[wuaffiliate]

Quote:

Originally Posted by Tedro /img/forum/go_quote.gif Sorry, Camera phone picture:

Badass i love how that looks, i'm definitely going to make my first desktop amp with plexi.

 

[IPodPJ]

Ti, on my 4-ch B22 build I am using a gain of 5 which gives an effective gain of 10 per channel, correct? I'm thinking it might be too much. With the HD800 @ 300 ohms and a 4.8V out from my source, the amp will put out 3W (or was it 6W, I don't remember what Steve said). The headphones only handle 1/2W. However, because I'm using a current output DAC, we are implementing the passive I/V resistors in the amp chassis. They will have a dipswitch so I can select from 3 different resistor values, giving me either 1.2V, 2.4V, or 4.8V. With 1.2V, the amp will give the HD800 480mW, and at 2.4V it will yield 2W I think.

So the question is should I leave the gain where it is? It seems to be the most common setting for the balanced Beta22. Or should I do away with the lower I/V resistor values and lower the gain? I'd like to be able to drive more demanding (less sensitive) headphones if the need arises, and I may not always be using the current output DAC. However the HD800 are my one and only headphone now and I have no intention of changing them anytime soon. My system is built around them.

Thanks.

 

[amb]

Gain of 5 is good. Maybe 8.

 

[IPodPJ]

Don't you think 8 would be too much? And does the gain of 5 yield a gain of 10 per channel? Or are you saying we should do 2.5 per board, if that's even possible?

 

[ShinyFalcon]

At 300 and 62 ohms, 5x is probably fine.

I'm seeing stacked film capacitors in some PSU's, and have been wondering what makes them special. In the σ11/σ22's case, they are C14/C14 & C15 respectively and are used as compensation caps for Q14. In the LCDPS, they're used before the rectifier bridge.

 

[amb]

Sorry IpodPJ, I was answering pila405's question and our posts crossed. He asked about using a γ2 with β22. Since γ2 is an unbalanced source with 1.4Vrms output at 0dBFS, an unbalanced β22 with gain 5 or 8 is good for HD800.

As for your amp, what source are you planning on using it with and what's its output level at 0dBFS (balanced)?

 

[IPodPJ]

Quote:

Originally Posted by amb /img/forum/go_quote.gif Sorry IpodPJ, I was answering pila405's question and our posts crossed. He asked about using a γ2 with β22. Since γ2 is an unbalanced source with 1.4Vrms output at 0dBFS, an unbalanced β22 with gain 5 or 8 is good for HD800. As for your amp, what source are you planning on using it with and what's its output level at 0dBFS (balanced)?

I apologize too. I got some of my numbers mixed up. The source is the Reference One or Reference Seven and it has an output of 5V via XLR, but I am not using the XLR outputs. We are implementing our own passive I/V conversion without the 0db buffer (which we have tested in a cable and it sounds great). The current output of the DAC (4.8mA, 2.4mA from hot to ground, 2.4mA from cold to ground) will run into a circuit inside the amp with a choice of 3 I/V resistor values that will yield 1.2V (600Ohm, 300Ohm per + and -), 2.4V (1.2kOhm, 600Ohm per + and -) and 4.8V (2.4kOhm, 1.2kOhm per + and -). With the current gain setting of 5 per board, 1.2V in will output 480mW to a 300 ohm headphone.

The volume would be maxed out to get full power. I guess this is ideal for the headphones, but shouldn't there be some headroom in there? And I'd rather have less gain with a higher resistor value than more gain with a lower resistor value. The less noise the better.

The boards have already been assembled with a gain of 5. But if they had to be changed they could be.

 

[amb]

Well, I guess you'll just have to give it a try to see.

 

[IPodPJ]

Quote:

Originally Posted by amb /img/forum/go_quote.gif Well, I guess you'll just have to give it a try to see.

Well, sure, that's ideal but the problem would be shipping back a 30+ pound chassis for modification.

Not cheap.

But I'm still wanting to know if a gain of 5 on a 4-ch means you'll be getting a gain of 10 per channel.

 

[johnwmclean]

IPodPJ, I’m using a balanced Buffalo at 4V output, my balanced β22 is set to a gain of 2 (effective 4). For the HD800 this is perfect for me, most of my listening is around the 11.00 - 12.00 o’clock position on my DACT, my lowest output recording would be around 2.30 - 3.00 o’clock. I’m a fairly loud listener btw, and I’ve have never run out of steam when it come’s to volume hope that helps somewhat.

 

[IPodPJ]

Hi John. Yes, that is very helpful. Thank you. Is it possible to do a gain of 3?

 

[ShinyFalcon]

Yes, following the convention (R4 / R3) + 1 for the left and right channels. As for stability on gain 3x, I don't know.

 

[NumLock]

So I would like to try to build one for myself. So all I need is the B22 and S22 kits + cases + connectors(headphones/rca/xlr)? Is that it? Sounds fairly easy. I work in a electronics lab so I have all the tools. I could even custom design and order PCB here but AMB has all the PCB needed right?

 

[oneplustwo]

that's about it... you can go to glassjaraudio.com and it's even easier! Jeff can be busy sometimes so it might not be quick... but his kits do make it super convenient.

you need to think about some things like how many channels, what size trafos, (gain), and things like that too.

 

[IPodPJ]

I can't change the gain. I forgot about one major discrepancy. We are adding a 4th input and it will be single ended, and will work with the balanced outputs. If I use a 2V source with a gain of 2 it won't be nearly enough. Looks like 5 is it.