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[Quoting fishski13]

one question though: do i need to worry about the output impedence with 5 ft. of 18 awg wire between the sigma11 and M3? the sigma11 will sit on a lower shelf, far away from the M3, and 5 ft. is enough to get me there without stressing the connections.

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[Quote]

i opted to not drill holes in the bottom of the M3 enclosure - the top doesn't get that warm, but where/how (ambient through a top hole, or heatsink directly) should i measure the temp with my Fluke 179, and what is a kosher number?

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Does the gain need to be altered depending on what the M^3 is driving?

I'm building one for a set of HD650s (without Bass Boost), but would also like it to be used as a pre, and as an integrated power amp driving a set of near-fields.

Will I need to switch gain as I switch function? (ie use R3 and R4 at 3K32, with some sort of multi-way multi-pole rotary to replace the 50K pot, switching from 0 (line out preamp) to 25K (headphone out) to 50K (full power)?)

What sort of output power will come from a 24V Sigma11?

Cheers
Sparks

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[Quoting Profsparks]

Does the gain need to be altered depending on what the M^3 is driving?

I'm building one for a set of HD650s (without Bass Boost), but would also like it to be used as a pre, and as an integrated power amp driving a set of near-fields.

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[Quote]

Will I need to switch gain as I switch function? (ie use R3 and R4 at 3K32, with some sort of multi-way multi-pole rotary to replace the 50K pot, switching from 0 (line out preamp) to 25K (headphone out) to 50K (full power)?)

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[Quote]

What sort of output power will come from a 24V Sigma11?

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[Edited by amb on 09-01-2008 at 11:33 AM.]

After it had cooled down I took a close look at it and checked it with a meter from the power supply onwards in a kind of initial setup routine and all the measurements check out healthy. After a long time pondering why it would go up in smoke and still work, I’ve thought of a reason which seems to fit. I was using a single run of speaker wire to bi-wireable terminals with temporary jumpers to connect in the tweeters. I’m guessing one of the jumpers was dislodged and shorted the + and – terminals of the speaker which caused some catastrophic result at the amp’s output. And my question is – is that a plausible explanation?

Also, can those resistors take a bit of a roasting and carry on reliably, or should I replace them?

That doesn't look too badly out of whack. What do you think? If the resistors don't really need to be replaced I think I'd be happy to leave them, because there's some blackening of the solder pads under the board and I'd hate to find that the pad was messed up once the old resistors were removed.

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[Quote]

Leave them alone

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Well I don't know if it's some sort of record but I finally put together a M3/STEPS combo I've had stashed in my cupboard since mid-2005! I'm going to say it was because I felt the components needed to 'stabilise' and the now 'classic' V1.0 PCB was not 'seasoned' enough to possibly provide the maximum audio subtlety... rather than the more mundane "life just got in the way" excuse...

Fairly standard setup I guess; Vishay-Dales, Wimas, Nichicon FG's and Bourns trimmers, gain of 11 and no bass boost... It went together and ran though the initial setup like a breeze with all my DC offsets being under 0.3mV when warm. I have to wonder if anyone likes tapping threads into those heatsinks though!?

Obviously I have to say a big thanks to AMB and Morsel but also to every one of you that has posted a problem, question and - inevitably - a solution on this thread over the last 3 years. The answers really are all here if you read enough!

Attached are a few ubiquitous build pics. The temporary enclosure it's in now is just a cheap 2RU chassis but has served me well in the past for mounting thanks to the movable bars it uses.

Interestingly the first time I powered it up I had all sorts of hum and hiss until I realised the paint on the chassis was so thick that most of the panels were not in good contact with each other. A quick run-around the fixing points with the Dremel gave me some improvement but it's wasn't until I also ground-down the points where the mounting bars attached to the case that it really quietened down. Finally, rotating the STEPS 90deg has made it totally silent. Even with my ER-6i's I hear absolutely no hum and only the faintest hiss between 3 o'clock and maximum... a great result for an all-in-one setup.

Eventually this will be split up and go into a custom enclosure. I'm going to wait until I've finished the Beta22 that just I've just started collecting the parts for and get all the enclosures machined at once… working on some designs to use a heap of 20mm aluminium plate I have access to.

The sound, well it's early days for me to seriously comment on the sound but basically after 20 hours of listening I have to say it's everything I'd hoped for. It really does work well with the HD650's, yet to give it a run with the K701's or DT-880's which I've lent to a mate...

Anyway, thanks again for everyone's (perhaps inadvertent) time and help. Can't wait to get started on the next build!

SATHIMAS
Hi together,
I've found the following problem while going through the initial check for my M³.
First readings are OK, about 20.5V across the OPA Pins and about half of that to IG.

