My JMSig w/ SSS Step Filters Build Thread

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rccolgan
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Re: My JMSig w/ SSS Step Filters Build Thread

Post by rccolgan »

67plexi wrote: Thu Feb 22, 2018 8:18 pm Your chassis look great but you should read this first

http://ampgarage.com/forum/viewtopic.php?f=4&t=18953
Noted. I did first reach out to Nik first and did follow through with some of the suggestions (reverb tube tracing, swapping reverb in/out) which did end up helping. Since I'm bringing my own chassis, it adds an extra variable to the equation where I have not got a direct search hit on the hum that I'm hearing with adjusting bias. Happy to learn from your experience in this area if you have anything to share.
Ryan
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rccolgan
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Re: My JMSig w/ SSS Step Filters Build Thread

Post by rccolgan »

Not sure if this is a red herring or not but I did find a thread asking the original poster if the hum was a multiple of the line frequency. I did note that the hum sounds a lot like the B note on my guitar which is close to a multiple of 60Hz. Coincidence? The member that posted the question didn't follow up with the thought process but I'm curious if that's something too.. I get off of work at 5 and actually looking forward to troubleshooting now after the help from this forum 8)

B1 61.74Hz 558.84
B2 123.47Hz 279.42
B3 246.94Hz 139.71

The note I was playing was B2 where it sends the amp into feedback. The amp is super quiet and I don't hear 60Hz hum with colder bias so my gut tells me it might not be related to bad filter caps but I'll start with swapping the OT and grounding the GNFB.
Ryan
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martin manning
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Re: My JMSig w/ SSS Step Filters Build Thread

Post by martin manning »

rccolgan wrote: Thu Feb 22, 2018 9:16 pmI did note that the hum sounds a lot like the B note on my guitar which is close to a multiple of 60Hz. Coincidence?
Nope. line voltage is 60Hz, after full-wave rectification the residual ripple will be 120Hz.
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rccolgan
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Re: My JMSig w/ SSS Step Filters Build Thread

Post by rccolgan »

M Fowler wrote: Thu Feb 22, 2018 7:20 pm Disconnect the NFB on the jack first. Must ground tail resistor

Mark
Mark, this worked!!! I'm able to quietly bias to 35mv no problem. Question. why and what am I gaining/losing leaving it this way? My understanding is the GNFB has a lot to do with cleans and punch of the amp.
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martin manning
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Re: My JMSig w/ SSS Step Filters Build Thread

Post by martin manning »

Disconnecting the GNFB is just a quick way to see if the OT is miss-wired.
sluckey
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Re: My JMSig w/ SSS Step Filters Build Thread

Post by sluckey »

Disconnecting the NFB is not a fix. It is just a quick check to see if the NFB is phased correctly. Yours in not.

Now you need to reconnect the NFB and move on to the actual fix. You must swap the OT plate leads or swap the output tube grid leads. One or the other. Not both.
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rccolgan
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Re: My JMSig w/ SSS Step Filters Build Thread

Post by rccolgan »

Doh!! :shock: Thanks!! Funny how it's always the thing you try to avoid, is actually the source of the problem lol. Going to swap the phase after my daughter goes to bed but she may wake up to some really sweet tones rocking the house 8)
Ryan
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rccolgan
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Re: My JMSig w/ SSS Step Filters Build Thread

Post by rccolgan »

We did it!! Swapping N and M on the layout did the trick and I kept my wire dressing in tact! Phew!! All-in-all I'm happy it was something easily fixable and thank you all for input! Now I'm on to building the cabinet :D
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M Fowler
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Re: My JMSig w/ SSS Step Filters Build Thread

Post by M Fowler »

Glad you fixed the problem.

While I was off enjoying my wife and two of my grand kids for my birthday meal you were in very capable hands.

Mark
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rccolgan
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Re: My JMSig w/ SSS Step Filters Build Thread

Post by rccolgan »

M Fowler wrote: Fri Feb 23, 2018 3:52 am Glad you fixed the problem.

While I was off enjoying my wife and two of my grand kids for my birthday meal you were in very capable hands.

Mark
Happy birthday! And also, congratulations on hitting 13,000 posts on the forum! wow!
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M Fowler
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Re: My JMSig w/ SSS Step Filters Build Thread

Post by M Fowler »

Thanks I'm a motor mouth apparently.
Last edited by M Fowler on Sun Mar 18, 2018 10:56 am, edited 1 time in total.
dbeasley
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Re: My JMSig w/ SSS Step Filters Build Thread

Post by dbeasley »

Mark has been around for a while ;)

Great build. Love seeing folks stepping away from straight clones and doing little different things to thier builds

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Re: My JMSig w/ SSS Step Filters Build Thread

Post by rccolgan »

I've been busy reverse engineering dimensions on SSS #004 head cabinet and combo cabinet and I'm almost done with 3D rendering the head cabinet to start the woodwork. I used Inkscape and various photos of #004 to virtually measure the cabinets based off one single known dimension (28.25" wide). I then reconstructed the head cabinet around these measurements which I believe is fairly accurate after repeating the forensic process with the 3D models. If anyone has knowledge to confirm/deny my virtual measurements, I'd be forever grateful! I used 18mm (.71" actual width in the 3/4" baltic birch ply I received) as the base.
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rccolgan
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Re: My JMSig w/ SSS Step Filters Build Thread

Post by rccolgan »

Full 3D render on the front. Up next is measuring the trapezoidal rear baffle.
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pompeiisneaks
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Re: My JMSig w/ SSS Step Filters Build Thread

Post by pompeiisneaks »

Wow super cool, quite the effort!

~Phil
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