[Jazper]

Quote:

Originally Posted by amb Many people here are just rehashing what they read from others anyway. Given a proper blind A/B comparison, much of the difference vanishes anyway (Don't believe it? Try it out sometime). If you hear something you like better, then you found the right opamp for you. If you can't hear a difference, then pick the cheaper one.

Agreed, however, there are two differences that had me choose the 637 over the 8610. The 8610's bass seemed recessed, and the highs were piercing. This was with my ms-1s and av710.. so ymmv. I also find the 637 sounds much better after it's warmed up whereas there isn't much difference between the 8610 before and after it warms up in the m3.

 

[rjkdivin]

I just got around to casing up my fourth M3. It's in a Lansing B2H08-V02B case that I was planning to use for just an M3 without a power supply. However, due to its height of 3 1/2", I found it would fit the Welborne PS-1 if I angled the transformer on a custom bracket and mounted the two PCBs at different heights so they could lap over a little. I was a bit concerned about EMI due to the cramped quarters, but it is as clean sounding as my other three, two of which have the PS in a separate case.

Now, since there is room, I'm considering larger heatsinks for the PS-1 since it is running a little hot with a 15v + 15v toroid.

 

[amb]

rjkdivin, nice case. I am a little concerned about the proximity of the transformer to the input traces too. I know you have the ability to run RMAA tests, so you should do a test of this amp and check the noise spectrum. If there is any interference, you'll see spikes at the AC fundamental (60Hz) and its harmonics. If you don't see any spikes, then all is well. Just fyi.

 

[rjkdivin]

I went back to my first M3 in the Silverstone separate cases to run the RMAA tests, and ran into a problem. In adjusting the signal levels, with volume at full on both the M3 and the M-Audio, and with 330 Ohms on the dummy load box, it only comes up to about -12db....not enough to run a meaningfull test. I re-checked the STEPS output voltage....24.5v, and re-checked all of the initial set-up items...rail voltage, pin 4/7 voltage, IG/OG, R5, R9 +/- from your instructions, and all are perfect. I even swapped in a different set of opamps with no change. The amp plays beautifully. Any ideas why this could be?

 

[amb]

rjkdivin, does this M³ have the default gain of 11 (i.e., R3 and R4 are 1K and 10K ohms)? If the gain is too low then you won't be able to achieve enough output for an RMAA test. That said, I have run RMAA successfully on the M-Audio Firewire Audiophile with amps with gain as low as 4 and it's still sufficient. Check the value of your R4 and R4 resistors just to be sure. Does this amp play equally loud compared to your other M³ builds when connected to the same source and headphones and the volume control set to the same position?

If that is fine, then something is attenuating the levels in your RMAA testing chain. Are the two channels equally low in level? Try swapping different interconnect cables just in case.

Edit: actually, even a gain of 1 should be enough because that's what loopback does.

 

[rjkdivin]

AMB,

Yes, I used default values for everything. I checked the values of R3 (1k). R4 (10K) and R4G (1K) in place. I even pulled out R4G to double check, and they all measured fine.

I visually verified all other resistors and all capacitors also. I have always been suspicious of C3 at the Mosfets and C1 at the Opamps because the markings didn't match my order with Mouser precisely. So I pulled them all out and they measured as follows:
C3 - .317nf or 317pf....sounds somewhat close to 220pf? They were labled 221.

C1 - .123nf or 123pf....about 4 times your design value of 33pf. They were labled 330. Could this be a problem?

As far as my test set-up, I haven't changed it from one test to the next, and it worked fine on my Par Mtls Separates M3. But just for fun, I switched interconnects, and it made no difference.

Now I need new capacitors anyway because I ruined one getting it out....terribly small little buggers!

This guy won't be ready for the HeadFi meet! Maybe just to look at....those Silverstone cases are nice!

 

[amb]

Quote:

Originally Posted by rjkdivin Yes, I used default values for everything. I checked the values of R3 (1k). R4 (10K) and R4G (1K) in place. I even pulled out R4G to double check, and they all measured fine.

OK.

