HeadWize: DIY Workshop > M³ headphone amplifier (part 2)

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DIY Workshop » M³ headphone amplifier (part 2)
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amb

Headphone Council

Joined: Apr. 1, 2004
Locale: Sunnyvale, CA. USA
Total Posts: 4408

Message [#220] posted on: 01-29-2009 12:11 AM CST (US).

C0G caps are superior to X7R for compensation purposes. They are thermally much more stable, and have better high frequency characteristics.

niksh

Member

Joined: Feb. 13, 2009
Locale: Kuala Lumpur , Malaysia
Total Posts: 6

Message [#221] posted on: 02-13-2009 02:17 AM CST (US).

I have successfully completed my M³ with the standard parts list as supplied by N Maher on AMB's M³ site except C7 470uF/50V (8 pcs)and C5 100uF/50V Nichikon bipolar and gain 0f 6 using 2k resistors.I am using AD843JNZ op-amps and a Y1 power supply built for 30V DC (16V-0-16V AC, 2Amp) using recomended parts. All the opamp have been bypass using BG HQ 0.1uf/50V.
I get an AC Voltage of 4.7mV across each of IG and OL, IG and OR, and IG and OG.
The DC voltage across OG and OL is 0.2mV and 1.0mV between OG and OR.
The DC voltage across IG and OG is 0.3mV, IG and OR is 0.5mV and IG and OL is 0.2V
DC Voltage across pins 4 and 7 = 28V, and pins 4 and 7 and IG, 13.97V and 14.03V respectively.
DC Voltage across each respective R9 is 85mV.
1)Why I could not only adjust BIOSOPR to 0.5V, the highest I could get is 0.48V. So I set for 0.45V
2)If the bass boost dial past 6 oclock (12 oclock = 0), the volume becomes attenuated a bit.
I am using M3 to drive my Fostex 206E speakers.
The M3 has clocked more than 30 hrs now and I realy love the M3, and excellent amp indeed with no trace of hum or hiss.
It is in different class compare to PIMETA with all the boitique parts mods, crossfeed and Total Airhead Amp which I am presently using.
Btw, US postal service is rather slow, it took more that 15 days from US to Kuala Lumpur, Malaysia.
I ordered parts from Mouser and it took only 4 days by Fedex. My sincere to u and Morsel for a great Amp.

niksh

Member

Joined: Feb. 13, 2009
Locale: Kuala Lumpur , Malaysia
Total Posts: 6

Message [#222] posted on: 02-13-2009 02:28 AM CST (US).

Sorry, the power supply is Q11 single rail and not Y1. I am so obsessed with Y1 DAC, which be my next project. Thanks.

amb

Headphone Council

Joined: Apr. 1, 2004
Locale: Sunnyvale, CA. USA
Total Posts: 4408

Message [#223] posted on: 02-13-2009 02:45 AM CST (US).

[Quoting niksh]
I get an AC Voltage of 4.7mV across each of IG and OL, IG and OR, and IG and OG.

This may not be a reliable reading, so don't worry about it.

[Quote]
The DC voltage across IG and OG is 0.3mV, IG and OR is 0.5mV and IG and OL is 0.2V

I hope you mean 0.2mV for IG-OL.

[Quote]
1)Why I could not only adjust BIOSOPR to 0.5V, the highest I could get is 0.48V. So I set for 0.45V

It depends on the Idss of the cascode JFETs. 0.45V is just fine. The M³ website says 0.4V-0.5V.

[Quote]
2)If the bass boost dial past 6 oclock (12 oclock = 0), the volume becomes attenuated a bit.

It shouldn't. I don't know why you're experiencing that.

[Quote]
I am using M3 to drive my Fostex 206E speakers.
The M3 has clocked more than 30 hrs now and I realy love the M3, and excellent amp indeed with no trace of hum or hiss.
It is in different class compare to PIMETA with all the boitique parts mods, crossfeed and Total Airhead Amp which I am presently using.

I am glad you're liking the amp.

niksh

Member

Joined: Feb. 13, 2009
Locale: Kuala Lumpur , Malaysia
Total Posts: 6

Message [#224] posted on: 02-13-2009 06:39 AM CST (US).

Yes, it is 0.2mV.
Btw, do you think that if I increase the voltage of the power supply to 36V, the sound would improved. At normal listening, the vol dial is only at 4 o'clock (12 o'clock = 0). At 7 o'clock the vol is very loud. The heat sink of the power supply is only slightly warm however the heat sink of the MOSFETs are hot but still touchable. (cover open).

amb

Headphone Council

Joined: Apr. 1, 2004
Locale: Sunnyvale, CA. USA
Total Posts: 4408

Message [#225] posted on: 02-13-2009 03:26 PM CST (US).

[Quoting niksh]
Btw, do you think that if I increase the voltage of the power supply to 36V, the sound would improved. At normal listening, the vol dial is only at 4 o'clock (12 o'clock = 0). At 7 o'clock the vol is very loud. The heat sink of the power supply is only slightly warm however the heat sink of the MOSFETs are hot but still touchable. (cover open).

Increasing the power supply voltage will make the amp run hotter. It will give you more maximum output voltage swing, but will not change the volume at any particular knob setting. If you can achieve the needed listening levels you require (without clipping) with the existing power supply voltage, then there is not necessary to increase it. There won't be any sonic advantage with higher voltages. Also, bear in mind that some opamps have power supply voltage limits such as AD8610 and AD8066.

