Davi Posted December 1, 2021 Share Posted December 1, 2021 Hi, Im currently using an Ampeg SVPCL preamp into a QSC 1850hd power amp, into 2x8ohm cabs daisy chained single channel with parallel switches engaged on the power amp, ive noticed the output of the Ampeg is very low and is possibly due to a voltage mismatch. What would be a good solution to this problem ? Maybe adding an EQ between the preamp and power amp or perhaps a boost pedal at the end of the pedal chain, im not sure. Any help would be appreciated. Many thanks Quote Link to comment Share on other sites More sharing options...
agedhorse Posted December 1, 2021 Share Posted December 1, 2021 Do you have the level controls all the way up on the power amp? Quote Link to comment Share on other sites More sharing options...
Davi Posted December 1, 2021 Author Share Posted December 1, 2021 Yes and full on the preamp output also Quote Link to comment Share on other sites More sharing options...
la bam Posted December 1, 2021 Share Posted December 1, 2021 I think these are notorious for struggling to drive a power amp I'm afraid. Hopefully someone will know a bit more. Quote Link to comment Share on other sites More sharing options...
Steve Soar Posted December 1, 2021 Share Posted December 1, 2021 Have you tried the pre into separate left and right channels? Quote Link to comment Share on other sites More sharing options...
Davi Posted December 1, 2021 Author Share Posted December 1, 2021 2 hours ago, la bam said: I think these are notorious for struggling to drive a power amp I'm afraid. Hopefully someone will know a bit more. It does seem that way, if it wasnt for the boost from spectracomp compressor on my pedal board it would be completely useless for band rehearsal Quote Link to comment Share on other sites More sharing options...
Davi Posted December 1, 2021 Author Share Posted December 1, 2021 26 minutes ago, Steve Soar said: Have you tried the pre into separate left and right channels? Yes, that brings everything to 8ohms and even less headroom Quote Link to comment Share on other sites More sharing options...
NAS Bass Posted December 1, 2021 Share Posted December 1, 2021 Try a power amp with a lower input sensitivity Quote Link to comment Share on other sites More sharing options...
Davi Posted December 1, 2021 Author Share Posted December 1, 2021 11 minutes ago, NAS Bass said: Try a power amp with a lower input sensitivity Ive got 2 QSC 1850hd Power amps, im considering selling them both and buying something that has the option of changing the input sensitivity from .775 to 1.5v 2 Quote Link to comment Share on other sites More sharing options...
Steve Soar Posted December 1, 2021 Share Posted December 1, 2021 Agreed. Quote Link to comment Share on other sites More sharing options...
agedhorse Posted December 2, 2021 Share Posted December 2, 2021 The preamp output must be -10dBu nominal then. The sensitivity difference between .775V and 1.16V is insignificant in this context. There are several versions of the SVP, it’s very possible that this is common with all SVP models. Quote Link to comment Share on other sites More sharing options...
Bigguy2017 Posted December 2, 2021 Share Posted December 2, 2021 Hmmm.... with the RMX1850 you've got plenty of watts available, so it's a problem at the amp input or amp output. What cabling method are you using? This could be a cabling issue. I'd connect amp ch1 to one 8R cab and amp ch2 to the other 8R cab (the other option is the two cabs paralleled to 4R and connected to the amp in mono bridge mode - this will give max amp power). As to the amp inputs you've got the option of bal XLR, mono jack or screw terminals - as the preamp outs are unbal mono I'd go jack-to-jack to the amp's jack ins with two mono jack cables. If things are still not loud enough it's either the preamp's out is low level (-10dB?) or the power amp (at +3.5dB) is not very sensitive, (and/or speakers are low efficiency). If it is a case of low levels then you need to make up an extra 13.5dB approx - you could use a HPF (Broughton) or compressor (dbx 166xs, Drawmer DL241) between pre and power amps to make up the gain... or it might be cheaper to swap the power amp. Quote Link to comment Share on other sites More sharing options...
Bigguy2017 Posted December 2, 2021 Share Posted December 2, 2021 18 minutes ago, Bigguy2017 said: Hmmm.... with the RMX1850 you've got plenty of watts available, so it's a problem at the amp input or amp output. What cabling method are you using? This could be a cabling issue. I'd connect amp ch1 to one 8R cab and amp ch2 to the other 8R cab (the other option is the two cabs paralleled to 4R and connected to the amp in mono bridge mode - this will give max amp power). As to the amp inputs you've got the option of bal XLR, mono jack or screw terminals - as the preamp outs are unbal mono I'd go jack-to-jack to the amp's jack ins with two mono jack cables. If things are still not loud enough it's either the preamp's out is low level (-10dB?) or the power amp (at +3.5dB) is not very sensitive, (and/or speakers are low efficiency). If it is a case of low levels then you need to make up an extra 13.5dB approx - you could use a HPF (Broughton) or compressor (dbx 166xs, Drawmer DL241) between pre and power amps to make up the gain... or it might be cheaper to swap the power amp. Or use an active unbal to bal converter like the Sonifex RB-UL1, Alice MatchPack or cheapo Art CleanBox to make up the levels (if you fancy some DIY the Sonifex has loads or room to add two jack sockets parallel to the phonos in). Quote Link to comment Share on other sites More sharing options...
bassman7755 Posted December 2, 2021 Share Posted December 2, 2021 7 hours ago, agedhorse said: There are several versions of the SVP, it’s very possible that this is common with all SVP models. I used to run an SVP-PRO into a QSC PLX 1602 and had no problems with levels - plenty of signal level with preamp out put on like 1/3rd volume. Id be tempted to get the preamp checked out for faults. Quote Link to comment Share on other sites More sharing options...
