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Monitor/keyboard powered speaker
Monitor/keyboard powered speaker
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Old 16th May 2019, 11:11 PM   #1
Vintage Audio Projec is offline Vintage Audio Projec
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Default Monitor/keyboard powered speaker

So as I play some keyboard it would be nice to have some kind of portable "powered" speaker So I could just go to a store and buy some plastic crap or.... I could build something myself.

I was also reading some threads about the Fane sovereign 12-250tc full range speakers that didn't sound bad.

So I was thinking of putting 2 of those in a small monitor and have a small "stereo" keyboard amplifier. Maybe i'll add a few universal inputs (I was thinking of adding 2 stereo inputs balanced/unbalanced RCA and 1 microphone input) Then I'll also wanted to add a linking option so it can be used for lots of things when needed. So far no problem.

I was also thinking of adding a highpass around 50Hz or something to use the power for something the speakers can play. SUB east power and I think around 50-60Hz is the lowest they will go.

So plain simple no dsp etc...

Then the next part is a good power amplifier to use. I still like class A/B for the mid & hi freuency's. It just sounds "better" all the times when I compared with class D. So I can think of creating a new amplifier design but why not use something that has been around and tested.....

So does anyone of you have an idea of power amplifier board/module to use for this. The speakers can have 250w continous but I like to have some headroom for transients so was thinking around 400w @ 8ohm (burst). They only have them at 8ohm so The power amp will have to deliver some voltage to get 400w @ 8ohm.

My personal choice of output transistors would be something of the Sanken MT200 packages. Profusion still has some of them.

I looked around for something but getting to 400w @ 8ohm is not that easy to find. There was a time when there was the LME49810 or LME49811 but they are already disontinued.... (WTF!!!???) Looking further I've also found the leach amplifier interesting. The double barelled super leach looks interesting as the output transistors get less voltage so it's easier for the SOA. What would be the maximum power supply rails to use when using this double barelled circuit? Leach SuperAmp Plans in the artical they say 93v per rail. Would be nice to have a little bit more Using 12 transistors 2sa1295/2sc3264 in the double barelled output circuit this could be very potent I think.

Antek has some 800VA 75v toroids. No load will be a little bit over 100v This will sag under load ofcoarse. If it could stay at 100v this will be around 600w of power. I think in reality 500w is possible

Anyone experience with this super leach amp circuit?
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Old 17th May 2019, 12:42 AM   #2
indianajo is offline indianajo  United States
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Dang, 2 x 400 w in two portable speakers? Honey Piazza makes do with a Peavey KB300 which has 3 inputs allows her to turn herself up & down in the mix without a sound man. She plays 100 person audiences outdoors with her husband Rod the harmonica man, a bass & a drummer. Saw them on KET Jubilee. Used KB300s with problems around here go for about $200.

+-93 v is rediculous for something portable. My PV-1.3k is +-85 v, 400 w/ch@8 ohms rms, weighs 55 lb, rack size & 8.5" tall. Has 5 pairs per channel MJ15024/25 TO3 output transistors, 8" fan. That is a lot of weight to carry around to get class AB. You'd do better with a PV1200 or PV2000 which have switcher supplies and weigh less. If you're going to stuff the amp in the speaker you're going to need a powerful noisy fan running all the time. If the amp is separate the fan can be under the stage or off to the side.

Not looking up the leach super amp. Probably no protection against the 1/4 phone plug to the speaker shorting out. No VI limter, no turn on thump elimator, no DDT to keep hour voice coils from melting if your source sound is square waves.

Lots of blown self powered speakers on the local craigslist. Class D and a cheapo power supply sells a lot of speakers, some repeat buys since the old one blew up right before an imporatant booked gig.

I find it cheaper to buy blown up stuff and rebuild. I've built a LM1875 and it motorboated due I think to point to point wiring. Etched 2 sided boards are required for IC amps IMHO. Warning the PV-1.3k cost $55 plus about $150 to rebuild but there were 124 blown parts. The PV-4C cost $20 e-bay and took about 7 parts & $55. The CS-800s cost $100 and worked when I got it but needed about $40 in new capacitors for full wattage plus the blown $.01 sacrificial input resistors. Watch shipping on e-bay, I only buy junk amps 100 miles away or closer. Prices above included shipping.

Blown mixer amps have the board inside, but as an IC amp probably are limited to 100 w/ch 8 ohm.
My next gig setup will be a mono 75 w mixer amp MMA-875T for my voice + keyboard, ($46 e-bay, two bad solder joints) plus a single PV1210 speaker. Built in low cut plus low high tone controls. I'm not that into stereo on keyboard, unless you are doing leslie speaker sims. Which is a whole other pedal or laptop+audacity plus 50 lb speaker to carry around.

antek 75 v toroids will supply +-105 at a total VA of 800. The tranformers in dead Peavey's are cheaper, sag is precalculated in the RMS output watts, come with a heat sink, fan, case, connectors, hum elimination wrapper & steel cage, pots blah blah. Reason I like peaveys, free schematics plus lots of help on PA forum & here. Crown probably okay but pricey around here, and QSC are hard to understand.

Happy shopping & building. I start this kind of stuff in the winter, not the spring outdoor festival season.
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Last edited by indianajo; 17th May 2019 at 01:07 AM.
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Old 17th May 2019, 05:25 AM   #3
Vintage Audio Projec is offline Vintage Audio Projec
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my experience with the most of those portable speaker/amplifiers is that they don't keep up.

On stage we use at least 500w for a passive monitor. it's not continous but gives you headroom for transients. Even when you use some gentle compression. A vocal eats power when they really start singing. +/-93 v is high but i'm not going full out on the power supply so the supply will collapse and the high power is only for transient peaks.

Many PA amps today are designed with this in mind and for music it is quite logical. I did a test once using a qsc pl6 amplifier and an averaging power meter. When playing music until the clip leds just started to sometimes flash we measured an average power of around 150w. The amp is rated 1300w and can really deliver this continous if needed. But on just normal music the continous average power was only 150w. This is the reason most speakers don't burn up.

Another option is to use a limiter and limit all the peaks but it sounds constraint..... I was also planning to add a sort of limiter Likewise the fane 12-250TC is rated at 250w continous. 500w program and 1000 peak. So if the amps can do 500w (burst) I think the speaker is used to it's full extend.
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Old 19th May 2019, 08:03 AM   #4
Vintage Audio Projec is offline Vintage Audio Projec
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Looking at the super leach amp it looks like it is possible to make it class G So for most of the time only the inner transistors do the work. And on peaks (burst) the outer will help. Operation stays almost the same but dissipation goes down a lot and there is still a lot of headroom.
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Old 22nd May 2019, 12:59 AM   #5
indianajo is offline indianajo  United States
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I've resurrected two amp dogs from the hand solder era (nineties) where the operators made beautiful looking solder joints that only worked sometimes, like the day it passed final inspection. And a organ I purchased, the internal/external speaker switch had no solder on it at all! You think you are better than pro operators that solder all day with a certified iron? Go for it. I know I'm not that good. I'm just persistant enough to find the failures in these dogs and make them bark to my tune.
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