Advice needed...

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Re: Advice needed...

Post by TriodeLuvr »

Rather than separate the V1 and V2 grounds, lift that lug off the chassis and ground it to the star. You might have to separate the preamp and PI grounds, but the small amount of current drawn across the common ground wire by the PI probably won't create an issue. It's too bad the lugs on the terminal strip are cut off in that location. They would make this work easier. I often assign more than one lug as signal ground, and more than one as B+, even when the same B+ feeds two stages. That provides the option of separating the circuits later if there's unwanted interaction.

Anyway, let's hope this quiets it down. If not, we'll have to look elsewhere.

Jack
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Re: Advice needed...

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TriodeLuvr wrote:
Thu 05/27/21 9:03 pm
Rather than separate the V1 and V2 grounds, lift that lug off the chassis and ground it to the star. You might have to separate the preamp and PI grounds, but the small amount of current drawn across the common ground wire by the PI probably won't create an issue. I often assign more than one lug as signal ground, and more than one as B+, even when the same B+ feeds two stages. That provides the option of separating the circuits later if there's unwanted interaction. Anyway, let's hope this quiets it down. If not, we'll have to look elsewhere. Jack
I got rid of the (pre) lug on the side (assuming eliminating it is the same as isolating it) ...and I used the 3rd of the 4 terminal connections which has the input jack and pre grounds all going back to the star on their own lead. The PI grounds are connected together and go to the star on their own lead as well. I separated the PI grounds because it's the only configuration I believe that hasn't been tried yet. Tying the pre and PI grounds together and running them back to the star is exactly the way it was laid out at the beginning except for the pre-cap being grounded at the pre section instead of directly to the star.
But it is, of course, also now grounded to the star but still connected up by the input jack. As a side note; the closer I get the guitar to the amp the worse the noise gets. I tried using the tube shields on V1 & V2 but it didn't help at all. Also the blue wire connecting the input jack tip to the grid isn't shielded; it's only an inch at best but just another observation.
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Re: Advice needed...

Post by The4thWatcher13 »

Correction: in the "original" layout Pre, PI, jack and vol were grounded to their own point up front. Not all going to the star, as I stated above. Also, I tried re-connecting V1 & V2 grounds all of which now go to the star on one lead. Both of the ways Jack recommended trying previously. Still no real difference in the level of buzz.
So to recap, for my own sanity, I've tried:
All ps caps to star, Pre & PI, connected, grounded up front.
Pre filter cap was moved from star to ground up front.
Pre and PI separated, Pre grounded up front, PI grounded to star.
Pre and PI separated, grounded to star on separate leads.
Pre and PI reconnected and grounded to star on same lead.
No appreciable difference in the level of buzz.
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Re: Advice needed...

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The4thWatcher13 wrote:
Fri 05/28/21 9:15 pm
Correction: in the "original" layout Pre, PI, jack and vol were grounded to their own point up front. Not all going to the star, as I stated above. Also, I tried re-connecting V1 & V2 grounds all of which now go to the star on one lead. Both of the ways Jack recommended trying previously. Still no real difference in the level of buzz.
So to recap, for my own sanity, I've tried:
All ps caps to star, Pre & PI, connected, grounded up front.
Pre filter cap was moved from star to ground up front.
Pre and PI separated, Pre grounded up front, PI grounded to star.
Pre and PI separated, grounded to star on separate leads.
Pre and PI reconnected and grounded to star on same lead.
No appreciable difference in the level of buzz.
Match my ground scheme, then try the Paul Ruby mod. Both can be seen here: files/JMPGuitars_18_Watt_Superlite_TMB_Layout.pdf

You'll note on my ground schemes the PI goes to the power amp star ground.

If that has no effect, post a demo of what the amp sounds like. Turn it up to a moderate volume level, plug a guitar in, wait 10 seconds or so, then also play the guitar a little.

Thanks,
Josh
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Re: Advice needed...

