stevie

[quote name='Bill Fitzmaurice' post='186525' date='Apr 27 2008, 02:59 PM']Very few tens go higher than 4mm, and those that do, like the BP102, have less sensitivity, so what you gain in one area you give back in the other. [/quote] Er, no... this is incorrect and quite misleading, not to mention confusing. The 6mm Xmax of the BP102 is a reasonable specification which will not lead to any loss of efficiency at bass frequencies. Higher excursions on a ten-inch driver might, but only because of a possible knock-on effect on cone area. Midrange efficiency is irrelevant for bass guitar amplification because there is always plenty to spare. Although the Eminence Beta 10 produces 5 or 6dB more than the BP102 at mid frequencies (100Hz and above), it's a different matter below 100Hz. Put either of these drivers into a typical 30-litre cabinet tuned to 40Hz and their sensitivity will be roughly the same between 40Hz and 100Hz - even though there is a big difference in both their Xmax and FS. In mav's case we are not even concerned about maximizing sensitivity, because he has an excess of amplifier power. What we are concerned about is maximizing output, and you do that by maximizing Xmax, or Vd if you like, although driver size is a given here. In a 30-litre box the Beta 10 will produce a maximum of 96dB at bass frequencies before it exceeds its excursion limits. The BP 102, on the other hand, will deliver a theoretical 104dB and handle 100 watts before Xmax becomes a problem. The difference between 3mm and 6mm excursion is clear, and definitely worthwhile.

[quote name='mav' post='186324' date='Apr 27 2008, 10:15 AM']So two different opinions ? I was thinking if TE could push 500watts out of there 210 they would. I also downloaded winisd but i'm having trouble working it out.[/quote] Bill's right. Can you imagine a pair of 10-inchers handling 500 watts of low B? Power handling is the amount of electrical power the voicecoil will take before it overheats. With bass guitar, your ten-inchers will reach their excursion limits well before that happens. If you're comparing drivers of the same size, xMax is the figure to look for: it tells you the excursion capability of the driver. The Eminence Beta 10 has an xMax of 3mm, which is pretty useless by today's standards. Look for a driver with at least 5mm. Then you need to deal with the question of whether the drivers will work properly in your cab. If you can spec the right driver you are likely to get a substantial improvement over what you have now. Stephen

Bought a very useful M-Audio soundcard/preamp from rorykins the other day that was exactly as he'd described it. He was also very quick to send it out. A good bloke! Stephen

The edge of the driver seems to be loose around a lot of the edge, I'm a bit hacked off with Thomann as I've emailed three people there since sunday and no one's responded. The price you pay for cheap gear I suppose! [/quote] Somebody has stuck a screwdriver through the surround when tightening up the screws - a classic! You could have a problem with a warranty claim, as some retailers might say that you did it. Anyway, if that's the only problem, you can easily fix it yourself if you want. Pop to your nearest DIY store and buy some glue that is suitable for foam rubber (I don't think PVA is suitable, though). Just make sure that the speaker is OK otherwise (no scraping voice coil) because glueing it back together will definitely invalidate your warranty. If there is more to it than just a damaged surround, I'd certainly persevere and get Thomann to fix it, as you will find it very difficult to get a suitable replacement. You have a 300 watt driver (ho hum) with a foam surround (i.e. low resonance), which is a very unusual animal. If it were me, I'd send the photos to Thomann and ask for a replacement driver. Just make sure they know that the speaker arrived that way. Also, if the goods arrived with you less than 7 working days ago, I'd cancel the contract with Thomann quoting the EU Distance Selling Regulations (http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CELEX:31997L0007:EN:HTML), as it would put a lot more pressure on them to sort it out. You would then have the option of returning the goods if you wanted to, although you'd have to cover the cost of getting them back. Stephen

[quote name='Mr. Foxen' post='168041' date='Apr 1 2008, 11:45 PM']Not sure if it is a guitar or bass head, the EQ goes down to 125hz, so I guess that means guitar. It asrrived today, but ain't had a chance to try it, might go for some biamp action.[/quote] I just thought it was a guitar amp because of what it said on the eBay ad, but I think you probably do have a bass amp. It looks exactly the same as mine and FJ's as far as I can see. Ohm did produce a range of guitar amps at around the same time - so I wonder why they called these GA (and why mine is a GA125)? Stephen

[quote name='Mr. Foxen' post='166188' date='Mar 30 2008, 12:41 AM']I won this a while back, should be arriving soon (had some fun with that). [url="http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&rd=1&item=190199467160&ssPageName=STRK:MEWN:IT&ih=009"]OHM head[/url] Is it similar to that? Will be paying attention to the things your mods achieve.[/quote] It looks very similar - like the guitar version of my bass amp. I didn't know they did head versions of these. For your info, I have noticed a few things about mine already. First, there is no proper support for the preamp PCB - it's supported by the input sockets only, which is poor engineering IMO. That led to dry solder joints on mine, although to be fair, it did take 20-odd years to happen. You might also like to check the two 5W wirewound resistors in the graphic section of the preamp to see if they are getting hot and burning the board. If you don't feel like replacing these with larger ones (I'd advise 17W), at least space them away from the board to improve cooling a bit. Then there is the hum problem I mentioned in my first post. If you feel that yours suffers from excess hum - and I'd be interested in finding out - take the preamp out (undo the screws and it just pulls straight out of the sleeve) and see if the situation improves. If it's problematic, you'll need to follow Dave's advice above. Finally, I'm wondering whether 8,800uF of power supply capacitance is really enough for an amp rated at 125/140 watts. I'd be tempted to double this, although it may be more of a problem for bass than guitar. I'd be interested to hear what the specialists think, though (Dave?), as the few instrument amps I've looked inside were also very stingy in this area. Stephen

Thanks for the advice, Dave. Most helpful. Stephen

Anyone familiar with the old OHM GA125 bass combo? I recently acquired one that was crackling. I resoldered a few connections on the PCB and managed to fix it. Resoldering and replacing components is about my limit, I'm afraid. The amp seems to be working now but I am concerned that two of the wirewound resistors on the preamp board are getting very hot. The amp is split into a preamp section (front) and a power amp section (back) with an umbilical cord between them which seems to carry the power from the power supply (on the power amp board) to the preamp. The two resistors are the first components in the preamp circuit at this point. The original resistors were 470 ohm, 5W wirewound, but as they were visibly burning the board, I changed them to 10W wirewound and spaced them away from the board. However, even these ones are still getting very hot. By hot, I mean you can touch them but you can't keep your finger on them for more than a fraction of a second. Is this normal? Second question for the experts. I have taken the amp out of the combo and installed it in an amp sleeve. The graphic section of the preamp is now closer to the mains transformer and is picking up losts of hum. Moving the preamp away from the transformer reduces the hum. So, I've turned the preamp round 180 degrees so that the input section is next to the transformer and the hum has gone (the power amp is now upside down in the sleeve, if you follow me). I'm not very happy about the power amp being upside down. I would have thought that the input section of the preamp would be more susceptible to hum than the graphic section. Any ideas what I should be looking for here, or is this normal? Finally, the compressor operates very oddly and degrades the sound of the bass. It's basically unusable. Is this also par for the course? Taking the amp to a repairman would cost more than the unit is worth. Any help in saving it from the landfill would be much appreciated. Stephen