Dang... New filter caps, changed grounding... Same issues! I'm out of ideas...
Reverb Circuit Hum
Moderators: pompeiisneaks, Colossal
Re: Reverb Circuit Hum
I don`t know if this will help you but I quote something I heard a while back while adding reverb to an amp.
"Fender grounded the RCA jacks at the jacks on the back of the chassis. Apparently this can cause ground loops in some amps.Solution is to isolate the reverb jacks from the chassis and ground jack and the 220K resistor (and 500pf cap) to the ground side of the cathode cap for that portion of the reverb circuit. "
By the way, does the amp work and sound ok when you take the reverb out of the circuit ?
"Fender grounded the RCA jacks at the jacks on the back of the chassis. Apparently this can cause ground loops in some amps.Solution is to isolate the reverb jacks from the chassis and ground jack and the 220K resistor (and 500pf cap) to the ground side of the cathode cap for that portion of the reverb circuit. "
By the way, does the amp work and sound ok when you take the reverb out of the circuit ?
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Stevem
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Re: Reverb Circuit Hum
Yes, that's what I want to know at this point!
Bypass that whole dam circuit and pump it into the PI section and report back please?!
Bypass that whole dam circuit and pump it into the PI section and report back please?!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Reverb Circuit Hum
There is hum even without any if the preamp tubes, so there must be a grounding problem. With each added tube, the hum increases a bit. I think I will start by isolating the speaker jacks...
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Stevem
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- Joined: Fri Jan 24, 2014 3:01 pm
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Re: Reverb Circuit Hum
Ok then, what hum frequency are you reading at idle at the speaker jack(s)?
Is it only there when you have a speaker plugged in as compared to a load resistor?
Is it only there when you have a speaker plugged in as compared to a load resistor?
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Reverb Circuit Hum
I revised the grounding scheme so the center taps, earth ground, filter caps, and speaker jacks Re all grounded at the lug near the inputs. I'm using Cliff jacks for the speaker jacks, so they are isolated from the chassis.
This arrangement eliminated the hum when only the rectifier and power tubes are installed. As I add back preamp tubes, the noise starts again. With V4 added, there is a slight 120hz hum. I think I've convinced myself that the remaining chassis-connected tremolo footswitch jack and reverb RCA jacks are causing a ground loop. Any thoughts on how to isolate panel mounted RCA jacks?
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Stevem
- Posts: 4589
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Reverb Circuit Hum
Yes, drill out those two rca jack mounting holes large enough such that your two jacks can clear them by a good amount, then get some sheet plastic or 1/4" Doll house plywood from a hobby store or some scrap 1/4" moasonite and make a mounting panel for the jacks and then drill 4 holes to mount the panel.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Reverb Circuit Hum
Here is the current state of the chassis. All grounds connect to the Ground Lug near the inputs, except the Dwell Pot, RCA Jacks, and Tremolo Foot Switch Jack that are grounded to the chassis. Once parts arrive, I plan to isolate everything, so there is only a single ground connection point on the chassis. Thoughts on this?
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Re: Reverb Circuit Hum
Well it may be preferable to ground the power amp components at the other end near the PT but if it`s working ok thats good.
The main thing though is just make sure the earth ground from the ac inlet is on its own on a short wire from the inlet socket and very securely fixed to the chassis as the law demands.
It`s called safety ground for a good reason! Lets not have any accidents ok!
I think isolating all the sockets is a very good idea too.
The main thing though is just make sure the earth ground from the ac inlet is on its own on a short wire from the inlet socket and very securely fixed to the chassis as the law demands.
It`s called safety ground for a good reason! Lets not have any accidents ok!
I think isolating all the sockets is a very good idea too.
Re: Reverb Circuit Hum
Yeah, you're right. I need to put the safety ground back to its original location near the power transformer.earl2 wrote: ↑Tue Feb 05, 2019 7:51 pm Well it may be preferable to ground the power amp components at the other end near the PT but if it`s working ok thats good.
The main thing though is just make sure the earth ground from the ac inlet is on its own on a short wire from the inlet socket and very securely fixed to the chassis as the law demands.
It`s called safety ground for a good reason! Lets not have any accidents ok!
I think isolating all the sockets is a very good idea too.
I local tech who is very familiar with this amp suggested I try tying *all* the grounds to a single location, including the safety ground. According to him, Laney used to do this on some of their amps, and it produces very quiet results.
However, lengthening the safety ground connection did make me nervous. I will fix that.
