I had a flyable rack for years dating back to 2002 w the VHT-GP3 mounted directly over the VHT 2/50/2 pwr amp. No Issues. No extra fans. However, for local work I have moved to a smaller, lighter rack and am about to start using the GP3 w a newly purchased LX-II. I was previously using w the Power Station v1 in a separate rack. I am reading a lot of about overheating and fan noise here, so it has me concerned re: should I / can I mount the GP3 directly over the LX-II ? or do I need a larger rack to add space between the 2? I have a 1RU fx unit above the GP3 and that needed a fan which I built into the side of the rack to suck air out from between the fx and the GP3. But it will have little effect on the LX-II which I will mount below the GP3. Of course, I could mount the LX-II under the fx unit and the GP3 under the LX-II,
since heat rises and I know the LX-II has air-ports on the top of unit but do not know if there are any underneath. btw the LX-II arrives tomorrow and 1st Summer show is Wed, so not a lot of time to experiment.
btw See if Steve remembers me 
I’m the guy who built a 3 button switching circuit w TTL logic for the GP3 back in '02
Hi Ray,
Welcome to the forum!
No need to add a space between the LXII and GP3.
As you can see below, the GP3 just barely overlaps the vent s on the top of the LXII. Fortunately, this is where the tube bases are, which is at a lower temperature area of the tubes. The hottest area of the tubes is in the middle of the vent area, so very similar to the GP3/Two/Fifty/Two rig you were using before.
Depending on duration and ambient temperature, you may find a little external fan activity helpful. It doesn’t necessarily have to extract all of the heat. It just helps to keep the air moving around so heat doesn’t accumulate in one particular spot.
Dave
Hi David
I used the LXII on the gig last night. Sounded great!
However, I was getting a 120 Hz ground loop harmonic which is quite audible.
I have the rack back in my studio today and the issue is still there. So let’s rule out house wiring.
It gets louder as I turn up the Volume on the LXII . It does not change if I turn down the Output of the GP3, nor does it change if I flip the GP3 ground switch.
It is worse with the FX unit wired in, but still noticeably wrong with only the GP3 wired direct to the LXII.
However, if I remove the IEC pwr cable from the FX unit and Lift the GND on the GP3 it is silent!
I never had this issue with the Power Station v1 or w the 2/50/2 with GP3 or GP3 and same FX unit.
I am not a big fan of lifting GNDs especially when singing on a house PA, that I have no idea how proper the house wiring/grounding is.
From my the BIG 24RU 80s rack days I have a bunch fibre washers that would remove the 1/4 jacks from the chassis but it looks like the ins/outs are probably already plastic, so not connected to the chassis as GND at multiple points. I could possibly try to isolate the rack ears from the rack rails to eliminate any GND loops via the front panels and thus allowing me to keep all three units 3rd prong chassis GND connected at the power strip.
But I haven’t tested if that would even fix noise. Any thoughts or advice on this?
Its worth noting the Power Station was not bolted into the same rack as GP3 and FX unit. It was sittin gon top of the rack. However, the 2/50/2 was bolted to the same rack.
Please advise. cheers, ray
Hi Ray,
I agree that you want to keep the LXII chassis connected to earth ground and I would definitely try isolating the LXII from the rack rails.
OG refrigerator racks were notoriously difficult to deal with in terms of the ground path. We didn’t like it, but the 2150 and 2100/Classic power amps had a trick internal washer that could be removed to help eliminate loops. We did it to appease the rack builders who wanted to blame it on the power amp because it didn’t have a ground lift switch. Never mid that power amps practically never have such a feature as they are the last thing in the ground path.
But it is what it is.
Try isolating the rails and see how it goes.
Dave
Hi David,
and Thank You!
2 things:
1- I do not have the GND lifted from the LX-II and def will not. The GP3 when not bolted to rails is quieter than when it is bolted. However, it is dead silent when I activate the GND LIFT switch.
Is this safe? I imagine the switch wouldn’t be there if it created an unsafe system but figured I’d ask, to be sure.
The FX unit adds more GND loop noise, if it is plugged into AC, even when OFF. The unit originally had a 2-prong AC cord built in. I replaced it with an IEC jack so I could use any IEC cable length needed. When I did that I also added the 3rd prong tied internally to the chassis only.(as it is a digital device). Thus, I think I should be safe lifting the 3rd prong at the power strip. ( something I normally hate doing. )
Between lifting the 3rd prong of the FX unit, activating the GP3s GND LIFT switch and keeping the LX-II connected to Earth GND via the power cable, I get a very quiet setup. Since I needed a bit more space in the back of the shallow rack to fit the LX-II, I have the LX-II bolted thru 3/4" of heavy rubber. And I think you guys have actually isolated the rack ears from the signal ground at the very least, because strapping the LX-II front panel to the rack rails has no affect on any GND noise.
Please let me know if you feel this is safe. At the end of the day, I’ll find out as I start the Summer’s festival gigs.
2- on all my VHT/Fryette power amps I actually keep the Presence at about 11 and the Depth at 1… opposite the factory settings, and thus I’m torn with whether I like the Presence switch on the LX-II on or off.
So I was very happy to see that there are pots that can be adjusted. However, the holes in the top panel are not even close to giving access to the mini-pots. It seems I’m going to have to remove the top panel to gain access. Am I missing something? s/n LXID240692
Thanks
cheers, ray
PS I’ve been A/B/C-ing the 2/50/2 class A & A/B, LXII and Pwr Station v1 in the recording studio. Using the same track and re-amping. Interesting difference of harmonic content. Class A still rules for the OD to shred stuff.
