[JiggaD369]

Hey guys. I just ordered my K701 and finally decided on what components I want to order for my first-ever M3. I should be ordering them this week but I had some questions before I completely jump the gun. For the Opamps, I've devided on the 637/627 for Jazzy/Acoustical type of music. Will those do fine or should I buy others opamps? Is there much difference between BP and AP versions? Also I read somewhere that if I'm using 637 on the right and left channels, I have to use 627 on the ground channel, right?

Concering the gain, I understand that for the 637/627 combo the gain must be atleast 8. But reffereing to AMB's website, high gain won't sound good on sensitive low-impedance headphones i.e. the K701. Am I on the right track or would a gain of 8 be fine with K701 (62 ohms impedance)?

And finally, this might sound like a dumb question since I'm new to this whole DIY electronics so forgive my dumbness. I'll be using the STEPS v1.1 PSU for the M3. When I look at the parts list on Tangent's website, it lists Amveco +/-15V 15VA transformer. If i use that transformer, what would be the voltage of the PSU? 15V or 30V?

Thanks for any help you guys provide. I really appreciate it.

 

[Teerawit]

Quote:

Originally Posted by JiggaD369 Will those do fine or should I buy others opamps?

They'll be fine but if you want to lower the gain, I'd suggest using the OPA627 in all 3 channels.

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Is there much difference between BP and AP versions?

not for headphone amps

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Also I read somewhere that if I'm using 637 on the right and left channels, I have to use 627 on the ground channel, right?

OPA627 must be used in the ground channel because the OPA637 isn't unity gain-stable and the ground channel runs at unity gain.

Quote:

Concering the gain, I understand that for the 637/627 combo the gain must be atleast 8. But reffereing to AMB's website, high gain won't sound good on sensitive low-impedance headphones i.e. the K701. Am I on the right track or would a gain of 8 be fine with K701 (62 ohms impedance)?

It depends on how much volume control range you want using the pot's swing.

Quote:

And finally, this might sound like a dumb question since I'm new to this whole DIY electronics so forgive my dumbness. I'll be using the STEPS v1.1 PSU for the M3. When I look at the parts list on Tangent's website, it lists Amveco +/-15V 15VA transformer. If i use that transformer, what would be the voltage of the PSU? 15V or 30V?

30V. However this is AC voltage and it will be 30 VAC under a full load, or about 37 VAC unloaded. However when it converts to DC, the voltage will be about 1.3-1.4 times higher. The +/- 12V transformer would be better if you want to run the amp 27 VDC or lower. The +/- 15V transformer would be better if you want to run the amp at over 30 volts.

 

[MisterX]

I think the AD8065's are a better fit with those cans.
One nice thing is you don't have to worry about the gain if you use them.

There is no sonic difference between the OPA637 AP and BP variants.

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Also I read somewhere that if I'm using 637 on the right and left channels, I have to use 627 on the ground channel, right?

Right... the OPA637 is not unity gain stable and as such you cannot use it in the ground channel.

Quote:

When I look at the parts list on Tangent's website, it lists Amveco +/-15V 15VA transformer. If i use that transformer, what would be the voltage of the PSU? 15V or 30V?

Approximately 30 volts.
The secondaries are wired in series on the STEPS circuit board.

 

[JiggaD369]

Wow. Very fast reaplies guys. Thanx. What iwould be the range of gain for the K701?

 

[MisterX]

3 to 5 depending on the source and how you feel about how much of the pot's range you use.

 

[JiggaD369]

Im not really a jerker on the knobs. I listen to mostly jazzy type of electronica so high volume is never a issue.

 

[MisterX]

3 then.

Of course you could always add a gain switch if you are not gonna add bass boost.
That way all you have to do is flip the switch when you want some Sennheiser lovin.

 

[JiggaD369]

Damnit!

There is no way I can use the 637s with K701s? Because Alot of people say they prefer 637 over 627 anyday.

 

[Teerawit]

Quote:

Originally Posted by MisterX That way all you have to do is flip the switch when you want some Sennheiser lovin.

LOL, so true!

Quote:

Originally Posted by JiggaD369 There is no way I can use the 637s with K701s? Because Alot of people say they prefer 637 over 627 anyday.

627 should be close enough.

 

[JiggaD369]

The thing is I already bought 2 637s.

 

[JiggaD369]

how much difference is it between 627AP and 637AP?

 

[amb]

The sonic difference between the 627 and the 637 is often quite exaggerated in these forums. If there is an audible difference it would be very, very subtle, and probably won't even pass a blind test. Te two chips are identical except that the 637 does not have an internal compensation capacitor, so its bandwidth and slew rate are higher. But both chips have high enough slew rate to make matters academic anyway.

Perhaps some of the amps that exhibit large audible differences between the two opamps are actually unstable when a 637 is used.

My advice is not to obsess about this. In the M³ there is a compensation capacitor that limits the bandwidth (rolloff -3dB point about 1.5MHz), so the difference between the two is even less of an issue.

 

[JiggaD369]

Quote:

Originally Posted by amb The sonic difference between the 627 and the 637 is often quite exaggerated in these forums. If there is an audible difference it would be very, very subtle, and probably won't even pass a blind test. Te two chips are identical except that the 637 does not have an internal compensation capacitor, so its bandwidth and slew rate are higher. But both chips have high enough slew rate to make matters academic anyway. Perhaps some of the amps that exhibit large audible differences between the two opamps are actually unstable when a 637 is used. My advice is not to obsess about this. In the M³ there is a compensation capacitor that limits the bandwidth (rolloff -3dB point about 1.5MHz), so the difference between the two is even less of an issue.

The perfect answer and from the perfect person to ask.

AMB, is there anyway to kick it up a notch (sound wise) by using different components than the standard ones listed on the site? Caps, resistors, etc.? Sorry if that is a stupid question but this will be my first DIY in electronics.

 

[amb]

Quote:

Originally Posted by JiggaD369 AMB, is there anyway to kick it up a notch (sound wise) by using different components than the standard ones listed on the site? Caps, resistors, etc.? Sorry if that is a stupid question but this will be my first DIY in electronics.

In my opinion, no. What is specified as "standard" is already very high quality. Some people like to dress it up with boutique parts, which is fine by me; but I would be very skeptical about real sonic improvements.

 

[JahJahBinks]

you can use resistors with closer matching and lower temperature coefficient (but you can always match them by hand and since they are placed relatively close to each other, ambient temperature would affect all of them at once). For capacitor, you can put Elna Cerafine.