Aleph 4 monoblocks with 4 ohm load speakers? - diyAudio
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Old 4th June 2014, 09:51 AM   #1
lotus72 is offline lotus72  Norway
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Default Aleph 4 monoblocks with 4 ohm load speakers?

Hello Pass Labs community. I have a nearly finished Aleph 4 100 watts (48 volts rails) monoblock project which I am reluctant to finish because of my 4 ohm nominal impedance speakers.

I am planning on using the aleph on my speakers from above 120 hz since I have subwoofers which will be tackling the rest of the sub 120 hz area. Anyway it is still a pretty low impedance and I wonder whether this layout without the bass frequencies will make it somewhat easier to manage for the Aleph. It is a D'appolito two way system with two Seas L17 REX/P midbass driver and one Aurum Cantus G2Si circular ribbon tweeter.

I have measured the speakers and the lowest impedance is at 230 hz with 4.1 ohms. It is pretty flat, rising steadily to 9 ohms at just before the crossover frequency at 2600 hz.
Impedance graph is attached.
Any tips and suggestion concerning this is highly appreciated. Real life accounts of similar setups is of course of best value for me. Thanks in advance!

Regards Rick, Oslo Norway
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Old 4th June 2014, 05:35 PM   #2
6L6 is offline 6L6  United States
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An aleph 4 will drive 4ohm speakers with authority, power, and control. There will be no lack of bass or bass control. There is no reason to think that the amplifier will have any difficulty at all. The aleph circuit is almost universally stable into any speaker load.
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Old 6th June 2014, 11:35 AM   #3
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As 6L6 already stated there is no chance of damaging the Aleph and if they are nearly finished then you should definitely proceed. I recently finished a set of Aleph mono's (thread here) and I would recommend you not make a decision on their sound quality with your speakers until they have had at least 50 - 60 hours of operation time. My Aleph's sounded a bit congested in the upper frequencies initially, but the sound opened up considerably after about 50 hours of run time.
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Old 6th June 2014, 11:51 AM   #4
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I run mine into B&W 683's which are a horrendous load with absolutely no problems.
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Old 6th June 2014, 06:42 PM   #5
lotus72 is offline lotus72  Norway
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Thanks for your replys. I have attached a few pics of how it is supposed to look. The main thing missing is the cabinet. Alloy 3 mm top and bottom and 6 mm front plate. I am ordering the alloy plates next week. Can't wait to get these blocks singing!
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Old 7th June 2014, 03:15 AM   #6
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4 ohm depends on how many watts you want and how much bias.

If you have enough supply and heat sinking to support a high bias current,
then it will work great.

Otherwise, think monoblocks.

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Old 7th June 2014, 01:31 PM   #7
lotus72 is offline lotus72  Norway
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Actually it is monoblocks! They are supposed to deliver 100 watts at 8 ohms. I was wrong about the voltage rails. They are 2x 38 volts. The coils are 2x 150 V of which I have two, so 600 volts per channel. Caps are 22x8200 uf 63 volt=180400 uf per channel.

I am not an engineer, but maybe some of you guys can comment on whether this is adequate concerning my speakers? I am planning on building a rather large cabinet with massive heatsinks on each side. The sinks are 400 mm deep and 266 mm high. I will use only aluminium for the rest of the cabinet.
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Old 7th June 2014, 02:55 PM   #8
Zen Mod is offline Zen Mod  Serbia
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good to go

post proper sch. of intended PSU
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Old 8th June 2014, 01:49 PM   #9
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Quote:
Originally Posted by lotus72 View Post
Actually it is monoblocks! They are supposed to deliver 100 watts at 8 ohms. I was wrong about the voltage rails. They are 2x 38 volts. The coils are 2x 150 V of which I have two, so 600 volts per channel. Caps are 22x8200 uf 63 volt=180400 uf per channel.

I am not an engineer, but maybe some of you guys can comment on whether this is adequate concerning my speakers? I am planning on building a rather large cabinet with massive heatsinks on each side. The sinks are 400 mm deep and 266 mm high. I will use only aluminium for the rest of the cabinet.

Are your transformers 2 X 38V or is that the actual DC rail voltage? I know you said that the rails are 38V but your language of "2 X 38" sounds more like the transformers output rating.

If 38V is the actual rail voltage that is a substantially lower rail voltage than the original Aleph 4 so if you bought enough heatsinking for the A4 then you will really be able to turn up the bias in your amplifier. The physical heatsink sizes you are posting don't do much good, do you have the thermal specs of your heatsinks? If you do have the specs then it should be fairly easy to approximate how much bias current you can run with the 38V rails.
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Last edited by Chamberman; 8th June 2014 at 01:52 PM.
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Old 8th June 2014, 04:14 PM   #10
lotus72 is offline lotus72  Norway
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I am refering to the transformers output. I have tried to locate specs for the heatsinks without success. They are called Fischer SK 93 265.9 SA-SL. They were bought back in 2004 from a Norwegian supplyer. If i recall correct they were quite expensive, around 450 US dollars for all 4.
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