A Modern Loftech TS-1 Audio Test Set

Where we discuss new analog design ideas for Pro Audio and modern spins on vintage ones.
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JR.
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Re: A Modern Loftech TS-1 Audio Test Set

Post by JR. » Thu Nov 30, 2017 10:19 am

The image I posted is a newhaven... Some models require 100pc minimums.

I like the KISS aspect of apha-numeric.....

With 16 characters I can display level and frequency simultaneously.

JR

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JR.
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Re: A Modern Loftech TS-1 Audio Test Set

Post by JR. » Sat Dec 02, 2017 3:42 pm

some relatively simple features I could add to the TS-too would be square wave and triangle wave.... One feature that speakers guys might like is a warble tone (to break up standing waves for speaker/room measurements).

Since I will read the frequency and level pots (or rotary encoders) in normal mode, I could also use them to step through menu functions/choices.

JR

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Re: A Modern Loftech TS-1 Audio Test Set

Post by brianroth » Sat Dec 02, 2017 8:52 pm

Hiya John. Part of my biz these days is finding/restoring analog recording desks.

When "flying" through a few dozen channels is my Olde Method using a square wave to quickly test the EQ circuits on each strip. Go/No Go as it is....

Sidebar....more often than not:

1. Ancient electrolytic coupling caps...LF loss.

2. Scratchy pots.

Bri
Professional audio and video systems design/installation/maintenance.
www.BrianRoth.com

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JR.
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Re: A Modern Loftech TS-1 Audio Test Set

Post by JR. » Sun Dec 03, 2017 1:25 pm

a square wave is easy-peasy.... using a look-up table, that would just be two values. :lol:

JR

PS: I think my new $10 VOM may make a 5V square wave output at 50Hz...not sure why but my fancy fluke doesn't

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mediatechnology
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Re: A Modern Loftech TS-1 Audio Test Set

Post by mediatechnology » Mon Dec 04, 2017 8:30 am

a square wave is easy-peasy.... using a look-up table, that would just be two values. :lol:
I don't think its that easy.
I've yet to see a true square wave from the output of any audio DAC.
You'd be better off squaring the sine out with a 15 cent comparator.

Square wave would be useful however.
I used to use the same trick as Brian to find bad caps.
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JR.
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Re: A Modern Loftech TS-1 Audio Test Set

Post by JR. » Mon Dec 04, 2017 10:17 am

mediatechnology wrote:
Mon Dec 04, 2017 8:30 am
a square wave is easy-peasy.... using a look-up table, that would just be two values. :lol:
I don't think its that easy.
I've yet to see a true square wave from the output of any audio DAC.
You'd be better off squaring the sine out with a 15 cent comparator.

Square wave would be useful however.
I used to use the same trick as Brian to find bad caps.
You need to think like an embedded designer about this. Adding extra glue for a single little used function is an expense we try to avoid. A raw square wave without bandlimiting is perhaps too extreme for testing (or not).

The output from the DAC should be useable as is, at most it may require an edge rate limited square wave (in the data file). Otherwise the multiple signal choices are a lot less attractive (KISS).

I will need to make one and see if there are Gibbs phenomenon issues (from DAC output decimation), but that may still be usable for looking at tilt/overshoot.

JR

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mediatechnology
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Re: A Modern Loftech TS-1 Audio Test Set

Post by mediatechnology » Mon Dec 04, 2017 10:53 am

You could use a PWM output for a cleaner square wave.
"There does seem to be a pattern where, the more difficult a truth is to stomach, the higher the hysteria levels go internally at Google."
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JR.
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Re: A Modern Loftech TS-1 Audio Test Set

Post by JR. » Mon Dec 04, 2017 12:36 pm

mediatechnology wrote:
Mon Dec 04, 2017 10:53 am
You could use a PWM output for a cleaner square wave.
I am not sure how..unless you are talking about a dedicated square wave only. I have a lot of experience making sine waves from PWM and not close to good enough for this project. Then that roughly 3V PWM modulated square wave signal would need to be amplified which in any real world scenario involves a LPF. Again more glue that can be avoided "if" I can get a usable square wave from the standard audio output.

Since this square wave will be used for audio testing I am comfortable with some bandwidth limiting. I guess I will need to see how bad it is coming from a codec to see if dedicated square wave circuitry is remotely worthwhile.

JR

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mediatechnology
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Re: A Modern Loftech TS-1 Audio Test Set

Post by mediatechnology » Mon Dec 04, 2017 1:48 pm

I was thinking you could use the PWM for square wave only and switch the input of the output stage electronically between PWM and DAC using a pad/DPOT for final coarse/fine level.
"There does seem to be a pattern where, the more difficult a truth is to stomach, the higher the hysteria levels go internally at Google."
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JR.
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Re: A Modern Loftech TS-1 Audio Test Set

Post by JR. » Mon Dec 04, 2017 2:13 pm

If I am already switching between different sound data files for sine, triangle, warble, whatever, a square wave is easy peasy and requires no glue.

JR

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