The diyAudio First Watt M2x

[SGregory]

I will experiment with other inputs in time.
So as I got further into testing I find that I was able to achieve 0mV offset and equal Vdrop across the resistors in the second channel. For the first one (the one I was concerned about), I ultimately set it so that the Vdrop was equal and found that the offset voltage was only 1mV. I don't expect that to be a huge issue.

I would much rather optimize the gain stage for best linearity and have a cap if needed. C1 is the lesser of the distortion evils. But lucky in that I was able to equalize and not have C1.

Final results:

Should never say Final......

Now onto the other M2x amp. These are part of a 3-way active system

 

[6L6]

A three-way system powered by M2x? That’s going to be neat!

 

[SGregory]

2 x M2x (mid & hi) and my 23yrd old Aleph 5. Maybe an f5T or an AlephJ if I am able to add enough bias to drive 4R speakers

 

[6L6]

Both of those work just fine with my 4R speakers…

 

[namghiwook]

I've planned wiring like this.

220VAC main -> 1.25A slow blow fuse -> inrush current limiter -> 400VA 21-0-0-21 toroidal transformer -> SLB power supply -> +/-24 VDC power chord beteween separate chassises -> M2X amp (or other first watt class A amps)

Is CL-60 proper for inrush current limiter or are there other recommendations?

 

[6L6]

Refer to SLB documentation. (But yes, it’s fine…)

 

[AudioSan]

I'm not sure that a 1,25A fuse will hold a 400VA transformer at start up. Not even at 240V mains. And sure not if the mains voltage is lower. You can try it, but have some 1,5A and a little higher rating fuses around just in case.

 

[namghiwook]

I've bought 1.5A fuses too.
I'll try a 1.5A fuse first.
Thank you for advising.

 

[toolkit]

New build alert! I've been running an F5 for a couple of years but without warning one channel went pop and after replacing the obvious items I ran out spares, but had some M2x boards built up so here we are.

I've installed Ishikawas and onto Dim Bulb tests.

On both channels it does what I expect - i.e. bright then straight dims to nothing.

But then I spotted after about 30 seconds the bulb starts to come back on again - not fully but then I didn't wait long before I switched off again.

This happens on both channels - is this actually expected behaviour as the circuit "warms up"? - or have I got something in wrong?

 

[Mark Johnson]

Link to Sept 2019

 

[toolkit]

Thanks Mark - thought I'd read that a while back and tried searching but obvs my query terms weren't very good.

 

[grataku]

M2x is back on the rig after two year hiatus. The isp7 with LM49720, rocking the best sound (IMHO) of all the input boards. 😉
Very detailed hint of sweetness and not fatiguing.
A nice BIG break from the vintage Vfet sound and the miniACA!

 

[namghiwook]

I've bought the jfets for Ishikawa daughter board.

Matched JFETs - Toshiba 2SK170/2SJ74 Quad 8-11mA

Are these right for Ishikawa?

 

[ItsAllInMyHead]

^ Yes

 

[slk23]

@Mark Johnson

Ordering parts for the IPS7 input board and the D45H11G is a bit hard to find. Is there an easy substitute?

 

[amandarae]

511-D45H11 should be good and there's 348 units available last time I looked at Mouser.

 

[slk23]

Thanks @amandarae

Any suggestions for ZTX696B subs? Mouser preferred. TIA.

 

[grataku]

ZTX696B

no joy on the mouser but I am not sure why we need 180v transistors. MJ should be able to explain.

https://www.digikey.com/en/products/detail/diodes-incorporated/ZTX696B/152467

 

[amandarae]

Unfortunately, I can only see Digikey as the only one with stock (1,702 pieces).
ZTX696B

 

[slk23]

Thanks @grataku and @amandarae. I was hoping to avoid multiple shipping charges but it seems like every project I work on these days requires orders from 2-3 vendors to get all the parts.