Downunderwonder Posted February 13, 2022 Share Posted February 13, 2022 Another possibility occurred to me. If there is clip indication on all the legs into the amp inputs it would mean there might only be 1/2 the potential driving happening. You really should get an XLR cable on the job. Quote Link to comment Share on other sites More sharing options...
Davi Posted February 13, 2022 Author Share Posted February 13, 2022 7 hours ago, Downunderwonder said: Another possibility occurred to me. If there is clip indication on all the legs into the amp inputs it would mean there might only be 1/2 the potential driving happening. You really should get an XLR cable on the job. Ive got an XLR, ill try it to see if there is any difference Quote Link to comment Share on other sites More sharing options...
Downunderwonder Posted February 13, 2022 Share Posted February 13, 2022 9 hours ago, Davi said: Ive got an XLR, ill try it to see if there is any difference Check it hasn't had one end jumpered. Should be fine if it's a mic lead but random patch leads can be weird. Quote Link to comment Share on other sites More sharing options...
BassmanPaul Posted February 13, 2022 Share Posted February 13, 2022 (edited) 20 hours ago, Davi said: I had the 2 cabs daisy chained out of 1 channel. I was under the impression that id get 600watts at 4 ohms and running 1 cab per channel would give me 360 watts at 8ohms, One cab per channel @ 8Ω gives you 720W with the input switched to parallel. This is how I operate my system. Running your power amp in bridge releases a vast amount of power which will, in the end, toast your speaker cabinets. Another related point is that a 1x15 will not handle the power that a 4x10 is able to. In use. if you must use this match up, stack the 4x10 in the bottom position so you can more easily hear the cries of pain from the 15. Thinking that a 15 will produce more lows is wrong. The close coupled four tens will be more capable of doing that and will have greater sensitivity. Just as a question: is the Cavern still active, pandemic aside? I played there in the sixties. LOL Edited February 13, 2022 by BassmanPaul 1 Quote Link to comment Share on other sites More sharing options...
fleabag Posted February 13, 2022 Share Posted February 13, 2022 Ditch the 1x15 and get another 4x10 , same model. Just run one cab per channel. That'll be your speaker / amp problem solved, at least. It would certainly shift some air That old myth of using a 15" for lows and 10's for mids/highs was busted a loooong time ago, and yet ...still being touted. Bit like the people who keep perpetuating , incorrectly, that guitars with Vibrato arms are called Tremolo arms. Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted February 13, 2022 Share Posted February 13, 2022 1 hour ago, BassmanPaul said: Running your power amp in bridge releases a vast amount of power which will, in the end, toast your speaker cabinets. Quite right. I ended up posting this in the FAQs on my forum in response to users toasting their drivers: When should I bridge? The answer is almost never. Forget about the silly power ratings that manufacturers post for bridged output, that's just advertising piffle aimed at the unwashed masses. Bridging isn't about power, it's about voltage swing. You use it when your amp doesn't have enough voltage swing to drive the speaker to its displacement limit. Nine times out of ten that's because the speaker has a high impedance, say 16 ohms. The tenth time is when your amp is rated at less than a quarter the power output that your speaker is. If you do bridge when you don't need to the doubled voltage swing quadruples your chances of blowing drivers. Bridging into multiple cabs also can cause the amp to overheat, as bridging typically doubles the minimum load impedance, while using multiple cabs lowers the load impedance. Quote Link to comment Share on other sites More sharing options...
agedhorse Posted February 14, 2022 Share Posted February 14, 2022 Bridging is about BOTH voltage and current. It's impossible to change one without the other, they go hand in hand according to ohm's law. The preamp has plenty of output available to drive the power amp. That's NOT the problem, no matter how some here keep trying without understanding the differences between "nominal input level", "nominal input sensitivity", "nominal output level" and "maximum output level". The ~3V rms maximum output level of the preamp is the same as +12dBu which is typical for a preamp like this with a nominal output level of either 0dBu, +4dBu or 0dBv. In pro audio, the maximum output level is typically extended to +26dBu, but that doesn't matter here. The nominal input sensitivity of the amp is 1.15V which is the same as +3.5dBu. Since the OP is able to get the output limit LEDs on the amp to flash, the problem appears to be AFTER the power amp (ie. speaker cable wiring, defective/damaged driver, cabinet wiring, or polarity issues within or between speakers), or is the result of grossly unrealistic expectations. Quote Link to comment Share on other sites More sharing options...
Davi Posted February 14, 2022 Author Share Posted February 14, 2022 (edited) 13 hours ago, BassmanPaul said: Just as a question: is the Cavern still active, pandemic aside? I played there in the sixties. LOL yes I was in there recently, it was packed out Edited February 14, 2022 by Davi 1 Quote Link to comment Share on other sites More sharing options...
