Buy a Function Generator

[s.mosfet]

hi,
i would buy a function generator, (300-400$)
Which is the best choice, DDS or analog?

i've seen:
isotech gfg-2120 (DDS)
tti tg330 (analog)
tti tg1000 (DDS)

1) Do analog generators have more distortion?
2) now i'm making audio projects, but i don't know which projects i'll make in the future...
so, what's the use for a 5MHz/10MHz generator? digital projects? what in particular?
(I'm not interested in the telecommunications right now)

thanks


thanks

[alm]

i would buy a function generator, (300-400$)

You should be able to pick up a decent unit for that amount of money.

Which is the best choice, DDS or analog?

Everything else being equal, DDS.

TTi sounds familiar to me, never heard of Isotech. But I've never seen any TTi equipment in the flesh, so can't really comment on quality.

1) Do analog generators have more distortion?

Yes. The sine in an analog function generator is usually a modified triangle wave, which resembles a sine on the scope screen, but is not very pure. DDS is basically a DAC generating the sine, and can be very pure for a function generator.

2) now i'm making audio projects, but i don't know which projects i'll make in the future...
so, what's the use for a 5MHz/10MHz generator? digital projects? what in particular?

Digital clock signals is one example (most micro controllers support clocks up to at least 16MHz or so). Testing stability at high frequencies. Testing frequency-dependent behavior of components like capacitors (bypassing digital circuits requires low inductance at target frequencies). Probably depends on your interests, I'm sure other people will have very different examples. The 1-10MHz is probably not critical for many users.

Note that there are also dedicated audio oscillators. They are much less versatile (only sine from 1Hz-100kHz or so), but can have lower distortion than even DDS function generators, and are useful for distortion measurement (source must be better than amplifier). Function generators are the jack of all trades of signal sources.

[s.mosfet]

i'm sorry...
300-400 €

[Bored@Work]

i'm sorry...
300-400 €

Even better (check the current exchange rate).

Now, as fare as I know, Isotech is one of those companies buying instruments wholesale and rebrand them (or getting them branded at the factory). TTi is a British manufacturer doing their own R&D.

[Ronnie]

Note that there are also dedicated audio oscillators. They are much less versatile (only sine from 1Hz-100kHz or so), but can have lower distortion than even DDS function generators, and are useful for distortion measurement (source must be better than amplifier).

I also plan to design audio pre and power amps in the next couple of years I'm considering the Elenco SG-9200 Audio Generator for US$213.20 from Test Equipment Depot. THD up to 50 kHz is 0.05% (-66 dB). What I don't like is its 600 ohms output impedance; I prefer 50 ohms output impedance.

http://www.testequipmentdepot.com/elenco/generators/audio-generators/sg9200.htm

[saturation]

I would also look at Instek's function generator, the 1003, which I own.  I also got it as a general signal source to include basic audio measurements, and its DDS sine waves go down to 0.05% THD or ~- 60dB so it says in the spec sheet; I've briefly confirmed that myself checking it via FFT output of the Rigol 1052E to see the harmonic content of its sine wave output.  Tequipment.net sells it for $150.

I do know that audio amp designers want distortion far below that, on the order or .005% and those signal sources are rarer and more expensive.  There are many on eBay of superb quality designed specifically for audio, usually brands by HP and Tektronixs, where clean output is more important than frequency stability.

Note that there are also dedicated audio oscillators. They are much less versatile (only sine from 1Hz-100kHz or so), but can have lower distortion than even DDS function generators, and are useful for distortion measurement (source must be better than amplifier).

I also plan to design audio pre and power amps in the next couple of years I'm considering the Elenco SG-9200 Audio Generator for US$213.20 from Test Equipment Depot. THD up to 50 kHz is 0.05% (-66 dB). What I don't like is its 600 ohms output impedance; I prefer 50 ohms output impedance.

http://www.testequipmentdepot.com/elenco/generators/audio-generators/sg9200.htm

[FreeThinker]

i'm sorry...
300-400 €

Even better (check the current exchange rate).

