I get it working...I know bass-ackwards... I mental state is not what is used to be... Hopefully I'll getting working before I pass on... :nerd:
Yeah mojo docs arent the best. Already caught one mistake on the layout that came with the amp...Notice the lack of missing a ground connection to to the cold track end of the volume pot?
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