Advice required on good quality hand held signal generator

gamve

Well-Known Member
Feb 9, 2013
50
1
236
Launceston, Tasmania, Australia
Hi Guys,
Need some advice on what people are using for test tone generation for setting recording levels bias etc in a portable unit.
I did a bit of research on WWW but the only thing I can find that looks half way decent is the NTI Minirator pro unit.
This is the unit I was looking at http://www.mcmelectronics.com/product/NTI-MR-PRO-/72-8605 These vary insanely in
price but they do look like they are good quality and have some other useful functions. I need to be able to set up my A80RC
myself (step learning curve both my machines are ex BBC London and do not have meter bridges) as I doubt there is a Studer
tech available anywhere near my home island state of Tasmania in Australia. Population here is only just over 500,000
Any help/advice is gratefully accepted
Cheers
Graham
 

stellavox

Well-Known Member
Apr 23, 2010
284
61
1,583
Hi Graham,

Welcome to the group. "Sounds like" to start, you really need to begin with a meter that can MEASURE audio signals rather than generate them. To check the reproduce capabilities of a deck, you put on a test tape; the first tone is typically 1Khz at some "standard level", say 250nW/m. Should you have a meter bridge, you can set this level to, say "0" VU on the bridge. Then there are tones to set the azimuth of the playback head, and finally frequency tones that sweep the audio spectrum to check/adjust overall response. I'll note here that most of the tones are sine waves - more on this later.

However, you don't have a bridge. I'd suggest you first look for an "all purpose" digital meter. Problem here is that you want to read AC volts, actually perhaps down to the 10's or 100's of millivolts, with a flat frequency response up thru the audio range. Most cheap meters, if they read AC at all, are only good for "perfect" sine waves, and only up thru mains frequencies (<100hz). What you need is a meter with what is called "True RMS Capability (TRMS)". When you look at the specs on this capability, you will see that their frequency response extends up into the audio range - how far depends on the meter. TRMS capability means the ability to "correctly" read a sine wave with a certain amount of inevitable distortion. Here in the US you can find decent meters for under $25 but probably have to pay $100 or more for TRMS capability.

Once you have the playback situation under control and want to "graduate" to record, you do need a generator, but the one you found seems like gigantic overkill. I know I've seen small simple units that generate "spot" audio frequencies (sine wave) for much less - remember that you need something that can output a signal at least into the 2 volt range - more ideally up to 10 volts or so.

Is Jaycar still around "down under"? - I remember them as being a very good source of electronics. Just checked MCM - they have a small "simple" audio generator (72-490) for $55 and a nicer "benchtop" unit (72-455A) for $180 - output levels up to +10dB. Looked quickly for TRMS meters and saw a Fluke for $140 BUT it's upper frequency response was only 1Khz. Good Luck!

Charles

ps - for us old farts, I have to put in a plug for using an ANALOG meter when making audio measurements - SOOO much easier to read (and interpret) especially when making (swept) frequency response measurements. Anyone (still) use a VTVM?
 
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microstrip

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May 30, 2010
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Welcome Graham. My non-orthodox advice would be get a PC with a good USB 192/24 soundcard and some measuring software. You can try the demo version of Spectraplus - it is free for 30 days.
It includes a really good generator and you can look for the performance of individual mechanical parts looking at the wow and flutter spectra. It is how I maintain my two A80's. There are really good databases with specific data for this machine in the net.
 

gamve

Well-Known Member
Feb 9, 2013
50
1
236
Launceston, Tasmania, Australia
Thanks Charles and Microstrip for your replies. Good advice on the PC methods but I really want to try and keep the things I love away from the things I hate, If you get my drift :) I sit in front of a PC all day at work and I don't really want PC's in my music room other than for burning a few CD's.
Charles I have the measure side of things sorted out, I have a Keithly 2015 which reads true RMS way past 20K, a good fluke and a Ballantine VTVM. I also have a set of McCurdy ATS100 meters (just need to learn how to use the meters). I got some 250nwb/m tapes in both 15ips and 7.5ips just recently from John French.
I was really asking about setting up the recording side. I really was wondering what you guys use, what's easy to use, what works well and what is reasonably priced. I sorta liked the idea of a hand held with XLR connections as I thought this would be very easy to use. I have seen similar items used a while ago, think it was on Youtube. I was surprised to find that there was frankly bugger all on Ebay and not much more on the net in these handheld type units. It seemed it was either a $100 unit (which looked like junk and had low output) or a $550 unit with nothing in between this pricing bracket. Surely there are some old pro hand held units floating around second hand somewhere. All other tape accessories seem to be relatively easy to find.
I will check Jaycar out, there is a store here locally.
 