Quote:

I have always been suspicious of C3 at the Mosfets and C1 at the Opamps because the markings didn't match my order with Mouser precisely. So I pulled them all out and they measured as follows: C3 - .317nf or 317pf....sounds somewhat close to 220pf? They were labled 221.

The 3rd digit on these caps is a multiplier. The label "221" means 22pF times 10^1 = 220pF. So it is correct. These are supposed to be 10% tolerance parts, so your measured result is out of whack. I would be suspicious of the measurement rather than the part itself.

Quote:

C1 - .123nf or 123pf....about 4 times your design value of 33pf. They were labled 330. Could this be a problem?

Same here: 33pF times 10^0 = 33pF, so it's correct too.

Quote:

As far as my test set-up, I haven't changed it from one test to the next, and it worked fine on my Par Mtls Separates M3. But just for fun, I switched interconnects, and it made no difference.

Well I don't know what to tell ya...

Quote:

Now I need new capacitors anyway because I ruined one getting it out....terribly small little buggers! This guy won't be ready for the HeadFi meet! Maybe just to look at....those Silverstone cases are nice!

Send me email and let me know which caps you need, I could bring a few to the meet where you could do an on-site repair. Just bring a soldering iron, solder and some needed tools along. It would be nice to have all your gear in working condition.

Once fixed, we could try doing RMAA testing there. I will be bringing my laptop, M-Audio Firewire Audiophile and other test stuff.

 

[rjkdivin]

Quote:

Originally Posted by amb OK. The 3rd digit on these caps is a multiplier. The label "221" means 22pF times 10^1 = 220pF. So it is correct. These are supposed to be 10% tolerance parts, so your measured result is out of whack. I would be suspicious of the measurement rather than the part itself. Same here: 33pF times 10^0 = 33pF, so it's correct too. Well I don't know what to tell ya... Send me email and let me know which caps you need, I could bring a few to the meet where you could do an on-site repair. Just bring a soldering iron, solder and some needed tools along. It would be nice to have all your gear in working condition. Once fixed, we could try doing RMAA testing there. I will be bringing my laptop, M-Audio Firewire Audiophile and other test stuff.

Well I rechecked 5 of the 6 capacitors....off the pcb....using a Fluke 187 autoranging. All close to the same: C1 - .123 to .129 nf C3 - .317 to .329 nf.

 

[amb]

Quote:

Originally Posted by rjkdivin Well I rechecked 5 of the 6 capacitors....off the pcb....using a Fluke 187 autoranging. All close to the same: C1 - .123 to .129 nf C3 - .317 to .329 nf.

I really think that your meter is not reading correctly. It may not be the meter itself, but perhaps the test leads have some "built-in" capacitance. This makes sense because in both cases it read about 90pF too high.

 

[tangent]

In my experience, my Fluke 189 doesn't do so well measuring below 100pF. I switch over to an AADE LC Meter II for that. But don't feel bad about the Fluke -- it'll go up into the microfarads, where the AADE unit will poop out.

 

[rjkdivin]

Quote:

Originally Posted by tangent In my experience, my Fluke 189 doesn't do so well measuring below 100pF. I switch over to an AADE LC Meter II for that. But don't feel bad about the Fluke -- it'll go up into the microfarads, where the AADE unit will poop out.

You and AMB are correct I think. My Fluke 187 with standard leads reads around .095nf, and without any leads its around .078nf......both in the neighborhood of my 90pf error in measuring the caps.

I have a 199 scope meter, but I haven't tried that yet to see if it makes a difference.

 

[SiuGuyGuy]

Today my m3 suddenly gone no sound. I had check thought it and found that seems the power supply of opamps gone wrong. First i check voltage bewteen pin4 and pin 7 of opamp socket, it got 2.7V. Then I check voltage of pin 7 vs power supply's V- is +23.4V, and Pin 4 vs pwr supply V- is +20.7V. My power supply is 24.5V.

Is that my TLE2426CLP fired? Or some other possible reason?

Thanks for help!

