obbm

[quote name='hatori' post='395998' date='Jan 31 2009, 10:31 AM']Is the power output of an all valve amp (Marshall JCM800) proportional to the impedance selected i.e. 100watts @4ohms 50watts@ 8ohms as is the case with SS amps?[/quote] No. The impedance selector is there to match the cab to the output stage, ensuring the output valves have the correct load so they will always deliver the full output.

This might help explain, otherwise there is a very good book by Morgan Jones which covers vale amp theory in depth. [code]Q:Will it hurt my amp/output transformer/tubes to use a mismatched speaker load? Simple A: Within reason, no. Say for example you have two eight ohm speakers, and you want to hook them up to an amp with 4, 8, and 16 ohm taps. How do you hook them up? For most power out, put them in series and tie them to the 16 ohm tap, or parallel them and tie the pair to the 4 ohm load. For tone? Try it several different ways and see which you like best. "Tone" is not a single valued quantity, either, and in fact depends hugely on the person listening. That variation in impedance versus frequency and the variation in output power versus impedance and the variation in impedance with loading conspire to make the audio response curves a broad hump with ragged, humped ends, and those humps and dips are what makes for the "tone" you hear and interpret. Will you hurt the transformer if you parallel them to four ohms and hook them to the 8 ohm tap? Almost certainly not. If you parallel them and hook them to the 16 ohm tap? Extremely unlikely. In fact, you probably won't hurt the transformer if you short the outputs. If you series them and hook them to the 8 ohm or 4 ohm tap? Unlikely - however... the thing you CAN do to hurt a tube output transformer is to put too high an ohmage load on it. If you open the outputs, the energy that gets stored in the magnetic core has nowhere to go if there is a sudden discontinuity in the drive, and acts like a discharging inductor. This can generate voltage spikes that can punch through the insulation inside the transformer and short the windings. I would not go above double the rated load on any tap. And NEVER open circuit the output of a tube amp - it can fry the transformer in a couple of ways. Extended A: It's almost never low impedance that kills an OT, it's too high an impedance. The power tubes simply refuse to put out all that much more current with a lower-impedance load, so death by overheating with a too-low load is all but impossible - not totally out of the question but extremely unlikely. The power tubes simply get into a loading range where their output power goes down from the mismatched load. At 2:1 lower-than-matched load is not unreasonable at all. If you do too high a load, the power tubes still limit what they put out, but a second order effect becomes important. There is magnetic leakage from primary to secondary and between both half-primaries to each other. When the current in the primary is driven to be discontinuous, you get inductive kickback from the leakage inductances in the form of a voltage spike. This voltage spike can punch through insulation or flash over sockets, and the spike is sitting on top of B+, so it's got a head start for a flashover to ground. If the punchthrough was one time, it wouldn't be a problem, but the burning residues inside the transformer make punchthrough easier at the same point on the next cycle, and eventually erode the insulation to make a conductive path between layers. The sound goes south, and with an intermittent short you can get a permanent short, or the wire can burn though to give you an open there, and now you have a dead transformer. So how much loading is too high? For a well designed (equals interleaved, tightly coupled, low leakage inductances, like a fine, high quality hifi) OT, you can easily withstand a 2:1 mismatch high. For a poorly designed (high leakage, poor coupling, not well insulated or potted) transformer, 2:1 may well be marginal. Worse, if you have an intermittent contact in the path to the speaker, you will introduce transients that are sharper and hence cause higher voltages. In that light, the speaker impedance selector switch could kill OT's if two ways - if it's a break befor make, the transients cause punch through; if it's a make before break, the OT is intermittently shorted and the higher currents cause burns on the switch that eventually make it into a break before make. Turning the speaker impedance selector with an amp running is something I would not chance, not once. For why Marshalls are extra sensitive, could be the transformer design, could be that selector switch. I personally would not worry too much about a 2:1 mismatch too low, but I might not do a mismatch high on Marshalls with the observed data that they are not all that sturdy under that load. In that light, pulling two tubes and leaving the impedance switch alone might not be too bad, as the remaining tubes are running into a too-low rather than too-high load.[/code]

