There are lots of amps on ebay which run from 12V.
There are lots of circuits about for in car audio.
What do you want??
You could run a lot of bridged amps, active crossovers and separate amps for woofer/tweeter/mid range.
I guess you could wind another circuit on the toroid and build something conventional?
There are lots of circuits about for in car audio.
What do you want??
You could run a lot of bridged amps, active crossovers and separate amps for woofer/tweeter/mid range.
I guess you could wind another circuit on the toroid and build something conventional?
300VA 12Vac means a secondary current of 25A
I would expect the secondary winding to be ~ 8sqmm to 5sqmm for that current.
That needs 3.2mm diameter to 2.5mm diameter.
Your secondary will not be a single wire that big.
It will be bi-fillar, or tri-fillar, or maybe even quad-fillar.
You can open up the internal connections to end up with multiple 12Vac windings.
Find out what you actually have and then ask the question again.
I would expect the secondary winding to be ~ 8sqmm to 5sqmm for that current.
That needs 3.2mm diameter to 2.5mm diameter.
Your secondary will not be a single wire that big.
It will be bi-fillar, or tri-fillar, or maybe even quad-fillar.
You can open up the internal connections to end up with multiple 12Vac windings.
Find out what you actually have and then ask the question again.
It would be not for car but home use.
I was thinking p.e. to a gainclone (but I don't know if voltage is enough in this case) or something similar easy to build , and it's not necessary to use all amps out of the transformer...
AndrewT, do you mean I should open up the transformer to get it into a dual supply? Maybe I didn't understand well...bur the transformer has only two output wiring (it's not tapped one). Anyway yes, the secondary is quite thick, quad filar.
I was thinking p.e. to a gainclone (but I don't know if voltage is enough in this case) or something similar easy to build , and it's not necessary to use all amps out of the transformer...
AndrewT, do you mean I should open up the transformer to get it into a dual supply? Maybe I didn't understand well...bur the transformer has only two output wiring (it's not tapped one). Anyway yes, the secondary is quite thick, quad filar.
Um… wait. I get the voltage doubler idea. Its problems are related mostly to large ripple. But with enough capacitance its not as much of a problem.
One needs to derate the +36 side tho' for VF forward voltage. Nominally these days at 1.2+ volts per ordinary stock diode/rectifier, its not insignificant. Also you've only got "charging pulses" 60-a-second (at 60 Hz) per capacitor, not 120-per sec for full-wave bridge rectifiers. Exacerbates ripple, this.
Likewise, each amplifier really doesn't have the ability to have output voltage excursions to either rail. Usually 1.5 to 2.0 volts less than rail. For both rails. Some amp designs get closer, but distortion becomes significant.
So…
VAC = 12.6 VRMS nominal
1.414 × 12.6 = 17.8 VPEAK
17.8 - 1.2 VF = 16.6 VRECT
2 × 16.6 = 33 VDOUB
0 + 2 = 2 VMIN
33 - 2 = 31 VMAX
31 - 2 = 29 VOUT output range
E²/R = 29² ÷ 8 = 105 WPEAK output
105 / ( 1.414² ) = 53 WRMS nominal output
Independently driving "bi-amping" or "tri-amping" one's speaker's individual cones would allow 2 or 3 times that wattage per speaker. Having left and right speakers again doubles output.
So one might reasonably concoct a stereo tri-amped setup that outputs 6 × 53 = 300 nominal output watts, RMS. In practice quite a bit less. Maybe 200.
But hey … 200 … 300 … makes little difference if the cones are individually 'amped'. Sweet system actually, even if the bass would be the most constraining part of the setup. I suppose you could do 4 Ω for them, which again changes the power-spread.
The main limiter is the 300 VA transformer. its only 300 VA. Probably can do 500 VA on big peaks, but not very often. And if the power supply is needing to supply that kind of wattage, 10,000 μF capacitors are wildly insufficient. The droop would be significant and 60 Hz intermodulation distortion would be a beast.
Probably having a series of 22,00 0 μF caps in parallel with 0.033 Ω resistors "in series" as a ripple reduction setup would probably be better.
At 10 amps RMS coming out of the power supply, 3 × 0.033 = 0.10 Ω. I²R = 10² A × 0.1 Ω = 100 × .1 = 10 watts.