 

[amb]

SiuGuyGuy, sounds like your Q5+ and Q5- died. Be sure to use proper "name brand" transistors for these, because I found some "no name" 2N3904/3906 not to meet the specifications. If you use opamps that draw a lot of current (e.g., THS4631D, or even in some cases OPA627/637) these transistors would burn up.

 

[GregVDS]

Hello, I begun now some months ago the DIY headphone amp quest. I made two Cmoys, different (buffered at output, then at input), implementing some Crossfeed filters in. I mainly listen with a Grado SR325i, and nothing else, since all my other headphones are crappy in comparison.

Now I want to take the big step and build an entire M³, with Linkwitz modified Crossfeed and Tangent Step PSU. I studied a lot the websites of Tangent and AMB, even asked some people on internet, but I still have some questions about details, or maybe more important things, Here I go:

-First, I want Crossfeed, so, I just put the crossfeed (linkwitz, tangent pcb implementation) in front of the M³ circuit, between RCA and M³ pcb input, right? How will interact the volume pot with the crossfeed? should I buffer the crossfeed between two OpAmp unity gain stages?

-AMB specific, what is the meaning of "Boutique grade", for Cerafine, very good, or barely ok? (I show my french-speaking-guy limits here, sorry)

-Consequently, are there big differences between Nichicon UHE serie and Elna Cerafine, for the last ones are difficult to find?

-Can I use Orange Drop polypropylene rated 200~400v for CBB? Is it worth it?

-My main music source will be the line out (not headphone jack, the one intended for hifi amp line in) of my 3rd generation iPod. I measure dc offset between right and ground, left and ground, in mV, correct? What amount is tolerable, only nothing, some thenth of mv, some mv?

-I the same context, How could I tackle down this DC offset if there is one?

-Can it be possible to lower the 1.5'' heatsink a little bit by sanding out some millimeters of material? which extremity, from the base or the top?

-I want to use a par-metal case (Thrice could answer me on these ones maybe?) and have a custom one (10'' x 8'' x 2'', hence the heatsink question) what screws are used, and would it be possible to replace front, top and back by top panel express ones? I would like to have them attached from inside, with no screws on the outside. Is it possible to fix the pcb in the box If I want the shafts of volume pot and bass boost pot useful for knob attachement, for the internal aluminium foil chassis is quite large (I need in fact the width and height of the hole in the internal front plate)? Is there some holes in the back plate or not? See the front.jpg here for my layout, any comments welcome

-Someone heard something about a 'Mark Burson Super OpAmp', with figures at least ten times better than the OPA627, look into ebay, australian product, is this for real?

-Volt gain is computed from R3 and R4, but for volume pot turned to max, or do I miss something?

-Why 4 C8, and not 3?

-Why no R1G?

-PSU 24V ok?

-Useful to have an internal metal divider between step and M³ pcb's? Par-metal 20-series has this option.

-I want to use a 4 pole 3 position rotary switch for Linkwitz; is it possible to position it just above the big M³ inscription on the pcb, or the heatsink is too close to the front panel (having in mind my wish to use the shafts of pots through the front panel)

-What shielded wire to use, or how to shield a wire?

for C7, what's better: 9 x 330µF, 6 x 470µF, 3 x 1000µF?

Ok, that's all I should know for now, many thanks if you're still there.

I hope to have at least some answers to progress in this.

Many thanks to all

GregVDS

 

[amb]

Quote:

Originally Posted by GregVDS -First, I want Crossfeed, so, I just put the crossfeed (linkwitz, tangent pcb implementation) in front of the M³ circuit, between RCA and M³ pcb input, right? How will interact the volume pot with the crossfeed? should I buffer the crossfeed between two OpAmp unity gain stages?

If you use the "high-Z" version of the crossfeed circuit then yes, it goes between the RCA input and the M³ pcb input. The volume pot should have little interaction with the crossfeed. Note that the crossfeed circuit will introduce a 6-10dB loss, so depending on your source and headphones you may need to increase the gain of the amplifier to make up for it.

Quote:

-AMB specific, what is the meaning of "Boutique grade", for Cerafine, very good, or barely ok? (I show my french-speaking-guy limits here, sorry)

Cerafine is considered boutique-grade. Generally, anything that are labeled specifically "for audio" and then priced significantly above standard stuff are "boutique".

