Zerofret

I sent them an e-mail and they sent me the whole service manual as a pdf - great service - can't whack that! [quote name='Hamster' post='433761' date='Mar 13 2009, 03:06 PM']Ok, in that case you get the schematics by sending them an e-mail [/quote]

Thanks Hamster but these links are just for owners manuals not schematics. Steve [quote name='Hamster' post='433694' date='Mar 13 2009, 02:23 PM']They're working for me? - [url="http://www.britishaudioservice.com/trace_operateinstru.shtml"]http://www.britishaudioservice.com/trace_operateinstru.shtml[/url][/quote]

Has anyone got a copy of the service manual or schematic for the Trace Elliot BLX SMC GP7 150 watt amplifier? It uses the 'Bipolar Bear' amp module. I would really appreciate if anyone could send me a link or email me a copy. The links on the British Audio Service website no longer work. Cheers Steve

Bill - You're right, I was totally wrong about the Legend 1518 - I meant to suggest the Legend CB15 which is designed for bass and has excellent sensitivity at the lower end. Its 4.8mm xmax is more like it too. I agree with you on the 4x10 route and it would be my choice as a player but there is still something to be said for that vintage sound from a big cab and a small valve amp that puts a smile on your face! Thinking about it it doesn't put a smile on your face carting it around to gigs and up three flights of stairs though...... Steve [quote name='Bill Fitzmaurice' post='275595' date='Sep 2 2008, 04:40 PM']The sensitivity ratings for raw drivers apply to above 100Hz, so that in and of itself says nothing about sensitivity where demands are highest, from 40 to 100 Hz. As for the Legend 1518, it's a guitar driver. In a typical cab sensitivity below 100 Hz averages only 92dB, and its 0.8mm xmax limits its average power handling in the bass range to only 20 watts. Sensitivity ratings given by speaker manufacturers are outright piffel and are useless for comparison purposes. But the more drivers one uses the higher the system sensitivity, as there are more driver motors utilizing the power. For that reason a lot of tens will give a better result compared to a smaller number of twelves or fifteens in the same overall pack space. With the same input two 2x10 cabs will have 6dB more output than one, and that 6dB is the equivalent of going from 50 to 200 watts. With the price of watts as low as they are today using a small amp with lots of cabs isn't the most size efficient route, but it can work if you so desire.[/quote]

Alex, Thanks for your comments and I would like to defend what I said. Regarding the impedance matching, I was refering to the Selmer Treble 'n Bass 50, the valve amp in question where it ought to be the same (or as close as you can get). I completely agree about solid state amps being different. It is definitely advisable to have some headroom on the driver's input power as running it close to the edge all the time with bass is not a good idea. I wasn't suggesting using a driver that would handle two or three times the power either, just a bit of headroom is useful for reliability. Anyway I guess it's not a valid argument anymore because you'd be hard pushed to find a 15" driver rated at 50 watts nowadays!! I didn't suggest that a ported cab was a compromise between an open backed and a sealed cabinet - I said that a vented cab was a compromise. A vented cab is usually a crude generic design where there is generally less science involved but it generally improves the lower bass response. A ported cab is design critical and driver specific - I thought that I got that across by suggesting sticking to a speaker manufacturers published designs but maybe not because I was probably rambling by then. Steve [quote name='alexclaber' date='Sep 2 2008, 03:57 PM' post='275544'] Lots of good points Zerofret! However... The speaker impedance should be greater than a solidstate amp's minimum impedance, it doesn't need to match. With a valve amp the speaker impedance should be similar to the output transformer tap impedance - if there isn't a matching one then you should use the next highest tap. The speaker power rating does NOT need to be in excess of the amp power rating. Also a ported cab is not a compromise between an open-backed and a sealed cab as at all frequencies above the port tuning frequency the air inside the cabinet is effectively sealed from the outside air.