NAS Bass Posted December 2, 2021 Share Posted December 2, 2021 2 minutes ago, bassman7755 said: I used to run an SVP-PRO into a QSC PLX 1602 and had no problems with levels - plenty of signal level with preamp out put on like 1/3rd volume. Id be tempted to get the preamp checked out for faults. In the past I've run quite a few different pre-amps (not an SVP PRO though) into a QSC PLX 2402 without problem Quote Link to comment Share on other sites More sharing options...
Davi Posted December 2, 2021 Author Share Posted December 2, 2021 1 hour ago, Bigguy2017 said: What cabling method are you using? This could be a cabling issue Im using a speakon to jack for the first cab then daisy chaining the next cab speakon to jack to get a 4ohm parallel connection. 1 hour ago, Bigguy2017 said: As to the amp inputs you've got the option of bal XLR, mono jack or screw terminals - as the preamp outs are unbal mono I'd go jack-to-jack to the amp's jack ins with two mono jack cables. The manual also gives the option of balanced jack. Ive been using unbalanced jack, tonight I will try a balanced jack to see if the 20kohm (balanced) to 10kohm (unbalanced) makes much difference. Quote Link to comment Share on other sites More sharing options...
la bam Posted December 2, 2021 Share Posted December 2, 2021 (edited) If it helps - and it may just be my unit - but I tried running my svp pro with a crown xls1500 power amp. Switched it to .775 and it was still way way underpowered. I then tried it with a bass amp, via the send/return, and it worked perfectly. Also worked great going out of the svp and into the input on the bass amp. Edited December 2, 2021 by la bam Quote Link to comment Share on other sites More sharing options...
bassman7755 Posted December 2, 2021 Share Posted December 2, 2021 (edited) 17 minutes ago, la bam said: If it helps - and it may just be my unit - but I tried running my svp pro with a crown xls1500 power amp. Switched it to .775 and it was still way way underpowered. I then tried it with a bass amp, via the send/return, and it worked perfectly. Also worked great going out of the svp and into the input on the bass amp. The effects return is usually more sensitive than the input on a dedicated power amp. Interesting that your SVP pro struggled with the crown amp, maybe these ampeg preamps have some poor quality control or something where the output isnt consistent between units or something. Edited December 2, 2021 by bassman7755 Quote Link to comment Share on other sites More sharing options...
Bigguy2017 Posted December 2, 2021 Share Posted December 2, 2021 39 minutes ago, bassman7755 said: The effects return is usually more sensitive than the input on a dedicated power amp. Interesting that your SVP pro struggled with the crown amp, maybe these ampeg preamps have some poor quality control or something where the output isnt consistent between units or something. Looks like the Ampeg pre output is low level (-10dB or less ? - not stated in the manual) and better suited to FX returns Quote Link to comment Share on other sites More sharing options...
Davi Posted December 2, 2021 Author Share Posted December 2, 2021 6 minutes ago, Bigguy2017 said: Looks like the Ampeg pre output is low level (-10dB or less ? - not stated in the manual) and better suited to FX returns There is very little technical information in the SVP-CL manual, it doesnt mention anything about the output level Quote Link to comment Share on other sites More sharing options...
Davi Posted December 2, 2021 Author Share Posted December 2, 2021 9 hours ago, agedhorse said: The preamp output must be -10dBu nominal then. The sensitivity difference between .775V and 1.16V is insignificant in this context. There are several versions of the SVP, it’s very possible that this is common with all SVP models. Would a boost pedal between the pre and power amp solve the volume issue ? Quote Link to comment Share on other sites More sharing options...
bassman7755 Posted December 2, 2021 Share Posted December 2, 2021 18 minutes ago, Davi said: Would a boost pedal between the pre and power amp solve the volume issue ? If it were me I would go for something like this https://www.amazon.co.uk/Behringer-MX400-Micromix-Noise-Channel/dp/B000KGYAYQ?th=1 Quote Link to comment Share on other sites More sharing options...
Davi Posted December 2, 2021 Author Share Posted December 2, 2021 40 minutes ago, bassman7755 said: If it were me I would go for something like this https://www.amazon.co.uk/Behringer-MX400-Micromix-Noise-Channel/dp/B000KGYAYQ?th=1 Ive got this tube preamplifier that I use at home, im wondering if this would solve the issue 1 Quote Link to comment Share on other sites More sharing options...
Davi Posted December 2, 2021 Author Share Posted December 2, 2021 TUBE ULTRAGAIN MIC100 User Manual 5. Specifications XLR Input Connector balanced/unbalanced Type transformerless, DC-decoupled input Impedance approx. 2 kΩ Max. input level +7 dBu / -20 dB with pad ¼" TRS Input Connector balanced/unbalanced Type transformerless, DC-decoupled input Impedance approx. 1 MΩ Max. input level +16 dBu / -20 dB with pad Audio Outputs Connectors XLR connector + ¼" TRS jack balanced/unbalanced Type transformerless, DC-decoupled output Impedance approx. 700 Ω balanced, approx. 350 Ω unbalanced Max. output level approx. +26 dBu @ 100 kΩ Quote Link to comment Share on other sites More sharing options...
agedhorse Posted December 2, 2021 Share Posted December 2, 2021 Yes, that would work fine. 1 Quote Link to comment Share on other sites More sharing options...
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