AC15 Layout question

[mort]

I was noticing on the original AC15's that the OT was placed far away from the PT. I'm not sure if that was for a reason or not but it made me think it might be ok to split them up to help balance the weight of the chassis for more comfortable carrying. Does this layout look problematic for any reason? The chassis will be situated like a marshall head with the controls on the front and power/spkr/fuses on the back. It shows the eyelet board and then there will be a small board to hold 2 more filter caps. With teh sockets spaced the way they are the leads will be the shortest and most neat. I'll just have some OT leads stretching across the back end.

Thoughts?

[Mick Bailey]

locating the PT as far away from the OT as possible certainly reduces the chance of induced hum from the PT magnetic field coupling into the OT, and the weight balance is much better. You don't say what the intended tube layout is, but for the same reason the early preamp stages can pick up hum from the PT if located too close.

You can use the headphone trick if you want to experiment with PT/OT location, but where you have them know is probably as good as you'll get them.

[Jazz P Bass]

locate the PT as far away from the OT as possible certainly reduces the chance of induced hum from the PT magnetic field coupling into the OT, and the weight balance is much better.

Can't tell you how many amps that I have lifted onto the bench where the 'weight balancing' was simply of no concern to the manufacturer layout dude.:9

Must be a real treat carrying them from gig to gig.

[Mick Bailey]

I've worked on a couple of CAA PT-100s lately. Insane wrist-breakers. A thin strap handle and 70% of the weight at one end.

Jim had the right idea with the 'offset' Marshalls. If you can't get the chassis balanced, at least make sure someone could carry the finished amp.

[Chuck H]

You definitely want the PT away from the preamp or any of it's leads. Likewise with the OT actually. And, as mentioned, you don't want the OT too close to the PT either. Wait! What!?! So where the hell do I put everything???... Have the PT at the output end of the chassis. You can locate the OT at the input end of the chassis, but you can't locate any output circuitry there. Twist leads and route them along the back of the chassis to the output circuitry. You may still have induced crosstalk that can cause instability. It happens, and experimenting is the only way to find what works. I do suggest using the "headphone trick" that Mick mentioned. One advantage to the AC15 in this scenario is the absence of NFB. If you find the amp suffers instability due to OT to preamp proximity it may be possible to squelch it by reversing the OT plate leads. No pesky NFB circuit to stop you.

On the issue of balance... I think the primary thing dictating layout is function. As a player I don't care at all if an amp is balanced or not when I'm playing through it. I'm happy to carry an imbalanced amp if it outperforms a more balanced one. If you get my meaning. I'd do the headphone trick and if you find a quiet, stable spot on the input side of the chassis, fine, otherwise just locate the OT where it works best. Other things can be done to balance the amp for carry and transport. You can offset the handle. If it's a combo you can offset the speaker/s too. If it's a big combo with casters on one end sure to locate them at the heavy end. If ian amp is heavy enough that some imbalance is a problem you can always use two handles. But really, for an AC15, if it's a little imbalanced I'd be willing to suffer that for the best possible performance. Locate the OT where it works best. Imbalance be damned. Laying out circuits is hard enough without taking ergonomics into account.