JBL L220 real sensitivity

Long story short, found a pair of L220 locally, had to redo the passive suspension and had the crossover recapped, they will need new veneer to get back to brand new condition which is what I aim at but now I have another concern, I know they are rated 90dbW/m, is that true sensitivity or real world one is lower?They started playing with a KT88 push-pull and I liked it, 45W if not wrong, I got the GAS of solid state and tried an 25W Class A amp but it can't make it, not yet at least, I am waiting to try with a higher output preamp (it's a no gain power amp designed by Mr Pass, the FirstWatt F4), just curious about real life sensitivity as I read of many builders claiming higher than real world sensitivity.Grazie

I don't know what the "real world" sensitivity of the L220s is, but they originally used the LE14A and then the LE14H (alnico and then ferrite version of the same woofer). This woofer is not a particularly sensitive design. It was designed to extend the frequency response over sensitivity so I would expect 89 to 90 dB with 1 watt is pretty accurate.

If your goal is a high sensitivity design to use with low power tube amps, I would consider alternative speakers.


Widget

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Originally Posted by Mr. Widget

I don't know what the "real world" sensitivity of the L220s is, but they originally used the LE14A and then the LE14H (alnico and then ferrite version of the same woofer). This woofer is not a particularly sensitive design. It was designed to extend the frequency response over sensitivity so I would expect 89 to 90 dB with 1 watt is pretty accurate.If your goal is a high sensitivity design to use with low power tube amps, I would consider alternative speakers.Widget

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By the specs they should deliver 90dbW/m, I am wondering as I read on another forum of people who took the duty of measuring modern speakers claiming 95+ db and finding out that real life spl is like 3-4db lower which means half of the perceived pressure, I know this is not the case of the L220 but I am struggling with power, I switched from KT88 tubes to 25W solid state class A and they don't deliver, I am waiting to get a preamp with higher output to pull out the whole juice out of the amplifier but in the meantime I am gonna go back to the tubes to move the white cones

It occurs to me, at least on the similar L222, that the name "Disco" would imply loud. That's gonna require some power. I believe the power rating for these was 200-watts which in JBL speak means double that for headroom. So 400-wpc would not be too much for them. And might be what they really need to perform. Considering the drivers, it should not be far off from the 250ti which are notoriously hungry for power. :dont-know:

An F4 is not going to satisfy those speakers no matter how much voltage your preamp can swing (imo). Now, if you have a balanced pair of them and used them as mono blocks, you'd have 100 watts per channel of class A and would likely be a happy camper unless you like to play music silly loud.

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Originally Posted by rusty jefferson

An F4 is not going to satisfy those speakers no matter how much voltage your preamp can swing (imo). Now, if you have a balanced pair of them and used them as mono blocks, you'd have 100 watts per channel of class A and would likely be a happy camper unless you like to play music silly loud.

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Well, if even the next to come preamp can't give enough of gain (supposedly 28-30db which is 7+ db over my Audio Research SP9) then the idea is to turn the F4 to a mono block and make another one, my only concern would be it has been built as dual mono which would turn into a waste.

Gain and voltage swing are interrelated, particularly with an amp like the F4. The F4 is unique as that it is a buffer. For full power output, it requires a signal voltage swing approximately equal to the F4 rail-to-rail voltage, or 40V peak to peak. This is about 14 volts RMS. A standard CD player line level output is 2 Volts RMS, therefore at a minimum you need a gain of 14V/2V = 7 out of your preamp. This equates to 17dB of gain (dB=20(log(gain)). Having an extra few dB of gain is helpful to deal with line level sources may have an output lower than 2 VRMS, such as from a portable player, tape deck, or phono preamp. If your preamp has a gain of 10, or 20dB, you're at full power on the amplifier unless your source is less than 2 volts. Still, you'll likely need to go the mono block route to get enough watts to listen significantly louder (imo). Using a preamp with 30db of gain will clip the amplifier pretty easily, again, unless your output voltage is significantly less than 2 volts. A pair of F4s delivering 100 watts of class A per channel would be pretty special, but I appreciate the dilemma. :-) As others have stated, JBLs do tend to like amplifiers that will give you more headroom and have lower output impedance than the F4 as well.

