"The Wire AMP" Class A/AB Power Amplifier based on the LME49830 with Lateral Mosfets - Page 12 - diyAudio
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Old 22nd September 2011, 06:46 PM   #111
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What power can I make with this and a +-15V 100W transformer per channel? Can this drive four 4 Ohm speakers (2x left 2x right channel)?

Last edited by Earfanatic; 22nd September 2011 at 06:48 PM.
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Old 22nd September 2011, 06:52 PM   #112
opc is offline opc  Canada
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Hi Guys,

I'll update the list later today.

Q&A:

Mr. Pass:

As one would expect, you are absolutely correct, and this could pose a problem for people looking to use the differential input option with a high impedance source.

The tests I ran were performed with a 50 ohm source, but it's not really safe to assume every preamp will have the same luxury.

To get the 130 ohm value are you assuming a 6-10k source driving the positive terminal with a differential signal? If you ground the positive input the input impedance of the - terminal should be 240 ohms, and the differential impedance should be 480 ohms correct?

On solution would be to increase the value of the 240 ohm resistors up to 1200 ohms and increase the feedback R's to 34K. This would of course impact the noise floor, but would provide closer to a 500 ohm input impedance. I can test this and report back.

While I have you here, I held aside a PCB for the NTD1 project I did a while back with the intention of sending it your way. Would you build it if I sent it?

Cheers,
Owen
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Old 22nd September 2011, 06:53 PM   #113
MrSlim is offline MrSlim  Canada
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Quote:
Originally Posted by glt View Post
(Please correct my entry. Thanks!)

2x full kits

I like the Connex SMPS300R (one per channel) because it requires no heat sink. The higher voltage models are an additional cost. If there is enough interest perhaps Connex can do a group buy version for this project?
Connexelectronic
Hmm.. cool idea, I'm thinking of a small desktop amp, I suppose this would do the job for both channels, if I kept it down to 75 -100 watts/ch wouldn't it?
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Old 22nd September 2011, 08:37 PM   #114
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2xfull kits for me please.

cheers, Markus
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Old 22nd September 2011, 09:36 PM   #115
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Quote:
Originally Posted by opc View Post
To get the 130 ohm value are you assuming a 6-10k source driving the positive terminal with a differential signal? If you ground the positive input the input impedance of the - terminal should be 240 ohms, and the differential impedance should be 480 ohms correct?
That's correct, the 130 assumes that the + is being driven opposite
phase.

Have you considered whether the chip will work with higher impedance
values in the networks?

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Old 22nd September 2011, 09:37 PM   #116
opc is offline opc  Canada
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I have a few questions for everyone looking to build the amp. Can everyone try to reply with the answers?

- What load do you plan to drive?
- What power output do you want?
- Do you plan to run differential or SE input?
- Will you build a higher voltage regulated supply for the front end?

I'm going to take these answers and specifically dial in at least two of the most popular configurations in terms of the compensation network. There are general single-pole values that will work for a large variety of power levels, but I can spend a little more time on at least two configurations to develop a two pole comp network.

Regards,
Owen
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Old 22nd September 2011, 09:48 PM   #117
QRikard is offline QRikard  Sweden
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Some more questions:
First how much does those connex supplies cost? Their website seems to be down at the moment.
Will it be a downside using those supplies compared to a toroid and rectifier assuming the front end has a separate supply on linear regulators?
In any case im interested in a GB for supply, i checked my local suppliers and there were no toroids with dual secondaries. I have seen those before but i couldn't find any now for some unknown reason...

Will the mute circuit solve any problems with unbalanced rails when the amp is turned on/off? I don't like the unknown clicks and pops some amps have, relay is one option.

The low impedance in balanced mode doesn't sound good in my ears. Maybe it's a good idea to add a buffer on the input, but that might in turn cause more trouble with supply due to the high voltage and low noise requirement. The cost and complexity is of course also another problem. I'm mainly curious on the available options here.

Is the 3-layer design cheaper than the 4 layer? Because the PCB manufacturers i have found charge the same amount for both 3 and 4 layer boards since the manufacturing process is the same (one layer is just etched away completely). If the price is the same is there a reason for using 3 layers?
I trust your choice but its nice to learn something new.

Finally when is the deadline for the GB? I'm interested in extra PSUs but i would like to check the alternatives first before updating my order (rectifier vs SMPS for example).

@opc
- What load do you plan to drive?
Unknown (need new speakers), but i want an amp that can handle most/all models on average volume without problems. If there is a reasonable GB for power supply im probably in for that.
- What power output do you want?
Unknown, see above.
- Do you plan to run differential or SE input?
I'm aiming for differential but i would like the SE option as well.
- Will you build a higher voltage regulated supply for the front end?
Yes

Thanks for all your time
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Old 22nd September 2011, 10:03 PM   #118
opc is offline opc  Canada
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Mr. Pass,

Quote:
Have you considered whether the chip will work with higher impedance
values in the networks?
I'm not sure if that is a question or a warning...

The app note mentions that you can push the value of Rf up to 47k, which would mean the value of Rin could be pushed up to 1k66 while keeping the same gain. They do mention the THD+N will be "slightly" higher due to higher thermal noise from the increased resistance. I'm not sure what constitutes "slightly" but I suppose it's worth a try.

That would push the input impedance up to a usable level for most sources, although it's still on the low side. I'll measure CMRR while I'm at it and see if there's even a benefit to it at all. If the CMRR is poor, then I might just scrap the differential input option all together.

Regards,
Owen
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Old 22nd September 2011, 10:11 PM   #119
MrSlim is offline MrSlim  Canada
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- What load do you plan to drive?
8 ohms
- What power output do you want?
75-100 watts (Max.. maybe 50-75)
- Do you plan to run differential or SE input?
SE
- Will you build a higher voltage regulated supply for the front end?
Yes
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Old 22nd September 2011, 10:20 PM   #120
rx7mark is offline rx7mark  United States
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I'll take 4 PCB's without parts kit.

Thanks
Mark
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