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Low-distortion Audio-range Oscillator
Low-distortion Audio-range Oscillator
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Old 7th June 2016, 05:01 AM   #5001
1audio is offline 1audio  United States
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Low-distortion Audio-range Oscillator
For very low level signals gold will work better than silver in a typical relay. Silver will need more current or contact force to make a good connection. The gold will actually weld at much lower levels. I think Coto published some stuff on this and a bunch of bits were sacrificed on the Blowtorch thread on this issue.

For low level signals mercury wetted relays are very good but have issues. The usual preference are relays with a wiping action on the contacts, which are a crossbar type of contact. There are some inexpensive latching relays of this type I'm told.

The insides of the Shibasoku represent a full proper relay implementation (and retirement options for the relay salesman) http://www.diyaudio.com/forums/equip...ml#post3393204
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Old 7th June 2016, 06:20 AM   #5002
davada is offline davada  Canada
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Here is a Grayhill similar to the Uni switch. Sells for 40USD. don't know anything about it just came across it.

These are the 71 series switches.
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Old 7th June 2016, 07:53 AM   #5003
jan.didden is offline jan.didden  Europe
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Quote:
Originally Posted by Bob Cordell View Post
Hi Jan,

There is a chapter in my book that covers this. It is chapter 13, section 11, "fuse, relay and connector distortion". It has distortion measurements of this type made on several relays as a function of frequency.

Cheers,
Bob
Thanks Bob, I will review that section carefully.

Jan
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Old 7th June 2016, 08:02 AM   #5004
jan.didden is offline jan.didden  Europe
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Quote:
Originally Posted by davada View Post
Here is a Grayhill similar to the Uni switch. Sells for 40USD. don't know anything about it just came across it.

These are the 71 series switches.
These are good switches, I've used then to switch low level stuff in the thermal transient test bed.

Jan
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Old 7th June 2016, 08:25 AM   #5005
Dave Zan is offline Dave Zan  Australia
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Quote:
Originally Posted by davada View Post
Here is a Grayhill similar to the Uni switch. Sells for 40USD.
Thanks, these look fine and even better that Jan has tried them.
With options for economical, medium and top-end, that lets me feel confident that there will be no availability problems on a crucial part.
So it looks like a direct PCB mount switch, no wires and it will simplify SMT NP0 capacitors.
Now I can move towards a finalized board.
I plan to fit it on a Eurocard, anyone have any pros or cons for that?

Best wishes
David

Last edited by Dave Zan; 7th June 2016 at 08:32 AM.
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Old 9th June 2016, 03:45 AM   #5006
1audio is offline 1audio  United States
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Low-distortion Audio-range Oscillator
RE Eurocard-
Overall I like the idea but it begs a few questions; I/O connection locations, controls and power connections. I would like both on the connector and on the front interface as options. Also what length?
Eurocard stuff is less common in the US. Finding case options will be important.
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Old 9th June 2016, 06:02 AM   #5007
Dave Zan is offline Dave Zan  Australia
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Originally Posted by 1audio View Post
RE Eurocard-
...I/O connection locations, controls and power connections. I would like both on the connector and on the front interface as options...
Personally I plan to make it a sub-rack module, like the Elma, Vero KM6 or Schroff.
Schroff looks the most reasonably priced so far but, as usual, any recommendations welcomed.
So the output, XLR very likely, and controls on the front panel.
Power via the connector at the back, from a power supply in the back of the rack, kind of a Eurocard version of the Tektronix TM500 system.

Quote:
Eurocard stuff is less common in the US.
If anyone else wants to build it then they can box it as they wish, just use the Eurocard as a plain PCB.

It should fit on the smallest standard card, 160 mm deep and still have spare space.
So I will probably fit a square wave option.
The last time I did that I used a 555 because it was simple, very cheap and fairly useful.
I am sure there are better options now, anyone have recommendations?
I am inclined to take it to a separate output, maybe BNC.

Best wishes
David
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Old 9th June 2016, 06:39 AM   #5008
jan.didden is offline jan.didden  Europe
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A separate square output would be good for external equipment sync and trigger.

Jan
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Old 9th June 2016, 08:37 AM   #5009
Dave Zan is offline Dave Zan  Australia
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Originally Posted by jan.didden View Post
A separate square output would be good for external equipment sync
I am not sure how practical it is to have the square wave run and still provide a super low distortion sine wave, there will be power supply noise and feed thru problems.
These can be overcome of course but is it worth the effort, when do I need a synchronized square wave?
I had the idea to have the square wave mainly so I can do distortion tests and then check square wave response all with one piece of equipment.
Since the square wave does not have to be super low distortion it is easy to make it heavy duty to drive 50 ohm loads.
And that seems natural to connect to a BNC.
It may be more useful to make the quadrature output available for sync, a la Cordell distortion analyser.

Best wishes
David
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Old 23rd June 2016, 02:58 AM   #5010
Dave Zan is offline Dave Zan  Australia
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Originally Posted by scott wurcer View Post
The reference reminded me of a question.
On p.156 he states that examples use NPN bipolar but P channel MOS because the P channels have a better back gate connection, to the source rather than the substrate.
This surprises me because I would expect the N channel to be preferable due to better speed and presumably the fabrication process could be done a complementary way so it's the N channels with the better connection.
So, is this not done simply because of some established practice in the fabrication process?
Or is there a reason, to better match the P and N devices perhaps?

Best wishes
David
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