Increasing voltage swing

As they are quite difficult to drive ("warbling" distortion from the headphone out on a Technics SU-V620 stereo amp, slightly less, but still audible from a Numark DM1100X DJ mixer), I read somewhere (here or head-fi) that someone suggested increasing the voltage swing to be able to drive the K701 loud and to its full potential without distortion.

I am going with the Sigma11 PSU and picked out the Amveco TE62064 2x18V 25VA toroidal transformer and OPA627AP op-amps, changing R10 on the Sigma11 to 4.99K, C1L & C1R to 10pF.

Bass boost

I wanted to go a touch more than subtle with the bass, and lowered Cbb down a notch to 0.15uF. The resulting graph looks very similar to the low end of the EQ curve I apply to most headphones on my Cowon iAudio X5L.

So, my electronics knowledge is kinda limited, even though part of my B.Eng was in E&EE. Have I picked out the correct components for increasing the output voltage swing? Or do I have to change the values of R3/R4 to change the gain aswell?

I'm guessing I'd need substantial heatsinks and a vented case for the extra amplification, would holes in the top of the enclosure be sufficient?

I'm attaching the spreadsheet I have with a parts list for both the M^3 and Sigma11 in case I've neglected to mention other changes, and in case someone can spot something I've not listed that I will need.

Oh, also, are the Alps pots from the AMB shop slotted or do they have a flat side?

[Edited by hardnrg on 04-24-2008 at 01:17 PM.]

Use 2.5" tall heatsinks if you can, and be sure the case is ventilated on the top and bottom for convection.

The Alps RK27 pot does not have a flat side. It has a small slot at the end of the (6mm diameter) shaft.

I wasn't sure about the pot because the Alps spec sheet has a flat and slotted version. The datasheet link on the AMB Shop page is outdated, here is the current link: http://www3.alps...RK271/RK271.PDF

The other thing that had me a bit confused was the description section of the Diodes for the sigma11 mentions CR4, which isn't in the Parts List, nor could I find it when looking at the PCB. I take it this is a typo? Or is it an option I've overlooked somewhere?

[Edited by hardnrg on 04-24-2008 at 04:06 PM.]

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[Quoting hardnrg]

The other thing that had me a bit confused was the description section of the Diodes for the sigma11 mentions CR4, which isn't in the Parts List, nor could I find it when looking at the PCB. I take it this is a typo? Or is it an option I've overlooked somewhere?

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I think the total cost with shipping is about £250 which isn't bad because I got a few frivolous extras like brushed aluminium case feet and a flush vandal switch...

...which I'm not sure how I'm going to get it to work.

Momentary to latch, but to switch the power it's running on?!

I know about flip-flops, bistables, J-K whatevers... it's just been a while hehe. I know it's possible to use a momentary switch to latch on/off, avoid bounce, etc etc... but I don't know how to do it when the momentary switch is being fed power from the power supply it is latch-switching...

Would I have to make some sort of standby power for the latch???

My head really hurts, I've been going round in circles enough just trying to buy all the components, and then thinking about this circular circuit problem, yikes.

My google skills are weak at the moment, all I can find are the usual solutions, and people talking about momentary guitar pedals working with their (guitar) amps

If it's just going to be way too hard I could settle on a rocker switch I guess... I just wanted a black metal switch to match the knobs

I had a feeling there was no way around having a 2nd power supply. Will have a read through the epsilon24 and sigma24 sections now

edit: is this a sensible layout for the M^3, sigma11, epsilon24, sigma24 and toroid?

I tried to arrange it so that the toroid is as far away from the input as possible, but not so far over that the amp is completely side-heavy, also this leaves a nice gap for the IEC wiring. The epsilon24/sigma24 are stacked and close to the sigma11 for switching...

The front panel is going to be arranged something very similar to this:

So the Alps pots will be wired off-board, and shouldn't get any noise induced from the low voltage line to the momentary power switch.

I figure I can shorten the screws or buy suitably length screws to mount the case feet so that there is enough clearance from the PCBs, or maybe tap the base of the case so that nuts aren't required.

[Edited by hardnrg on 04-26-2008 at 12:04 AM.]

If you use up to 10mm standoffs it looks like the pots will overhang a 12.5mm high cap (such as a Panasonic FC) in the C5- positions, but not so that it interferes with the pins. It looks quite tight, though.

I don't think you've made the hole for the pot shaft big enough in your front panel. The shaft itself is 6mm, but the threaded section which carries the mounting nut is more like 8mm. I'm assuming you'll be using the mounting nut to fix the pots through the 1.5mm of metal that's left after the front and rear recesses are machined.

I may be wrong here, but a 41mm diameter recess for a 39mm knob seems like it would leave too big a gap. Maybe someone could advise?

A machinist might do a lot of that job with a 6mm cutter, so you could increase the corner radius of the rear pot cutouts to 3mm since it's not critical.

Could you post a link to those posh feet?

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[Quoting miles hand]

...

I may be wrong here, but a 41mm diameter recess for a 39mm knob seems like it would leave too big a gap. Maybe someone could advise?

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[Edited by Ferrari on 04-26-2008 at 04:49 PM.]

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[Quoting Ferrari]

I have used 1mm gap surrounding the knop on my builds and it looks OK to me.

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It certainly does look OK, Ferrari.

I was thinking that if hardnrg was going to have the panel CNC machined he could take advantage of the excellent accuracy and bring the gap down to 0.5mm or so. I used to be a cabinetmaker and a gap of 1mm on something the size of a small amp's front panel doesn't look quite fine enough. Except when you do it, of course

I'm adding an Opus DAC to my M3. I'm told if I could tap 12v from my M3 board I could use that to power it (actually regulated to 7.5V). Since I'm using a 24V supply this is ok ? Where can I pull it from off the board, or in simple terms where do I connect my + & - wires ?!

Thanks!

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[Quoting mnemonix]

Hi,

I'm adding an Opus DAC to my M3. I'm told if I could tap 12v from my M3 board I could use that to power it (actually regulated to 7.5V). Since I'm using a 24V supply this is ok ? Where can I pull it from off the board, or in simple terms where do I connect my + & - wires ?!

Thanks!

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[Quoting miles hand]

Could you post a link to those posh feet?

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Mitron are the manufacturers of the aluminium case feet. There are three versions, which are all listed at Performance PCs:

Brushed Aluminium
Shiny Silver
Shiny Gold

There are also some other case feet:

MNPCTech

Silverstone

[Edited by hardnrg on 04-29-2008 at 04:09 PM.]

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[Quoting fierce_freak]

Will the upcoming OPA827 be usable in the M3? Looks like it to me, but I'm not the best with these things (also just realized forgot to check pin-out).

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However my dc offset is a concern plus I am getting no output and the Headphones are not blown.

I am using the Sigma 11 set at 24V

Measuring between IG and OG
ground is .71 mv
IG and OR
right is 6.4MV
IG and OL
left is 4.23MV

Any ideas where I should start looking into this?

I am using the OPA134PA in all three channels. I built the M3 basically stock.

Thanks in advance

[Edited by eddystoner on 05-03-2008 at 03:51 PM.]

How about posting some good photos of these areas of your build?

The output jack was it. DOH. what a Dummy.

Anyway thank you for all your hard work on these great projects.