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A lower powered β24

beta24

Re: A lower powered β24

Postby BesPav » February 28th, 2017, 12:29 am

amb wrote:
BesPav wrote:Sophisticated one can ask for easy A/AB switch...
If case and heatsinks are already huge why not to fully use them time to time?

The whole idea with this variant is to allow a smaller, lighter build... :)


Ti, are you really joking?
In what aspect 4U case with ~40 Wt output power would be a smaller build?
;)

I think it better to be encapsulated in case like this:
https://www.modushop.biz/site/index.php ... uct_id=726
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Re: A lower powered β24

Postby amb » February 28th, 2017, 3:41 am

Where is the joke? As I mentioned in the intro post, this variant allows you to use smaller power transformer(s) and heatsinks. Nowhere did I say that you need a case as big as those for the standard or class A variants. It's up to the builders to decide what case to choose, taking into account the dimensions of all major components.
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Re: A lower powered β24

Postby BesPav » February 28th, 2017, 5:45 am

Nowhere, Ti, of course, but case size are mostly defined by PCB dimensions.

In classic setup PCB's are placed vertically at the side heatsinks, due to this case are limited by 4,5" height (if transistors will be mounted in perpendicular to PCB via L-brackets to heatsinks).
If one will place PCB's at the bottom of the case - than there will be some benefit in case height.
Or we can place PCB between two heatsinks, so the transistors of different sides of PCB would be placed at different heatsinks.


Please, don't take offense, i just want to discuss overall construction of the amplifier case and places for its main components.
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Re: A lower powered β24

Postby jmc » March 1st, 2017, 2:13 am

Hi Ti,

Would it be possible to adapt this version for headphones, like a class A headphone amp/class AB speaker amp?
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A lower powered β24

Postby amb » March 1st, 2017, 3:39 am

jmc wrote:Would it be possible to adapt this version for headphones, like a class A headphone amp/class AB speaker amp?

Yes, but:

1. It's massive overkill. To use an amp that could swing 18Vrms and deliver tens of amperes of current, to drive headphones that only need a couple of volts and some milliamps of current?
2. The β24's input impedance is low (5KΩ to ground on each of the cold and hot pins, or 10KΩ differentially). This is a characteristic of the fully-differential topology used. While that's no problem for most preamps to drive directly, it is too low to insert a volume pot or attenuator there. Typically you'll want the volume pot resistance to be less than 1/10th the input impedance of the following stage. That means using a 500Ω pot, which is too low for many preamps or sources to drive. To solve this problem, you would need to add a buffer stage (such as a α24) between the pot and the β24.
3. A gain of 15 is too much for most headphone amp applications. While reducing the gain is possible, all the compensation capacitor values need to change too.
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Re: A lower powered β24

Postby poseidonsvoice » March 1st, 2017, 11:27 am

Ti,

Whether I want to build the full Class A version or a lower powered version that is Class A for X watts and then Class AB up to 40 watts, I was wondering which boards I should order.

Is it (2) β24 boards, (2) σ22 boards, (1) ε24 board and (1) σ24 board for a stereo differential amplifier? Of course, I will also order the respective semiconductors, JFETS, etc... from your AMB shop.

Thanks,
Anand.
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Re: A lower powered β24

Postby amb » March 1st, 2017, 3:21 pm

poseidonsvoice wrote:Whether I want to build the full Class A version or a lower powered version that is Class A for X watts and then Class AB up to 40 watts, I was wondering which boards I should order.

Is it (2) β24 boards, (2) σ22 boards, (1) ε24 board and (1) σ24 board for a stereo differential amplifier? Of course, I will also order the respective semiconductors, JFETS, etc... from your AMB shop.

- You need two β24 boards for stereo
- You have the option of one or two σ22s (one for both channels, or one for each channel)
- You would use a ε24 if you want to use a momentary pushbutton power switch
- You don't need a σ24
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Re: A lower powered β24

Postby jmc » March 2nd, 2017, 9:05 am

amb wrote:
jmc wrote:Would it be possible to adapt this version for headphones, like a class A headphone amp/class AB speaker amp?

Yes, but:

1. It's massive overkill. To use an amp that could swing 18Vrms and deliver tens of amperes of current, to drive headphones that only need a couple of volts and some milliamps of current?
2. The β24's input impedance is low (5KΩ to ground on each of the cold and hot pins, or 10KΩ differentially). This is a characteristic of the fully-differential topology used. While that's no problem for most preamps to drive directly, it is too low to insert a volume pot or attenuator there. Typically you'll want the volume pot resistance to be less than 1/10th the input impedance of the following stage. That means using a 500Ω pot, which is too low for many preamps or sources to drive. To solve this problem, you would need to add a buffer stage (such as a α24) between the pot and the β24.
3. A gain of 15 is too much for most headphone amp applications. While reducing the gain is possible, all the compensation capacitor values need to change too.


Thanks, Ti. My problem is that I don't have any good speakers nor the space to have them and I have been dying to listen to the Beta 24 for years now :D
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Re: A lower powered β24

Postby amb » March 2nd, 2017, 9:16 am

The β22 would be the appropriate alternative for headphones. It's almost the same circuit, except it isn't fully differential.
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Re: A lower powered β24

Postby K3cT » March 3rd, 2017, 12:43 am

amb wrote:
jmc wrote:Would it be possible to adapt this version for headphones, like a class A headphone amp/class AB speaker amp?

Yes, but:

1. It's massive overkill. To use an amp that could swing 18Vrms and deliver tens of amperes of current, to drive headphones that only need a couple of volts and some milliamps of current?
2. The β24's input impedance is low (5KΩ to ground on each of the cold and hot pins, or 10KΩ differentially). This is a characteristic of the fully-differential topology used. While that's no problem for most preamps to drive directly, it is too low to insert a volume pot or attenuator there. Typically you'll want the volume pot resistance to be less than 1/10th the input impedance of the following stage. That means using a 500Ω pot, which is too low for many preamps or sources to drive. To solve this problem, you would need to add a buffer stage (such as a α24) between the pot and the β24.
3. A gain of 15 is too much for most headphone amp applications. While reducing the gain is possible, all the compensation capacitor values need to change too.


Ah what would DIY be without some overkill here and there? ;)

But I think it's very possible for the γ3 to drive the β24 directly am I right? Assuming for headphone application of course.
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