Tom - This can unfortunately get complicated. But first, two essentials - the speaker impedance must match that of the amplifier and second, the speaker rating must be in excess of the RMS wattage that the amp is putting out. OK that's out of the way so now the blurry bit. The perceived loudness of a speaker system is largely dependant on the sensitivity of the loudspeaker driver used and this is measured in dB and represents the SPL (sound pressure level). The sensitivity figure tells you how loud a speaker driver sounds for a specified input (assume a loudness factor of 2 for every increase by 3 dB).This figure can be as low as 80 dB for 1W of input and measured at 1 Metre to around 104 dB. The difference of 24 dB doesn't sound a lot but it means that the 104dB rated speaker needs .004 of the power needed by the 80dB SPL rated speaker to produce the same perceived loudness. OK, it's unlikely that you will be comparing speakers at either extreme but just look at what the maths tells us in real life - The first speaker would need a 100 watt amplifier to make it sound as loud as the second speaker running from an amp of just 0.4 watts. So you can see, the speaker and its enclosure is probably more important to 'volume' than you thought! In the early days speakers didn't handle much input power with and drivers rated at 15 - 25 watts were common place. Granted, bands weren't necessarily as loud back then but some of those old speakers tended to be very efficient and required less wattage to sound loud. by comparison a modern loudspeaker can be designed to handle incredible amounts of input power but can be a lot less efficient. Most manufacturers have gone for reliability as the major factor and one of the problems with speakers in the old days was that we were always replacing them because they were easily blown in spite of their superior sensitivity and loudness. Fortunately there are now modern 'vintage' speakers that are using the old techniques and styles to bring back some of that old speaker magic without the puny power handling that made the originals so vulnerable. What about the cabinet? Well if you seal a cabinet up completely (an infinite baffle design) the speaker cone is damped and easier to control especially at high volumes. If you have an open backed cabinet, you have very little control over the speaker cone and at high volumes it is likely to cause excessive cone exertion. By allowing some of the air pressure out of the cab (venting) it is possible to get a good compromise between the two extremes of design. Going further, a properly ported design can bring some of the rear out of phase bass, wasted from a speaker cone and port it back in phase from the front of the cabinet increasing the efficiency of the cabinet but, more importantly, improving its bass response. To confuse matters further, every speaker driver has its own inherent resonance (the larger the cone, the lower the resonance) and every enclosure is going to have its own resonance and the idea is to try and keep the resonance out of the playing range which with smaller cabinets is difficult to do. Because the cabinet is also going to depend on the kind of speaker used, it's a good idea to get recommended enclosure plans from the speaker manufacturers themselves. The Selmer Treble 'n Bass was often used with the Goliath speaker cab of which there were two versions - the '50' with a single 18" driver and the '100' with an 18" and a 12" driver! The Goliath 50 used a Goodmans Audiom 91 rated at 50 watts RMS and had an impedance of 15 ohms. The cab measured 39.75" x 24" x 16" and came up to your waist! I've no idea what the SPL was for this driver but it certainly packed a punch if a little lacking in the mids. I think if I was in your shoes, I would build a substantial plywood cabinet and fit something like an Eminence 15" Legend 1518 which has an SPL of 102.2dB Apparantly Fane are producing a vintage range of instrument speakers and if you look at their website under 'bass guitar' it says "coming soon" so that might be worth a look. Steve

Bass cabs have a nasty habit of vibrating themselves 'loose'. I have had several 1x15" cabs to repair that have developed 'flapping' at higher volumes where it is suspected that the speaker itself is at fault. What it has turned out to be is that the glue holding the baffle board (the panel that the speaker is bolted to) has dried out to become useless and the whole cabinet goes into a horible vibration. Driving screws through the sides of the cabinet into the front panel crudely but sucessfully cures the problem but you obviously don't want to do this if it isn't the problem! Recruit someone to keep hitting a bass note that makes the flapping noise whilst you squeeze the sides if the cab to see if it changes the sound at all or stops the flapping altogether. If that does make a difference, drive those screws home! Of interest, on a Peavey cab I recently had in, this had the aforementioned rattly cabinet and whilst trying to identify the problem I swept a generator up and down the frequencies to look for resonances and found to my horror that the cab would resonate at around 41Hz or effectively bottom E (give or take 0.2Hz) which is just where you don't want it to resonate! Come on Peavey, you can do better than that - no wonder the cab tried to make itself come apart at the seams! Obviously taking a cabinet apart and re-gluing/bracing etc is the more professional way to deal with this kind of problem but that takes a lot of time. In the case of the Peavey, I diagonally screwed the baffleboard into the sides at roughly 5" intervals and then when the grille was in position you could no longer see the screws. OK, without hearing your problem, I can't guarantee that you have a compromised cabinet - it maybe the speaker itself, but in view of the fact of how common this is I would give the cabinet squeezing a try. Cheers Steve

