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Old 5th December 2008, 09:52 AM   #181
col is offline col  Australia
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tsnell, makesure you join the 41hz.com forums and study all the postings relating to the amp9-basic. Especially the soldering of the diodes by V-bro. The AI isn't that good and you need to complement it with info from the forum.

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Old 5th December 2008, 10:03 AM   #182
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O, btw, the reason I recommend a 100-150 ohm series resistor is that it cut off that first lower frequency bumb of the piezo and only leaves the one at around 5-8KHz. Remember piezos are capacitive loads so a series resistor is a 6 dB/octave highpass filter while a series capacitor acts as an attunator (lowers sensitivity).

When used with the P.Audio drivers it's extremely important to cut that first lower frequency bumb because the woofers actually produce sound very well up to about 4-5 KHz at which point it drops off sharply so you don't want your tweeter to produce any sound under about 4 KHz.

And I might say that it's also primarily for this reason piezo tweeters get a bad rep. Use a 100-150 ohm series resistor on the piezos and use a suitable matching woofer that produce sound to about 4-5 KHz and any piezo tweeter will sound acceptable, high quality piezos will even sound quite good.
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Old 8th December 2008, 12:49 AM   #183
tsnell is offline tsnell  Australia
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Thanks for the tip col, Iíve just signed up. Thereís a whole bunch of good info on there. One thing Iím looking for though is a clear description of how to hook up a 3.5mm headphone jack to the inputs of the Amp 9 Basic. Iíve had a search but havenít seen anything there yet. Do you (or anybody) know of a thread or details somewhere? I am using it for stereo use so will probably connect inputs 1&2 together and to left channel and inputs 3&4 together and to the right channel.

I have been pricing batteries/solar panels etc. To keep costs low and to keep flexibility/simplicity I will make the system 12V. If I find that the amp needs a bit more grunt I will add a 12V to 24V step-up DC-DC converter like the car laptop power supply ones discussed on the 41Hz forum.

As for hooking up the speakers, if I am using 8 tweeters in total as suggested by anomalous then should my wiring look like this?
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File Type: jpg output wiring.jpg (47.0 KB, 1073 views)
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Old 8th December 2008, 02:10 AM   #184
tsnell is offline tsnell  Australia
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Sorry, CAD ate a few decimal points there (they would be some big coils!). Supposed to read 0.22mH
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Old 8th December 2008, 02:41 AM   #185
col is offline col  Australia
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looks good to me. Didn't you say you have 4 of the P-audio 10" 4ohm drivers though? Are you only going to use 2 of them?

Don't understand your problem with wiring the 3.5mm jack/socket. It would be the same as wiring RCAs? Once you get your amp9-basic AI there is a circuit diagram that will tell you which pins are positive and which ones are negative.

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Old 8th December 2008, 03:08 AM   #186
tsnell is offline tsnell  Australia
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Hey col, yeah I figured hooking up the headphone jack would be very common and pretty straight forward but I just hadnít seen a diagram or anywhere showing it yet. Iím sure it will all become very clear once I have the amp 9 in hand.

I will be using all 4 P audio drivers and all 8 Pyle piezos. There will be a pair of woofers in each bass reflex enclosure wired as per the above diagram. The two woofers in one enclosure (left channel) will be hooked to output 1 and the other 2 woofers (right channel) to output 3.
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Old 8th December 2008, 04:24 AM   #187
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you only need one resistor for the tweeters.

so for one channel (two sides, two tweeters per side)

---------------[res]-----------o +
| | | |
P P P P
| | | |
--------------------------------o -


heres some pics to show you what i meant about cutting and joining a pair of piezos


Click the image to open in full size.


Click the image to open in full size.

a bit messy - but it was a rough cut job with a hand saw just to show you what i meant - normally i use a proper table saw and sled.

150 ohm is much too high for the series resistor.

My understanding is this:

the series resistor does not form a high pass filter - it in fact is a low pass (high pass filters require the cap in series and the resistor in parallel with the load - this is the other way round)

It is a low pass filter designed to prevent high frequency oscillations (100kHz or so) in the amp. the psn 1167's have a capacitance of around .12uF, and the manufacturer recommends a series resistance of 30ohms - this results in a lowpass filter with a corner freq of around 44kHz.

for 4 of these in parallel, the resistor should be about 8 ohms to maintain the same corner freq, and certainly no more than 15 ohms. 150 ohms, with 4 piezos in parallel, gives a low-pass corner freq of about 2.2kHz - definately not what you want.

the series res should be a 10W non-inductive type.

cheers,

ben

ps: the piezos went into the mail today
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Old 8th December 2008, 04:58 AM   #188
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tsnell, if you are using 2 x P-audio 10" per channel it's best to wire them in parallel so that the amp9 sees them as a 2ohm load, especially if you are going to be powering them from 12v. Adjust your low pass accordingly. 3khz, 6db will be nearer 0.10 mH.

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Old 8th December 2008, 05:07 AM   #189
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tsnell, just had another look at your wiring diagram. It's wrong, wire the drivers in parallel and then put the choke before them, using one only of the right value (0.10mH). For the piezos do as Ben suggested.

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Old 8th December 2008, 11:58 AM   #190
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I'm sure the advice given by col and anormalous above is well intended but it's certainly not how I would do it. And I can't guarentee my design will work as intended if it's followed.

In fact I will almost guarentee that you will not have sufficient cooling to the amp9 if you parallel the woofers to 2 ohms and use a 24 volt supply at a later time.

With an amp9 I recommend using each of the outputs to drive one set of speakers, where we define a set of speaker as a woofer and any form of tweeter.

I recommend that with piezo you do not filter the woofers and that you parallel connect the piezos to the woofer with a series resistor. With one piezo between 100 and 150 Ohms and with 2 piezos half that for 47 or 68 Ohms standard values. These resistors need only be 1 Watt types but I recommend the carbon 3 Watt types I use.

I strongly recommend that if you do decide to use piezo that you have plenty of excess wire and that you "face" the woofer terminal plates to face the tweeter cut-outs so that if you want to upgrade to a real tweeter at a later date you can dismount the piezos and fish out the wires to woofer, cut the wire and insert a real x-over filter. I just glued the filter component directly to the tweeter horm but note that the proximity to the magnet will affect the inductor so you need to get a multimeter that can measure inductor values to get it completely accurate.
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