tony ky ma

Industry Expert
Aug 21, 2010
630
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930
Whitby Ontario Canada
ps - for us old farts, I have to put in a plug for using an ANALOG meter when making audio measurements - SOOO much easier to read (and interpret) especially when making (swept) frequency response measurements. Anyone (still) use a VTVM?[/QUOTE]

A old tech guy like me still use all analog equipment , a VTVM is more easy to check the noise level
tony ma
 

microstrip

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May 30, 2010
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Thanks Charles and Microstrip for your replies. Good advice on the PC methods but I really want to try and keep the things I love away from the things I hate, If you get my drift :) I sit in front of a PC all day at work and I don't really want PC's in my music room other than for burning a few CD's. (...)

I understand you pretty well. But once you get the old instruments - and I also have some analogue instruments, great to for quick readings and to follow a trend - remember that the PC alternative is a great way to calibrate and check them - e.g. I check my analogue Kenwood wow and flutter meter with my PC.

I remember we had a similar debate in a TapeProject forum - you can look at their Tape Tech section for great advice from friendly experts. I have bought some old measuring equipment from Ebay, but I found I was spending more time checking and servicing it than aligning my machines. :)

http://www.tapeproject.com/smf/index.php?board=7.0
 

stellavox

Well-Known Member
Apr 23, 2010
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My audio instruments are the Amber 4400 and ST 1500A . Depending on how far one's addiction progresses, it's also really nice (necessary??) to have a generator with the ability to produce an asymmetrical waveshape so you can check absolute polarity - which the Amber can do.
 

microstrip

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May 30, 2010
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(...) Looked quickly for TRMS meters and saw a Fluke for $140 BUT it's upper frequency response was only 1Khz. Good Luck!

Charles

ps - for us old farts, I have to put in a plug for using an ANALOG meter when making audio measurements - SOOO much easier to read (and interpret) especially when making (swept) frequency response measurements. Anyone (still) use a VTVM?

Charles,
Just to add that long ago, as I did not have access to the proper measuring equipment at that time, I tried measuring TRMS using a DIY home built thermal converter!
 

Bruce B

WBF Founding Member, Pro Audio Production Member
Apr 25, 2010
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Too add further, even though you hate the PC route, you can get workstation software that will do it all. I can output all kinds of signals, measure inputs and even adjust azimuth with the numerous scopes they provide. It really is an all-in-one unit without having 2 or 3 outboard machines.
 

microstrip

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May 30, 2010
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So, besides Spectraplus, what other software is recommended?

This audioasylum page debates several packages.
http://www.audioasylum.com/cgi/vt.mpl?f=tubediy&m=212146

For very basic measurements sometimes I use the excellent free Soundcard oscilloscope - the generator even includes a programmable sweep, independent channels and phase angles. When used with the graphical cursors is is accurate enough for tape service purposes.
http://www.zeitnitz.de/Christian/scope_en

But the secret trick for excellent tape sound is carrying the last measurement with a good old analog VOM - it purges the system from any residual digital nastiness.
 

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gamve

Well-Known Member
Feb 9, 2013
50
1
236
Launceston, Tasmania, Australia
Hi Bruce,
Point taken. I admit I did not think along the lines of having a one tool fits all solution. I will reconsider my aversion to having a PC based solution. I do already have a reasonable PC set up that is dedicated to just music stuff. This PC was my old work station that was retired from my office recently. I guess I would only be looking at a decent sound card and the appropriate software. I have not researched this option, can you kindly suggest a good starting point for the workstation software? suitable soundcard etc
Cheers
Graham

Too add further, even though you hate the PC route, you can get workstation software that will do it all. I can output all kinds of signals, measure inputs and even adjust azimuth with the numerous scopes they provide. It really is an all-in-one unit without having 2 or 3 outboard machines.

WOW that was fast three posts snuck in while I was typing!!!
 

gamve

Well-Known Member
Feb 9, 2013
50
1
236
Launceston, Tasmania, Australia
All sorted. I found a more reasonably priced signal generator and then found the one I misplaced...DOH
I have a scope at work so I think I now have all the gear I need. Thanks for help and advice all

DSCF2880_zpsde69ba97.jpg
 

Speedskater

Well-Known Member
Sep 30, 2010
941
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368
Cleveland Ohio
For a signal generator, I would use a portable music source. Some care would be needed to get repeatable level setting's and to keep the DSP chip from getting into the act.
 

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