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Old 18th April 2006, 11:44 AM   #101
Tyimo is online now Tyimo  Hungary
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Default SEWA V1 is singing

Hi Mad!

The Easter Rabbit brought me a new amp! The SEWA V1! :-))

I finished the amp yesterday and now I am in the burn in process, but the sound after 2 hours is already super!

I build the amp fast with "recycled" parts what I had at home, but I think soon I will build a qualty case for the amp .

Tech specs:
PSU:300VA 2x24 V torroid, 100.000uF/ channel, RC filtering, 6W12R thermistor.

Circuit: IRFP 044 for Q1 and IRFP240 for Q2. Yageo resistors, nothing special. 2 amp bias with 30V.

Case: 43x30x5 cm, 5mm aluminium plate. around 10 kg.

Sound: excellent!!Now I am in trouble to say which is my favorite amp. :-) Maybe the Zenlite has a bit more sentiments, but your SEWA V1 is really a good amp. I use my BOZ for preamp.
Strong-detailed-controlled bass, super dynamics, warm but not muddy sound, and very-very good sound stage.
Tha amp worked flawless from the first turn on. Totaly deadly quiet on idle. I can't here any "hisss" sound even from 1 cm from the woofer!!! No turn on thump or anyproblem.

Thanks Mad that you posted and shared your design!

Next week I will try to make a big test with my amps: ZEN, Ballanced 25W ZEN, ZenLite, Aleph5, Hiraga Le Monster, JLH1969, Gaincard, SEWA V1 and a ZV4 (from a friend)

I would like to ask you: is it possible to make a SEWA with Aleph CS?

I will post some pics, but sorry for the bad quality.

Greets and thanks again!

Tyimo
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Old 18th April 2006, 11:47 AM   #102
Tyimo is online now Tyimo  Hungary
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Inside or it is better to say under the amp. :-))
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Old 18th April 2006, 04:28 PM   #103
Mad_K is offline Mad_K  Norway
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Looks really cool Tyimo (better make that HOT)! Nice work! I especially like your chassis design! Looks like you used the pcb layout I provided? The sound you are describing is very similar to my experience
However, it looks to me that you have nowhere enough cooling. Do you have cut-outs for the MOSFETS so they have direct (but electrically isolated) contact with the heatsink? Also, by laying the heatsink down flat you loose the convection effect and may have reduced it's effect by 50%. Have you measured the temperature on the mosfet body? (shouldn't be much above 100'C) From the picture I would say that your heatsink arrangement would suffice for 25W/ch, and you are pumping out 60W/ch!
It seems your chassis building skills are up to it, so I would consider starting with that quality case sooner rather than later.
Yes, it is possible to make a SEWA Rev.1 with Aleph CS. But if you can take the heat, a CCS as designed sounds better

Keep up the good work! I'm looking forward to the report from your big test. Are all those amps yours?
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Old 18th April 2006, 05:41 PM   #104
Tyimo is online now Tyimo  Hungary
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Hi Mad!

Thanks for the praise!!! If I would have had more time and money I would have had built the amp in better quality...., but the first important was the sound! I like it more and more.
I think an amp is good, if the listener want to play the music again and again. I listened Patricia Barber's CD 2 times one after the other...

Quote:
Looks like you used the pcb layout I provided
Yes! I liked very much your PCB design. Clear and elegant.
Next time I would redraw the R12-16 bias network to only one cearmic power resistor. We had a listening test with 2 Hiraga amp, one with metalfilm and splited resistors and one with ceramic power resistor. The last one was better to our ears. I would like to try it with your SEWA too.

Quote:
However, it looks to me that you have nowhere enough cooling
You will not believe, but the heatsink is more than enough for the amp! Basicaly the whole case is a heatsink! I like to build this way my cases, because the 400x300x5mm alu plate and the 50x50x2.5mm L profile alus conduct the heat very easy away. The whole amp is ca. 45-50 C, but tomorrow I will measure the mosfets body temperature.

Quote:
Do you have cut-outs for the MOSFETS so they have direct (but electrically isolated) contact with the heatsink?
No. Usually I fix the Fets direct to the 5mm alu plate which conduct the heat to the Heatsinks too. I use silicon grease between the Fets and alu plate and heatsinks.

Quote:
Are all those amps yours?
Yes! Except the ZV4. It is my friends.

I hope I can finish My new Hybrid preamp next weekend and I can report you about the result!
What is your preamp for the SEWA V1?

Thanks and greets:

Tyimo
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Old 18th April 2006, 05:54 PM   #105
Mad_K is offline Mad_K  Norway
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Good! I was a little worried about the heat... I use my Passlabs X2 Rev.1 clone for preamp, but BOZ or BZLS should be equally good
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Old 20th April 2006, 12:13 PM   #106
Tyimo is online now Tyimo  Hungary
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Hi Mad!

I have to write you again!
After couple of hours of burning in, the amp's sound getting better and better. I know it is very hard to explain how is a sound of an amp, but I think the most important what I have to say about your design is that:

The presence feeling is unbelievable strong!!!

The 3D stage reproduction is fascinating. You had true when you wrote :I can honestly say that it really lets me "Live The Music".


I have 2 questions:

-Can you tell me how can I calculate the output power of my amp?

-I observed a strange phenomenon: after 1/2 hour of warm up I can hear a low noise coming from the tweeters. It is not a "humm", but something like with 50 hZ flutter. Like in a Switch type PSU.
It is make me nervous, because the amp was totaly quiet even from 1 cm, but now I can here this noise from 20 cm! :-)
But seriously, where could I look for the problem?

Thanks and greets:

Tyimo
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Old 27th April 2006, 05:43 PM   #107
Tyimo is online now Tyimo  Hungary
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Mads! Are you out there?!?

Thanks for God, the strange noise is gone! It was only that one day when I observed.

Can you tell me how can I calculate the output power of your amp?


Greets:

Tyimo
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Old 27th April 2006, 06:16 PM   #108
Mad_K is offline Mad_K  Norway
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Glad you like it About that noise; I have no ideaa. Mine has been running for months, and I have never experienced anything other than sweet music...

The basic formula for power is Prms=Urms*Irms
rewritten utilizing ohm's law:
Prms=(Urms*Urms)/R
Prms=Irms*Irms*R.
R=speaker impedance.
Irms is 0,707*Ipeak (or Upeak). Maximum Ipeak is your bias current. Figure Maximum Upeak (0,5*V+)-2V.

Example: V+=30V. Bias 2A. 8ohm speaker.

Upeak=(0,5*30)-2=13V
Ipeak=2A
Urms=13*0,707=9,2Vrms
Irms=2*0,707=1,414Arms

To know if you are voltage limited or current limited into any given load, you can just calculate with both voltage and current. The lowest Wattage number is the correct one.

Prms(U)=(9,2*9,2)/8=10,6Wrms
Prms(I)=1,414*1,414*8=16Wrms

For a 8ohm load, the amp is voltage limited to 10W.

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Old 28th April 2006, 04:46 AM   #109
Tyimo is online now Tyimo  Hungary
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Thanks for the formula Mad!!!

Soon I will report you about the "monster" listening tests! :-))

Don't you want to modificate your PCB that it could hold a 6800uF or even 10.000 uF output caps?

Greets:

Tyimo
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Old 28th April 2006, 05:57 AM   #110
Mad_K is offline Mad_K  Norway
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You're welcome 4700uF is the largest size of Elna RJH from my supplier, but I've also tried 22000uF Evox Rifa PEH200 (chassis mounted) with good results (when bypassed with a PHE426). My recommendation if you want/need large outputcaps; mount them on the chassis
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