[ttnl]

Hi, please help me with an optimal configuration for M^3 amp. My source will be Ipod (maybe better source later), and my headphones include Senn Hd600, Grado SR225 and Ety ER4ps.

1. Please recommend me an optimal gain setting for this amp (at least for use with Hd600 and Sr225).
2. Is the default bass good enough to skip the bass boost feature (I am not a bass-head)?
3. What opamps should I go with?
4. What Voltage setting for the Sigma PSU is optimal?

If you can, please answer all the questions, because those are issues I still confuse. Thanks so much for your help

 

[Fungi]

1. 2 is fine for pretty much everything in my experience; however some opamps are unstable at under 5 (like the OPA637)
2. Indeed, unless you want more bass out of your Etys or something.
3. AD8610, OPA637/627, AD843, AD825 are commonly recommended.
4. Check out the Power Supply section here

 

[Shahrose]

Quote:

Originally Posted by Fungi /img/forum/go_quote.gif 1. 2 is fine for pretty much everything in my experience; however some opamps are unstable at under 5 (like the OPA637) 2. Indeed, unless you want more bass out of your Etys or something. 3. AD8610, OPA637/627, AD843, AD825 are commonly recommended. 4. Check out the Power Supply section here

I disagree about the gain. I think it'd be good to have a gain of 5 minimum and preferably around 8-11 for the HD600s. As for the opamps, go for the OPA637/627 if you want a smooth, warm sound and the AD8610 if you want a colder, brighter sound (and less soundstage). A 24V setting on the M^3 will be more than enough btw. Also, forget the bass-boost if you're not a basshead, it'll be a waste of money.

 

[onesandzeros]

Quote:

Originally Posted by Shahrose /img/forum/go_quote.gif around 8-11 for the HD600s.

I finished my M3 about a week ago. With a gain of 7, and HD580s, I rarely get the volume knob past 10 o'clock on classical guitar recordings. With rock cds, never past 9. I used OPA637s, so I couldn't go too low, but based on my experience so far, a gain of 5 would be plenty.

 

[Fungi]

I have a gain switch for 2/5, and I couldn't imagine not having 2 for IEMs. 5 is plenty for everything, unless you have a really really quiet source or something.

 

[LostOne.TR]

I found 8 to be too high also. (going with the idea that my 15k resistor with attenuation from crossfeed arrives at around 8).

Not sure if I ever hit 12 o'clock even with k240 sextetts at that setting.
My audio technicas barely had any play on the volume knob, they just kind of hovered between the sounding more or less matched for volume and clearly being unmatched. Earbuds (the more efficient ones) were clearly in the volume mismatch area unless I went a bit louder than I'd like to have.

I'm not sure about a good minimum for gain yet, plan to play around with that to find out.

 

[ericj]

Quote:

Originally Posted by Fungi /img/forum/go_quote.gif I have a gain switch for 2/5, and I couldn't imagine not having 2 for IEMs. 5 is plenty for everything, unless you have a really really quiet source or something.

or you have something that's actually hard to drive.

 

[Fungi]

Quote:

Originally Posted by ericj /img/forum/go_quote.gif or you have something that's actually hard to drive.

Even on my K240DF I only had to go from 6 o'clock to 9, so I'm figuring you'd need something like a K1000 or really hungry orthos for higher gain, and if you have those you should know the kind of gain you need for those beasts

 

[Beefy]

Why not implement the bass boost pot as a variable gain control? That is what I did on my build; 5k in each of R3 and R4 with a 50k Alps pot, leave out Cbb, giving gain from 2-12 and no bass boost. You can shunt the pot out of the circuit if you don't use it (as I have done), keeping the gain at 2.

Despite popular opinion, I didn't find that OPAMP choice was especially critical in this amp. I tried AD8610 and OPA627, which are 'supposed' to be like night and day, and the differences were minimal at best.

27V is a good voltage for an S11. It will take the lower voltage AD*** OPAMPS, but still have plenty of swing even when used with OPA***.

 

[tintin47]

Quote:

Originally Posted by ericj /img/forum/go_quote.gif or you have something that's actually hard to drive.

I have a gain of 4.1 on my CK2III, and I never take the volume past 12, even with high Z phones like senns.

 

[ericj]

Quote:

Originally Posted by tintin47 /img/forum/go_quote.gif I have a gain of 4.1 on my CK2III, and I never take the volume past 12, even with high Z phones like senns.

I hate to break it to you but senns aren't hard to drive.

I mean things like damped yamaha and pmb orthos. And piezoelectric headphones.

And yeah, it depends very much on the voltage you get from your source, too.

 

[ericj]

Oh, and the power supply voltage depends on the opamp you use.

If you go with the AD parts, the max is 27v and sonically you might be better off with 24v with an ad8610 - they start to sound thin and spidery as the voltage goes up.

opa627/630 sound just dandy at 36v though.

 

[chris_ah1]

Guys, what is the difference between the OPA627 and 637 in terms of sound?

Was thinking of going M3 route too and well I also fancy using IEMs from time to time so a gain of 2 would be great along with 8....but I guess I can only go with 3xOPA627 then?

I do find it funny though that everyone here thinks gain of 8 is more than enough but rudistor insist on giving gain of 15 on their NX-03.

Also, does it matter what opamp is used for ground channel? Does it have to be 3xOPA627 or 3xOPA637 or can it be 2XOPA627, 1xAD8610/AD797 etc.

And for general opamp choices in L+R, what specs matter? And what different or same specs matter for G? Slew? current output? voltage noise? current noise? voltage out? PSRR/CSRR?

Thanks.

 

[chris_ah1]

double post

sry

 

[Beefy]

Quote:

Originally Posted by chris_ah1 /img/forum/go_quote.gif Was thinking of going M3 route too and well I also fancy using IEMs from time to time so a gain of 2 would be great along with 8....but I guess I can only go with 3xOPA627 then?

No.... why would you think that? Many OPAMPs are fine at both a gain of 2 and 8.

Quote:

I do find it funny though that everyone here thinks gain of 8 is more than enough but rudistor insist on giving gain of 15 on their NX-03.

Not 15x as we are talking here, but rather a gain of 15dB. I believe this equates to a gain of 5x.

Quote:

Also, does it matter what opamp is used for ground channel? Does it have to be 3xOPA627 or 3xOPA637 or can it be 2XOPA627, 1xAD8610/AD797 etc.

You can mix and match GND versus L/R, but GND has to be unity gain stable. So you cannot, for example, use 3xOPA637.

Quote:

And for general opamp choices in L+R, what specs matter? And what different or same specs matter for G? Slew? current output? voltage noise? current noise? voltage out? PSRR/CSRR?

Just stick with the recommendations on AMB's website, and you will be fine.