So, gotta use 5 watt resistors, each.
GoatGuy
nigelwright₇₅₅₇;5219471 said:
I replied after your comment. But a darn good way to use a modest output power supply is to tri-amp your speakers and (in stereo) use 6 amps. They're cheaper'n dirt these days. Also, the LF-pass, LF-HF bandpass and HF-pass tri-amp filters are also pretty easy to build. They also allow tuning of the cut-pass frequencies and overlap. Hard to do right with passive speaker LCR networks.
Moreover, the "clipping" problem is quite a bit mitigated by channeling the power where needed. I myself use 4 Ω - 8 Ω - 16 Ω LF, MID, HF speakers just like how motorcycles always have smaller rear brake disks and larger front ones to "mechanically" (impedance) match our ear's band sensitivities to the output of the amplifiers. Bass: 2 8 Ω cones in parallel. Mid: 1 8 Ω cone. Treble: 2 8 Ω cones in series.
Just saying. There might be "simple" setups that don't use the resource (300 VA transformer) very adequately - hence (and I agree) your advice of just selling it (or maybe just buying another one, and put in series!).
BUT this site is DIYAudio. We're into all things audio, not least of which is technologically interesting, pleasing and high accuracy audio. Y'know?
GoatGuy
I have always preferred the simpler approach.
One power amp (stereo mixed to mono) and full range speakers (no crossover) . A lot less to go wrong. It worked reliably on a mobile disco for 40 years, never had any complaints.
On my first amp build it worked off +/- 25volts DC.
I was absolutely horrified at how little volume I got out of it before the transients clipped. Since then I have always designed and built much higher voltage power rail amps.
Its maybe not such a problem these days with modern highly compressed music.
Thanks for the reply. My own experience echoes yours, exactly. I was “horrified” at how little output I got with an 8 Ω speaker on a ± 25 volt supply. But in a recent build, I decide to "just try" the tri-amped approach, as I outlined above. Still a ±25 VDC supply; a simple D-class amp for each of the "three" speakers per channel. They're only $9/ea from Mouser. What can I say! Cheap. The result went from “horrified” to “wow! ridiculous! amazing!!!”.
I guess what changed was 4× the potential power and the power confined to particular frequency bands. The only clipping I encountered was near max-theoretical output, and even that was essentially confined to the bass. 4 Ω ( 8 Ω || 8 Ω ), getting about 100 W/channel in the 25 Hz to 350 Hz band. With program compression (which you allude to), even the bass clipping was quite well controlled.
My total output power? 100 WPC bass, 50 WPC mid, 25 WPC treble. 350 total watts. And it is easily reaching 250 “nominal watts” without clipping at all.
Pretty simple! But definitely a new update on an old idea.
GoatGuy
PS: my "tri-pass" filter arrangement? Simple RCRC filters on the inputs of the Class-D amplifiers. Nothing special. Calculate the 2nd order response on a Old Man basic calculator and a pad of paper. Butterworth, baby. Butterworth. Works too! I only used D-class chip-amps; I don't think I spent more than $20 in passive components all in. Oh, maybe $30 or $40 when you include the rectifiers and big capacitors for the power supply.
Cheap, but good.
And so efficient that NO HEAT SINK needed! Gotta like that, old friend. That's worth the learning curve of dealing with Class D.
GoatGuy
Cheap, but good.
And so efficient that NO HEAT SINK needed! Gotta like that, old friend. That's worth the learning curve of dealing with Class D.
GoatGuy
Good idea the voltage doubler, it would add some Volts useful to my circuit...but also I could consider to put hand to the transformer for secondary rewiring (it seems to me faisible with some care).
To reply to Nigelwright, I had the same idea and the transformer is altready to auction on ebay .
Last edited:
OK, so each secondary lead is made out of four wires. Split them all and you'll get four 12V AC secondaries. Then connect them, two by two, in series and you'll get 2 x 24V AC which will give you about +/- 32V DC rectified and that's good for many nice amps. Take care about secondaries phasing.
If you still don't understand what to do, build this:
Boostor, an ideal companion for a Circlophone on the move
Member
Joined 2009
Paid Member
I understand the procedure, unfortunely each secondary has four stiff wires welded together. I must necessarely open up the transformer to see how they are linked and maybe separate them. It seems to me a little tricky
Attachments
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.