Tranny Installation & Hum

[rawnster]

Just thought I'd refresh the cool headphone method when placing trannies. I started a new build this week, and thought I'd give this method a shot. Worked very well. To find the place to mount the OT that will omit the least hum, just move it around on the chassis and listen to the hum. When it's the quietest, mark it, drill it, bingo bongo, done. One minor detail is that you've got to power up the PT. I held the 16ohm wire to the tip of the headphone jack, and the ground wire to the sleeve of the jack.

Very cool. Just thought I'd share. Having a dead quiet amp certainly is worth the added procedure.

[Zippy]

How close is the hum-free location to the location per the traditional TW layout?

[rawnster]

How close is the hum-free location to the location per the traditional TW layout?

About a 1/4inch closer to the back edge and a few degrees off axis from square. It's amazing how such small movements create a huge difference in hum. It's easily heard through the headphones.

And I should mention that even this spot wasn't totally noiseless. There was a small bit of higher frequency buzz. But when I would turn it slightly from this spot, hum would return. The only place on the chassis that was the quietest (no buzz or hum), was on the complete opposite side of the chassis...over by the V1 slot.

[paulster]

The Wreck PT is magnetically noisy!

Clearly Ken wasn't bothered by a bit of induced hum but it's something that's always irked me about the standard Express transformer locations.

It would have been better to have the OT to the side of the PT rather than behind it, or to have both of the trannies rotated around their axes by 90 degrees to put the OT in the minimal hum spot.

[angelodp]

Can you expand on this method a bit. What degree of build are you at, are the Trannys powered?

[jaysg]

Having played with it myself, the TW layout doesn't center the OT vs. the PT. If it did, then that would be lowest hum. I think that's why you had a slight rotation.

[Cliff Schecht]

Or you could switch to toroids in your TW builds and really cut down on the hum. I placed the first tube of my Express build about 1" away from the toroid and find that even with the amp wide open through a 4x12 cab, the hum is always minimal. If anything, the high-gain induced hiss is much more prominent than any hum. Even Glen's '89 Express clips have a bit of high end hiss in them when he isn't playing.

[rawnster]

Can you expand on this method a bit. What degree of build are you at, are the Trannys powered?

Are these questions for me? "What degree of build are you?" If you're asking how far along am I with the build, then I'd say I'm in the beginning stages. Had a blank chassis. Just completed most of the hole layout, and was preparing the chassis for the outside components, (reverb tranny, choke, PT & OT, and tube sockets). All of those items are mounted but not wired into the circuit. Only the PT is partially installed (connected to AC) due to headphone method discussed earlier in the thread. The OT is bolted in bolted in but now wired up at all. Is this what you're asking?

During the headphone method, the OT was NOT connected to anything in the amp. Only the 16ohm tap and ground wire was loosely connected to my headphone jack (by loosely I mean held by my left hand...and I'm not left-handed:-) ). The OT just sat on chassis where I could move it around at will. The PT was connected to the power switch...and the power switch was wired to the IEC socket. That's it.

[angelodp]

Rawn, yes sorry for my inelegant request. That is precisely what I was looking for. Now what about the opposing side approach, if that is the most quiet.

Ange

[rawnster]

Rawn, yes sorry for my inelegant request. That is precisely what I was looking for. Now what about the opposing side approach, if that is the most quiet.

Ange

No problem.

That's a good point. I think I'll definitely consider that on my next rocket build. Since I've already placed components on this build, I see how quiet it is when it's fired up. The rocket circuit is quiet without much stressing over tranny placement. I was just being anal this time around with the trannies. and I wanted to try the headphone trick.

[ckpop]

I agree the TW is a little noisy between the hum and the hiss but not really a problem. Yes we would all like a dead quite amp but there are a few things to consider.

Signal to noise ratio to me determines if it really is a problem or not. The trainwreck even if it is a little noisy you can't hear it when you are playing.
Out on the road I can give a number of rigs from Neil young to Joe Perry that without playing are noisy setups. It's just the nature of the beast.

I mentioned to a guitar/engineer who tried one of my express amps if the noise was a problem and he replied "No not a problem we have ways around that, not a concern.

So if just are trying to improve on the hum I'm all for it but the above reasons are probably why it was not an issue with Ken.

[Richie]

I'm all for it but the above reasons are probably why it was not an issue with Ken

maybe the wood dowels were also used to dampen hum vibrations

[ckpop]

Richie You never know, ken worked in mysterious ways : )

[ampmike]

Thanks Rawnster,
Im building a twin right now and the output tranny holes on the chassis are not drilled for the Mercury so this is a perfect time for me to try this method.So i get some power in the main tranny and then hookup the headphones,I thought you had to butcher your headphones so I never tried it,But thanks to your post I think I can do it.Thanks Man,Mike C

[gearhead]

The OT just sat on chassis where I could move it around at will. The PT was connected to the power switch...and the power switch was wired to the IEC socket. That's it.

Wow, since I always drill holes before anything goes in the chassis, had never occured to me. What'd you do with other dangling OT wires, tape em up?