HeadWize: DIY Workshop > β22: A discrete, cascoded, fully complementary, pure class A amplifier (part 3)

Message [#381] posted on: 02-18-2009 06:41 AM CST (US).

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Looks ok...

housing

Message [#382] posted on: 02-18-2009 10:07 AM CST (US).

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Hi Ti,

Is the 4P2T paddle switch that you used on the group built balanced β22 for controlling balanced/unbalanced in this one: Mouser#633-M204201E? Thanks in advance for a response.

[Edited by housing on 02-18-2009 at 10:08 AM.]

amb

Message [#383] posted on: 02-18-2009 10:25 AM CST (US).

Joined: Apr. 1, 2004
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[Quoting housing]
Is the 4P2T paddle switch that you used on the group built balanced β22 for controlling balanced/unbalanced in this one: Mouser#633-M204201E?

It's Mouser 108-1M41T1B1M1QE-EVX.

housing

Message [#384] posted on: 02-18-2009 10:32 AM CST (US).

Joined: Dec. 16, 2006
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[Quoting amb]
[Quoting housing]
Is the 4P2T paddle switch that you used on the group built balanced β22 for controlling balanced/unbalanced in this one: Mouser#633-M204201E?

It's Mouser 108-1M41T1B1M1QE-EVX.

Ti, thanks. That saves me a couple of bucks. <big grin>

Message [#385] posted on: 02-18-2009 03:40 PM CST (US).

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I'm thinking about driving a pair of Boston Acoustics VR965's with a three board B22. They're floorstanding 8 Ohn speakers with integrated powered subs but I didn't know if they would meet the threshold for being "efficient" speakers that the B22 could drive without too much trouble. Keep in mind, driving the speakers would only be a rare occurence since I have a seperate intergrated amplifier that would do the work most of the time, but I thought it would be fun to at least compare and do some listening with the B22 on occasion. They're in a small room, only about 15x10 and I wouldn't expect to pump a lot of volume into them.

Any thoughts would be appreciated. Thanks!

amb

Message [#386] posted on: 02-18-2009 04:32 PM CST (US).

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oneplustwo, the main concern is to keep the MOSFETs from overheating (both the power supply and the amp). The β22 and σ22 websites has the information you need, so read it.

Message [#387] posted on: 02-18-2009 05:47 PM CST (US).

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Amb - I did read the website and I understand generally what it says:

"... allows the β22 to drive any headphone load, or light-duty speaker applications. The enclosure housing the β22 should be well ventilated. If higher sustained output currents are required (e.g., when driving speakers at moderately loud volumes continuously, or when using inefficient or 4Ω speakers), then larger, offboard heatsinks should be used."

I guess I'm unclear about how you would quantify "light duty." Would you say that in general, all 8 Ohm speakers at normal volumes would be light duty? Or if there is a threshold for MOSFET/heat sink temperature that shouldn't be exceeded?

I have read a number of folks' experiences saying that driving speakers has worked fine, but haven't seen any guidance on specific parameters that would make it safe vs. unsafe. Maybe that's not a fair question as perhaps it's not black and white. If so, my apologies. Otherwise, any direction would be appreciated.

amb

Message [#388] posted on: 02-18-2009 10:02 PM CST (US).

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oneplustwo, the answer isn't black and white. There are simply too many variables at play. Speaker efficiency and impedance characteristics, room size and acoustics, the listening distance and playback levels, the type of program material being played, all of these are factors. Keep a watchful eye on the MOSFETs' temperatures and don't let them get too hot. Too much heat may cause shortened reliability or outright failure.

Message [#389] posted on: 02-19-2009 10:39 PM CST (US).

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Is there a recommended way to wire up multiple RCA inputs? I believe the pictures I've seen just have them wired in parallel.

Also, if I wanted to wire in multiple headphone jacks, I believe wiring them in parallel would be fine as well. With the understanding that if they're different headphones with different impedences especially, the volume would be different. I assume there aren't significant concerns about not having enough power to drive two pairs of headphones?

Am I missing anything?

[Edited by oneplustwo on 02-19-2009 at 11:15 PM.]

amb

Message [#390] posted on: 02-20-2009 12:28 AM CST (US).

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oneplustwo, for the input, paralleled connections are usually used only for loop-out purposes (so that you could daisy-chain amps together and drive them from a single source). If you want to connect multiple sources, then you need a selector switch.

For the output, you can connect the jacks in parallel, and the amp will drive all connected headphones simultaneously. It's not a problem for the β22 (there is ample power). But as you said, if the headphones are different models/impedance/sensitivity, then they won't all be at the same loudness.

fc911c

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Message [#391] posted on: 02-20-2009 01:03 AM CST (US).