[quote name='martinbass7750' post='394316' date='Jan 29 2009, 08:14 AM']Hi Tony, AN amplifier is designed to run into a minimum load of say 4 ohms. If you take the load below this you will draw excessive current from the output stage and cause damage. (current = voltage / resistance in ohms) As you add a speaker cab in parallel the value of the load resistance is reduced. e.g. 2 x 16 ohm cabs = 8 ohm load ohm load, 4 x 16 ohm cabs = 4 ohm load. Hope that helps. Cheers Martin[/quote] Please note that the above only applies to solid state amplifiers. Valve amplifiers should ideally always use the output transformer tap matched to the speaker cabinet impedance, so if using an 8-ohm cab then set the speaker impedance to 8-ohms.

[quote name='ashevans09' post='394228' date='Jan 28 2009, 11:56 PM']Hey there, Being the sad and dozy sod that I am I've been wandering around various forums and came across the info that an all valve head puts out the same wattage at any ohmage. So, that considered, were you to run a cab with an all valve head, is there any particular benefit in going for an 8ohm cab over a 4 ohm cab? Ta! Ash[/quote] The most important thing is that you select the output transformer tap to match the cabinet impedance.

[quote name='Beedster' post='393570' date='Jan 28 2009, 12:14 PM'][attachment=19308:CIMG0437.JPG] Volume pots are original and the tone pot seems to be the same age and condition. Is this a standard volume pot for the era, I've seen a few like it in pics elsewhere? Why is it so bloody big! Chris[/quote] It looks like a double ganged pot. Are both sections wired?

Welcome aboard. Second drummer in a fortnight. You could be starting a trend. Aldershot Eh? Hmmm. Just around the corner. Good luck with your search for a singing bass. If I were 40 years younger then I might jump at it.

Have a browse through [url="http://www.hearingprotection.co.uk/index.php"]ACS's Site[/url]. They have several options and they make pretty much all of the in-ear monitors for people such as Handheld, etc.

How many do you need Don?

[quote name='tonybassplayer' post='390433' date='Jan 24 2009, 03:12 PM']Now funny that you should have mentioned that as one of my ideas is to take songs from Grease, Dirty Dancing, Blues Bothers, Commitments and Mamma Mia etc and build a show around them We already play some of them and they go down really well I know that I shouldn't really say this but when you are up there playing the one thing that makes you feel good ( and overrides the long drive, no time for soundcheck, no food for 8 hours, no free drinks, hard load in, missed solo's etc etc etc ) is seeing a packed dance floor 8 bars in to the fist song [/quote] The guy that I played for about 4 years ago had a strange mix of oldies. he hadn't been born when the songs were new and eventually I twigged that they'd all been used in movies. They went down with all age groups because the youngsters knew them. Don't limit yourself to the musicals, they are some great number in Shrek, From Dusk Til Dawn, etc. Did I mention Twist And Shout/La Bamba?

We used to segue: Sweet Caroline 500 miles Hi Ho Silver Lining I'm a Believer Songs that have been used in the soundtracks of movies in the last 20 years or so.

[quote name='drumbloke' post='388275' date='Jan 22 2009, 10:17 AM']Depping in a few bands at the moment, just realised that not all Bassists 'sit' on the same side of the drummer. I thought it was a set up area constraint but most bands I have played with recently the Bassist has been on the left hand side of me (ride cymbal). Me ol' mate Pete (Thunderthumbs) plays on me right (Hi hat side). Just wondering if there was a preference to which side you like to be on? Or did you just naturally fall on that side?[/quote] Most drummers I play with have the Hi hat on their left. Are you a left-handed drummer or are you looking at this from the audience viewpoint? Anyway facing the audience I prefer to stand to the drummer left, next to the snare/hi hat so I can see the Kick pedal easily.

Oh that is a bu**er. Welcome to the unemployed musicians club. It's a shame you can't sign on and draw some dole. Hang in there. Something is bound to turn up.

[quote name='obbm' post='380181' date='Jan 14 2009, 12:33 PM']I suppose you'd call it Rock covers - Thin Lizzy, G 'N' R, Dire Straits, Bon Jovi, Clapton, Chuck Berry, Quo, AC/DC, ZZ Top, Bryan Adams - all the usual suapects. Three of us are retired and the average age is 57.5, but that doesn't deter us.[/quote] Please forget what I said about the band. I decided to walk due to musical differences between the drummer and myself. It had been niggling me for some time and the last rehearsal just confirmed my views. so bandless again.

