[tigger]

Hi, I'm a complete newb with DIY electronics. I've got all the tools and some of the parts for my project. The board and other parts are coming from Tangent.
My problem at the moment is finding the values for R3-R6 assuming I'm going with a Jung multiloop configuration.
I am also unsure of required gain. I will be using headphones from Grados - AKG - Senn.
Any help would be much appreciated.

Yes I tried the search function but nothing usefull came up.

 

[JMT]

I would recommend you use Tangent's Electronic Calculator to help determine these values. Another thing I would do is to use DIP sockets in the R3 - R9 strips. That way you can experiment with different resistor configurations and set the gain to your tastes without having to desolder.

 

[tigger]

I already did this but I'm not sure of the results.
For a gain of 5, I get values of 2.55k ohm for R3& R5, and 10.2k ohm for R4 & R6.
I have no way of knowing if this is correct or not before I order parts.

 

[da_burl]

Tig:

You probably need to do what I had to do, print the article on tangentsoft and read it about 10 times!

You have two different loop gains, the inner loop is the two resistors associated with the opamp, R5 and R6. The outer loop is R3 and R4. R3 and R4 set the overall gain. There are two more "restrictions, the outer loop values should be lower than the inner loop values, so R5 should be 5-10 times higher than R3 (I reversed Tangent's wording). And you want a pretty high gain on the inner loop (200 to 400 believe it or not), to limit the bandwidth of the opamp and make it more stable (and there are some posts somewhere that this also substantially decreases distortion).
The gain calculator gives you values for either of the loops, but not both together.

So take a simple example rounding your values to real standard values:

R4 - 10K
R3 - 1K
results in a gain of 11 (this is the standard CMOY configuration)

So now you want R5 5-10 times higher than R3, so:

R5 - 5K (actually 4.99K)

Now to get a gain of 200, you would need R6 to be 1M

On top of all this, you said you have several different sets of cans, generally speaking, you can set a lower overall gain (2 or 3) for Grados, which are 32 ohms, and if your AKG's or Senns are 600 ohm cans, you should probably go with the standard gain of 11. Don't really listen to me on this, I don't have any 600 ohm cans (but I would like some 580's or 600's someday). So you'd better build two!! Sorry about your wallet!
Actually, just do what JMT said, order sets of resistors for both gains, and use sockets on the meta42 board, and see if you can reach a decent compromise, maybe your aforementioned gain of 5 would be okay.

yeah, buy lots of resistors, that's the ticket!!

Good luck

da_burl

 

[tigger]

Thanks for the input. This is a very steep learning curve and Tangent's site is quite a tease, trying to figure all this stuff out. I've ordered 99% of the parts including the pcb and also ordered all the parts to build a Cmoy as well. I have a JMT built Meta 42 so I can always peak inside for guidance.
I'm really excited about this new hobby, even at my age and am looking forward to creating more neat toys!

 

[TommyTheCat]

Da_burl, so you would say a gain of 2-3 would be nice enough for some 225's? Would something like 4-5 be a lot of gain for Grados?

 

[finleyville]

I've found that most people that configure for Grado's tend to set their overall gain between 4 and 7. If you have AKG's or Senn's the gain seems to work better at 10-15.

 

[tangent]

Quote:

I've found that most people that configure for Grado's tend to set their overall gain between 4 and 7. If you have AKG's or Senn's the gain seems to work better at 10-15.

That's way high, finleyville. Sure, it'll work, but I like my volume knob to not be so touchy. I like it to sit at about 3/4 full volume at normal listening volume, so that the channels are well matched and I still have a bit of headroom if I need it for a quiet recording.

For Grados, a gain of 2-3 works pretty well. For most 500 series Senns, 5-6 is plenty. All of this assumes a reasonably strong source. You might have to raise it a bit for a particularly weak source. And if you add crossfeed, you do need to double your gain value from this point. I've built amps with gains as high as about 20, which had crossfeed, had to drive inefficient headphones, and were driven by weak sources. Most of the time, I stay in the 10 neighborhood with crossfeed, or the 5 neighborhood otherwise.

Gain is not free. With too much gain, you're sacrificing adjustability on the pot, you're bringing your noise floor up, and you risk blasting your ears if you accidentally turn the volume knob too far.

 

[finleyville]

Quote:

Gain is not free. With too much gain, you're sacrificing adjustability on the pot, you're bringing your noise floor up, and you risk blasting your ears if you accidentally turn the volume knob too far.

I totally understand and agree with this. It's just that my V1 META has an overall gain set at 13 without any problems. My volume knob is only about 1/2 full volume for a comfortable listening experience. I do not use any crossover circuits and I only use a Sony V6 (for now.) Is this a normal occurance? Or have I done something wrong? Just wondering...

 

[tangent]

That's normal, Finleyville. I'm just saying that I like the volume knob to be a bit farther along at normal listening volumes. Safety, noise level, accuracy, and fine control all play into my reasoning. But, none of that means your amp will fail with a gain that high.

 

[da_burl]

I'm using a gain of 3 with Alessandro MS2's, which are almost exactly Grado SR-325's. It seems to be fine. In fact, it sounds fabulous. Grados are more interested in current than voltage. I suppose I have a pretty strong source, either a Parasound DAC, or an MAudio sound card. I "think" the DAC can get close to 4V, but I haven't actually measured it. No PDCP's, although my D25S sounds okay with it too. Haven't tried anything else but 2, and I had other problems there, so didn't really get a chance to compare. Tangent is the one who originally told me 2-3, and I believe him! Thanks again.