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The4thWatcher13 wrote:
Fri 05/28/21 3:39 pm
As a side note; the closer I get the guitar to the amp the worse the noise gets.
I would have replied sooner, but our power is out due to a storm.

Josh, have you ever seen a ground loop act like that?

I know this is a long shot, but is there any chance the input jack is wired wrong?

Jack
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Re: Advice needed...

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JMPGuitars wrote:
Sat 05/29/21 6:23 am
Match my ground scheme, then try the Paul Ruby mod. Both can be seen here: files/JMPGuitars_18_Watt_Superlite_TMB_Layout.pdf
You'll note on my ground schemes the PI goes to the power amp star ground. If that has no effect, post a demo of what the amp sounds like. Turn it up to a moderate volume level, plug a guitar in, wait 10 seconds or so, then also play the guitar a little. Thanks, Josh
I'll give it a look and give it a try, Josh, thanks. One thing I've been dealing with is trying to determine exactly how much amp "noise" inevitable or acceptable. The noise isn't bad until you get up to 3/4 or so. I didn't know I could post an audio file here. That'll help too.
Also do you think with my 1"in lead from the jack "tip" to the grid should be shielded? And is the shielded lead in your diagram grounded on one end (at the jack)
Last edited by The4thWatcher13 on Sat 05/29/21 2:17 pm, edited 2 times in total.
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Re: Advice needed...

Post by The4thWatcher13 »

TriodeLuvr wrote:
Sat 05/29/21 10:27 am
The4thWatcher13 wrote:
Fri 05/28/21 3:39 pm
As a side note; the closer I get the guitar to the amp the worse the noise gets.
I would have replied sooner, but our power is out due to a storm.
Josh, have you ever seen a ground loop act like that?
I know this is a long shot, but is there any chance the input jack is wired wrong? Jack
No worries here, Jack. As long as you and yours are OK. I've got a "shorted" or "switched" input the tip goes directly to the grid of V1 and a 1M R goes to the ground tab that lifts when you plug in a plug, and then to the ground tab. The grounding input jack isn't shown on my schematic, apologies. I've got new Cliff jacks coming soon.
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Re: Advice needed...

Post by JMPGuitars »

TriodeLuvr wrote:
Sat 05/29/21 10:27 am
The4thWatcher13 wrote:
Fri 05/28/21 3:39 pm
As a side note; the closer I get the guitar to the amp the worse the noise gets.
I would have replied sooner, but our power is out due to a storm.

Josh, have you ever seen a ground loop act like that?
I don't think so, but guitars getting closer to an amp will increase feedback (if there is any), so this may be along those lines. I think we need to hear what the noise actually sounds like.
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Re: Advice needed...

Post by The4thWatcher13 »

Well, I'm attempting to upload a sound sample of the amp and the noise it's making. Something odd happened today as well. The amp started an oscillation, something which hasn't happened to date and I've been standing in the same spot every time I've tested the amp. It also kind of sounds like the buzz may actually be getting worse.
On the recording the amp was set at 50% and tone at about 75%. Forgive my lack of guitar skills, I'm actually a drummer! (..I bet that clears up a lot! :D ) Last night I moved the 1M/R on the input jack which previously went from the tip tab to the ground lift tab to the ground tab. Now it goes from the tip tab to the ground tab to the ground lift tab. This enabled me to move the resistor further away from the V1 cathode CR and also seemed a more correct per Josh's layout.
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Re: Advice needed...

Post by TriodeLuvr »

When routing wires, it helps to consider the various connection points in terms of the impedance to ground. For example, the highest impedance - and therefore the most susceptible to picking up stray signals - would be grids. OTOH, a bypassed cathode of a common-cathode stage is very low impedance. It will have almost no AC voltage on it. As a result, it's not possible for a wire connected to such a cathode to radiate into (or be affected by) a grid circuit. The two can be right next to each other without issues.

