# 1971 YBA-1 BASSMASTER // viva Analog MODS



## 360+ (Mar 13, 2011)

Hiya folks ... been awhile eh

hadn't done a YBA-1 in years, and will not hesitate saying how great this thing sounds // with a distortion tone to die for ...

here's a write-up of what I did :

1971 Traynor Bassmaster MODS - viva Analog

now, about that faint residual (AC) hum when the volumes are turned up ...

I'm a little puzzled why I couldn't eliminate (nearly) all of it as I usually can in other chassis' ...
it was a tad high for my taste, but still ok of course ...
just a little higher than usual, that's all

leaky power Tx is all I can think of ... ?!
comments welcome


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## nonreverb (Sep 19, 2006)

I don't think the interference is from the power transformer. It, for good reason, is located on the other side of the chassis from the input. Since it can be manipulated by the volume control, that would suggest it resides somewhere in the primary gain stage. Do both volumes give the same result when on independently?


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## bolero (Oct 11, 2006)

hey JC, good to see you here

my Univibe+ is still going strong 

Cheers!


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## 360+ (Mar 13, 2011)

Hey Bolero /// ... great to hear from you, thx!!



nonreverb said:


> I don't think the interference is from the power transformer. It, for good reason, is located on the other side of the chassis from the input. Since it can be manipulated by the volume control, that would suggest it resides somewhere in the primary gain stage. Do both volumes give the same result when on independently?


Hi Nonreverb, thx for the reply ...

yes, I've worked on enuff amps to know how the trannies are laid out in yer typical chassis ...
and why ...

it seems there's a not un-common complaint that hum starts as soon as you hit the power switch in YBA1's
ie., before the tubes warm up

I figured it was due to poor grounding in the chassis
now, that turn-on hum is all gone with the re-wiring I did ...

but when I turn up either volume control there's a background hum that still remains
(with guitar volume at zero, both inputs shorted) ...

usually, in other chassis, I can get all the hum out pretty much
not here

I also noticed that my Strat picks up a lot more hum than usual in close proximity to the amp
making me think the magnetic shielding on the mains iron is not very effective

it's not the tubes, it's not the grounding ...
must be the PTx

curious to hear from other techs who've worked on YBA1's


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## nonreverb (Sep 19, 2006)

I've worked on many Traynors over the years and have found they can be a wee bit temperamental at times. I've seen ones where the power transformer actually vibrates slightly (sings) due to loose windings. If you really want to eliminate it as the source of the problem, you can try taking the bolts out and changing it's position. You might not be able to solve it but you'll know for sure. I've tried this method once or twice before just to satisfy my own curiosity.

A couple more possibilities. Perhaps shielding the input grid wires from the jacks to V1. If there's any interference around them and since they're sitting 34K above ground, it might be just enough to induce some interference in them.
Have you tried a different tube in V1 to eliminate that possibility?


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## 360+ (Mar 13, 2011)

yes, I tried different tubes ... nor was the tranny vibrating physically
normally I don't have to shield the front wires, but point well taken ...

thx much


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## alwaysflat (Feb 14, 2016)

You can check that all of your shorting inputs are actually shorting and shorting well, maybe clean them with a burnishing blade or tiny nail file. Because it increases with volume suggests its introduced in V1 stages. You might want to see if you can increase the distance of your heater wiring from the grids of V1 or associated components. Kill any florescent lamps nearby (?) . I presume here that you've already assured it is not 120Hz. 
I always thought the volume related hum was a warning to "Kindly step back or this may hurt."


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## mhammer (Nov 30, 2007)

Hey JC,

Regards from Ottawa.

Mark


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## 360+ (Mar 13, 2011)

thx Aflat, yes I considered these ...
in fact, all AC devices in the room got unplugged, no fluoro or SCR dim'd lights either ...

