How Important is the physical OT Placement, hum question

frischmann · Post by **frischmann** » Sat Dec 06, 2008 1:22 am

Yeah,
I was really looking forward to this working.
I didn't do the head phone thing but I did route the OT wires correctly with some slack and played with the location a bit, It didn't make any difference.

It may be that the D'lite chassis just isn't big enough to accomodate a choke and a Bassman OT.

Or,
It could be something else. I had to really get my hands in there to get this done, I had to dig under the relay boards and a bunc of other un-fun stuff.

I may have bumped a ground, It sounds good it's just the noise floor is too high. With the PAB, it's way too high.

I'll see if I can post some pics.

Structo · Post by **Structo** » Sat Dec 06, 2008 1:31 am

I'm thinking it has to be fixable because I have read about quite a few guys putting bigger iron in there D'Lites.

Your problem kind of scares me though....

I plan on possibly putting mine in tomorrow.

I bought the Prosonic OT from Angela.

frischmann · Post by **frischmann** » Sat Dec 06, 2008 2:01 am

[IMG:640:480]http://img376.imageshack.us/img376/8792 ... 008oq5.jpg[/img]
By pfrischmann, shot with DSC-W70 at 2008-12-05

[IMG:640:480]http://img376.imageshack.us/img376/3130 ... 009xh1.jpg[/img]
By pfrischmann, shot with DSC-W70 at 2008-12-05

[IMG:640:480]http://img376.imageshack.us/img376/5175 ... 001sg4.jpg[/img]
By pfrischmann, shot with DSC-W70 at 2008-12-05

frischmann · Post by **frischmann** » Sat Dec 06, 2008 2:02 am

What do you guys think?

bnwitt · Post by **bnwitt** » Sat Dec 06, 2008 2:07 am

Wow, obviously the postion of a transformer is really important. This thread has gone to 3 pages!

KT66 · Post by **KT66** » Sat Dec 06, 2008 10:40 am

I always use the headphone trick on my builds too, but I don't use headphones anymore, I just use my scope. I thought this article about reducing induced hum from the PT was interesting : http://home.comcast.net/~machrone/bjr/bjrhum.htm

Structo · Post by **Structo** » Sat Dec 06, 2008 4:53 pm

Heheheh, looks like a tin foil hat for the output transformer.

Frischmann,
I don't have a choke on mine so I hope I can keep my OT in about the same spot.
If I have to drill new mounting holes that is going to be bad because of the drill tailings but in the past I made a masking tape thing to catch them.

One thing I notice about your amp in the last picture.

When I first got my amp going I had the standby switch wire routed too close to the AC wires and it induced some 60Hz hum into the amp.

Once I separated that wire that goes from the switch to the board the hum went down noticeably.
I ran it between the power board and PT.

frischmann · Post by **frischmann** » Sat Dec 06, 2008 6:00 pm

Cool tip Structo,
Thanks.

I guess I'll check my grounds and fix that and some leads dress I messed up getting the OT in place...Next. I put back the old OT....

Then get rid of the choke.....

If either of those fix it, I may have to see if I can squeeze the choke and OT in really close together.

This time I won't mount anything until I hear it under full gain with the PAB on.

Is there any reason a coudn't put the choke after the OT....so it goes

PT, OT....choke?

That would make life much easier....

Last, I start running wires outside...

bnwitt · Post by **bnwitt** » Sat Dec 06, 2008 6:37 pm

Structo wrote:Heheheh, looks like a tin foil hat for the output transformer.

Yep. Nice to know someone gets my warped sense of humour.

Structo · Post by **Structo** » Sat Dec 06, 2008 7:25 pm

frischmann wrote:Cool tip Structo,
Thanks.

I guess I'll check my grounds and fix that and some leads dress I messed up getting the OT in place...Next. I put back the old OT....

Then get rid of the choke.....

If either of those fix it, I may have to see if I can squeeze the choke and OT in really close together.

This time I won't mount anything until I hear it under full gain with the PAB on.

Is there any reason a coudn't put the choke after the OT....so it goes

PT, OT....choke?

That would make life much easier....

Last, I start running wires outside...

I am far from a design EE but I would think as long as the choke is in the right place electrically it would be ok.

frischmann · Post by **frischmann** » Sun Dec 07, 2008 12:55 pm

Hey Structo,
How'd it go?

tubetek · Post by **tubetek** » Sun Dec 07, 2008 1:56 pm

"Is there any reason a coudn't put the choke after the OT....so it goes

PT, OT....choke?"

Marshall did it alot (see JTM45 and PLEXI series) I do it sometimes, but still use the headphone test on scratch builds.
Tom

Structo · Post by **Structo** » Sun Dec 07, 2008 5:12 pm

I haven't made the swap yet....

Family, other things are keeping me busy but I hope to do it in the coming week.

novosibir · Post by **novosibir** » Mon Dec 08, 2008 1:08 am

Fischerman wrote:FWIW the Soldano SLO has the OT over at the preamp end and it's a high gain amp.

Not only Soldano does it this way:

[img:800:533]http://www.larry-amplification.de/dino9 ... 061-01.jpg[/img]

[img

604]http://www.larry-amplification.de/briti ... 4735.1.jpg[/img]

My chassis are made of stainless steel, what's not shielding magnetic fields (but also doesn't lead magnetic fields), so with a chassis of aluminum it also shouldn't be a problem!

But you have to put a shield inside the chassis right above the grommets, where the primaries & secondaries enter the chassis and below the board, so that these cables are running like in a sandwich, until they've reached the rear edge of the chassis - as seen on the attached photo.

Larry

frischmann · Post by **frischmann** » Mon Dec 08, 2008 7:20 pm

Wow,
Larry. Those look amazing.

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