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Originally Posted by rusty jefferson

Gain and voltage swing are interrelated, particularly with an amp like the F4. The F4 is unique as that it is a buffer. For full power output, it requires a signal voltage swing approximately equal to the F4 rail-to-rail voltage, or 40V peak to peak. This is about 14 volts RMS. A standard CD player line level output is 2 Volts RMS, therefore at a minimum you need a gain of 14V/2V = 7 out of your preamp. This equates to 17dB of gain (dB=20(log(gain)). Having an extra few dB of gain is helpful to deal with line level sources may have an output lower than 2 VRMS, such as from a portable player, tape deck, or phono preamp. If your preamp has a gain of 10, or 20dB, you're at full power on the amplifier unless your source is less than 2 volts. Still, you'll likely need to go the mono block route to get enough watts to listen significantly louder (imo). Using a preamp with 30db of gain will clip the amplifier pretty easily, again, unless your output voltage is significantly less than 2 volts. A pair of F4s delivering 100 watts of class A per channel would be pretty special, but I appreciate the dilemma. :-) As others have stated, JBLs do tend to like amplifiers that will give you more headroom and have lower output impedance than the F4 as well.

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I kinda understand the point, the preamp is almost fully available components wise, waiting for RCAs and then have to get a potentiometer, case is always here (almost the most expensive part in these builds), now it's about to my guy to put it all together, it is based on the BA-3 front end so it should (...) be F4s best match and, in any case, I am gonna try and have it with twin output so that if things still don't work out with time I can add another F4 and have a powerful mono block setup, I have to try and figure how to bridge the existing one and then if the other one also has to be identical (with dual mono construction) or which route to take but first the preamp and maybe sell my AR SP9

I spoke with a friend last night who has an F4 and mentioned a few weeks ago he was building the BA-3 front end boards, but not for a preamp. He replaced the F4 front end boards with the BA-3 boards, which is apparently a thing, and is very happy with the results. Much better drive. He's not using a preamp now and is driving directly from his dac/preamp with a large improvement in transparency. He's ordered parts to build the mono-block pair though as it still wasn't driving him 90db speakers to the levels he wants.

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Originally Posted by rusty jefferson

I spoke with a friend last night who has an F4 and mentioned a few weeks ago he was building the BA-3 front end boards, but not for a preamp. He replaced the F4 front end boards with the BA-3 boards, which is apparently a thing, and is very happy with the results. Much better drive. He's not using a preamp now and is driving directly from his dac/preamp with a large improvement in transparency. He's ordered parts to build the mono-block pair though as it still wasn't driving him 90db speakers to the levels he wants.

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Hello,I know that's a way many build their F4 like so they can go straight in with a 2V input and get the full potential out of the F4, I underestimated the power hunger of the L220 (and have no intention, to today, to change them for something else even tho, at least here in Italy, I could sell them in the blink of an eye) and since I have almost it all to build the BA-3 based preamp (2x power supply, 2x transformer, BA-3 board, case, input switching board, preamp big caps, mosfets...) the route is to build it and if the output still doesn't make it then another F4 and use them as mono-block in the hope that 50W in Class A would make the big old JBL sound as loud as with the KT88 do right now.

Update about L220 vs FirstWatt F4, I got brave enough to open the F4's lid and measure the bias and, surprise surprise, one channel running at about half of the supposed voltage and the other one at about one third and, unfortunately, if I could raise the better working channel almost to the supposed to be working values the other one won't climb so it is about to partially dismantle and swap some resistors aiming at reaching the correct values and then give it another run with the big white woofers...