[Quoting amb]
[Quoting fc911c]

Will a ballanced B22 with two S22 ps drive Polk LSi9 speakers ok?

Not only must the power supply be beefed up, you must also run larger heatsinks on the amp and the power supply. All the concerns are described at the β22 and σ22 websites, under "Board & heatsinks".

ok Thanks

If I use the B22 as a preamp with a B24 do I still need to use the larger heat sinks and additional power supplys??

Thanks
Frank

amb

Message [#392] posted on: 02-20-2009 01:10 AM CST (US).

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[Quoting fc911c]
If I use the B22 as a preamp with a B24 do I still need to use the larger heat sinks and additional power supplys??

No, the standard board-mount heatsinks and one σ22 power supply is sufficient. In fact, if it's going to be used only as a preamp, I would configure the σ22 for +/-24V output and set the amp's output quiescent current to 80mA-100mA. This makes the amp run cooler.

Message [#393] posted on: 02-20-2009 01:55 AM CST (US).

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Thanks Amb,

For the input selector switch, do I just need a DPDT switch? Something like this? http://spec.e-switch.com/G-T/G510580.pdf

Also, just out of curiosity, what happens when you do wire the inputs in parallel? If you just leave one source off, does it still work for the source that is on? Can you damage anything? Does sound quality suffer for some reason?

-J

[Edited by oneplustwo on 02-20-2009 at 02:05 AM.]

amb

Message [#394] posted on: 02-20-2009 02:15 AM CST (US).

Joined: Apr. 1, 2004
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[Quoting oneplustwo]
For the input selector switch, do I just need a DPDT switch? Something like this? http://spec.e-switch.com/G-T/G510580.pdf

A DPDT switch is fine if you only want to select between two sources. If you have more, then you need more poles (2 more per source).

[Quote]
Also, just out of curiosity, what happens when you do wire the inputs in parallel? If you just leave one source off, does it still work for the source that is on? Can you damage anything? Does sound quality suffer for some reason?

When the input jacks are all wired in parallel, and you have more than one source connected, then one source will "see" another (even if the power is turned off). The output of any device, be it a source, amp or something else, should never be connected to that of another. At a minimum you may experience degraded signal, or worse, they could "fight" and one or both of them might be damaged.

fc911c

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Message [#395] posted on: 02-20-2009 10:08 AM CST (US).

[Quoting amb]
[Quoting fc911c]
If I use the B22 as a preamp with a B24 do I still need to use the larger heat sinks and additional power supplys??

No, the standard board-mount heatsinks and one σ22 power supply is sufficient. In fact, if it's going to be used only as a preamp, I would configure the σ22 for +/-24V output and set the amp's output quiescent current to 80mA-100mA. This makes the amp run cooler.

Hi
I would like to keep the B22 as is, will this be a problem? Are there any settings that need to be changed in this case?

Thanks
Frank

BTW MO is on the way for my order.

[Edited by fc911c on 02-20-2009 at 10:11 AM.]

amb

Message [#396] posted on: 02-20-2009 03:27 PM CST (US).

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[Quoting fc911c]
I would like to keep the B22 as is, will this be a problem? Are there any settings that need to be changed in this case?

No change is necessary (assuming your β22 is already wired with pre-out jacks). If your β22 is a 4-channel balanced configuration, the pre-out jacks should be 3-pin male XLRs, and don't forget to connect pin 1 to ground. If your β22 is a 3-channel active ground config, then the pre-out RCA jacks' ground should be connected to input ground, not the output of the ground amplifier.

housing

Message [#397] posted on: 02-20-2009 10:30 PM CST (US).

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[Quoting amb]

Note that when switched to unbalanced inputs, the - amps have their inputs grounded, so that they become active ground buffers similar to a 3-channel active-ground amp (except in this case there is a separate ground amp per channel). In this mode, the "balanced" headphones are actually driven with unbalanced signals, only the + terminals of the headphone transducers "see" a varying signal. The - terminal is held to zero volts.

In this configuration, is it only the R+, L+ and G should be connected to the unblanced headphone jack or unbalanced RCA output as the R- and L- signals have been grounded?

amb

Message [#398] posted on: 02-20-2009 10:43 PM CST (US).

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That's correct. For minimum ground contamination, the unbalanced TRS headphone jacks' sleeve contacts should be wired directly to the PSU board's ground, not to the β22 board or the input jacks.

housing