Discussion in 'The Rack Space' started by Alex Kenivel, Oct 5, 2016.
That is some awesome rack engineering, Brian. I appreciate the pic of the back, great cable organization, gave me some ideas. Thanks.
Here's the back panel I like to use - it the Mid Atlantic UCP modular system.
Wow! What kind of power strip is that? How is it affixed to the side? Could Dual Lock work? That could replace the Furman 6x strip I keep on the bottom, too fat for on the side. How deep is your rack? Mine is about 16.5", but could probably still get a single strip on the side.
Most of my rigs have been 14" deep, some as deep as 16.5". The metal power strip has metal "ears" that allow it to be screwed into the side of the rack. Dual lock could work. On SUS-4 racks I like to mount the extra power supply to the side rails that connect the back to the front. Look carefully at the lower left corner of this image and you'll see the plugs sitting inside on the bottom left...
Here's a better shot of the side mounted power strip:
Nice. I think I might be able to put together a jayvee version of yours.
i still think the rig you made for shawn at fountain valley mesa boogie back in the day was the neatest wiring i have ever seen and just a monster tone rig. if i recall correctly the roland rsp550 had a really nice leslie sound you liked.
have you experimented much with wire other than the mogami?
Thank you for the kind thoughts and words! Yes, Shawn's rig sounded very nice... I have a feeling his "bone tone" was a major contributing factor.
Love the chorus, leslie and modulated reverb in this box so much it's been in nearly every rig I've ever done.
Yes, I've been a fan of Mogami for a long time. I've also had good experience with many others, but it's the workability of Mogami I like the most. I'm used to how it strips and takes heat. I run the two center conductors as a twisted pair and the wrap-shield as ground, sometimes floating one side of the cable or the other. The thin 2944 was great for touring rigs due to it's light weight and great sound. Less weight means less strain on connectors and PCB mounted jacks.
That's a great solution. Thanks for sharing!
Brian, could you please elaborate on this. Under what conditions would you float ground and on which side of the cable would you float it? I am assuming you are talking about an unbalanced signal carried on a cable with a hot & a ground.
Yes - unbalanced cable with hot and ground. Every rig was different, and some runs required lifting ground at the output end of a cable and only connecting shield at the input side in order to solve a ground loop or DC conflict. On conversion cables I would typically connect shield to the ground of the balanced input and leave it disconnected at the other end - again, depending on the gear being connected. There is really no concrete rule to follow as standards were never clear - some gear has chassis ground, some use circuit ground, and others were floating ground.
Here's the back of my two-head rig that I wired using a "star ground" - all cables are lifted and all chassis grounds were lifted as well. Then, each piece was connected to common/star ground with the green ground wire.
This is extremely interesting. Could you please run through the mental / physical process you use when preparing to wire up a complex rig.
Do you test each piece of unbalanced gear beforehand to determine whether it has chassis ground or circuit ground?
Do you wire each piece of gear in, one by one, check for ground loops, then experiment with lifting ground on the connecting cable to discover if this solves the problem at hand? Do you use a temporary ground lift cable? - I have seen cables with the ground wired to an alligator clip for experimentation.
On that rig with star grounding how do you actually connect the wire to each piece of gear? Do you add a grounding post to each units' chassis or does the green wire actually get patched to the circuit somehow?
Cool pics Brian!
After using and building so many different kinds of stereo and w/d/w systems, have you come to favour one format over another? What are the things that you find most appealing to a stereo setup vs. w/d/w, for example?
It's been 30 years since I did this for a living, please forgive me if I do not recall some details - ha!
1. Yes. In the beginning I checked each piece to see if it was chassis, circuit, or both to ground. I really only wanted ONE path to ground (earth) so I would just experiment to see how each piece wanted to be grounded and provide no noise.
2. Yes - start from the power amp to the cabs... quiet? Yes. Okay, add the mixer before the power amp... quiet? Yes or no? Then I would work my way all the back to the guitar one component at a time.
3. Yes - temp ground-lifted cables with alligator clip. This allows you to isolate one cable at a time during the process described in #2 above. My temp cables had a long lead on the alligator clip so I could run it to the barrel of the connector or to a rack rail or to a chassis if needed. This helps identify where a ground loop may be occurring and then you can test with a multi-meter.
4. The star-grounded rig had one ground wire per piece of gear. Trial and error determined if the ground wire was connected to the chassis or input jack sleeve.
Hope this helps!
My favorite rigs were the two-head stereo systems. Two independent power sections deliver the best stereo image and feel. Switching between the front-ends of both amps provided enough sonic flexibility yet kept the tonal flavors complimentary.
W/D/W is sexy when playing at home and completely impractical live. FOH does not hear or think your mix like you do and I never had success translating the "in front of rig" experience to the audience. I can't begin to imagine how tough it would be to get right with a band using "ears" - most of the other players would not have your effects in their mix.
Did you made it by yourself? In HRI I discovered a guy that used to convert pedals into racks. He did some projects for a forum member, like a whammy DT and a pigtronix looper.
Pigtronix Infinity looper in a rack? Yeah man.
I am as obsessional as you have been to have only one path to ground per unit. Would you say star grounding is the best option? With star grounding did you also lift the ground pin from each power cable? With star grounding where did you feed the collective / star bunch of wires into?
I guess my question is... "Is star grounding the CURE for all grounding issues?"
My usual preference is not to lift the ground pin from the power cables, to have each unit's chassis electrically isolated from other units AND isolated from the rack rails - that is relatively easy to achieve. However I have struggled with the occasional unit where I thought I needed a ground-lifted cable but when I used it I got no sound and assumed it was because of no signal flow. I got around this by using an Ebtech hum eliminator but to be honest I could notice I reduction in tone quality due to the transformers in that Ebtech unit.
I have heard a lot of opinions on this topic. I know Lonnie Totman disagrees with me completely - he says the best option is to ensure each unit has solid electrical contact with the rack rails and to lift power cable ground pins on every unit except one, usually the poweramp.
Your racks are the most amazing creations I have ever seen. I am also interested in any tips you have for running a multiple preamp system. Obviously since you are switching between the front ends of both amps in your dual head system you must have some good suggestions for how to do it "the right way"
In response to JK above:
Notice on the star grounded rig photo there are green wires all going to a terminal strip - that's the star point, and its connected to the main AC ground. Ground was lifted from all power cables and chassis and then re-connected to the star point.
"Is star grounding the CURE for all grounding issues?"
Yes - it is a comprehensive solution. No - it's not the "end all, be all" solution. After doing a few star-grounded rigs I abandoned the practice and started applying the concept using the rack rail as the common ground. Start with all AC plugs grounded, chassis grounded, and then lift AC and audio cables as needed.
I'm not a fan of trying to isolate all units from the rack rail - especially if the rig will be moving (tour, gig, etc.). See above. I agree with Lonnie on this topic.
Multiple preamp sources
I feed two preamps (amps) with a Jensen JT11P-1 isolation transformer with RC network. I mount the trans in a hammond box or the rack interface and connect it in parallel with the grounded "through" signal. The guitar only sees one "load" and sounds and feels like normal. The output of both preamps go to a loop - Amp A goes to the input of the loop, Amp B hits the return. The result is both preamps are fed input and you have a programmable A/B "preamp chooser" via the loop.
Clear as mud?