obbm

[quote name='dub' post='227520' date='Jun 26 2008, 05:11 PM']My pickup has no dummy coil. I disconnected the input and output of the pre-amp and connected the selector switch to the volume.[/quote] You've answered my question. Yours must be a pre-91 SR5 which has much simpler coil switching. You can't do what you've done on the later version and retain coil switching as the pre-amp has a balanced input.

[quote name='dub' post='227457' date='Jun 26 2008, 03:40 PM']I just bypassed the musicman pre-amp to see what it would sound like before installing a switch. The surprising thing was more output with no pre-amp and no hiss at all. The pre-amp set flat just seems to add loads of top end and hiss, so I'm just going to leave it without the pre-amp connected. I'll have no onboard eq but the output is louder, quieter, less trebly and I won't need any batteries.[/quote] Just out of interest which wire did you intercept and what coil mode is it in?

Are they captive or IEC mains leads? Have you tried different ones? Check for an Earth/Neutral miswire in the plugs if they are not the moulded type.

[quote name='bassjamm' post='226444' date='Jun 25 2008, 08:59 AM']Hmm...just read through that but didn't see that bit. I saw a bit about mixing ohms but it didn't make any sense. I read there that you shouldn't exceed the amps load though as it can cause it to short out. Surely if i were to use the 2.67 overall load of the 2 cabs, on the 4 ohm switch, then i would in effect be putting too much of a load on the amp when in that mode...? But not so if i used the 2 ohm switch?[/quote] It's not about exceeding loads as with a solid state amp. You mustn't think about a valve amp in the same way as a solid-state amp. In a valve amp the output transformer is there to provide a virtual load for the output valves. There are separate output taps so whether you use, in your case, 2-ohm or 4-ohm speakers, the load on the output valve anodes remains the same and that the amp is operating on the optimum part of its load-line. If you put a mismatch on then you are altering the performance characteristics. This phenomenon does not occur in solid-state amps. What he is saying is that if you set your tap to 4-ohms and use a speaker of impedance of equal to or less than that then it should be OK. If you are unsure about this the contact Ampeg technical Support and get the word from them. They designed it so they should be able to advise you according. The other alternative is to get another speaker 4-ohm or 8-ohm cab and do it properly.

[quote name='niceguyhomer' post='226408' date='Jun 25 2008, 08:09 AM']Any progress/news with the modification Dave?[/quote] Not yet Al. The body is still away being fettled.

According to [url="http://www.geofex.com/tubeampfaq/taffram.htm"]this[/url] it would appear that it would be safer using the 4-ohm tap. [quote]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. [i]It's almost never low impedance that kills an OT, it's too high an impedance. [/i] 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.[/quote]

I've gone back heavyish. A single cab that is the same height and depth, but slightly wider than the two 1x12s, but heavier and an amp head that weighs as much as my original 6U rack system. Overall the new set-up is physically only slightly bigger but the tone is huge.

I'm sure I said this a long time ago but bolt the old and the new guards together and using the old one as a template gently open up the hole in the new to match the old one.

File away, carefully.

No need to go down to 2-ohms if you get a secondary power amp. You can run one set of 4-ohm spekers from the Eden. Take a line out to the secondary power amp, and if it's a 2-channel device then you can run a set of 4-ohm speakers from each channel. 6 x 8-ohm cabs in total. Is that enough air movement?

[quote name='Bill Fitzmaurice' post='225034' date='Jun 23 2008, 02:09 PM']The technical acronym for this proceedure is RTFM. [/quote] Indeed it is but I was just being polite and diplomatic.

[quote name='phil_the_bassist' post='224864' date='Jun 23 2008, 11:33 AM']ok ok ok...even tho (several years ago) I did my physics A-level I still have a nightmare getting my head around this whole wattage/ohms thing! Broken down: Low ohms = more watts get through = louder. I get that bit, maybe not the why or how, but I get that it happens. Now, the big question...I've got a Hartke HA5500 (so that's max output 500w@4ohms but it's currently running 250w@8ohms) and I've got a VX215 cab thats rated upto 500w@4ohms. So, they're matched, it should all work OK but on the speaker outputs on my head it's saying '8ohms'. Does anyone know how I can get the full 500w@4ohms? Will I need to send it back to the factory, or is there a secret switch I need to flick? Any Ideas?[/quote] I strongly recommend that you read paragraph 2 on page 8 of the Hartke 5500 User Manual.

[quote name='karlbbb' post='223859' date='Jun 21 2008, 09:53 PM']Do they not make 12-ohm speakers? 12-ohm speakers, 3 in parallel = 4 ohms![/quote] Nope! 4, 8, 16 or 32 ohms. 3 x 16-ohms in parallel gives 5.3-ohms which is the impedance of the Eplifani UL310. Interestingly the SWR Goliath Senior 6 x 10 is also 5.3-ohms. As long as you have a powerful enough amp it makes f***-all difference having 5.3-ohms.