Re: Reverb Circuit Hum
You know.... Matchless made a model with Reverb and Tremolo, 450 of them actually, the only AC30 type amp they made with Reverb:
<<The JJ-30, or John Jorgenson signature model was the true flagship of the Matchless line. This two input class A amplifier has Gain-Tone-Speed -Depth-Reverb-Cut-Master controls.Also a half power switch, speaker phase switch, output impedance selector switch, AC acc. outlet, extension speaker jack, a very nice padded handle,a very sturdy cab with a T brace in front of the speaker which stiffens the unit and also protects the speaker from your foot.
This amp has a load of gain and is very LOUD.The reverb also sounds better with the 12AT7 due to the increase in bandwidth. It still sounds like a VOX but with a Fender / Marshall edge. And no VOX ever had as much gain as this amp. The JJ has about as much gain with the the volume on 12:00 CHT as the Maz does full up. Less than 40 of these amps were ever produced, and they are the absolute pinnacle of the matchless amplifier company's offering while Mark Sampson was running the company up until the mid to late 1990's. It is essentially the EF86 side of the C-30 amp, but with the addition of the best sounding tube driven tremolo and reverb ever heard. >>
So it seems Mark Samson sorted this out. Can anybody source a schematic of this amp? Well, then there's the Chieftain which is still Class A but EL34s..
<<The JJ-30, or John Jorgenson signature model was the true flagship of the Matchless line. This two input class A amplifier has Gain-Tone-Speed -Depth-Reverb-Cut-Master controls.Also a half power switch, speaker phase switch, output impedance selector switch, AC acc. outlet, extension speaker jack, a very nice padded handle,a very sturdy cab with a T brace in front of the speaker which stiffens the unit and also protects the speaker from your foot.
This amp has a load of gain and is very LOUD.The reverb also sounds better with the 12AT7 due to the increase in bandwidth. It still sounds like a VOX but with a Fender / Marshall edge. And no VOX ever had as much gain as this amp. The JJ has about as much gain with the the volume on 12:00 CHT as the Maz does full up. Less than 40 of these amps were ever produced, and they are the absolute pinnacle of the matchless amplifier company's offering while Mark Sampson was running the company up until the mid to late 1990's. It is essentially the EF86 side of the C-30 amp, but with the addition of the best sounding tube driven tremolo and reverb ever heard. >>
So it seems Mark Samson sorted this out. Can anybody source a schematic of this amp? Well, then there's the Chieftain which is still Class A but EL34s..
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Most people stall out when fixing a mistake that they've made. Why?
Re: Reverb Circuit Hum
Ok, so I isolated all the remaining connectors and pots. The hum is reduced, but a prominent white noise *shhhhhh* remains at all volume levels. There is clearly something very wrong with the reverb circuit - when I turn up the reverb knob even a bit, I start to get a lot of squealing feedback. Thoughts on the most likely mistake?!
Re: Reverb Circuit Hum
Well it did cross my mind that this particular one tube reverb circuit was normally injected around a simple 100 - 200k mixer resistor. In this case Vox/Ampeg style there are two more gain stages involved relative to the dry signal. V2a on the way in and V2b on the way out. Whether that is causing this problem in some way I don`t know.
What immediately comes to mind with hiss is tubes and sockets (remove one at a time to test) or a bad solder joint.
If I were you though I would just disconnect that reverb altogether for a moment and make sure the amp is working normally with it out of the circuit , i.e. disconnect the input to the dwell control and the grid of V2b. At least then you could start to narrow down where this problem starts.
What immediately comes to mind with hiss is tubes and sockets (remove one at a time to test) or a bad solder joint.
If I were you though I would just disconnect that reverb altogether for a moment and make sure the amp is working normally with it out of the circuit , i.e. disconnect the input to the dwell control and the grid of V2b. At least then you could start to narrow down where this problem starts.
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Stevem
- Posts: 4589
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Reverb Circuit Hum
When you add( or remove) gain stages to do whatever functions you may then then be outputting a signal to the PI section that is of the wrong phase.
Every time audio signal goes into a grid and comes out the plate it has then flipped phase.
If you reverse the what should be the brown and blue plate wires on the output tubes from the OT do your squeal and noise issues get better or worse?
Every time audio signal goes into a grid and comes out the plate it has then flipped phase.
If you reverse the what should be the brown and blue plate wires on the output tubes from the OT do your squeal and noise issues get better or worse?
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Reverb Circuit Hum
Thanks for the comments! I'm remembering that before I started trying to "fix" things, the reverb actually worked (LOL!)
I think I will first try to restore the original wiring scheme and see if I can't get it to sound better. The squealing and hiss are relatively new developments...
Who knows... with the predicted Snowmageddon in the Seattle area, I may have a lot of time to work on this!
I think I will first try to restore the original wiring scheme and see if I can't get it to sound better. The squealing and hiss are relatively new developments...
Who knows... with the predicted Snowmageddon in the Seattle area, I may have a lot of time to work on this!