Maybe the amp is oscillating all the time. That sometimes sounds like a buzz. It might also explain why the location of the guitar changes the symptom. Like Josh said, it would help to hear it.

Jack
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Re: Advice needed...

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TriodeLuvr wrote:
Sun 05/30/21 7:41 pm
When routing wires, it helps to consider the various connection points in terms of the impedance to ground. For example, the highest impedance - and therefore the most susceptible to picking up stray signals - would be grids. OTOH, a bypassed cathode of a common-cathode stage is very low impedance. It will have almost no AC voltage on it. As a result, it's not possible for a wire connected to such a cathode to radiate into (or be affected by) a grid circuit. The two can be right next to each other without issues. Maybe the amp is oscillating all the time. That sometimes sounds like a buzz. It might also explain why the location of the guitar changes the symptom. Like Josh said, it would help to hear it. Jack
Thanks Jack, every time you comment I look at this amp with different eyes. I appreciate it. I posted an audio file, above, earlier of the buzz sound etc. I also re-routed my heater wiring away from V3/V4's grid where previously they were kind of bunched up in close proximity and also ran under the grid circuitry. It didn't have much if any affect but a lesson still learned. I'm anxious to learn what you think of the buzz sound. The first leg of the heater run to V1 goes under both pots as well. I've been wondering about that also since I'm not definite about where and where not to run it. I think I can move it from that location if it's OK to run it over the "red/black/red" plate supplys & ground wire in forground of the picture below. I also re-added a 47uF/63V bypass cap to the OPT cathode ground resistor. It had been suggested somewhere earlier in the thread and it was there during the proto build but was so hidden I had forgotten about it. Again no affect on the buzz. (I didn't forget anything else! :oops: ) I've also added yet another current version of the schematic. Which is constantly updated for, at the very least, my own sake.
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Re: Advice needed...

Post by TriodeLuvr »

Well, it sounds like the first stage grid might be picking up heater hum. Can you clip your scope across the speaker and see what the buzz looks like? I just want to rule out a high frequency oscillation. If it just looks like buzz, you might need to rotate the V1 socket so heater wiring isn't crossing the grid circuit. You could also heat V1 with a battery or DC bench supply temporarily to see if the buzz goes away. I'm thinking the grid circuit is picking it up, and it's riding into the guitar - and the wiper of the guitar's volume control - through the input jack. The wiper grounds the buzz when the guitar is turned down, and that's why it gets quiet. Just a theory...

That low frequency oscillation could be several things. Did you replace all the parts in the old amp, including coupling caps and tube sockets?

Jack
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Re: Advice needed...

Post by JMPGuitars »

That buzz is not fantastically significant. It couuuuuuuuuld be the things we're talking about, or it could simply be a need for some chopsticking. Or made worse by the guitar pickups.

Regarding the oscillation, you need to determine if it's being caused by the amp, or being picked up by the amp. I spent a year chasing an oscillation once that was caused by a power supply in another room.

Chopsticking might help determine both, but if you have anything new plugged in, or power supplies (wall warts, laptop style bricks etc...) that you can unplug and see if the oscillation goes away, that may help determine the source. I use filtered inlets nowadays to reduce this issue.

Thanks,
Josh
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Re: Advice needed...

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TriodeLuvr wrote:
Sun 05/30/21 11:09 pm
Well, it sounds like the first stage grid might be picking up heater hum. Can you clip your scope across the speaker and see what the buzz looks like?
Here are pics of the buzz at the output jack and the vol-pot wiper. Full amp vol, full guitar vol. No oscillations today so far.
TriodeLuvr wrote:
Sun 05/30/21 11:09 pm
I just want to rule out a high frequency oscillation. If it just looks like buzz, you might need to rotate the V1 socket so heater wiring isn't crossing the grid circuit. You could also heat V1 with a battery or DC bench supply temporarily to see if the buzz goes away. I'm thinking the grid circuit is picking it up, and it's riding into the guitar - and the wiper of the guitar's volume control - through the input jack. The wiper grounds the buzz when the guitar is turned down, and that's why it gets quiet. Just a theory...Did you replace all the parts in the old amp, including coupling caps and tube sockets? Jack
Yes, all components of this amp are new accept the Vol, Tone pots and the jacks. All of which will be replaced by new parts arriving tomorrow. Side Note: I've been thinking about not having a grid stopper resistor on this amp and was reading the Valve Wizard page about it (Miller Effect). I then put the scope meter on Hz, probes on output, and started the buzz. The meter measured it at +20MHz. When trouble shooting I know it's good to deal with and rule out one aspect at a time but the thought crossed my mind and I took a quick measurement.
[Top pic: output] [Bottom pic: vol wiper]
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Re: Advice needed...