[Edited by amb on 02-13-2009 at 03:27 PM.]

habba

Member

Joined: Feb. 14, 2009
Locale: singapore
Total Posts: 14

Message [#226] posted on: 02-14-2009 06:53 AM CST (US).

Hi guys,

I've just finishing setting the M3 up(without casing yet).
and i've got a problem. everytime i connect my itouch and play, the playing and the rca plugs seems to get charged up, and i'll get these little shock when i touch them. music is playing fine, but there's alot of hum on the background, and it goes even louder when i touches the vol pot.

any advice?
(my dmm just failed me seconds ago... gonna get a better one tml.)

onesandzeros

Member

Joined: Dec. 26, 2007
Locale: Killadelphia
Total Posts: 6

Message [#227] posted on: 02-14-2009 01:32 PM CST (US).

Hello all,

I'm having a little trouble interpolating values for C1R and C1L with OPA637s, 1k ohm resistors in R3 and 6.19k in R4. Any suggestions? My Cmoy has a gain of 11, and I rarely get the volume past 9 o'clock, so I'm just trying to rein in this M3, heh. Available for those C1 positions are, in pF: 10, 15, 18, 22, 27, and 33. Maybe 18s or 22s? I'm lousy at math, and the 637 isn't recommended for a gain of 5, so there's no suggested value there. <big grin> I won't be changing opamps.

Thanks!

amb

Headphone Council

Joined: Apr. 1, 2004
Locale: Sunnyvale, CA. USA
Total Posts: 4408

Message [#228] posted on: 02-14-2009 01:39 PM CST (US).

habba, please describe your AC, transformer and power supply wiring.

onesandzeros, why not just stay with the default of 33pF? It works well with all the recommended opamps.

habba

Member

Joined: Feb. 14, 2009
Locale: singapore
Total Posts: 14

Message [#229] posted on: 02-14-2009 10:22 PM CST (US).

Hi,

I'm using some laptop charger i found for psu, it's spec is 24v 500ma. I've did a reading before, it actually only gives out 22v.
I had connected the DC socket to the V-/V+ which are side by side.
I've ground the vol pot, and it seems that it had reduce the humming, but there's still hum when i touch the vol knob.
And i still kind get a mild shock when i touch the metal casing of my player.

Beefy

Member

Joined: Feb. 29, 2008
Locale: Perth, WA, Australia
Total Posts: 58

Message [#230] posted on: 02-14-2009 11:08 PM CST (US).

According to AMB's website, the ground pads near the volume pot are not properly connected to the ground plane on v1.01 boards. So you haven't actually grounded the volume pot yet.

And I'm not 100% sure on this but you might need to ground the bass boost pot as well......?

habba

Member

Joined: Feb. 14, 2009
Locale: singapore
Total Posts: 14

Message [#231] posted on: 02-14-2009 11:17 PM CST (US).

I've bridge the IG to C5L- already as stated on the website.
So i'm pretty sure it's grounded.

My bass pot doesnt hum when i touch it. only the vol pot.

habba

Member

Joined: Feb. 14, 2009
Locale: singapore
Total Posts: 14

Message [#232] posted on: 02-14-2009 11:28 PM CST (US).

Another thing to add, I'm hearing the hum without source as well.
And i touch my rca cables, it just increases it further.

Beefy

Member

Joined: Feb. 29, 2008
Locale: Perth, WA, Australia
Total Posts: 58

Message [#233] posted on: 02-14-2009 11:54 PM CST (US).

Hmmm, well beyond my skill then <frown>

But I do recall reading that testing without a source connected is not a good idea. Something about grounding the inputs?

[Edited by Beefy on 02-14-2009 at 11:55 PM.]

habba

Member

Joined: Feb. 14, 2009
Locale: singapore
Total Posts: 14

Message [#234] posted on: 02-15-2009 01:26 AM CST (US).

Ahhh my bad,
The rca plugs wasnt earth properly.
But it's all fix and no more hum.

The vol knob hum still exist whenever i touch them.

habba

Member

Joined: Feb. 14, 2009
Locale: singapore
Total Posts: 14

Message [#235] posted on: 02-15-2009 10:14 AM CST (US).

Hi,

I've got another problem. after fixing everything to my casing, the dc offset voltage from ig to ol was 18mv, while the rest was under 0.5mv.

Opamp pin 4 - 7 , 19.8v
pin4 to IG , 9.7v
pin7 to IG, 9.8v
R5, 0.45v
R9, 80mv

the rest of the values for the other channel are almost the same, but the dc offset was larger only for my L channel.

amb

Headphone Council

Joined: Apr. 1, 2004
Locale: Sunnyvale, CA. USA
Total Posts: 4408

Message [#236] posted on: 02-15-2009 04:16 PM CST (US).

What opamps are you using? Some opamps may exhibit higher DC offset than others.

Mister X

HeadWize Fanatic

Joined: Jul. 23, 2003
Locale: Kalamazoo, Michigan
Total Posts: 606

Message [#237] posted on: 02-15-2009 04:27 PM CST (US).

[Quote]
I'm using some laptop charger i found for psu

Is the ground "terminal" on this PSU's plug isolated?

And.
One of the easiest checks for high DC offset in one channel is to swap the op-amps between the channels.
(if the offset moves with the op-amp...the op-amp is the problem)

onesandzeros

Member

Joined: Dec. 26, 2007
Locale: Killadelphia
Total Posts: 6

Message [#238] posted on: 02-15-2009 05:03 PM CST (US).