Bill Fitzmaurice

[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.

[quote name='LawrenceH' post='1063054' date='Dec 18 2010, 06:02 PM']I can see where you're coming from but a 45-year-old recording from the dawn of the roundwound, multitracking and close-mic-ing era is hardly representative of 'most' record producers I think they got with the program pretty quickly, and they were pretty good at getting acoustic jazz recordings down by the late 50s. This true live sound, would be the same one that was on the typical low-xmax, undersized box pre TS speakers used by most artists of the day? With the need to be loud enough that's gotta be at least as limiting as the recording aspects.[/quote]All I know is that, with the exception of 'My Generation' where the bass solo would have been pretty silly sounding low-passed at 1kHz, the tone heard on 'The Who' recordings bore no resemblance to the Ox live.

[quote name='LawrenceH' post='1062972' date='Dec 18 2010, 04:13 PM']Getting a meaty bassline to jump out of a tranny radio without absolutely shagging the speakers places quite tight constraints on how you commit it to record! But most record producers are clueless? I wonder how most pop records were 'meant' to sound?![/quote] There's two lines of thought there. One is the way the producer wants it to sound, the other is true to the band's live sound. Ent made it no secret about how he felt about the butchering of his tone, which was accomplished by low passing so severe that his RotoSounds ended up sounding like tape-wound LaBellas. It had nothing to do with modes of playback, everything to do with conformity, and most odd that Ent put up with it.

[quote name='TimR' post='1062593' date='Dec 18 2010, 11:01 AM']2). Soundman is not always your best friend - ideally you have your own who knows what you are supposed to sound like. Alternatively the venue soundman listens to your band playing and talks to you before even touching his PA and learns very quickly what you want. In reality you get someone who is only interested in turning the system up to 1.1 gigawatts to show it off. 3). Bands don't have producers - Someone who listens to your tracks and says OK I know you like that fill there, or you like that bass tone, but guys - it's just doesn't work live.[/quote]When it comes to getting the bass right in the PA I'd say 90% of soundmen are clueless. Record producers aren't much better; I only heard the Ox's true tone on one track, 'My Generation'.

[quote name='Chopthebass' post='1062144' date='Dec 17 2010, 06:54 PM']Hilarious [/quote] I though it odd that a thread about one myth, having too much power on tap, went so long without the even more pernicious myth, that of under powering, being raised. To have the same poster apparently believing both to be true: priceless. No offense to the OP.

[quote name='Lozz196' post='1061620' date='Dec 17 2010, 09:36 AM']I would need to use both cabs all the time, to obtain the 450 watts at 4 ohms, [b][i]due to under-powered issues[/i][/b].[/quote]

[quote name='Phil Starr' post='1059843' date='Dec 15 2010, 01:35 PM']I agree with you about the speaker making not much sense as a piece of design. It just seems lazy to me, but I might be missing something.With a magnet giving Qts of 0.29 there's leeway for lowering the response or using a longer voice coil as this thing is still excursion limited.[/quote] It probably boils down to money. You can get a lot more out of an eighteen than the Sigma will give, but the cost would put it beyond the price point that Yamaha can command.

Perhaps the cab design pre-dates the woofer, and it was originally loaded with a driver that need a larger box. That, or Yamaha wanted to go lower than what 175L allows. IMO an eighteen loaded cab with a 50Hz f3 makes little sense.

[quote name='Big Mick' post='1055329' date='Dec 11 2010, 02:52 PM']Ooohhh, the top is on, very exciting!!! [/quote]Where are the braces???

[quote name='Raph' post='1054527' date='Dec 10 2010, 04:37 PM']Eminence BP102-4 Anyone have a cab using one or more of these? If so, any opinions? I'm intending to make a 1x10" cab to use with 250-300W amps, not intending to use extension cabs therefore 4ohms. It's rated at a rather weak hifi-esque 90.5dB/W/m but I've compared the freq curve to speakers rated at 98-99 and most of the usable frequencies are only 2-3dB down, and there's a big dip in the 500-2k range[/quote] The answers to your questions are to be found on the SPL and Maximum SPL charts when you model the driver in the proposed cabinet and compare the result to other drivers. Manufacturer driver data sheet charts don't reflect results in an enclosure, only response above 200Hz, and they don't show maximum SPL.

[quote name='LawrenceH' post='1055428' date='Dec 11 2010, 04:25 PM']Not sure I get the sense of what you mean with the arrays though, crossover points there are more determined by the constraints of the vertical spacing with respect to the lows and mids.[/quote] The vertical spacing doesn't enter into it, as the distance between the LF and mid elements of adjacent cabs in stacked arrays is less than the CTC distance between those within each cab. For example, the JBL Vertec VT4888. The woofer CTC is about 24 inches, which is 1wl at 565 Hz. The CTC distance from woofer to woofer in adjacent cabs is about 15 inches, 1wl at 900Hz. The actual crossover used is 350Hz, well below the maximum allowable of 565Hz. That's all about system efficiency, as the direct radiating woofer sensitivity is only 98dB, whereas the horn loaded mid sensitivity is 102dB.

[quote name='LawrenceH' post='1055062' date='Dec 11 2010, 10:43 AM']Second, regarding the more complex comb filtering that one gets at greater-than-1/2-wavelength spacing, I wonder about allowing full-range signal to (or exit from) only a subset of the drivers in the stack, it's an obvious idea so it must have been implemented in some systems in the past. Even considering the typical 4x10 though, I wonder how much difference it really makes in practice to perceived (rather than measured) tonal consistency. Ears tend to be a lot more forgiving of changes to electric instrument sounds than, say, vocals. I must say I've not heard the PJB stuff, I would be interested to.[/quote]I can't say what PJB does, but to work as well as possible they should have the outermost drivers low-passed at their 1 wavelength center to center distance, the next set lowpassed at their 1wl/CTC, etc., culminating in a center row run full range. This is a commonly seen scheme with horizontal TV center channel speakers, and for that matter it's how the crossover points are determined with multiway PA line array cabs with with woofers outermost, the tweeters in the center and the mids between the two. The short CTC distance of the PJBs is no panacea. The result of using a number of drivers horizontally placed without appropriate filtering can be seen in applets such as those found here: [url="http://www.falstad.com/mathphysics.html"]http://www.falstad.com/mathphysics.html[/url] A 4x10 done correctly would low-pass one vertical pair of drivers at the 1wl/CTC frequency. A friend built a 4x12 for his guitar playing son, including what he called a 'sweet switch'. The son greatly prefers the sound of the cab with the switch engaged. Unbeknown to him so doing turns off one of the vertical driver pairs.