However I turn the BIASOPG, nothing happens - DC voltage stays at 2,3mV.
_______________________
AMB:
The opamp must be installed to do this step. You measure the voltage across R5,
not relative to ground. Also, the trimpot is multi-turn, so you may have to turn
it quite a number of turns to see any change.
If this still doesn't help, then check your Q3 and Q4 JFETs and BIASOP trimpot.
Make sure they are installed in the proper orientation and reflow any suspicious solder joints.
___________________
SATHIMAS
Thank you for the fast reply AMB.
OPamp is installed and I'm measuring across (means right before and behind) the resistor.
I tried the full range of the trimpot...

Just resoldered all joints in the area - with no effect
____________________________
AMB
First, check that the BIASOP trimpot has the expected range of resistance change
(i.e., with the power off and all capacitors discharged, measure the resistance across
the trimpot's outer pins, you should read from 0 ohms to 1K ohms while adjusting it
from one end to the other.
Then, try reflowing the joints of Q2, R6, R7 and the BIAS trimpot.
Power up again to see if this fixes the problem….
__________________________
SATHIMAS
I tested the trimpot - it is working correctly.
I'll put the project to rest for a while then - University is starting again right now
and I don't have enough time for that now. I only started the check because I hoped that all would work
Thank you for your help nonetheless.

______________
Now that’s what I found yesterday:
I went through the same test procedure for every channel now and it’s the same everywhere.
Turning the trimpot has no effect.

Can simply all suspicious transistors be damaged? How can that be?
Maybe I made some stupid mistake – but I don’t see any differences
when I compare my board to others.

I can’t desolder and checkQ3 and Q4 atm but desoldering equipment is on the way.
(Orientation is correct.)

My voltage between 7 and 4 are correct, but between 7 and IG reads 1.9V, and -24.3V for 4 and IG (power supply is 27V). So I'm guessing it is a problem with the TLE or Q5-/Q5+. Where should I start?

Thanks

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[Quoting set300b]

Hi AMB, a sanity check: given the unlimited current nature of Sigma 11, would a single S11 fed by a 30VA, 30V x 2 transformer, be enough to power two M3 (in balanced mode)? Quiescent current will be at ~100mA.

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Assuming you'll set the σ11 for 30VDC output, you'll need a 15V+15V transformer (or 30VCT, or 30V single-secondary) for the M³, though, not 30V+30V. 30VA should be adequate. Note that 30VDC supply voltage is too high for AD8610 or AD8065 opamps.

[Edited by amb on 10-05-2008 at 06:22 AM.]

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[Quoting amb]

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[Quoting set300b]

Hi AMB, a sanity check: given the unlimited current nature of Sigma 11, would a single S11 fed by a 30VA, 30V x 2 transformer, be enough to power two M3 (in balanced mode)? Quiescent current will be at ~100mA.

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No problem at all using one σ11 to power multiple boards. The current capacity of the σ11 is the same as the σ22, and one σ22 could supply up to four β22s. The only thing to be mindful of is transformer VA rating and heatsink/ventilation.

Assuming you'll set the σ11 for 30VDC output, you'll need a 15V+15V transformer (or 30VCT, or 30V single-secondary) for the M³, though, not 30V+30V. 30VA should be adequate. Note that 30VDC supply voltage is too high for AD8610 or AD8065 opamps.

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Yes, I actually meant 15V+15V. Thanks.

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[Quoting amb]

nroth, the TLE2426 is blown.

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Thanks so much, that was exactly it. I actually had gone ahead and ordered new op-amps, preparing for them to be bad also. To my surprise, all the op-amps were still good. I guess I have an extra pair of OPA637AP's. Went ahead and replaced the ground AD8610 with a OPA627AP.

The AD8610 needs a SOIC-8 to DIP-8 adapter, so you need to order one from Cimarron Technology (part number 970601). They used to sell AD8610s pre-mounted on the adapters, but looks like it's been discontinued, but it probably wouldn't hurt to call and inquire. What you listed in your spreadsheet as the adapter is actually the opamp socket, which you also need.

For the LED, how about Mouser 78-TLHB4400 (blue diffused 3mm)?

You did not list anything for the power supply or the casing and hardware.

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[Quoting amb]

headphone1235, for the 2W 1.0 ohm resistors you can use Mouser 282-1.0-RC. For the 2N3904 and 2N3906 I recommend using the same manufacturer for both, so 512-2N3904TFR and 512-2N3906TFR would work.

The AD8610 needs a SOIC-8 to DIP-8 adapter, so you need to order one from Cimarron Technology (part number 970601). They used to sell AD8610s pre-mounted on the adapters, but looks like it's been discontinued, but it probably wouldn't hurt to call and inquire. What you listed in your spreadsheet as the adapter is actually the opamp socket, which you also need.

For the LED, how about Mouser 78-TLHB4400 (blue diffused 3mm)?

You did not list anything for the power supply or the casing and hardware.

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Thanks for the quick reply, I've updated the spreadsheet to your recommendations.

For the power supply I'll use the σ11, Im a bit confused in which transformer I'd have to buy. The mains I have is at 240V and I'm looking for the right transformer, I've got a website that sells a selection of transformers: http://www.altro...ea=prod&grp=354

Which one do you recommend for my kit?