Tone generator question

[duduac]

I don`t have a proper tone generator and I am running a software from my Iphone to the tape recorder. Now when the manual says " Apply a 1Khz, +4dbm test signal to the input 1..." How the heck do I set my tone generator to +4dbm? I could not find any where how to and now I`m just stuck with this without knowing what to do. I know it is stupid.

Cheers

 

[miroslav]

Your generator (whatever it is) has to be able to put out a +4 dBm signal....and them you can set/choose it.

Not sure how far you will get using an iPhone app for that.
Calibrating a tape deck requires more dedicated test/measurement equipment.

 

[jpmorris]

The output signal should read around 1.228v on an AC voltmeter for a +4 signal.
What kind of recorder is it, though? Usually if it wants +4 it's expecting a balanced XLR input, and the iphone is going to output unbalanced -10 dBv or something unless you have some kind of special interface for it.

 

[Hammerstone]

Hmmm when I opened up a new tape I didn't know where to set the levels for tones so I just used 0dB at 1kHz for a reference. Am I doing it wrong?

 

[toddyjoe]

I have used computer software and mobile-phone software to generate tones before for double-checking tape decks but it is a bit of a headache. It worked best with a computer with decent software and a high-quality DA converter and I ended up having no trust in the phone-app tests.

In either situation I had to ensure the "tone generator" was actually outputting a clear and steady sine wave as that was sometimes a problem using equipment not designed for this purpose. I then had to make sure I had the right audio connectors and adapters because my phone in particular did not have an XLR jack (go figure). Then I had to get out a quality true-RMS multimeter that would accurately measure AC voltage at 1 kHz and the other frequencies I would be using as most cheap digital multimeters are neither true-RMS nor accurate outside a narrow range of a few hundred Hertz. I then had to figure out ways to get the computer and/or phone to accurately output the correct AC voltage correlating to the reference levels at a given frequency, which sometimes would not work because the computer software or phone would only adjust in single-decibel increments that did not allow enough accuracy in voltage adjustment. After all was said and done I was proud of the DIY accomplishment but lost at least a day's worth of hobby time that I could have spent making music if I had simply bought a cheap tone generator on Craigslist.

 

[miroslav]

The tool to have is an NTI Minirator....it has the tones and levels needed for doing audio system calibrations.

 

[duduac]

has any of you guys tried the Velleman Handheld

The minirator is quite too expensive for me haha

 

[miroslav]

Which model are you looking at?

 

[duduac]

Velleman Handheld HPG1

 

[duduac]

any thoughts???

 

[ecc83]

Douglas Self's book, Small Signal Amplifier Design is a goldmine of information and circuits.
There is a very simple line up oscillator based on the TL072 that uses simple diode stabilization and not the now hard to source thermistor.
Distortion is about 0.5% quite good enough for response/bias tests (tho not for distortion of course!)

Beware the digital multimeter for audio! I have checked several at work and only my trusty old Fluke 83* has a flat 20-20kHz response. Many meters, even so called "true rms" jobs start to droop as low as 2kHz. Cheapest solution is to buy as good a quality 0-10, 0-3 analogue meter movement of 1mA fsd and build an amp round it using an NE5532 and OA91 Germanium diodes. You can calibrate that at 100Hz and be pretty sure it will still be right at 20kHz (or find someone like moir to check it!) .

Can't do simple electronics builds? Learn! Otherwise you are doomed to failure working with analogue gear IMHO!

*They were about 300quid many years ago mind!

Dave.

 

[TimOBrien]

Audacity, the free audio editor has a tone generator built into it.
You can specify Hz and duration.
Just make a .wav file and export it to just play on your phone.

Keep it simple....

 

[jpmorris]

Audacity, the free audio editor has a tone generator built into it.
You can specify Hz and duration.
Just make a .wav file and export it to just play on your phone.

Keep it simple....

I'm not sure that will solve the problem of outputting a balanced +4 signal from the phone's headphone sockets...