Now, as fare as I know, Isotech is one of those companies buying instruments wholesale and rebrand them (or getting them branded at the factory). TTi is a British manufacturer doing their own R&D.

Isotech I believe is the tradeing name for RS brand products.They may respec a standard unit or (more likely ) Simply rebadge  them.I have an old TTi TDS 220 fg and the build quality is great.
GeeK note! Did you Know That Clive Sinclair (Uncle Clive to you Speccy Fans) owned Thandar?.

[Crippled]

Is the Chinese VC2003 any good?

[saturation]

As a rule, no.  3 reasons, I've read about quality control problems with this brand, regardless of whose name is on it.  If you can return a defective one and finally get a good one going, you still can't say if the product lives up to its specification sheet.  For its typical sell price of $200, there are better options.

Except for the sweep and AM modulation features on this model, you can get excellent basic waveform generation specs from the Instek 1003, which as an example, is a branded model of an ODM FG also sold as Quakko, under a slightly different casing. See bottom pics.

  
Victor reviews:

http://www.amazon.com/Sinometer-2MHz-Function-Generator-VC2002/dp/B000JD0BVG/ref=sr_1_24?s=hi&ie=UTF8&qid=1293105674&sr=1-24

http://www.eham.net/reviews/detail/7839

Victor also goes by the name Sinometer & more rarely, Mastech.




The Instek & slightly upgraded clone [both sell ~ for $150].  The Instek is calibrated by Instek, a cal certificate is included in the box which details how the cal was made.  The Quakko doesn't have a cal certificate but includes an integrated frequency counter, and a output -40dB attenuator :

Is the Chinese VC2003 any good?

[Crippled]

Thanks for the reply.
Dave reviewed a more expensive instek and the frequency was very jumpy.
I think I go for the BK 4001A.

[saturation]

Yes, that Instek Dave reviewed is an analog FG, they are all 'jumpy', the cheaper they are the jumpier they are.  As prices rise, the more stable the waveforms are and the higher their capable frequency.

The DDS types are a different technology for doing the same thing.  Instek is one of the few recognized names to have such a stable, high quality output DDS FG for such a low price.  

There is a detailed thread on FG here:

https://www.eevblog.com/forum/index.php?topic=633.0

The B&K model 4001a
http://www.tequipment.net/BK4001A.html

is a better alternative to the Victor at near the same price.  

The B&K is well respected  its frequency stability is 0.2% at 24 hours, the Instek is .002%, or 100x more stable.  You can compare the specs side by side, and because B&K and Instek are reputable, those numbers are quite certainly true.  

If you really need sweeping, AM/FM/PW modulation etc., you'd have to move up the model line of DDS and they do become more costly than analog generators, so you'd need to weigh the importance of such features to your budget.

Thanks for the reply.
Dave reviewed a more expensive instek and the frequency was very jumpy.
I think I go for the BK 4001A.

welcome, enjoy.

your working is really good. Thanks for sharing

[Ronnie]

Looks like B&K model 4001a is not applicable for audio design since sine wave distortion is specified on the high side "less than 2% (1Hz - 100kHz)". I prefer less than 0.1%.

[saturation]

FGs are general purpose signal sources; if you really need < = 0.1% THD, you need a dedicated low distortion audio generator.  They have better quality but limited frequency range, usuall to 200kHz, for about the same cost as a FG capable of going to 3 MHz.  Many very good old ones are on eBay for about $50-100, with claimed THD under 0.008% such as the Tek SG505, assuming they are still in spec.

https://www.eevblog.com/forum/index.php?topic=633.msg7686#msg7686

The Instek 1003 DDS FG is about 0.18% THD+Noise.

Looks like B&K model 4001a is not applicable for audio design since sine wave distortion is specified on the high side "less than 2% (1Hz - 100kHz)". I prefer less than 0.1%.