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Old 26th December 2009, 09:29 PM   #31
n_maher is offline n_maher  United States
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Thanks glt, I'd seen that post and was looking for confirmation that the caps could stay without penalty. I may remove them, since it would allow for much lower profile stacking of the boards.

Also, what's the output impedance of this amp? I'm curious given the inductor and resistor that are in series with the output.
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Old 27th December 2009, 01:43 PM   #32
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Quote:
Originally Posted by n_maher View Post
Thanks glt, I'd seen that post and was looking for confirmation that the caps could stay without penalty. I may remove them, since it would allow for much lower profile stacking of the boards.

Also, what's the output impedance of this amp? I'm curious given the inductor and resistor that are in series with the output.
The output impedance of the Ventus at Audio frequencies is virtually the same as the DCR of the inductor. Which is something less than .05R (I don't have the datasheet open). At frequencies where the inductor impedance begins to rise the parallel resistor will dictate the output impedance. This would be in the Mhz frequency range.

The output inductor is actually optional. I added as a safety measure against capacitive cables. It will keep the amplifier very stable. If you find you don't need it you can simply use a jumper there instead.

Cheers!
Russ
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Old 29th December 2009, 01:50 PM   #33
n_maher is offline n_maher  United States
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Russ,

Thanks for the output impedance explanation, I'd measured the resistance across the inductor/resistor assembly and found it to essentially be 0 but just wanted to make sure I wasn't missing something.

If you get a chance could you bounce back to page 3 and have a look at a couple of the questions I asked there? Specifically I'm curious about implementing a pseudo gain switch and also how best to approach offering both SE and balanced inputs.

Thanks in advance.

Nate
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Old 9th January 2010, 12:21 AM   #34
glt is offline glt  United States
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Default A couple of questions before I start building the kit

1- L1 and R1 are both optional? I can connect the output directly to a headphone such as HD580?

2- With balanced input, I can DC couple the output of OPUS?. In fact, no dc blocking caps all the way to the headphone?

3- To nulll the offset: What to do with the inputs when nulling the output

Thanks!
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Old 9th January 2010, 10:57 PM   #35
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Quote:
Originally Posted by glt View Post
1- L1 and R1 are both optional? I can connect the output directly to a headphone such as HD580?

2- With balanced input, I can DC couple the output of OPUS?. In fact, no dc blocking caps all the way to the headphone?

3- To nulll the offset: What to do with the inputs when nulling the output

Thanks!
1) Yes, but you will need to short one of them

2) Yes.

3) The best is to connect them to your source. Or short the inputs to GND.

Cheers!
Russ
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Old 11th January 2010, 02:06 PM   #36
n_maher is offline n_maher  United States
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2) For non-inverting use: Reduce R2 to 221R and make R4 47K (this will set the input impedance). Connect -IN to GND. Then adjust R5 and R3 set the gain. Gain = 1+(R5/R3). For unity gain simply omit R3. For example. Using R5 of 1K and R3 of 1K would get you a voltage gain of 2, which is 6db.
Russ,

Could you please clarify how to configure the amp for unity gain? Do you completely omit (do not populate) R3 for unity gain or should you jumper this position? I'm assuming it's the former and not the latter.

Any progress on the manual?
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Old 11th January 2010, 08:42 PM   #37
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Hint: Gain = 1+(R5/R3), as Russ has answered already.

What is the result of the equation if R3 becomes infinite (R3 → ∞) ?
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Old 11th January 2010, 08:46 PM   #38
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If you short R3 (0-ohm), the Ventus will throw a DIVIDE_BY_ZERO exception
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Old 11th January 2010, 08:48 PM   #39
n_maher is offline n_maher  United States
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If you short R3 (0-ohm), the Ventus will throw a DIVIDE_BY_ZERO exception
Thanks Brian, that's what I figured but I'd always rather err on the side of caution and double check before applying power.
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Old 26th January 2010, 02:11 AM   #40
n_maher is offline n_maher  United States
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Well the Placid BP is up and running checks fine. Any advice, hints, tips, etc. before I think about applying power to the Ventus boards for the first time?
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