Pete Millett ATEST

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jack
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Re: Pete Millett ATEST

Post by jack » Mon Mar 20, 2017 9:37 am

Andrew wrote:
Mon Mar 20, 2017 9:24 am
This is my circuit, it's simple enough.
Yep - that's the same as the App Note one, however, a tiny (semantic) point...

The symbol in your schematic is for an N-channel enhancement mode (normally off) MOSFET, and DN2540s and similar are depletion mode (normally on) devices - the symbol is subtly different. See https://en.wikipedia.org/wiki/MOSFET#Circuit_symbols - the symbol in the App Note is correct.

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Re: Pete Millett ATEST

Post by Andrew » Mon Mar 20, 2017 12:49 pm

Yeah, should be solid lines, not dashed. The schematic is from Eagle, I can't recall but it was art work I was after to make a PCB up. My guess is I just choose a part that had the correct pads and worked backwards, well that's my excuse anyway.

If you want the Eagle files I can post them up, Max?

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Re: Pete Millett ATEST

Post by Max N » Tue Mar 21, 2017 8:15 am

Thanks guys, that's very helpful
Andrew wrote:
Mon Mar 20, 2017 12:49 pm
If you want the Eagle files I can post them up, Max?
Thanks Andrew. I think I can do a reasonably tidy job with those adapter boards, and I've ordered a few, so I'll give that a go. Your little boards are undoubtedly the tidiest solution, so if I struggle with the adapters I'll come back to you if that's OK?

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Re: Pete Millett ATEST

Post by Max N » Mon Apr 22, 2019 8:03 pm

I can't believe its 2 years since I built my ATEST and I'm finally getting around to using it.....the years are flying by too fast.
BTW, the audiotester website was AWOL for a while but is now up again. I've downloaded the trial version and will get a licensed copy if I get to grips with it.
Before I start, I was reading Pete's page and saw that the input is differential but not balanced. Also, if the -ve input signal goes above about 10V RMS, the input amp will clip. If I want to measure balanced signals above this level, what are my options? I guess I could attenuate the signal before feeding it to the ATEST. Or build a Broskie unbalancer, or some other balanced to unbalanced conversion circuit......

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Re: Pete Millett ATEST

Post by Nick » Mon Apr 22, 2019 8:47 pm

1:1 coupling transformer maybe if you want to measure signals with a sizeable common mode voltage.
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Re: Pete Millett ATEST

Post by Max N » Mon Apr 22, 2019 9:08 pm

Thanks Nick. I was planning to measure the secondary of a bifilar wound 1+1:1+1 interstage at about 70V signal level (140V PP). I was thinking that if I ground one side of the secondary (to suit the ATEST input) then that would throw off the capacitive coupling of the bifilar interstage?

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Re: Pete Millett ATEST

Post by Nick » Tue Apr 23, 2019 1:38 am

Well, you could check if it matters by measuring the TX then change the phase of the output and see if it makes a difference.

If not let the secondary side float. Not sure if you are using a laptop or desktop to run the atest.
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Re: Pete Millett ATEST

Post by Max N » Tue Apr 23, 2019 8:17 am

I don't think I can change the phase of the output - the two secondary windings are joined at the centre. So there are only 3 secondary leads (primary is the same). So if I swap the two 'end' secondary leads, then output valve 1 will get the signal that was going to output valve 2 and vice versa, but the transformer won't see any difference?
(As it happens, I have been thinking about opening the transformer up and separating the two centre-tap enamelled wires and attaching another lead, but I haven't done that yet because it will make a bit of a mess - I'll need to cut through the varnish and remove the plastic covers....)
I will try grounding one end of the secondary and see what happens.

I'm planning on using a Windows 10 laptop with a Focusrite 2i2 USB interface. I have used an 8i6 for many years as a DAC on my iMac and I've been happy with it.

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Re: Pete Millett ATEST

Post by Nick » Tue Apr 23, 2019 8:54 am

Ok, so if the secondary is the bifilar windings, won't the centre tap be grounded in use anyway, so just measure centre to secondary, and then repeat for other phase. I may not be understanding what you are trying to do.
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Re:

Post by Paul Barker » Tue Apr 23, 2019 10:04 am

Dave the bass wrote:
Fri Dec 27, 2013 12:19 pm
Dunno if anyone else has seen this but the December issue of 'Everyday Practical Electronics' has construction details of another USB Interface that might be interesting to some here too. I've scanned the spec of the device in for your perusal.

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Re: Pete Millett ATEST

Post by Max N » Tue Apr 23, 2019 10:43 am

Nick wrote:
Tue Apr 23, 2019 8:54 am
Ok, so if the secondary is the bifilar windings, won't the centre tap be grounded in use anyway, so just measure centre to secondary, and then repeat for other phase. I may not be understanding what you are trying to do.
I’m trying to minimise the distortion of the push-pull driver stage at the output of the interstage.
I hoped to include in the measurement things like cancellation of even-order harmonics.
You’re right I could measure the distortion of one phase and assume all the even harmonics will cancel in the following stage, but actually that will depend on how well everything is balanced etc.
And then if I wanted to experiment with ways of introducing (or preserving) some 2nd harmonic, it would be easier if I could measure the differential signal to see if I was succeeding.

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Re: Pete Millett ATEST

Post by Nick » Tue Apr 23, 2019 11:04 am

Ok, so in that case you do need a differential input. You could make something up using one of the THAT Corp balanced receivers, they are easy to use and not hugely expensive. Though of course you would need to attenuate accurately to not overload the inputs.

http://www.thatcorp.com/1200-series_Hig ... _ICs.shtml
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Re: Pete Millett ATEST

Post by Max N » Tue Apr 23, 2019 6:42 pm

Thanks Nick I'll look into those.

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Re: Re:

Post by Dave the bass » Tue Apr 23, 2019 9:13 pm

Paul Barker wrote:
Tue Apr 23, 2019 10:04 am

Dave has photobucket allowed use of their images in forums again ? Or are you subscribed?
It seems some images yes.

I've not subscribed so cant upload anymore as I'm well over the freebie limit.
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Re: Re:

Post by pre65 » Tue Apr 23, 2019 9:22 pm

Dave the bass wrote:
Tue Apr 23, 2019 9:13 pm
Paul Barker wrote:
Tue Apr 23, 2019 10:04 am

Dave has photobucket allowed use of their images in forums again ? Or are you subscribed?
It seems some images yes.

I've not subscribed so cant upload anymore as I'm well over the freebie limit.
Same with me.
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