Quote:

-Consequently, are there big differences between Nichicon UHE serie and Elna Cerafine, for the last ones are difficult to find?

In the M³, electrolytic capacitors are only used in the power supply rails, not in the signal path. In my opinion there is no advantage of using Elna Cerafine over Nichicon UHE in this application, but don't let me stop you from using the boutique stuff.

Quote:

-Can I use Orange Drop polypropylene rated 200~400v for CBB? Is it worth it?

You can use the Orange Drop if you like, as long as it physically fit the board and the leads not too thick to go through the holes. The high voltage rating is total overkill and not needed in this circuit.

Quote:

-My main music source will be the line out (not headphone jack, the one intended for hifi amp line in) of my 3rd generation iPod. I measure dc offset between right and ground, left and ground, in mV, correct?

Yes.

Quote:

What amount is tolerable, only nothing, some thenth of mv, some mv?

Any DC offset at the input to the amp will be amplified by the gain of the amp (at max volume). The amount of DC offset that is tolerable depends on the type of headphones you have. Lo-Z phones are more likely to be damaged by offset, and I would suggest no more than a few mV maximum at the input of the amp.

Quote:

-I the same context, How could I tackle down this DC offset if there is one?

Insert a coupling capacitor, either at the output of the offending source, or at the input of the M³ amp to block the DC.

Quote:

-Can it be possible to lower the 1.5'' heatsink a little bit by sanding out some millimeters of material? which extremity, from the base or the top?

If you must grind down the height, do so at the top of the heat sink.

Quote:

-I want to use a par-metal case (Thrice could answer me on these ones maybe?) and have a custom one (10'' x 8'' x 2'', hence the heatsink question) what screws are used, and would it be possible to replace front, top and back by top panel express ones?

If you use short standoffs (like 1/8") and apply an insulating plastic sheet below the board to keep anything from touching the case, then the board with 1.5" heat sinks will fit in the 2" tall Par Metal case. However this arrangement will cause your volume/bass boost knobs to be a bit below the center line of the front panel.

All screws in the Par Metal 20 series are 6-32 thread machine screws. You can replace the front with a custom panel from Front Panel Express but all the other pieces have bends in them. I am not sure Front Panel Express will make such pieces.

Quote:

-Someone heard something about a 'Mark Burson Super OpAmp', with figures at least ten times better than the OPA627, look into ebay, australian product, is this for real?

Don't waste your money. It's a scam.

Quote:

-Volt gain is computed from R3 and R4, but for volume pot turned to max, or do I miss something?

Yes. When we speak of amplifier gain we imply the volume at max position. The volume control then introduces a loss (from none at maximum to 100% at minimum).

Quote:

-Why 4 C8, and not 3?

Its for power rail decoupling. There can be any number of them, and since there is room for 4, we put 4 in there.

Quote:

-Why no R1G?

Because R2G already serves that purpose.

Quote:

-PSU 24V ok?

Yes.

Quote:

-Useful to have an internal metal divider between step and M³ pcb's? Par-metal 20-series has this option.

Yes.

Quote:

-I want to use a 4 pole 3 position rotary switch for Linkwitz; is it possible to position it just above the big M³ inscription on the pcb, or the heatsink is too close to the front panel (having in mind my wish to use the shafts of pots through the front panel)

You will have to determine this yourself, based on the dimensions of your switch and how you would mount the board and switch.

Quote:

-What shielded wire to use, or how to shield a wire?

If your input wiring is not longer than a few inches then there is no need to use shielded wires. Just twist the ground and signal wires together. If you have longer runs, then use coaxial shielded wires, like a microphone cable.

Quote:

for C7, what's better: 9 x 330µF, 6 x 470µF, 3 x 1000µF?

All else being equal, 9x330 would provide the lowest ESR, but all else is not equal even between selections of the same line of capacitors. In reality it is not going to make much difference. We provide holes on the board for those who obsess about these things so they could do what they like.