FYI, the filament wiring in this chassis is set way higher away from the rest of the wiring than, say, in a vintage Fender ... I don't think it's filament induced hum, although it is a possibility since I didn't lead dress the amp too much (didn't feel it needed it)

like I said, walking up to the amp with gtr plugged in (and turned on) induced a bit more hum than usual ... but of course, not enough to make the amp unusable ...
I'm shooting for zero, that's all


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## 360+ (Mar 13, 2011)

mhammer said:


> Hey JC,
> 
> Regards from Ottawa.
> 
> Mark


Hi Mark, ... I think you might be interested in some of my new audio technology applications
// ... 

in the last week, 
a "Stereo Phaze" using two PWM-antiphase-P45's, 
and a Duino-WAH (high precision version of MXR Env Filter)





https://www.youtube.com/watch?v=YoxyRGNwzes&feature=youtu.be
fun stuff ...


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## mhammer (Nov 30, 2007)

In fact I did see that last week, and thought it sounded decent. I'm planning on retiring this fall, and hope to (finally) have some time to dig into my Arduino and my Raspberry Pi deeper than I have to date. Joel Korte at Chase Bliss has gotten me intrigued about the possibilities of digital control over analog paths.

You may have some cheaper sources out where you are, but I often order from these folks in Niagara Falls, who seem to have some decent prices on small micro-controllers: Arduino - dipmicro electronics

BTW, I loaned your Inside Fender and Marshall Amps book to Richard "nonreverb" Vernon. I hope he gets something out of it. I know I did.


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## 360+ (Mar 13, 2011)

much obliged Mark, ...

lately interest for my book has been coming mainly from amp emulation and modeling guys
ie., software designers
I'm also pleased to say that research in this area is still on-going, 

for those who might be curious, have a look here:

https://aaltodoc.aalto.fi/bitstream/handle/123456789/14420/article3.pdf

good time to retire and get into coding ...

I suspect some kind of Arduino explosion is about to hit the DIY-pedal world in a (semi) big way 
especially after characterizing the %-to-resistance relationship of the PWM-gate technology like I did last week 
the math that was previously missing in the DIY arena

I'll be posting details about that at my blog shortly

~jc


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## WCGill (Mar 27, 2009)

Re: Noise-grounding may be an issue on the first stage on some circuits. I try to attach signal grounds to the input jack, either with or without the first stage power supply cap. If it's a multi-cap, not an option. Sometimes shielded from the volumes helps. Love your site.


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## 360+ (Mar 13, 2011)

Thank-you for that WCGILL,

that's a valid point, but in a 60's Fender amp I can get zero hum using the exact same wiring as I had in this amp
so, became curious about why it wasn't dead quiet here

point well taken ...


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## WCGill (Mar 27, 2009)

I've found over the years that with high impedance circuits in amps it's art as well as science. Fenders are quieter than they have any right to be. I tried to rewire an Ampeg "correctly" and found the original grounding scheme which made no sense whatsoever to be the quietest iteration. I've had a noisy Traynor that exasperated me and no solution was ever found. Perhaps you have that one. ;-)


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## 360+ (Mar 13, 2011)

the tube era design crews at Ampeg weren't afraid to experiment, at least make use of science where needed ...
it would be interesting to read a description of the grounding in that amp you describe
... that's very interesting in itself

Ken Fischer told me he was part of the original SVT design gang, and explained the things they had to do to tame that monster ...
I also did have a few chats with Jess Oliver when I worked on my buddy's 435 Rhapsody Accordian amp,
the rare one with the built-in "Univibe" style shifter ... 

both gentlemen had incredible depth of knowledge


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## WCGill (Mar 27, 2009)

It's this one:

http://el34world.com/charts/Schematics/files/ampeg/Ampeg_r-12-r.gif

I tend to ground in order of signal/current and find it works for me but the Reverbrocket is a different beast, and a noisy one at that. In the end I did make it quieter with some shielded wire but the main culprit seems to be the non-shorting jacks. It's not possible to get an idea of the grounding from the schematic. Yup, the boys at Ampeg were no fools.


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