pantherairsoft Posted November 7, 2011 Share Posted November 7, 2011 Hi folks... After some advice. I've recently invested in a Pre and power amp set up. Finally got everything together today and had a good play. EBS 1v2 & Crown XTi 1000. Set up and running fine. No problems. Noise free etc etc... Until I plug my pedalboard in. I use a huge pedalboard as part of my setup and it's vital to what I do. Going bass to Pre to power works fine. Add the board and the power amp produces a loud low frequency hum with static-like harmonics. Very low, prob around 50hz, similar to unplugging the jack from your bass and putting your thumb on it, thoigh mixed with the actual signal. The sound is definately produced by the power amp as increasing volume makes it louder, where as reducing volume and pushing the volume on the preamp produces a clean (er) signal. Take the board out and it's perfect again. I've spent 2 years building this board and investing in noise free powering systems and it's very successful. I usually get no hum at all from my signal chain. To ensure something had not gone wrong with the board I have tried the board through 3 bass amps today as well, all provide noise free signal, but not the XTi. As the Pre/power set up works flawlessly without the board and the board works flawlessly with every other amp I'm pretty sure there is no 'fault' - but I'd hate to think I have invested in an amp that hates my setup. Half the reason I went for the XTi was its reputation with noise filtering etc etc I've just had to rehearse with my HD350 again due to the noise issues. Tried thing like swapping cables, tuning off lighting, trying different plug sockets etc but nothing changes - but given it works fine without the pedalboard I doubted this would be an issue. Ideas/suggestions? Shep Quote Link to comment Share on other sites More sharing options...
Sjonnie Posted November 7, 2011 Share Posted November 7, 2011 Where I the pedal in your setup? Between pre and power amp, in front of the pre amp, or in the effect loop of the preamp? Quote Link to comment Share on other sites More sharing options...
pantherairsoft Posted November 7, 2011 Author Share Posted November 7, 2011 They are before the Pre amp... Bass - pedalboard - preamp - poweramp Based on the same principle of running it before a 'regular' bass amp. I've never ran it though an effects loop as I want it 'effected' by my EQ settings. Quote Link to comment Share on other sites More sharing options...
BassBod Posted November 7, 2011 Share Posted November 7, 2011 Try using "hum frees" on the rack rails of both the pre and per amps - little plastic things that stop the two chassis from grounding. I've had success with those in rack setups. Experiment with where you put the pedal board signal - front of preamp/effects loop etc Look into hum eliminators (Ebtech?) or quality audio transformers/isolators (Orchid Electronics have a few products that may help) I'm sure its fixable... Quote Link to comment Share on other sites More sharing options...
pantherairsoft Posted November 7, 2011 Author Share Posted November 7, 2011 I'll check out the hum free stuff - its just frustrating that without the board there is no hum? I'll try the effects in the loop when at the studio on Wednesday but I hate the way many effects sound in a loop - given I've spent months refining the sounds in conjunction with it being Pre EQ I'm eager to not have to go down that route! I'm certainly not in a position to invest in additional audio processing equipment. This was an expensive move as it was. Quote Link to comment Share on other sites More sharing options...
BassBod Posted November 7, 2011 Share Posted November 7, 2011 Don't worry - the Orchid stuff is very good quality and not exactly expensive (£19 for an inline transformer). Send John an email describing your equipment and symptoms...he'll have some ideas. Quote Link to comment Share on other sites More sharing options...
nottswarwick Posted November 7, 2011 Share Posted November 7, 2011 Email crown too. Quote Link to comment Share on other sites More sharing options...
nottswarwick Posted November 7, 2011 Share Posted November 7, 2011 Also try each pedal separately Quote Link to comment Share on other sites More sharing options...
pantherairsoft Posted November 7, 2011 Author Share Posted November 7, 2011 [quote name='BassBod' timestamp='1320698940' post='1430315']Don't worry - the Orchid stuff is very good quality and not exactly expensive (£19 for an inline transformer). Send John an email describing your equipment and symptoms...he'll have some ideas.[/quote] Email on its way! [quote name='nottswarwick' timestamp='1320699304' post='1430325']Email crown too.[/quote] I've posted on the crown forums, which seem to have regular input from Crown tech folk. [quote name='nottswarwick' timestamp='1320699470' post='1430329']Also try each pedal separately[/quote] I've tried that. It seems to be related to the power supply running the board. Everything other than 1 unit is powered from a GigRig Modular Power System/Generator. As long as the board is powered the noise is there. Doesn't matter what's powered. I can't get the GigRig to induce any hum or noise to the signal chain in any other circumstances though or with another amp. Quote Link to comment Share on other sites More sharing options...