 

[duduac]

I also found this one Elenco

 

[ecc83]

I'm not sure that will solve the problem of outputting a balanced +4 signal from the phone's headphone sockets...

+1. Generating the tone is only half the battle. The signal generator must also produce a well specified LEVEL into whatever load is connected.

Dave.

 

[Hammerstone]

Can you elaborate please?

 

[ecc83]

Can you elaborate please?

Certainly.
My trusty Levell TG0528 audio generator has an output voltmeter scaled in V, mV and dBu (N.B. dBu is archaic enough, let us leave the even more ancient dB "em" in the audio dustbin of time please!) and the output is adjusted by a precision switched attenuator and a fine control pot...BUT! That level only holds true for a load of exactly 600Ohms, any form of resistive attenuator is going to be load sensitive.

Now the whole issue with tape recorders is that their frequency response is highly level sensitive, squash and all that, so you must know with some precision the signal voltages you are squirting in. Big, bruising 1/2track pro machines can usually be specc'ed at -10vu but anything slightly "domestic" is best done at neg 20vu (and you can't read -20 with any sort of accuracy on a vu meter,not that you should use the machine's meters for lineup anyway as a rule) Levels become even more important if you have a Dolby machine.

Computer generated tones:
VERY accurate frequencies but the level is totally dependant on the sound card. I just checked the output of my HP i3 lappy 10mins ago. Generated 1kHz at neg 6. Slammed the internal VC to max and the headphone out was 0.501V rms on me trusty Fluke 83. That's -3.8dBu INTO A VIRTUAL OPEN CIRCUIT! Note also that the machine would only produce 1volt rms for 0dBFS and therefore could not deliver the OP's +4dBu. Another brand/mark of computer will produce a different result (tho', once calibrated will be very stable and accurate) . One answer is to build a booster with say 20dB of gain, you could use two sides of an NE5532 and have a balanced output at very low impedance. This could be "calibrated " at 100Hz with a bog S meter and you could be pretty sure it would hold up at 10kHz.

Clear as mud?

Dave.

 

[duduac]

Hi Dave, I wish I could spend some time doing what you said, but right at this moment building something like that is not feasible as I hardly have any spare time between university, work, music and also family. Hopefully, one day I will have the chance to do that, but for now it is just a dream. As I noticed you are very good with electronics could you give me some advice with a tone generator? I have these options;

- Velleman Handheld HPG1
- Elenco
- Kikusui ORC-27A ( It`s a valve generator and the seller said it is working)

I also found this brand new chinese one, but I`m quite unsure if I can trust this one

- TAG101 Audio Generator

I don`t want to break my piggy bank so if you could give good cost-benefit oscillator for calibrating my Tascam MS16, MCI JH110a and Tascam 388 would be heavily appreciated.

 

[ecc83]

Hi Dave, I wish I could spend some time doing what you said, but right at this moment building something like that is not feasible as I hardly have any spare time between university, work, music and also family. Hopefully, one day I will have the chance to do that, but for now it is just a dream. As I noticed you are very good with electronics could you give me some advice with a tone generator? I have these options;

- Velleman Handheld HPG1
- Elenco
- Kikusui ORC-27A ( It`s a valve generator and the seller said it is working)

I also found this brand new chinese one, but I`m quite unsure if I can trust this one

- TAG101 Audio Generator

I don`t want to break my piggy bank so if you could give good cost-benefit oscillator for calibrating my Tascam MS16, MCI JH110a and Tascam 388 would be heavily appreciated.

Go for the Velleman. The TAG 101 is second hand and therefore you cannot trust the calibration.
The Velleman will deliver up to 8volts pk to pk that's about +8dBu and should be plenty. It has a source Z of 50Ohms and so should be fine.

Now! What I need is a pink noise generator of about the same price!

Dave.

 

[duduac]

Oh man! That`s just great! Thanks for all the help!! I`ll try to get this week and I`ll let you know!

BTW why do you need a pink noise generator? Have seen this Velleman kit?

Cheers