Bill Fitzmaurice

[quote name='Bloc Riff Nut' post='1109968' date='Jan 31 2011, 02:54 PM']I don't know how to cut 100Hz using the EQ of my Markbass CMD 102P.[/quote]Unless you have a graphic or parametric EQ you can't cut one frequency. Even with those you can only cut a band of frequencies centered at or near 100 Hz.

[quote]Putting casters on a cab should decouple it from the floor, right, so is there a reason NOT to do this?[/quote]There is no such thing as mechanical coupling, so don't worry about that. But less than perfectly level floors can result in the cab being tippy, or one caster not having any load on it, and it may then rattle. Carry some bits of foam rubber in your kit to put under the casters in that case.

[quote name='2008escottp' post='1100314' date='Jan 23 2011, 06:47 PM']Might be a stupid question but I'm a novice with this.

If I have a 500watt amp and want to run 2 separate speaker cabs, do they both need to be at least 500watts?[/quote]Preferably. That's because most speakers will only take half their thermal rated power, if that, before reaching their maximum output capability. It would be nice if manufacturers provided both the thermal rating and the displacement limited power rating, but not a single major manufacturer does. Ampeg is the only major manufacturer that consistently has very conservative thermal ratings, which are close enough to the displacement limited ratings so that you can safely assume them to be accurate and useful.

[quote name='GUI101' post='1098200' date='Jan 21 2011, 06:06 PM']I checked out their websites and they don't do 18inch speakers unless you are a manufacturer and buy in bulk.
anyone have any ideas or advice??[/quote]Buy one from a retailer.

[quote name='icastle' post='1095871' date='Jan 19 2011, 07:45 PM']Unfortunately, 50KΩ is not a preferred value so you're not going to find it in Maplins.[/quote]100K will do in a pinch.

[quote name='willyf87' post='1088179' date='Jan 13 2011, 10:39 AM']Got a little giant 1000 and a schroeder cab on the way. I see there are 2 pin and 4 pin speakon cables out there, which do i need and can anyone tell me the difference?[/quote]Whatever the respective owner's manuals say you need.

[quote name='fretmeister' post='1084722' date='Jan 10 2011, 02:44 PM']So disconnect at the "non-tweeter" end of the wiring?[/quote]
Disconnect the high-pass filter.

[quote name='icastle' post='1084688' date='Jan 10 2011, 02:26 PM']No other wiring needed - just disconnect it (make sure you don't leave bare wires or connectors floating around inside the cab though). [/quote]
That leaves the potential for the amp to see a dead short at the filter corner frequency. The disconnect should take place before the high-pass filter.

[quote name='bassman2790' post='1082948' date='Jan 9 2011, 05:18 AM']How much 'real' volume difference is there between 450W and 170W or even between 300W and 170W?[/quote]Not enough to be concerned with, because for the most part watts are moot.
What does limit output is driver displacement. Going from a total of eight tens to two reduces displacement by 75%, which combined with the 75% reduction in power handling reduces maximum potential output by 12dB. In simple terms a 2x10 will sound somewhat less than half as loud as two 4x10s. You're probably best off going to a pair of 2x10s , that way you can use the one if the gig is small enough to get away with it, both when it isn't.

[quote name='TimR' post='1081637' date='Jan 7 2011, 06:16 PM']As Bill intimated earlier. The power output is not linear. This is why you get power compression at the top end of the amplifiers range.[/quote]
Linearity in audio is rare. It isn't with speakers, it isn't with amps. If I designed amps for a living instead of speakers I'd have the reason for this particular non-linearity at the tip of my tongue, but it lies too far back in the recesses of my memory to retrieve it.

[quote name='flyfisher' post='1081561' date='Jan 7 2011, 04:57 PM']Hmm. Not sure. PSU inadequacy seems, to me, to be an economic issue rather than a purely technical issue, i.e. the limitation [u]could[/u] be eliminated by design.[/quote]I believe that it's not the PSU, it's the output devices. Somewhere in my files I've got the reason why amps can't double their full power output when the load impedance is halved. Of course I can't find it when I need it. If it could be done you'd see it done, and it isn't.

[quote name='dincz' post='1077700' date='Jan 4 2011, 02:16 PM']The degree to which an amp falls short of this ideal seems to me to be an indication of the shortcomings of its power supply.

Any thoughts?[/quote]
It's not a shortcoming, merely the reality of how amps work. At low signal levels current does double into a halved impedance load, so power doubles as well. But at full power the actual current delivery increase, and therefore power increase, averages only 70%. That translates into an actual full power level increase of only 2dB. That small figure, combined with the fact that few speakers can actually make use of more than half their rated power before reaching their mechanical limits, makes the oft seen "I want a 4 ohm speaker to get all the watts out of my amp" a generally fruitless quest.

[quote name='paul_5' post='1075940' date='Jan 2 2011, 07:28 PM']I had heard that Billy Sheehan dropped Ampeg because they are now made in China, and he wanted something built in the USA.[/quote]I believe Ampeg is made in Viet Nam. Samson products, including Hartke, are made in China.

