[rockinrob86]

Which of these do I need?!

I am a tinkerer, and do own and use an old scope.  I have an audio generator program on my phone that I will send a test signal into devices for, but I would really like to get the real deal and quit plugging my phone into amps - also, I have no idea what voltage the phone signal is.

Looking on ebay for something pretty cheap - this will mostly be used to troubleshoot guitar amps, stereos, the occasional mic or preamp build and tape machine tune ups.

I have a 70's/early 80's era phillips scope that works great for my purposes. 

[cyrano]

The phone signal is headphones. Low impedance, rather high voltage. Up to over volt or so.

Buy an audio millivolt meter to start and KNOW how much voltage is coming out of the phone? Or use the scope to measure it?

I mean, an older, cheap audio generator isn't gonna add much, unless you want the looks of it.

[ruffrecords]

I have a 70's/early 80's era phillips scope that works great for my purposes.

Use it to measure the phone output level.

Unless you want to try measuring distortion, any of the mentioned types of signal source will do.

Cheers

Ian

[Tubetec]

I got the Feeltech FY6800 arb gen some time back , it has its short comings , but for the price its hard to beat .
I also got a pair of HP 200cd oscillators , one Ive serviced and aside from some frequency drift across the ranges it works great  ,with a modern frequency counter to measure HZ you can set it much more accurately than what you read off the dial .

Search 'FY6600' and a link to EEV blog should show up top , theres about 70 pages on the Feeltech , all kinds of performance mods and tweaks you can do to make it better , for audio its good enough out of the box .

I dont own a mobile or smartphone so I havent much to say about using them for sound testing , making or recieving a call while using the phone output might cause interference in your circuits though . Computer software based test programs have come of age now too, REW allows testing that previously required a large trolley loaded with expensive test gear .

[rockinrob86]

I just don't like hooking my phone into circuits when tracing issues - even though I know I've built a proper pad, a  slip up would be problematic!

It also is annoying to have to always search for adapters, etc.  I would just prefer to have a dedicated bench sinewave/squarewave generator  with a knob that says 1V and a frequency knob.  No fuss, no danger to the phone, etc.

I will check out the suggested link, thanks!

I found this on ebay - https://www.ebay.com/p/LG-Precision-Function-Generator-GOLDSTAR-Fg-8002-A31/1251536342?iid=303109833589&chn=ps

[JMFahey]

Get a used old style Audio Generator, which has a frequency dial, multiplier switches so you cover all thye range, switch selectable output level , but MAIN point: is a true sinewave generator, so inherently low distortion. (so pure sinewave).

Function generators *synthesize*  the waveform, basically  a triangle wave which gets bent by diodes to approximate a sinewave, not the same.

Yes, they can go from 1 Hz to 1 MHz easily ... I never need such a range, so ...

EDIT: typical headphone output is around 200mV RMS, some reach only 100mV .

Impossible to get 1 V RMS out of a 3.7V lithium battery powered system.

[Tubetec]

The trick with the digital gens is post attenuation , dont dial down the output level digitally that will increase distortion , FY66/6800 is 14 bit and it beats my HP200cd by a distance in distortion terms as long as I attenuate after the output .
The arb does allow a few extra functions like sweep ,modulation and offset voltages etc and two phase locked output channels.
There are plenty of really good low distortion  oscillators , modern enough transistorised , much less hassle than a valve unit from the 50's , Kenwood had a few very low distortion oscillators ,bound to available cheap now ,check 'fleabay

[ruffrecords]

I just don't like hooking my phone into circuits when tracing issues - even though I know I've built a proper pad, a  slip up would be problematic!

It also is annoying to have to always search for adapters, etc.  I would just prefer to have a dedicated bench sinewave/squarewave generator  with a knob that says 1V and a frequency knob.  No fuss, no danger to the phone, etc.

I agree. I once wired up a phantom power switch wrong which meant +48V was always on one pin of the input XLR. My expensive Lindos test set did not like it at all. Fortunately it has built in fuses for idiots like me. They sent me some spares which I fitted easily and I was soon back in business. However, I learnt my lesson, and after that I always feed test signal via a fat Sowter 600:600 transformer which is pretty bullet proof.

I found this on ebay - https://www.ebay.com/p/LG-Precision-Function-Generator-GOLDSTAR-Fg-8002-A31/1251536342?iid=303109833589&chn=ps

I had something very similar when I started out. It is quite easy to do a quick response check by setting the dial to 20 and flicking from 20Hz to 200Hz, to 2KHz and then 20KHz. The square wave function is also useful for checking transformer ringing.

Cheers

Ian

[abbey road d enfer]

Function generators *synthesize*  the waveform, basically  a triangle wave which gets bent by diodes to approximate a sinewave, not the same.

That used to be the norm, but now many use DDS (direct digital synthesis). Depending on the D/A converters, THD can be as low as 0.03% with the 12-bit types.

[Tubetec]

I tried Sillanumsofts 'Visual Analyser' to look at the output of my 14 bit DDS ,
Distortion rises and falls depending on output frequency and how it relates to clock frequency , least favourable setting around .5% thd, which is what the machine spec says , most favourable setting about .0025% . Its very apparent on the FFT when you hit the sweet spots ,harmonics and noise drop by at least 20-30 db , I might try setting a stepped sweep only using favourable frequencies . Its funny but while auditioning the unit ,as I changed the frequency  I thought I could hear some little impurities in the sine creep in and out , FFT backs that up .

With VA working at 96khz the scope and fft display nicely even on an old pc , its not as polished as REW ,but its also less complicated to set up ,bears a strong resemblance to older Ymec audio tools ,but with enhancements .Does THD and THD+N ,but no breakdown of the individual harmonics like REW . It does have a calibratable Volt meter with different scales that also seemed to work very well , freely scaleable size in the window  makes it very easy to read from a distance.

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