Because we are talking BASS here, there is a difference to the normal argument of solid state vs valve. In a domestic Hi-Fi situation, a well designed valve amp can be inderscernable from a well designed solid state amplifier. In that situation extremely low distortion figures along with a linear response over a wide frequency range combined with very low noise characteristics, are what matter. It's true however that most valve amps in a hi-fi situation introduce a warmth that is to be encouraged rather than designed out because it sounds so damned good. Output power in most domestic situations is relatively low and equipment remains static and not subjected to a rough ride in the back of a van every night! OK let's move on to guitar amps. The electric guitar is predominently mid range and the demand that a player puts on his or her amplifier/speaker is usually out and out volume and as the volume increases so does the distortion. On a big HiWatt or Marshall, your ears can start bleeding before you start to hear any distortion (unless you overdrive the first stages and back off the master volume). With smaller amps, the audible distortion starts earlier and gets progressively 'dirtier' as you crank up the gain. Unless you're a C&W or jazz player most guitarists want distortion. They want volume and distortion and become deaf before they're 60. Pardon? So the argument for valve vs solid state is usually quite straightforward - valve amps sound great with guitars when they distort - even bad ones. Solid state amps sound crap when they distort. Guitarists wanting a clean sound only are probably better off with a solid state amp unless they're looking for a particular signature sound of something like a Fender Twin Reverb for instance. So now it's the mighty bass, a punisher of all amps valve or solid state. Bassists seldom want distortion, we usually want 'punch' or 'tightness' or 'depth', maybe even something 'stomach moving' - it's a totally different vocabulary to guitarists and a totally different requirement for amplification. Unless you are prepared to spend a small fortune on a valve rig, there is generally more punch for pound in a solid state rig. It's easier to tightly couple an output stage to a speaker and achieve a high damping factor with a semiconductor amplifier than it is with a valve amp. The higher the damping factor (Zsource = Zload divided by DF), the greater control the amp has over the speaker movement and with bass this is really important. Valve amps usually have a much lower damping factor and lack the speaker control but nevertheless sound 'warmer'. There is much more need to audition bass amps and speakers than any other set-up because there are so many pros and cons in either camp. Personally, some of the best bass sounds I've heard have come from solid state rigs and that's coming from someone who's a huge valve fan! Also there's always a lot of focus on amps but choice of speaker is equally important with bass. The cone, and therefore coil excursion, is much greater at low frequencies and as the coil moves outward away from the gap the magnetic field is reduced. To some extent is self governing if the peaker can handle the power - however this results in a kind of compression which affects the punch. Using smaller drivers (that's why multiple 10" drivers are used a lot) rather than one massive speaker can minimise this, but you need more of them of course. Some drivers are designed for bass very much in mind whilst others are more generic, even though nowadays they're usually capable of handling the power. Beware the cheap bass cab! Actually, I don't think that there is an argument for solid state vs valve; it's more 'horses for courses' and there's good and bad in both camps - I've started to use my ears more and be less biased towards the technology used to produce the sound. After all anything is better than what I started with - a Rosetti bass played through a rather inadequate hi-fi amp of the era into a couple of Wharefdale 8" speakers. I blew the speakers regularly and eventually used the bass guitar as a bow and arrow. Steve

Unless you've got a specific problem or fault, there is nothing wrong with Sovtek valves! - they are rebadged and fitted by most of the top amp makers. A lot of valve specialists including Groove Tubes use them for some of their valves. They are well made and stand up to some fair old hammer. If you don't mind a slightly cleaner sound their EL84M (M for military) is a cracking valve, able to stand up to more punishment than a regular EL84. Cheers Steve [quote name='john_the_bass' post='265242' date='Aug 19 2008, 09:26 AM']Oh no - it doesn't [i]need[/i] new valves an a speaker, it's just got a set of crappy Sovteks for the output and an HH Invader speaker - they both need swapping for something a bit better and the covers will stop anymore of the tolex getting whacked off![/quote]

Probably the most common ECC83 out there is by JJ Tesla - these are made in the Slovak Republic and the old Tesla factory has been making valves for a long time. Good value at around £8 and work well and are very reliable in my experience. they even got a 'Great Gear' award from Better Guitar. Look at the review here: [url="http://www.betterguitar.com/equipment/other_gear/eurotubes/jjel84.html"]http://www.betterguitar.com/equipment/othe...bes/jjel84.html[/url] Cheers Steve [quote name='benwhiteuk' post='263868' date='Aug 17 2008, 11:05 AM']Thanks Steve. Very interesting and informative stuff; It seems crazy that the spec of certain valves has changed over the years which is effectively making them incompatible with some amps, but I guess that improvements in manufacturing technology and a better understanding of the physics of the valves has probably lead to it? So there is definitely a case for the more expensive and vintage valves to sound noticeably different to cheaper newer valves, but they’re not fundamentally ‘better’ or ‘worse’, just subjectively different? Are there valves that you think sound cheap and nasty, or ones that you just don’t like or wouldn’t use? – again, I’m talking more specifically about the ECC83/12AX7 pre valves.[/quote]

