Randy, TungstenAudio, many thanks for your help.
I am - again - overwhelmed by the helpfulness of this community
I am - again - overwhelmed by the helpfulness of this community
Just checking in with my progress to keep Randy happy with the 2 month stipulation on these giveaway boards.! 😉
Found a good UK manufacturer of heatsinks at an affordable price. I got 300x160x40 and quite heavy fins etc. Let's see if they are adequate.
Planning on a capmx psu but only if I have the voltage headroom.
Found a good UK manufacturer of heatsinks at an affordable price. I got 300x160x40 and quite heavy fins etc. Let's see if they are adequate.
Planning on a capmx psu but only if I have the voltage headroom.
I'm following the capmx thread Fran but haven't read it today so I'll catch up soon in there.
GD Rectifiers in Sussex. These 2 cost me just under £70. They have a 400mm section but is nearly twice the price due to support and demand.
Also one that is 160mm tall but putting the vanes in the 'wrong' plane. I considered these with a fan at the back end , making somewhat of a fan heater, but decided to try a conventional alignment first.
GD Rectifiers in Sussex. These 2 cost me just under £70. They have a 400mm section but is nearly twice the price due to support and demand.
Also one that is 160mm tall but putting the vanes in the 'wrong' plane. I considered these with a fan at the back end , making somewhat of a fan heater, but decided to try a conventional alignment first.
Good stuff.
You can always make it as a "stand upright" model. That's what I'm doing with the aleph 60.
You can always make it as a "stand upright" model. That's what I'm doing with the aleph 60.
Thats a cool looking thing!
Guys can I lose 2v with a CRC? I've got another big old transformer here. But it's a little on the hot side and into my Capmx psu and on a 12ohm load u have about 26v. If i went thru a CRC with maybe more R than C I wondered if I can get to 24V??!
With my capmx and the 12r load I have just under 1mv of AC ripple.
Guys can I lose 2v with a CRC? I've got another big old transformer here. But it's a little on the hot side and into my Capmx psu and on a 12ohm load u have about 26v. If i went thru a CRC with maybe more R than C I wondered if I can get to 24V??!
With my capmx and the 12r load I have just under 1mv of AC ripple.
Run 26v. That’s a-ok. I’m running mine at 26 or 27 (and was running those) using 20+20 donuts that I had in hand. You’ll be just fine.
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Thanks Randy. The dissipation thru the main heatsinks is a consideration as they are on the marginal side for now. With what I have I'm either at 18v or 26! The one that gives me 26 has 4 x outputs so I can use 4 x bridge rectifiers into 2 x separate Capmx psus....one per channel.
I just ran a 4225 Antek on my quasi/scope using a fixed 15R and a pot that was next to my scope set at 20R. Both work fine with primary side set up for 120 or 240.
My parts arrived last week. Yesterday I finished the boards. For testing purposes I will use the enclosure of my M2x and it's power supply.
I hooked everything up and switched it on using a dim bulb tester. Everything went fine from the first try, no smoke! 🙏 I was able to set DC offset voltage zu less then 10mV. After that I had to lower the IQ from 2.5A to 2.1A . I did not start with the AC Current gain setting yet. I also did not have the time to hook up speakers.
The 2x18V 400VA toroid is somewhat weak, the rail voltages are down to 21.5 V with a IQ of ~2.1A er rail. I will order a more beefy toroidal transformer.
I hooked everything up and switched it on using a dim bulb tester. Everything went fine from the first try, no smoke! 🙏 I was able to set DC offset voltage zu less then 10mV. After that I had to lower the IQ from 2.5A to 2.1A . I did not start with the AC Current gain setting yet. I also did not have the time to hook up speakers.
The 2x18V 400VA toroid is somewhat weak, the rail voltages are down to 21.5 V with a IQ of ~2.1A er rail. I will order a more beefy toroidal transformer.
