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Power supply questions for β24 monoblock build

beta24

Power supply questions for β24 monoblock build

Postby Kernle 32DLL » October 6th, 2018, 5:23 pm

Hi everyone!

After reading for quite some time here, I finally weigh in with some questions. I'm currently building a β22, and in the process sourcing some components for a future γ3 + dual monoblock β24 AB build.

I have some questions in regards to power supply, and I thought it should be worthwhile to ask them here:

Ground:
Looking at the documentation... the input ground doesn't seem to go anywhere (besides binding input minus to input ground for unbalanced input). Where does it apply? From looking at the β24 schematics, it looks like it is supposed to go directly into the board (the molex connector in the middle). I assume the ground pin on the β24 is supposed to bind to the σ22 output ground?

Resistors (both β24 and σ22):
Instead of using the Vishay-Dale resistors I would like to use Xicon MF-RC resistors (thats what I use for my β22 build). I would go with the 1/8W 270-*-RC resistors (excluding R45-R48). For the σ22 I would go with the same resistors, although the part list recommends the 1/4W 271-*-RC resistors (but the part list also says to go with 1/8W... confusion...). Any reason for using the 1/4W 271-*-RC resistors for the σ22s?

The unregulated supply:
The documentation states to go with a "250VA+" transformer per channel. As I am sourcing transformers from Avel Lindberg, I would go with two 250VA transformers in that case. Is that OK, or should I go with two 330VA transformers?

The regulated supply (σ22):
As mentioned above, I'm sourcing transformers from Avel Lindberg - unfortunately they do not have 15VA transformers with 35V+35V. The lowest they go for these secondaries is 160VA, which seems vastly overkill per channel. On the other hand, is there any harm to using such a transformer?

The switching circuit (ε24):
This is a bit tricky in regards to my dual mono build, as each amplifier will have its own isolated case. But unlike as in this build, I would like for both amplifiers to turn on with a single button. So I thought to install a single ε24 in one of the two amps, and duplicate the output signal via cable to the other amp, where it will drive its relay, too. Is there anything to consider if building it this way (e.g. loosing overheating protection)?

Using a separate case for power supply?
In regards to the ε24 question: Option B would be to have a separate case, housing all the power supply related stuff, and run umbilical cables to the amps (in lieu to the β22 reference build). However, I have problems adapting the β24 reference design to such a setup. My main concern is what to do with the ground signal in the β24 case (the power supply case would be bound to AC earth). Should any ground signal bound to the amp case, in that scenario? I assume all the signal connections go straight into the β24, and the same applies for the regulated supply (see first question about ground). Also, unlike the β22 boards, the β24 boards do not seem to have screw-holes which connect with ground. In any case - should anything else adapted when going with this option? I presume, I could leave out the Zobel network. But no harm in leaving it in?

Thanks, and greetings from Germany :)
Kernle 32DLL
 
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Re: Power supply questions for β24 monoblock build

Postby amb » October 7th, 2018, 9:16 am

Kernle 32DLL wrote:Ground:
Looking at the documentation... the input ground doesn't seem to go anywhere (besides binding input minus to input ground for unbalanced input). Where does it apply? From looking at the β24 schematics, it looks like it is supposed to go directly into the board (the molex connector in the middle). I assume the ground pin on the β24 is supposed to bind to the σ22 output ground?

See the power supply diagram in the PDF documentation. They all connect to a common star point.

Resistors (both β24 and σ22):
Instead of using the Vishay-Dale resistors I would like to use Xicon MF-RC resistors (thats what I use for my β22 build). I would go with the 1/8W 270-*-RC resistors (excluding R45-R48). For the σ22 I would go with the same resistors, although the part list recommends the 1/4W 271-*-RC resistors (but the part list also says to go with 1/8W... confusion...). Any reason for using the 1/4W 271-*-RC resistors for the σ22s?

Except for the following, 1/8W metal film resistors are fine for all the rest.

- Metal oxide 2W output resistors (on σ22)
- Caddock resistors (on the β24)
- 22Ω 10W temporary current limiting resistors
- 10Ω 5W ground loop breaker resistors

The unregulated supply:
The documentation states to go with a "250VA+" transformer per channel. As I am sourcing transformers from Avel Lindberg, I would go with two 250VA transformers in that case. Is that OK, or should I go with two 330VA transformers?

250VA per channel is fine. But you can use 330VA if you wish.

The regulated supply (σ22):
As mentioned above, I'm sourcing transformers from Avel Lindberg - unfortunately they do not have 15VA transformers with 35V+35V. The lowest they go for these secondaries is 160VA, which seems vastly overkill per channel. On the other hand, is there any harm to using such a transformer?

160VA is way overkill. You can get a custom-made transformer from SumR (more specifically, from their Primrose Audio division). For both types, I recommend shielded transformers (peripheral magnetic core bands, electro-screen between primary and secondary). Epoxy encapsulation would be a nice touch.

The switching circuit (ε24):
This is a bit tricky in regards to my dual mono build, as each amplifier will have its own isolated case. But unlike as in this build, I would like for both amplifiers to turn on with a single button. So I thought to install a single ε24 in one of the two amps, and duplicate the output signal via cable to the other amp, where it will drive its relay, too. Is there anything to consider if building it this way (e.g. loosing overheating protection)?

You could do that in theory, but the ε24's voltage regulator may not get sufficient cooling if it's asked to drive all those relays at once (including the bleeder resistor relay). The small transformer for the ε24 would also need to be upsized.

Honestly, unless you have a remote control, I don't think turning on/off each amp separately is such a chore compared to one amp. I do that currently in my system because it's bi-amped.

Using a separate case for power supply?
In regards to the ε24 question: Option B would be to have a separate case, housing all the power supply related stuff, and run umbilical cables to the amps (in lieu to the β22 reference build). However, I have problems adapting the β24 reference design to such a setup. My main concern is what to do with the ground signal in the β24 case (the power supply case would be bound to AC earth). Should any ground signal bound to the amp case, in that scenario? I assume all the signal connections go straight into the β24, and the same applies for the regulated supply (see first question about ground). Also, unlike the β22 boards, the β24 boards do not seem to have screw-holes which connect with ground. In any case - should anything else adapted when going with this option? I presume, I could leave out the Zobel network. But no harm in leaving it in?

Since you're building monoblocks, keep them so. The main advantage of monoblocks is complete separation of power and ground, and the ability to place each amp near the left and speaker for shorter speaker cable lengths. Don't make things more complicated than they need to be.

I recommend installing the Zobel network to avoid any problems with ultrasonic instability that might be caused by the particular speaker and cable's impedance characteristics.
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Re: Power supply questions for β24 monoblock build

Postby Kernle 32DLL » October 7th, 2018, 6:40 pm

Thanks for the detailed response!

SumR especially was a good suggestion. I will contact them in the coming weeks.

Regarding ε24 et all - you are right. I will just go with two individual monoblocks, and see how that goes. But now that you mentioned it, I will probably look for a way to have them turn on and off remotely. Maybe I can double-purpose the IR remote for the γ3 or something.
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