nottswarwick Posted November 7, 2011 Share Posted November 7, 2011 Try a new power lead to the amp. Quote Link to comment Share on other sites More sharing options...
pantherairsoft Posted November 7, 2011 Author Share Posted November 7, 2011 Would issues with cabling etc not be a constant issue? As opposed to just when interacting with a specific other piece of equipment? I'll try it all the same on Wednesday, just asking out of curiosity. Quote Link to comment Share on other sites More sharing options...
nottswarwick Posted November 7, 2011 Share Posted November 7, 2011 Maybe. And I don't quite know how earth loops work but the frequency of the hum is mains related. Is there a ground lift switch on any of the gear. I have a similar issue in my studio where my Roland drums him unless I lift the ground on the di box I use. Quote Link to comment Share on other sites More sharing options...
pantherairsoft Posted November 7, 2011 Author Share Posted November 7, 2011 Unfortunately not. There is a ground lift in the DI out of the EBS Pre - but not on the general amp side of things. Quote Link to comment Share on other sites More sharing options...
BassBod Posted November 7, 2011 Share Posted November 7, 2011 Its often all fine...until you add that one extra piece! That's what I've always found in rack setups - several combinations are sometimes fine..but equally just two pieces together are enough to give you a problem. Even when made by the same company, to be used together! An audio transformer at the input of your amp/end of pedalboard chain could sort it. So could isolating the pre and power chassis earths from each other in the rack case (rails). Its well worth the time/cost of investigating and sorting out in your rehearsal space, as its a fairly controllable environment. Its always a lot harder when these things happen without warning on a gig (like when you DI from the amp..and the earth lift switch does little or nothing to that annoying loud hum in the PA). Good luck...and don't go disconnecting any earths wires! Quote Link to comment Share on other sites More sharing options...
pantherairsoft Posted November 7, 2011 Author Share Posted November 7, 2011 Ha. Don't worry - no wires will be disconnected! I'll investigate the input transformer. For £19 I imagine it being a useful tool in the spares box even of it doesn't solve this particular issue. Trying to isolate racks from each other is easy to do without spending anything to start with - ill just physically separate them outside of the rack to try and eliminate the issue. As for sorting our rehearsal room out - its a prehistoric building with even older wiring. In the past I've had lots of problems with effects pedals. Once I moved over to the GigRig Generator system and stopped having load of power supplies etc it all cleaned up and I've had no issues since. It's a shoddy building though. Quote Link to comment Share on other sites More sharing options...
Sjonnie Posted November 7, 2011 Share Posted November 7, 2011 Check the cable between the preamp and the poweramp. Do you have other cables, what cable do you use at the moment? If it is a balanced cable try an unbalanced one. The amp has no ground lift as far as I can see, if you can make a cable where the ground is not connected, that would be the same as ground lift. Quote Link to comment Share on other sites More sharing options...
pantherairsoft Posted November 7, 2011 Author Share Posted November 7, 2011 The cable I'm using is a TRS - XLR. I'll try a TS-XLR, however I'd of thought, as mentioned already that surely I'd get the hum without the pedalboard if it was down to amp cabling? I'll add that to my list of stuff to try on Wednesday though Quote Link to comment Share on other sites More sharing options...