I had a similar problem with some pedals a few years ago. The problem is that some 9-volt power supplies have a well regulated output and some don't. Some pedals have on-board regulation and some don't. If you use a badly regulated psu with a badly regulated pedal you get hum. You don't say which Wall-wart you are using.

[quote name='ben_eat_pie' post='223270' date='Jun 20 2008, 09:45 PM']just wondering if anyone knows or can explain why there are no 3/10 cabs in producion (that i know of anyway), i'd like of with a horn...! might be something to do with wiring and impedance... i havn't a clue... that was a guess! ben[/quote] For starters I suggest that you explore the Epifani range. I think you might find a 310 there. In fact oldhorsemurphy has an Epi UL310 for sale on this very forum. Impedance is generally 5.3 ohms i.e. 3 16-ohm speakers in parallel, but you treat it as 4-ohms.

[quote name='Toasted' post='222694' date='Jun 20 2008, 09:52 AM']What position are you having the J put in, Dave? 60's or 70's [/quote] 60s. Don't forget I also have a DJ4.

[quote name='niceguyhomer' post='222693' date='Jun 20 2008, 09:49 AM']When will you have yours done Dave and who's doing the work? I can't wait to hear the outcome [/quote] The body was sent to the gallery on Monday. Ale reckoned about a week. When I get the body back I'll put it all back together. I have a spare Stack-knob set of pots so I might try those initially. Maybe a U-Retro later. Do you still get down this way on business? If so you are welcome to try it. Before you rush off and do it the same you have to consider that a Squier p-bass special would cost the same as the modifications, but it just wouldn't be the same and I just don't like the colour.

[quote name='niceguyhomer' post='222666' date='Jun 20 2008, 09:29 AM']Dave - if I go ahead with the mod, will I have to ditch the Fralin P pup fitted as standard and buy the set or can I just buy the J pup?[/quote] You can just buy the Jazz although I'd email Lindy first. Have a look [url="http://www.fralinpickups.com/bass.asp#jazz"]here[/url]. It's the "Split-Jazz Bass Replacement Style - wound as two coils under a stock cover for hum cancelling". I'm sure you could get one at a good price from the USA. i got my set from Angela's. Very good service.

With my crap hearing I also find a P a bit woolly which needs to be tightened a bit. For a short while I had a Fender Aerodyne and found the mix of P and J pick-ups very fleible and to my liking so I decided to go for it with the DD. We shall soon see if I've been wasting my money.

[quote name='niceguyhomer' post='222267' date='Jun 19 2008, 04:16 PM']The P pup is a Fralin and if I was going ahead, I'd probably go for a Fralin J. They actually make a PJ set so I'm assuming any issues re; humming / output would have been resolved. Making me think now that I should just sell / swap the bass. It'd probably be simpler [/quote] This is the description of the set I bought: [quote]Lindy Fralin Premium Precision/Jazz Bass Pickup Set! Includes set of vintage style Precision Bass 'split coil' pickups and a 'split coil' humbucking Jazz Bass bridge pickup, both brand new in the box! Lindy's 'split coil' design for the Jazz Bass bridge pickup involves two side by side RW/RP coils. You get all of the growl of a vintage Jazz Bass pickup without the noise! This design also overcomes the compatibility problems encountered when trying to mate other P-Bass sets with a Jazz Bass Bridge pickup. No matter how you combine the pickups with your volume controls the lowest possible noise floor is maintained with the highest possible output. If you're building or upgrading a P/J Bass, this is the best pickup set you can buy. Black fibreboard coil forms, alnico magnets, vintage style magnet wire, black plastic pickup covers. Good mounting hardware is included. Exact replacement for Fender and most other P/J Basses.[/quote] It'll be interesting to see if it lives up to the spec. I'm sure it will.

[quote name='bassicinstinct' post='221089' date='Jun 18 2008, 08:04 AM']Make an appointment with a decent Chiropractor [b]now[/b]. You'll be glad you did, believe me.[/quote] +1 I had a similar tingling fingers problem a couple of years ago. It turned out to be a lower back problem.

I've taken the plunge Al and sent the DD body off to have the routing done for a bridge jazz pick-up. Also having a side jack fitted and a battery box put in to give me maximum future flexibity.

[quote name='JJTee' post='219811' date='Jun 16 2008, 01:05 PM']Hi there, Anyone know where I can obtain a power cable to run from a Dunlop DC Brick to a Demeter Compulator, which I believe requires a positive tip jack. Cheers, Julian[/quote] How many do you need?