Designing a universal diff-in/diff-out Head Amp

[billshurv]

And if anyone in europe is getting a set of boards I'll share the cost as MOQ is usually 5

 

[mkc]

Hi Bill,

Check out PCB Prototype & PCB Fabrication Manufacturer - JLCPCB. We use them for prototypes and such. They are very reasonably prices. And when ordering check how much it actually costs to order 20 or 50 pcb's. Usually it's very cheap to double or triple the number of pcb's

Cheers,
Mogens

 

[grufti]

The first clone that I am aware of has come to life. It still needs the switches and thermal coupling of the input transistors, and some day a box to live in, but that's about it.

Thank you again, Hans.

 

[Hans Polak]

The first clone that I am aware of has come to life. It still needs the switches and thermal coupling of the input transistors, and some day a box to live in, but that's about it.

Thank you again, Hans.

Well done, nice soldering.

Hans

 

[mdesgeans]

Thank you for this work Hans and for sharing. I'll build one set too.

I struggle finding the 2412 0,5µF PET film Capacitors mentioned in the BOM

 

[grufti]

You can probably find 0,47µF PETs. No significant difference.

 

[mdesgeans]

You can probably find 0,47µF PETs. No significant difference.

No, I find only a 2416 PEN 0.47µ, not fully fitting and not exactly same technology

 

[brianco]

And if anyone in europe is getting a set of boards I'll share the cost as MOQ is usually 5

Yes please...me too (x2 sets for UK)

Thanks.

 

[grufti]

2220 PET caps are going to be a fairly good fit. WIMA and AVX have those.

 

[mdesgeans]

2220 PET caps are going to be a fairly good fit. WIMA and AVX have those.

Thank you Grufti. I saw those ones already but abandonned them, the pad not being as wide as recommended in the datasheet, but they can fit, yes. Still I wonder

@Hans, I know you mentioned not to be involved in any build but are you indeed using 2412 PET film caps for C7/C8?

 

[billshurv]

Yes please...me too (x2 sets for UK)

Thanks.

That's enough for an order. At some point as soon as I've cleared the things on the bench I'll order them (hopefully in next month)

 

[Hans Polak]

I missed the contributions of the last few weeks for some reason.
I’ll come back to the 0,5uF caps that I used.
I have 3 complete sets left of base board + 2 transimpedance boards, so if anybody is interested for € 10,- + VAT per set plus cost of shipment, send me a PM.

Hans

 

[Hans Polak]

@Hans, I know you mentioned not to be involved in any build but are you indeed using 2412 PET film caps for C7/C8?

This is the cap that I used from Mouser.

CB042D0474JBC AVX | Mouser Nederland

Hans

 

[mdesgeans]

Thank you Hans

 

[Hans Polak]

Two additions:

1) In the Mouser link above, you are directed to the correct 0,47uF component, no worries, however I believe they made a typo. There is no such thing as a CB042.... this must be CB047......
The same component from Farnell is listed as 1657965.

2) In the BOM a ADA4528 is listed. There are two versions, one with 1 amp and one with 2.
The version needed here is a ADA4528-2A with 2 amps.

Hans

 

[Hans Polak]

For convenience, I have collected all information in the first posting of this thread.

Hans

 

[timgrindell]

Hi Hans,
Assuming a fairly "standard" MC cartridge with an output in the 0.25--0.5mV range and wanting to use your Universal Diff-in/Diff-out Head Amp with your Non-plus-ultra Phono stage would you suggest using your head amp with the MM version (OPA1641) of the Non-plus rather than with the 797 higher gain version?
Any thoughts, advice or recommendation?
Much appreciated
t

 

[Hans Polak]

Hi Hans,
Assuming a fairly "standard" MC cartridge with an output in the 0.25--0.5mV range and wanting to use your Universal Diff-in/Diff-out Head Amp with your Non-plus-ultra Phono stage would you suggest using your head amp with the MM version (OPA1641) of the Non-plus rather than with the 797 higher gain version?
Any thoughts, advice or recommendation?
Much appreciated
t

Sorry for my late reaction, I missed your posting.
Well, both can be done. Since I already had the NPU Phono Amp with the AD797, I 'm using the Head amp now with a low 10dB gain setting in front of it.
But the advantage of using the OPA1641 in the MM setting, is that you have both an MC and an MM phono amp at your disposal and you wouldn't have to match AD797 amps.
In that case the gain of the Head Amp should be 20dB higher.

Hans

 

[timgrindell]

Thank you for your generosity in providing the designs and in giving your advice.
From reading the NPU article it seems that a possible 3rd method, ie reducing the gain of the 797. is not really feasible.
I love the square wave in the NPU article and will add that project to my "To Do" list.
best
tim

 

[Markw4]

Having had quite some time listening to the Transimpedance Head Amp, around 100 LP's, I came to the next conclusion that I wanted to share.
Although there is no measurable difference between Power Bank or Wall Wart, there is quite some difference in listening experience.
Sound with the mains adapter is a bit chill and analytical, whereas the sound with the Power Bank, a clear winner, is a warm and involving.

I came across a similar issue with dacs, wallwarts, and power banks. In my case the problem was caused by common mode noise from the wall wart centered around 1 or 2 MHz (as detected with a portable shortwave radio using the external antenna input as a probe input). I'm sure you will understand what must be happening. Anyway, getting rid of the common mode noise fixed the audible sound quality issue for me.

Power banks may have some of that too, but at least it doesn't form a ground loop when other equipment in the system is grounded. In some cases power bank switching regulator noise can still cause its own problems, but usually not so much as wall warts often tend to do.