3below Posted February 14, 2022 Share Posted February 14, 2022 17 hours ago, agedhorse said: Bridging is about BOTH voltage and current. It's impossible to change one without the other, they go hand in hand according to ohm's law. The preamp has plenty of output available to drive the power amp. That's NOT the problem, no matter how some here keep trying without understanding the differences between "nominal input level", "nominal input sensitivity", "nominal output level" and "maximum output level". The ~3V rms maximum output level of the preamp is the same as +12dBu which is typical for a preamp like this with a nominal output level of either 0dBu, +4dBu or 0dBv. In pro audio, the maximum output level is typically extended to +26dBu, but that doesn't matter here. The nominal input sensitivity of the amp is 1.15V which is the same as +3.5dBu. Since the OP is able to get the output limit LEDs on the amp to flash, the problem appears to be AFTER the power amp (ie. speaker cable wiring, defective/damaged driver, cabinet wiring, or polarity issues within or between speakers), or is the result of grossly unrealistic expectations. Does this mean that the stated pre amp output of 0dB in the Sansamp RB1 manual is almost meaningless? The manual not indicate whether it is dBu, dBV or dBm and we now know it has maximum output of ~3V rms. The manual states "The standard output level range of the SansAmp RBI is 0dB due to the popularity of digital recorders, which are unforgiving to excessive input levels. This prevents overloading the input of a digital recorder.", Is it the case that that the 0dB figure is the capability we just "have to know" it can do far more? My background is Physics / Engineering not pro audio. As said above, the flashing clip limit LEDs does suggest that the problems are after the power amp (I missed the clip LED statement, read the op too fast). Quote Link to comment Share on other sites More sharing options...
agedhorse Posted February 14, 2022 Share Posted February 14, 2022 0dB is nominal, the difference between dBv, dBu is not important here knowing the MOL is over 3V rms. 1 Quote Link to comment Share on other sites More sharing options...
Tech21NYC Posted February 15, 2022 Share Posted February 15, 2022 The RBI has more than enough output to work with the QSC. The problem here is when you try to shoehorn a pro-audio amp that is designed mainly for a sound reinforcement application in a musical instrument application. These types of amps spec out the input using a sine wave test tone at 1 kHz. The RBI is an instrument preamp and produces intentional distortion which is why we can't offer the same type of specifications. We have measured our rack units in the past and they can put out well over the voltage required. You need to account for how a bass guitar signal is represented to the amplifier. Musical instrument signal level is not like a sine wave test tone or a voltage measurement that is constant. It has a wider range and the amplifier must be able to amplify the "average signal level" without peaking out and causing amplifier distortion. (At least not with a SS amp.) If the power is set to the rated output when playing softly you will run out of headroom when playing at your peak volume. The last thing you want to do is run an amp like the QSC or any power amp right up to it's rated output. If you do so, any peaks will cause the amp to distort and for the limiter to engage. Here is some information from Crown regarding amplifier power. 2 Quote Link to comment Share on other sites More sharing options...
Davi Posted February 17, 2022 Author Share Posted February 17, 2022 On 13/02/2022 at 19:29, Downunderwonder said: Check it hasn't had one end jumpered. Should be fine if it's a mic lead but random patch leads can be weird. One of the jack leads had melted from the bridging experiment, ive replaced the jack with a speakon, now using both channels parallel with limiter swiches on and 50hz filters on, havent had the chance to test it properly as I had to go back home to, but will after the weekend. Quote Link to comment Share on other sites More sharing options...
Downunderwonder Posted February 17, 2022 Share Posted February 17, 2022 47 minutes ago, Davi said: One of the jack leads had melted from the bridging experiment, Next thing to melt will be a speaker coil if you keep that up. Not often you get such a vivid warning but otherwise get off scot free. 2 Quote Link to comment Share on other sites More sharing options...
Davi Posted February 23, 2022 Author Share Posted February 23, 2022 So I got down to the rehearsal room last night and ran a speakon lead out of each channel of the QSC into the 2 cabs, had 50hz filter on and clip limiter switches on, parallel mode switches on, plenty of volume and sounds good, the Sansamp gain at 12 oclock and output 2 oclock, using a Fender Jazz bass in passive mode, im noticing the clip LED on each channel of the QSC is still coming when playing harder, im not hearing any distortion or anything unpleasant, is this ok ? Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted February 23, 2022 Share Posted February 23, 2022 The clip indicator is probably reacting to the in initial attack. Since it's a power amp, not an instrument amp, the indicator is probably calibrated with the expectation of the signal being compressed. Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted February 23, 2022 Share Posted February 23, 2022 (edited) Double post, tried to delete the second one, I guess this forum software doesn't have a provision for that. Edited February 23, 2022 by Bill Fitzmaurice Quote Link to comment Share on other sites More sharing options...
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