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Old 2nd October 2011, 04:55 PM   #1
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Default active 3-way system... one a single PCB!

Since ages, I wanted to design a good active 3-way system, with ALL parts on a single board. Just connect transformer, three drivers and the input signal and GO

Now, it's finished. I didn't want to go the chips-amp way, so I used three discrete power amps. Combined with Linkwitz-Riley 12dB/octave filters and a thermal protection.

To be exactly, this is all on that single board:
A: one power supply consisting of 2X 10,000F/40V electrolytics (charged to 2X 37 Volts) to power the two power amps for mid and high,
B: one power supply consisting of 2X 10,000F/63V electrolytics (charged to 2X 60V) to power the bass-amp,
C: two discrete power amps, using fast transistors throughout the design, 2SA1303 / 2SC3284 as output devices,
D: one discrete power amplifier using fast and rugged components throughout, 2X 2SA2151A / 2X 2SC6011A as output devices,
E: a 3-way active crossover, Linkwitz / Riley, second order, using the latest opamps by National Semiconductor
F: parallel stabilization for the opamps
G: thermal shutdown using a relay in the input

This all got crammed on a PCB measuring just 100 X 184mm. This PCB is mounted flat on a heatsink measuring 150 X 200mm.

First measurements using an Audio Precision system one showed perfect behavior of the filters and amplifiers. Level of the mid and high amps can easily be adjusted by turning a pot on the PCB. Idle-current of all amps can be adjusted using 12-turn pots. That's easy!

A transformer of 2X 25V and 2X 15V is needed for this, power around 300 Watts minimum.

First impression: with just 2X 25V transformer on ALL amplifiers (put a bridge in the connector instead of the 15V windings) sound was extremely powerful, accurate and LOUD, LOUD!! Did I already mention it was LOUD?! Even bass-consuming music like Gigi D'agostino came out like someone was hammering my head every time

Now it is a success, I'll just HAVE to have me some of those double sided PCBs made in a more professional quality than the one I made myself for the prototype!!

I plan to combine it with three pairs of loudspeakers:

1. the Visaton VIB extra II that I made years ago, with a Dynaudio D76-AF in it,

2. a new project using a vintage 12" Philips woofer, and a 2" dome midrange by Philips, combined with a DT-300 tweeter by Monacor,

3. another new project using a Seas alu-woofer, midrange TBA, and some kind of Ribbon tweeter.

And HERE the question to you all comes: does anybody have good experiences with a cetain make and type of ribbon tweeter? I'm new to these, but I heard some in Adam loudspeakers... and all I thought was <WWHHOOOWW!!!>

Thanks in advance,

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Old 2nd October 2011, 06:04 PM   #2
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Congratulations on getting a good result with your prototype. Just one comment though, have you considered what will happen if the mains voltage goes 10% high? You would have higher voltages on the power supply caps than they are rated for.

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Old 2nd October 2011, 06:20 PM   #3
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I calculated all for a mains voltage of 240 Volts, even then the voltages on all electrolytics remain UNDER their rated values...
Normally, we have 230 Volts and in Europe, this is fairly stable. I never, ever measured 240 Volts here.

In addition, I used QUALITY capacitors, no Chinese rubbish for me

I once tried how much a Philips 10,000F/100V capacitor could handle: I had to go OVER 110 Volts just to have a current flow of 1mA... so there is some room over the specs. Of course, I never recommend this, but a 40V rated Philips capacitor will not die when it has 41V on it for a day or so.

But, you certainly have a point in regions where mains voltages do vary wildly...

Thanks for the hint,

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Old 21st June 2013, 08:10 AM   #4
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Location: Amsterdam
Originally Posted by 325addict View Post
Now it is a success, I'll just HAVE to have me some of those double sided PCBs made in a more professional quality than the one I made myself for the prototype!!
beetje laat, bijna 2 jaar verder, maar ben wel benieuwd of je hier nog verder mee gekomen bent ?

oops, sorry, english it is

bit late, almost two years later, but was wondering if you made any progress ?
where solid state amplification is like photography, tubes are for painting. sometimes the best solution is to paint over a photograph.
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