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JMPGuitars wrote:
Mon 05/31/21 7:41 am
That buzz is not fantastically significant. It couuuuuuuuuld be the things we're talking about, or it could simply be a need for some chopsticking. Or made worse by the guitar pickups.
Regarding the oscillation, you need to determine if it's being caused by the amp, or being picked up by the amp. I spent a year chasing an oscillation once that was caused by a power supply in another room.
Chopsticking might help determine both, but if you have anything new plugged in, or power supplies (wall warts, laptop style bricks etc...) that you can unplug and see if the oscillation goes away, that may help determine the source. I use filtered inlets nowadays to reduce this issue. Thanks, Josh
Thanks Josh, I'm heading for my Chop-sticks now. More to follow..
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Re: Advice needed...

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1mS/Div is too fast to see 60 Hz energy. At 1mS/Div, your scope can only display 10 mS of time across the screen (10 divisions). A 60 Hz wave has a period of 16.7mS (1 ÷ 60). 10mS or 5mS is needed to display hum.

That aside, what is the signal on the left side of the display in the first photo? It appears to be something in the neighborhood of 7 kHz.

Jack
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Re: Advice needed...

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TriodeLuvr wrote:
Mon 05/31/21 6:23 pm
1mS/Div is too fast to see 60 Hz energy. At 1mS/Div, your scope can only display 10 mS of time across the screen (10 divisions). A 60 Hz wave has a period of 16.7mS (1 ÷ 60). 10mS or 5mS is needed to display hum. That aside, what is the signal on the left side of the display in the first photo? It appears to be something in the neighborhood of 7 kHz. Jack
Still images were pretty hard to capture at .5mS/Div. But here is a pic of the repeating waveform. Last night I also moved the heater wiring from underneath the V1 grid. The buzz is still there and doesn't seem to have changed.
The left most aspect of the buzz in the image you mentioned is gone now. I've yet to try to power the V1 heater with DC but maybe I'll try that later today. I definitely have issues with AC here in the garage and I've tried a number of different fixes. I've got several AC filters like B&K TR110 Direct/Iso-pack and OneAC CL1101.5 power conditioner. None affect the current issue as far as I can tell. Setting up AC supply in a shop would be a good instructional for those needing it. It may exist somewhere so I'll look. I'm in a garage with one 15A service to the house. Not optimal I guess. Also new 1M Vol and 2M tone pots, Cliff jacks etc arrived today.
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Re: Advice needed...

