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Old 26th December 2008, 07:33 PM   #41
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Lightbulb Soft start circuit – update

I decided little bit change philosophy of my soft start circuit and replace fixed suppress resistor by thermistor (I have two because removed them from connection between GND and earth. Reason is that after voltage grow up around 9 volt on both power supply DC rails Aleph starts work and consume large current (given current source on output stage – class A topology). It cause permanent voltage drop on suppress resistor and disable fully charge big capacitors (6.5 ohm suppress resistor enable capacitors charge proximately to half of full DC voltage all time). When soft start period finish relay bypass suppress resistor and directly connect power supply with halfway charged capacitors to mains. It for sure cause to activate switch off breakers on the wall.
Thermistor instead fixed resistor offers elegant solution. Thermistor handle power supply soft start. Relay bypass thermistor after proximately 40 seconds and thermistor can cool down – be prepared for next soft start sequence. Additionally thermistor will not generate any heat during normal amplifier operation (there is enough heat from power stage).
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Old 6th January 2009, 01:15 PM   #42
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Lightbulb Aleph tweaking - cables, current source

Yesterday I read very helpful thread: “Top ten ways to a better Aleph?” Top ten ways to a better Aleph?

Today I assembled tantalum capacitor across zenner diode in current source and made bi-wiring cables/connection between Aleph and speakers. I again listened several CDs: Michael Jackson – History, Baraca soundtrack, Air – Pocket Symphony, Enigma... Because I like house, drum&bass music didn't mist Pendulum – In Silico, Kosheen...
Previously I wrote that my Aleph don't like complicated music – electronic music. It is not true anymore!!! After mentioned changes sound is more detailed, more space, faster=more air, bass is more clean and sound dynamics is better.

Next possibility for tweaking is rectifier....
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Old 11th January 2009, 09:25 AM   #43
elac310 is offline elac310  France
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I'm not sure tantalum capacitors are the best choice; as far as I know, this type is largely considered to be the worst in any type of decent audio equipment; if I'm not mistaken, the caps accross the zener should have a small value anyway (some have recommended 10uF, others prefer max 1uF to limit the "bump" when switching on/off); such values are available as reasonably small film type caps (MKP, MKT), which are much faster and would thus be even more effective. I'm just a hobbyist, so you may want confirmation from a more experienced DIYer.
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Old 11th January 2009, 04:10 PM   #44
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Default Soft start circuit v.0.3 - final version (finished and working)

Hi all

Today I replaced soft start board components from previous version PCB to new one. It's working perfect... thermistor bypassed by relay after few seconds. Here areschematics and picture of completed board:

http://www.facebook.com/photo.php?pi...&id=1386409150

http://www.facebook.com/photo.php?pi...&id=1386409150


Elac310
Thank you for your advice. I agree with you that tantalum capacitor is not good situated for this purpose. I'm going to order Panasonic bipolar capacitors and some WIMAs for my Aleph...

I like this amplifier. It's working perfectly and has good sound.
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Old 11th January 2009, 04:17 PM   #45
Gyuri is offline Gyuri  Hungary
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Very beautiful, clear work, congratulate!

Gyuri

Once, possibly then I...
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Those who would have deserved the life they are all dead already. "Oh, my dead dears!" - Captain Cat
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Old 13th January 2009, 07:30 AM   #46
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Default Recitfier - which diode?

Rectifier diodes – which one?
Today I started look for some fast diodes with soft recovery characteristics for my Aleph. After some simulations on PSU Designer II (found on duncanamps.com) I know that:
- Initial charging current peak (with applied soft start) reach up to 46A over rectifier diodes
- Capacitors are charged by 19A pulses (peak)
- Power supply output current not exceed more than 6A
Simulation parameters:
Mains 50 Hz; Secondary winding (nominal output)= 37.5V , 7.5A; rectifier BR1 BRIDGE25; single cap. 96mF 5mOhm; Rz=10Ohm
On market are available several diode models and I’m unable to decide.
1. 60EPU04 – very robust, but maybe too fat (it’s my favorite, trikve.sk offers diode for 4.60EUR)
2. RURG8060 – very robust, but maybe too fat, high drop voltage=3.2V max.
3. MUR3020WT – I’m afraid that this diode unable handle initial current peak (few pulses) during charging capacitors.
What do you think, recommend…do you know any better models?
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Old 13th January 2009, 04:07 PM   #47
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Default Nice work

Hello Thomas

I have just being admiring you amplifier on all the nice pictures,
nice work. :-)
I my selv have being working on the same project, Aleph 4 for about 2 years.
It is playing but i haven' made my powersupply god enough, so I have some humm in my speakers, but it is still playing nice and with good sound.
but maybe I can get some good idears from your project :-)

Best regards John
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Old 14th January 2009, 08:29 AM   #48
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Smile Hello John

Thank you… I also spend about 2 years to build this Aleph and lot of money. I should say that it is most expensive construction/project which I ever build. If you want to have good playing Aleph you can’t make compromises.
I don’t have any issues with noise caused by any part of amplifier. I followed few basic rules to achieve good working amplifier:
- Be very hardworking, patient, more patient, even more patient, think twice before you something cut, build…
- Good/proper amplifier parts landscape = put transformers and 230V cables far from audio parts; use nature shielding by chassis and enclosure
- Power supply design and components = Input RFI filter; I used shielded toroid transformers; filtration cap front off each rectifier; high quality electrolytic capacitors BHC Aerovox ALS31 (one of the most expensive part in power supply 8 pieces cost around 335 EUR); Fat cables, terminals, capacitors hard-wiring by Cu plates; No ground loops (given by PCB design and properly wired circuits)!!!
- Passive cooling, tons and tons of aluminum (another very expensive part of amplifier
- Fat gold plated speakers terminals
- Good cables on audio path – I mean connection between input RCA and XLS terminals to Aleph PCBs
Additionally I removed connection between earth coming from wall terminal to enclosure and ground from secondary site of power supply (make it clear: enclosure is still connected to earth coming from wall). I decided to cancel earth and ground connection over thermistor because it caused lot of noise to my speakers.
Currently I’m tweaking my Aleph for better sound. I’m going to replace some capacitors in audio path and little bit redesign rectifiers.
If I can somehow help you with your Aleph…feel free ask me I share my knowledge maximum as it possible.

Have a nice day and good luck.
Tomas
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Old 14th January 2009, 08:36 AM   #49
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I forgot mention that also important use good resistors, capacitors, match input MOSFETS, match output MOSFETS. Very good idea is read this thread: Top ten ways to a better Aleph?

Tomas
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Old 17th January 2009, 06:41 PM   #50
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Question Rectifier diodes - which one?

I was looking around on Internet, read some articles...and made decision to use Schottky diodes and use rectifier for each power supply rail. I have two favorites diode models:

IXYS DSA70C100HB DIODE, SCHOTTKY, TO-247AD, 2x35A, 100V 2.53 EUR
IXYS DSSK 60-015A DIODE, SCHOTTKY, TO-247AD, 2X30A, 150V 3.63 EUR

I found some useful information here:
http://sjostromaudio.com/joomla/inde...1&limitstart=7

and here:
http://www.ixys.com/pdf/SelectorGuide.pdf
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