EBS_freak Posted November 7, 2011 Share Posted November 7, 2011 Some pointers - Make sure your pre/power amp are running off the same plug as the board so they have a common earth. Take your pre/power amp out of the rack and make sure they aren't touching. Humfrees can help with getting proper isolation within the rack. Make sure you have a buffered pedal last in your chain - something like a Boss pedal. This is similar to an audio transformer and you may have one lying around. In my experience true bypass causes more problems than it's worth. A good buffered pedal > true bypass. Unplug your board and add one pedal at a time to your signal path... see if there is a problematic pedal and see if moving the position in the chain makes things better. Ensure that all your interconnects are good and properly screened. Quote Link to comment Share on other sites More sharing options...
pantherairsoft Posted November 7, 2011 Author Share Posted November 7, 2011 [quote name='EBS_freak' timestamp='1320707182' post='1430471'] Some pointers - Make sure your pre/power amp are running off the same plug as the board so they have a common earth. Take your pre/power amp out of the rack and make sure they aren't touching. Humfrees can help with getting proper isolation within the rack. Make sure you have a buffered pedal last in your chain - something like a Boss pedal. This is similar to an audio transformer and you may have one lying around. In my experience true bypass causes more problems than it's worth. A good buffered pedal > true bypass. Unplug your board and add one pedal at a time to your signal path... see if there is a problematic pedal and see if moving the position in the chain makes things better. Ensure that all your interconnects are good and properly screened. [/quote] Cool. They are currently running from the same socket. I'll try taking them out of the rack to see if that helps - its on my check list! I do have a buffered pedal last (Boss DD-20) I tried a number of pedals earlier and it did not seem to matter what pedals were powered, more that the pedal power supply was on. I'll try this in more detail on Wednesday All interconnects are George L's. Connections seem fine when not used with this amp, and I have had a little wiggle of each one, but given the size of my board, swapping 1 cable out at a time is a days work, so I have not had the chance to do this in depth. Quote Link to comment Share on other sites More sharing options...
Soliloquy Posted November 7, 2011 Share Posted November 7, 2011 It sounds like the pedal power supply. I'm not a million moles from you, about 30 or so, you're welcome to come over and try using my power amp. Quote Link to comment Share on other sites More sharing options...
pantherairsoft Posted November 8, 2011 Author Share Posted November 8, 2011 [quote name='Soliloquy' timestamp='1320708889' post='1430497'] It sounds like the pedal power supply. I'm not a million moles from you, about 30 or so, you're welcome to come over and try using my power amp. [/quote] It does sound like the pedal power supply - but I've put that supply and board through so many poor venues (that make other musicians gear go crazy) with no noise at all. It has performed flawlessly. Annoying that interaction with 1 bit of kit causes this! I'm currently without transport (bit of a pain), but if I sort that before I sort the issue here I'll be happy to take you up on your offer. Quote Link to comment Share on other sites More sharing options...
pantherairsoft Posted November 8, 2011 Author Share Posted November 8, 2011 Dan & GigRig has suggested it sounds as though something is open circuit and acting as a radio. His 1st suggestion would also be (as other above have suggested) changing the cable from Pre - Power amp, and pointed out the fact that using TRS for this is not necessary. Another check added to my list for the mornings hunt! Quote Link to comment Share on other sites More sharing options...
Sjonnie Posted November 8, 2011 Share Posted November 8, 2011 [url="http://www.crownaudio.com/amp_htm/ampfaqnew.htm"]Some background info[/url] (look for: How can I get rid of the noise in my system?) TRS versus TS cables will probably not make a difference (with the emphasis on probably), disconnecting ground from the XLR cable should. Quote Link to comment Share on other sites More sharing options...
pantherairsoft Posted November 8, 2011 Author Share Posted November 8, 2011 [quote name='Sjonnie' timestamp='1320761316' post='1430959'] [url="http://www.crownaudio.com/amp_htm/ampfaqnew.htm"]Some background info[/url] (look for: How can I get rid of the noise in my system?) TRS versus TS cables will probably not make a difference (with the emphasis on probably), disconnecting ground from the XLR cable should. [/quote] But disconnecting the ground is potentially dangerous... Quote Link to comment Share on other sites More sharing options...
nottswarwick Posted November 8, 2011 Share Posted November 8, 2011 [quote name='pantherairsoft' timestamp='1320761660' post='1430972'] But disconnecting the ground is potentially dangerous... [/quote] I could be wrong, but I don't think that disconnection of the ground on an XLR is dangerous - otherwise why would all DI boxes / DI outputs etc allow this. Don't confuse this with disconnecting the ground on a mains lead - this IS dangerous, since if there is a fault and there is no earth on a piece of equipment (which would be the case if the lead had no earth), the metal case would become live. So, try it - as long as it is a signal lead and not mains, you will be fine. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.