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JMPGuitars wrote:
Mon 05/31/21 7:41 am
That buzz is not fantastically significant. It couuuuuuuuuld be the things we're talking about, or it could simply be a need for some chopsticking. Or made worse by the guitar pickups.
I've heard all kinds of amps over the years but only own one other tube amp, '67 Sunn Solarus combo, and it doesn't have anything like this kind of buzz. I think anyone would consider it significant given anything past 50% on the guitar or amp produces a great deal of buzz.
JMPGuitars wrote:
Mon 05/31/21 7:41 am
Regarding the oscillation, you need to determine if it's being caused by the amp, or being picked up by the amp. I spent a year chasing an oscillation once that was caused by a power supply in another room. Chopsticking might help determine both, but if you have anything new plugged in, or power supplies (wall warts, laptop style bricks etc...) that you can unplug and see if the oscillation goes away, that may help determine the source. I use filtered inlets nowadays to reduce this issue. Thanks, Josh
I did Chop-stick the tubes, amp etc. but to no affect except the expected amplification of the tap on the preamp tube. In regard to the oscillation; sometimes I'll hear a little tick, tick...oscillation, then it's gone.
I just started for the first time several days ago as well.
The AC situation here is certainly not optimal. I've turned everything off except the amp and the result is pretty much the same though I can tell that certain things like my laptop do have an a minor effect on the amp. These things just don't affect other audio equipment to the point where I've had to address it to any degree. I went further into my AC situation in my reply to Jack above. Thanks Josh!
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Re: Advice needed...

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Well, the sweep has gone from being too slow to too fast. :) It should be set to 5 or 10mS/Div, not 0.5mS. The two scope divisions in the last photo aren't displaying 60 Hz. That's the same high frequency signal (6 kHz or 7 kHz) that was evident in the first photo. I don't know if this is being generated by the amp. There are quite a few devices in homes (and garages) now that emit large EM fields. Televisions, computers, sprinkler controllers, even wall-mounted light dimmers. It's possible you're picking that up somehow.

Ignoring the HF stuff for the moment, I think you'll need to gut the filament wiring and redo it from scratch. It's simply not located where it needs to be, and I think running it across the front panel under the pots is really a problem. If it was me, I would start at the transformer wires and go to the output tubes. Then wire from one of the output tubes to the 12AX7, then to the 6AV6. Also, don't push it down onto the chassis. That's where the all the signal circuitry is. Position all the runs one or two inches above the amplifier circuitry and sockets, and drop it down onto the tube pins in each location. It's a misconception that running twisted pair along a metal chassis helps shield it. Not sure what kind of wire you're using; this is obviously easier with solid wire because it holds its shape better.

Jack
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Re: Advice needed...

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TriodeLuvr wrote:
Tue 06/01/21 5:55 pm
Well, the sweep has gone from being too slow to too fast. :) It should be set to 5 or 10mS/Div, not 0.5mS.
The scope is actually set on 5mS/Div, though it's not shown in the last photo. I think what you're seeing is the styling on the knob. The marker is a raised line pointing to 5mS/Div. You are correct that in the first two photos the scope was set at 1mS/Div tho.
TriodeLuvr wrote:
Tue 06/01/21 5:55 pm
The two scope divisions in the last photo aren't displaying 60 Hz. That's the same high frequency signal (6 kHz or 7 kHz) that was evident in the first photo. I don't know if this is being generated by the amp. There are quite a few devices in homes (and garages) now that emit large EM fields. Televisions, computers, sprinkler controllers, even wall-mounted light dimmers. It's possible you're picking that up somehow.

Ignoring the HF stuff for the moment, I think you'll need to gut the filament wiring and redo it from scratch. It's simply not located where it needs to be, and I think running it across the front panel under the pots is really a problem. If it was me, I would start at the transformer wires and go to the output tubes. Then wire from one of the output tubes to the 12AX7, then to the 6AV6. Also, don't push it down onto the chassis. That's where the all the signal circuitry is. Position all the runs one or two inches above the amplifier circuitry and sockets, and drop it down onto the tube pins in each location. It's a misconception that running twisted pair along a metal chassis helps shield it. Not sure what kind of wire you're using; this is obviously easier with solid wire because it holds its shape better. Jack
You know, I wondered about that earlier when you were talking about "elevating" the heater trans CT ground wiring. At first I thought you actually were talking about physically elevating the heater runs because I wasn't familiar with the function. But when we then started talking about "elevating" the heater trans CT with the two resistors I just assumed that that was the entirety of what you were conveying. I better start asking more questions when in go to wonderin'! Never the less I'll get right on it. Good time, I guess, to install the new jacks and pots as well. Thanks Jack!
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