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- Morsel's M³ page

[Edited by amb on 02-24-2008 at 03:20 PM.]

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[Quoting Iggurk]

Measured again with the amp off --> Nothing, 0 Ohm

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O ohms or no reading?

O ohms is a short circuit and we don't want that.
No reading is an open circuit and that is what we want between the out ground of the amplifier and the power supply ground.

When I wrote 0 Ohm I mean no reading.

I've rewired everything following AMB schema, completed the setup and tried to connect it to a source, and....

It works, more or less...

The E12 board always switch on/off every ~4 seconds, I only ear music for half a second.

I've followed the E12 setup successfully, Between G2 and pin 6 of U1 I've only 0.4 mV, tried to lower that by adjusting VR1 without success, whatever the direction I turn the value doesn't change.

Could it be the reason ?

I've been able to more or less set the ε12to work nearly as expected.

So, I've been able to listen (finally) my new M3 unit.

Something strange, when I compare the sound of the new unit, there is an important lack of bass compared to the old one.
That's really strange, because only the Cbb bass boost and C5 (lower voltage) caps are different, all other parts are identical.

The bass boost is also "less" efficient", and the Cbb caps value are the exact same (0.1).

Any idea of the reason ?

Except that the amp sound rather good as as pre-amp.

OL to left, OR to right and G2 to ground.

But,...

you must be right somehow, because the lack of bass is only present on the headphone jack, not on the pre-out (at least I didn't notice it at all)

the jack could be defective ?
the E12 board ?

Can I check if the signal that reach the jack is good ?

[Edited by Iggurk on 02-25-2008 at 02:38 PM.]

If you have a 1/4" TRS plug (no wires), insert into your jack and check that you have 0 ohms between ε12's outputs and the appropriate plug contacts: OL -> tip, OR -> ring, G2 -> sleeve.

here is how I've wired the E12:

20 MOhm between my G1 and G2...

Could have been wise to name G1 and G1' if there behave differently, don't you think?
(at least for dummy M3 builder as me...)

Measured 0 ohms between ε12's outputs and the appropriate plug contacts: OL -> tip, OR -> ring, G2 -> sleeve

[Edited by Iggurk on 02-25-2008 at 03:07 PM.]

Done, and believe it or not, it's now perfect.

Many many thanks for all the support you're providing.

best regards

It's a fairly standard BOM, AD8610's, Nichicon caps, 24v supply, Neutrik jacks. Found some perforated aluminum sheet for the tops of the Hammond cases.

Sounds good too!

nine

Those are some different looking component adapters. What are they?
(don't think I have ever seen red ones before)

The adaptors are Ares from Digi-Key

I also wanted to say thanks to AMB for all the work that went into the design of this amp. It's truly impressive.

nine

I’ve built lots of electronic kits in the past, so my assembly and soldering skills should be up to the task. But I’ve only ever built complete kits before – never had to select my own parts, and for the time and effort I’m going to invest I want to get it right first time, for an absolute top notch final result. This is especially important considering I live in Australia, and local sourcing of parts is an absolute shocker. We have Farnell and RS Components down here, but their prices are ridiculous and their stock levels terrible. As it is, I’m going to be hit with 3 lots of international shipping (AMB, Mouser, Digikey), and don’t want to have to pick up something else later!

Obviously I’m going to pick up everything that I can from AMB, covering me for volume pot, JFETs, MOSFETS, S11 transistors, heatsinks, the rail splitter and 1µF caps. I’m fairly comfortable with resistor and capacitor selection – Vishay resistors and trimpots, Nichicon UHE and Kemet caps, except for the 1500µF caps in the power supply which will be Panasonic FC (Mouser is out of stock of 1500 µF UHEs). Amp transistors and diodes will be bog standard Fairchild, but I’m springing for the expensive Vishay current regulators in the S11 (they seem important). Audio connectors are Neutrik, Ecomate power connectors between power and amp, internal connectors Molex and Phoenix, and it will all be put in Hammond cases with perforated tops. Hopefully it looks as good as -nine-'s job just a couple of posts up! So now the actual issues……

1. Any favourite ‘boutique’ components or other upgrades that actually have a positive effect on sound quality? Or does the goodness mostly come from the MOSFETS, opamps and good design?

2. Power supply transformer. I can get the Amveco from Digikey, but thought that due to weight and shipping it would be better to get one locally. I was looking at these options:
tinyurl.com/344d5a
www.rsaustralia.com.au stock # 257-4963 – can’t hard link unfortunately
I’m inclined to go the cheaper option from Altronics since it is straight 240V (keeps the wiring clean), and it claims a better regulation than the more expensive one from RS. Any suggestions?

3. Is EMI filtering on the incoming mains worthwhile?

4. LEDs, voltages and accompanying resistors. Lets say I’m looking at this particular Blue LED tinyurl.com/2udr9m with 3.5V forward voltage and 30mA typical current. In the calculator, that is a supply voltage of 24V, for a resistance of 683 ohms? The resistor then has to dissipate 20.5^2 / 683 = 0.61W. That seems really excessive, so I’m wondering whether I have done my calculations correctly?

5. Variable gain. I was thinking of using 1kohm in both R3 and R4, along with a 10kohm Alps pot. This would give me variable gain of 2-12. Unfortunately, I can’t find the 10kohm Alps in stock anywhere that I’m purchasing other stuff. I could use 5kohm in R3 and R4 with a 50kohm Alps for an identical 2-12 gain, but I’m worried that the total resistance will be too high – AMB recommends below 50kohm to prevent noise. Thoughts?

6. Opamps! I’m going with AD8610A all round to start with, but was thinking of also sourcing some OPA627/637 to experiment with for harder to drive headphones. But will I actually get a decent peak-to-peak voltage from the 627/637 with only a 24V supply?

7. Any component that is potentially easy to kill, that I should perhaps buy spares for?

I think that is everything now. Thanks for reading my mini-essay, and I look forward to your replies!

Cheers,
Beefy

[Edited by Beefy on 03-02-2008 at 08:29 AM.]

I'll start ordering parts later today, and post pics when I'm done!

Ok, I've been able to get the board to work well once I removed the pre-amp output, tested it for hours without any issues, sound quality really good, no distortion, nothing, just perfect.

Then I sold the amplifier, and now, the guy who buy it is having troubles.

At mid level he as l lot of saturation, and sound level isn't that high.

What could it be ?

Broken cable during transport ?
Gain not adapted to his headphone?
source issue?
other?

regards

He told me that at mid range with volume there is saturation, not clipping.