An interesting and controversial topic! Getting down to the nitty gritty though - Some of the differences are real and some are just not there and people are willing to jump on the bandwagon of this 'old is best' thing. If you can buy new old stock Mullard EL34, ECC83 and GZ34s or GEC KT88, Sylvania 6550 etc etc then that's fine but to pay the silly premium people want for old valves is plain barmy. In the 60s and 70s I dealt with more valves than I can remember and occassionally even a good brand would fail prematurely or be faulty from new; matching was virtually unheard of as most amp designs where made with valve availability in mind. I regularly run amps with all manner of the latest Russian or Chinese valves and they sound great. In the early 1990s some really bad valves came over from China and ever since then there has been a distrust in Chinese valves. We have to get over it as there are some great valves being made in China. One of the most overlooked problems is the spec of new valves being different to the originals - this doesn't make them bad but it is a real problem when trying to make like for like comparisons. A lot of the new makers rationalise their production, so the internal build of a valve could be quite a bit different to the originals and the specification will be different. An ECC83 (12AX7) can have a lesser or greater gain characteristic or even linearity than an original type. This can change the sound but the difference is not necessarilly an inferior sound, just different and can be subjectively better or worse. In the case of a guitar amp, where Hi-Fi is definitely not a consideration, this is rarely a problem. Output valves in a cathode biased amp are less of a problem from a compatibility point of view and using different manufacturers valves will generally produce similar results but you do have to watch the nomenclature - A 6L6 will not always be a suitable replacement where a 6L6GC has been specified for instance - Over the years some manufacturers have taken a valve type and upped its specification which means an original type would now be unsuitable. In a grid biased design, the bias setting is critical and needs adjustment every time output valves are changed - if not the valves can have shorter lives, have a harsher sound, or the opposite depending on their characteristic. I'll stop before I really get going!! Steve

[quote name='Bassassin' post='207416' date='May 27 2008, 05:59 PM']I think I can help... I made my own for my Kasuga Rickenbugger: A kindly Rick-owning BCer sent me a clear, top-down photo of the real thing, which I fiddled with & edited until I had this: [attachment=9076:cropx1.jpg] Through trial & error (and a bit of actual measuring!) I worked out the appropriate dimensions for my headstock - then I used my graphics prog (I used Paint Shop Pro but any image app should do) to print it at the size I required. I then used the printout to draw a template on a bit of 3mm Perspex, which I cut to the appropriate shape with a jigsaw. Perspex is pretty brittle, but cuts, sands & polishes really easily so it was quite straightforward to get a good result. I imagine the same thing done with scratchplate plastic would be easier still. J.[/quote] Jon, Thanks very much for that - it's turned out really well on your Kasuga. I will get cracking with it and post the result when it's finished. I appreciate you taking the trouble. Steve

[quote name='Bassassin' post='206922' date='May 26 2008, 11:00 PM']I must admit I'm a sucker for borderline-unplayable weirdos myself occasionally - if one of these came my way, it would be a challenge to try & get it playable & gig it! I do quite like the pickups. Kinda relieved you're not the Ebay Zerofret - although he's pretty straight-up & seems fairly knowledgeable about JapCrap! J.[/quote] Jon - Have you any idea where rik style headstock truss rod covers can be obtained or a template so one can be cut out of plastic laminate? I'm getting more determined by the minute to gig this firewood. Steve

[quote name='ped' post='206507' date='May 26 2008, 12:54 PM']Hi Steve, Chris was telling me about this one. We completely forgot to come and have a look at it. Apparently it is quite a toneful little beast? We have a few die-hard Ricken-faker experts here so hopefully we can find out where it came from... Cheers! P.s get building the pick-axe bas NOW![/quote] What something like this Chris? Probably the best use for the Kay! Cheers Steve

[quote name='Bassassin' post='206506' date='May 26 2008, 12:54 PM']Hi Steve - your bass is a Kay KB-24. If you go over to the "Marketplace" section, there's a Ebay sub-forum, wherein you'll find a thread dedicated to Rickenbacker copies in all their bizarre & wonderful forms - and the occasional Kay does pop up. Also - unless your username's a coincidence, there are one or two auctions in there you might find familar! Jon.[/quote] Thanks for the info Jon. My eBay username isn't the same as my Basschat name so there's someone else out there masquerading as yours truly - it's not just the guitars that are fakes! I hear that the Kays are pretty darn bad. Well this one is worse than that but for all of that, it has something. Even with its complete dullness and lack of everything you'd want in a bass guitar with no sustain to speak of and damped to high heaven, I'm still determined to play it live. Got to go, the nurse is here with the medicine. Steve