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One aspect of power supply construction that does not get a lot of discussion on these forums is the type of rectifiers used. Normally, one would expect to see a rail voltage of +/– 22.5V from a sufficient size transformer with 18Vac secondaries. 400VA should be enough, even with a higher bias current of ~ 2A. When I see a report of low rail voltage in this situation, I suspect the bridge rectifiers are part of the issue.
The most commonly used monolithic rectifiers are the GPBC35xx series, which are not efficient at converting AC to DC. Their combined voltage drop, relative to 1.4 x Vac, is typically about 3.5V. There are other rectifiers that do a better job.
The easiest thing to try would be swapping in a pair of VS-26MB-40A bridge rectifiers. I have seen a 1V gain in rail voltage from this substitution. For an amp with higher bias current, such as the example above, one could also try the VBE 60-06A, which may have even lower forward voltage drop in this application. The VBE part is in a larger SOT-227 package, but is still easy to use.
The most efficient rectifiers are the newer synchronous rectification circuits based on the LT4320-1 Ideal Diode Bridge Controller. These have worked very well for me recently, including my VFET amp and recent re-build of my M2x. I actually got +/– 25Vdc rails in my M2x from the Triad 160VA, 18Vac transformers.
These are all less expensive to try than buying a new power transformer.
The most commonly used monolithic rectifiers are the GPBC35xx series, which are not efficient at converting AC to DC. Their combined voltage drop, relative to 1.4 x Vac, is typically about 3.5V. There are other rectifiers that do a better job.
The easiest thing to try would be swapping in a pair of VS-26MB-40A bridge rectifiers. I have seen a 1V gain in rail voltage from this substitution. For an amp with higher bias current, such as the example above, one could also try the VBE 60-06A, which may have even lower forward voltage drop in this application. The VBE part is in a larger SOT-227 package, but is still easy to use.
The most efficient rectifiers are the newer synchronous rectification circuits based on the LT4320-1 Ideal Diode Bridge Controller. These have worked very well for me recently, including my VFET amp and recent re-build of my M2x. I actually got +/– 25Vdc rails in my M2x from the Triad 160VA, 18Vac transformers.
These are all less expensive to try than buying a new power transformer.
@TungstenAudio thanks for your reply 🙂 Yes I indeed use the GPBC35xx bridges, I don't know the exact model number. I will definitely try your suggestions.
The transformer is made by toroidy.pl, it is potted and it used to run very warm in my M2x build. I wanted to switch to a non-potted version for better thermals (and less used space). I also wanted to use a 2x 19V or 2x20V to reach a DC Voltage of 25V - 26.5V.
But I will try different bridge rectifiers first.
The transformer is made by toroidy.pl, it is potted and it used to run very warm in my M2x build. I wanted to switch to a non-potted version for better thermals (and less used space). I also wanted to use a 2x 19V or 2x20V to reach a DC Voltage of 25V - 26.5V.
But I will try different bridge rectifiers first.
The cheapskate in me suggests that before you spend the money on more parts, try to fire it up with your existing donut and bridges. Will that extra volt or 2 make a huge difference?
Thanks Randy, I already fired the amp up. I am getting 21.5V DC with my 2x18VAC Transformer. But after using the Aleph power calculation spreadsheet I am aiming for 26V / 2.2A per channel. I will probably install the Aleph in a 5U / 400 Modushop Deluxe enclosure, but not any time soon because of the costs..
Here’s a newly born Aleph 60 mono in deluxe 4U chassis with Antek as-4225 and 400va donut cover. I need to finish making the other channel. It sings nicely on the test speaker. It is also very quiet on my test speaker and headphone hum tester. The real test will be on horns. I need to get covers on and let it cook for a long time.
Does anyone know of nice hole plugs to fill in the other side of the rear plate? I would like some black plastic plugs to close up the extra input and speaker terminal holes.
Does anyone know of nice hole plugs to fill in the other side of the rear plate? I would like some black plastic plugs to close up the extra input and speaker terminal holes.
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