The editor of BGM came up from Devon and supported the SE Bass Bash in September. He had his own session and talked about the magazine and answered a number of questions about the magazine, some quite pointed. At the end of the day it's a commercial undertaking. If you don't like it OP then I challenge you to start a rival magazine and make it pay. BTW I have no connection with BGM, it's editorial staff or its publishers.

For some time now I have been looking for an alternative jack for pedal board patch cables. One that is smaller than the ubiquitous Neutrik, equally robust and ideally cheaper. I believe that I now have the answer. It seems to fit all the boxes and will take both the VanDamme Classic Instrument cable (on the right) and the rather excellent Klotz La Grange on the left. The connector is made in Australia by Amphenol who, if you haven't heard of them, have been making connectors for the military and the automotive, broadcast and telecoms industries for as long as I can remember. Up to 500mm the VanDamme version will be £8.50 and the LaGrange will be £9.00. I have a made a 300mm sample of each so if anyone would like to volunteer to check them out then drop me a PM.

From one oldie to another, welcome. I used to be the oldest but I think BassAce is now.

[quote name='Linus27' post='383509' date='Jan 17 2009, 07:37 PM']So your saying that as both my cabs are 8 Ohms, if I ran them through the LG1000, I could use either one of the two 500 watt amps running at 4 OHMS getting the full 500 watts (maybe to much for my cabs) or both 500 watts amps at 8ohms getting about 350-375 watts. However, if I used the LG350 with my two 8 ohms cabs, they would run at 4 ohms giving me the full 350 watts from the LG350. Have I got that right??[/quote] Correct, but as Merton has already pointed out it all depends on how far up you wind the volume control. You have control of the power control. Just because your Elise will do 100+, it doesn't mean you go everywhere at max power and max speed. Amps are no different.

[quote name='Linus27' post='383466' date='Jan 17 2009, 06:45 PM']I've got an Ashdown MAG115 1x15 Deep Speaker Cab which has a power handling of 250 watts. I will be getting an Ashdown MAG210T 2 x 10 Deep Speaker Cab which has a power handling of 200 watts to go with it. Will the LG1000 be too powerful for these two cabs? Just wondering if its worth getting a LG350 as a spare head for my two cabs or get the LG1000 as my main head. No point getting the LG1000 if its to powerful for my cabs.[/quote] I take it that both your cabs are 8-ohms. I've not had the chance to gig the LG1000 yet but will on Feb 5th at the Lion Brewery Jam in Ash where I will use it with two 8-ohm 1x12s. That should show up how it handles 2 x 8-ohm cabs instead of 2 x 4-ohm. I estimate the LG1000 should put out about 350-375 watts into 8-ohms. As far as your cabs go you would have lots of headroom but always with the risk of overdriving. The LG350 with 350-watts into 4-ohms would be a better match to your cabs.

Look great but just get in the way when playing.

[quote name='~tl' post='383079' date='Jan 17 2009, 11:07 AM']The other option would be to use a small mixer in front of the amp. That would allow you to independently set the levels of your instrument and MP3 player.[/quote] ... but the amp EQ would effect both bass and MP3s. If the amp has an Effects Send & Return you could take the bass out from the Effects Send, mix in the MP3s with either a small mixer or even a passive resistor network and then retun the mixed signal to the FX return.

Indeed welcome. I spent a very happy 2-weeks in Austin a few years ago making an album. Have you ever come across Eric Blakely, Ron Irwin, John Main or Bill Kirchen?

[quote name='OldGit' post='381425' date='Jan 15 2009, 04:00 PM']It's his fault so many of us got Sevens, well that and fact that Chapman had already product placed the Elan for Emma Peel in The Avengers..[/quote] And then went to to place an Esprit S3 and an Esprit Turbo in Bond films.

[quote name='Linus27' post='380188' date='Jan 14 2009, 12:38 PM']Dad rock [/quote] Grandad Rock please.