'Getting all the watts out' at best results in 2dB additional output. Moot. Changing drivers is an expensive proposition. If you're not finding the 2x10 straining I'd leave well enough alone.

It's value as a collectors item far exceeds that as a working speaker. I'd box it back up again and store it in a safe place and let its value appreciate.

[quote name='Christophano' post='1073629' date='Dec 31 2010, 07:34 AM']In essence, I would be treating the amp like a pedal.

Shoot me down if this is a stupid idea.[/quote]
A forty pound pedal does seem over the top.

[quote name='Christophano' post='1073206' date='Dec 30 2010, 05:03 PM']But the dummy load should manage to stop my amp from being damaged surely? Unless the internet has fooled me....[/quote]
Tube amp? They don't like higher impedance loads than the tap is rated for, and aren't bothered by lower impedance loads. Most come with output jacks that short the transformer with no load. But I thought this was a direct out? Why run with the speakers disconnected? For silent recording run your bass into the board.

[quote name='Christophano' post='1073036' date='Dec 30 2010, 02:26 PM']In the pictures, they look like they have big heatsinks.... I will of course make sure they are decent enough... I don't want things cooking![/quote]
Dummy loads don't give the same result as speakers, because speakers are complex reactive loads, not resistive.

[quote name='Steve Spector' post='1071234' date='Dec 28 2010, 03:26 PM']What would I lose with 2 212s instead?[/quote]Nothing.

[quote name='JTUK' post='1069432' date='Dec 25 2010, 09:07 PM']Ampeg 8x10 is 800watts so that should handle most amps. And they are low powered drivers for 10"
You aren't going to get a 15" anywhere near that output and nominaly half that. In order to get a power spread on the two cabs the 15" would need to be double the impedance of the 8x10 given those ratings..that is besides anything esle.
Why would you bother to do this when the 8x10 is such a big lift into the gig and would cover 99% of the time. The 15" would add nothing to the set-up...it isn't balanced in any way and you don't need the extra cab/speaker. There are other cab configs I'd consider and if you had a very large stage area and a concert rig then 2 8x10', but this 15" and and 8x10 is nothing but putting extra cabs on stage to no good effrect, IV/IME..therefore a useless idea.

Vanity gone wrong, I'd say.

I don't rate Ampeg 8x10's of old..... not sure this is an Ampeg you have, though.. and that is because I have played through too many tired hammered versions and the power was very low but I would fully expect them in decent nick to outperform a single 15" every day of the week and twice on sundays.

Certainly, Aguilar, Boogie, Orange and even Ashdown are all rated no less than 1200watts per cab..[/quote]
A bit long winded, but essentially correct.
Low frequency output is primarily determined by total driver displacement, not watts. That of an average 1x15 is 350cc, that of an average 8x10: 1100cc.

[quote name='Mr. Foxen' post='1068677' date='Dec 24 2010, 07:42 AM']It will make the impedance on the output transformer very unhappy.[/quote]
Only if run alone, and that would be a very bad idea. I always loaded my amps with a direct out to eliminate having to carry another piece of gear, and the DIY cost of adding one came to way less than buying a box.

[quote name='Christophano' post='1068247' date='Dec 23 2010, 04:11 PM']Yep, I'm with you, still learning so you will have to bare with me....

Would I be right in assuming that when you say the inverter stage, that's the preamp stage? So you are suggesting tapping it with a balanced XLR with appropriate cap and resistor to drop and power down to a suitable level?

Chris[/quote]Yes. On your schematic you'll find the inverter tube just before the power amp tubes. It inverts the signal 180 degrees to drive half the push-pull, while the other half is driven by the pre-inverted signal. You tap the input and output, DC isolate both taps with a 0.1uF 400v cap, pad it with 100kohms of resistance, run it through a 1meg stereo audio taper pot, send that to the XLR out.
[quote]the added harmonics and compression of power pentodes/tetrodes is very different to that of the smaller triodes and that coupled with the limited response and added distortion of the power transformer gives a notable difference that gives even more noticible as you crank it, especially with an amp like the one the OP is using.[/quote]It still has an order of magnitude less coloration than that delivered by the speaker. If you want the same tone going to the desk as you hear out of the rig only a mic will give it.

[quote name='Mr. Foxen' post='1067877' date='Dec 23 2010, 10:59 AM']Won't this give you a preamp out only, whereas between speaker and amp will give the tone colouration from the power stage also?[/quote]Power stage coloration is minimal, especially when compared to that of the speaker. If coloration is what you're trying to capture you need a mic.

Have a good tech install an XLR out. He only has to tap both sides of the inverter stage, capacitor isolated and resistor padded, with an output level pot for good measure. You probably don't understand a word of that, a good techie will.

[quote name='JTUK' post='1063321' date='Dec 19 2010, 05:54 AM']Entwhistle sounded very poor on TV recordings[/quote]As did everyone on TV in those days. I saw him live, so that's my reference.