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Offline chirality

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waveform generator advice
« on: May 21, 2018, 11:20:17 pm »
Hi all,

Apologies if this seems all too commonly asked around here. I'm just looking to get a function generator soon mainly for audio electronics/testing and I've narrowed it down to the Rigol DG1022Z and Siglent SDG2042X since both seem readily available and popular around here. Seems like audio-dedicated ones are $1500+ which is out of my budget.

Been looking at the datasheets and reading reviews on each for days and my head hurts, lol.

I'm aware of the price difference, bandwidth, and voltage constraints of each. Trying to keep my budget <$500.
Spec-wise, the Siglent seems better, eg. 16-bit vs 14-bit, but noise and distortion figures seem very similar (in datasheets, at least).
Do all think the Siglent would have that much more of a purer signal over the Rigol for audio work?
Does either do white/pink noise generation better than the other?

I take it that both do harmonic generation well?
Are there any major 'gotchas' between sweep functions? Between the library of built-in waveforms?
The UI of each are different; hard to tell which is best. Is the Rigol more intuitive? Can all of Siglent's functions be accessed without using the touch screen?
Are major firmware bugs ironed out on each for the most part?

I'm open to any other makes/models too but prefer new ones vs used. Any other new waveform generators on the horizon?

Really look forward to any thoughts and feedback.
 

Online tautech

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Re: waveform generator advice
« Reply #1 on: May 21, 2018, 11:32:38 pm »
SDG2042X
Yes all functions are available in the manual UI.
Bugs are mostly very few now and the only one we're waiting on is for Ext Ref default and visual indication.

There's a big thread on them here:
https://www.eevblog.com/forum/testgear/the-siglent-sdg2042x-thread/
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Online nctnico

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Re: waveform generator advice
« Reply #2 on: May 22, 2018, 12:08:25 am »
One thing to watch out for is log sweep. On my Siglent SDG1010 that doesn't work correctly (it is a stepped sweep).
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline blackdog

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Re: waveform generator advice
« Reply #3 on: May 22, 2018, 12:32:39 am »
Hi chirality,

I have the SDG2042X and one fine thing is the flatnes if yo0 stay below 1MHZ and i mean below! 1MHZ, 0.001Hz below it enough, then its delevers a perfect square wave!
On a good scope there are no abberations observable.

This does not mean that above 1MHz it is no longer good, that it is certainly, but not so perfectis is better than my other generator (Hameg and Rigol)

The distortion in the audio range is well under 80dB.

But maybe you have different applications, so do a lot of reading in the manual.
within a week or two I can test something for you if you have special questions about this generator.

Kind regards,
Bram
“Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe.”
 
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Offline chirality

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Re: waveform generator advice
« Reply #4 on: May 22, 2018, 05:35:18 pm »
Are there any advantages going with an analog function generator for audio work these days? I'm guessing they have a continuous rotary dial while changing parameters like frequency and voltage? I see Aim-TTi still make the TG300, perhaps others.
 

Online nctnico

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Re: waveform generator advice
« Reply #5 on: May 22, 2018, 06:10:11 pm »
I'd stay clear from the analog function generators. Their frequency is very unstable and they have a lot of other drawbacks like not being able to see the waveform parameters. You can use the rotary dial on a digital function generator to change frequencies quickly if you want. That even works on the cheap Feeltech function generators.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 
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Offline RoGeorge

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Re: waveform generator advice
« Reply #6 on: May 22, 2018, 06:29:59 pm »
Are there any advantages going with an analog function generator for audio work these days? I'm guessing they have a continuous rotary dial while changing parameters like frequency and voltage? I see Aim-TTi still make the TG300, perhaps others.

If all you want is audio, then just use a good sound card, like 24bits/96K, or 24/192.

A DDS generator is not for audio. It will have huge distortions and harmonics (compared with the ones introduced by the audio chain you intend to measure). Way to much to measure the performances of any average audio amplifier. Don't even think about very precise measurements for high end audio equipment.

Offline chirality

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Re: waveform generator advice
« Reply #7 on: May 22, 2018, 07:05:08 pm »
Well, I had asked since the SRS DS360 suited for audio use appears to use analog + DDS somehow  :-//

http://www.thinksrs.com/products/ds360.html

Just wish something like it where a bit cheaper for hobby use. Getting a cheap USB sound card is a great option but I prefer something dedicated or standalone. Perhaps a project would be to make my own.

Anyway, I appreciate everyone's input so far!
 

Offline RoGeorge

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Re: waveform generator advice
« Reply #8 on: May 22, 2018, 07:50:40 pm »
At the first glance, the DS360 have a 20 bit DAC, and judging by the price, those are probably real 20 bits (AFAIK Siglent's 16 bits are in fact only 14 real bits + interpolation, hence similar distortions between Rigol and Siglent), and most probably DS360 have good noise filters at output, all optimized for audio. I have no idea what is DDS + analog, and don't have the time to dive into researching that, sorry.

If you want to test audio performances, you will also need a sampling device or a signal analyzer for audio. Looking at the signal (or measuring it) with an oscilloscope will tell you only if something is terribly wrong.

For general hobby, including audio, a DDS is a nice tool to have on the bench. For general hobby, I will not like to limit the band to audio signal only, so I will prefer a general DDS, like Rigol or Siglent. I have a Rigol DG4102, and I'm not very happy about it. If it would be to buy again, I will probably go for a Siglent in the hope that will be better than my current Rigol (I never had Siglent, so zero personal experience with it).

Building your own generator sounds like an interesting project, too, with a lot of fun and experience to gain in between, also less expensive.

It's your call which choice will suit you better.
« Last Edit: May 22, 2018, 07:56:41 pm by RoGeorge »
 
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Online tautech

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Re: waveform generator advice
« Reply #9 on: May 22, 2018, 07:55:10 pm »
Are there any advantages going with an analog function generator for audio work these days? I'm guessing they have a continuous rotary dial while changing parameters like frequency and voltage?
With the Siglents, once any numeric parameter is selected you can further select just which digit you wish to adjust in single unit steps with the rotary encoder.
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Offline GregDunn

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Re: waveform generator advice
« Reply #10 on: May 25, 2018, 03:25:54 am »
Always some good recommendations on here!

I'm also looking for an arbitrary waveform generator with sweep functions in the audio range (10Hz-100KHz).

However, I don't need low distortion or noise, necessarily.  I have a modified Heathkit IG5218 which I'll actually be using for a measurement signal source - but I need something to provide a swept signal, tone burst, etc. in order to get a quick visual indication of how the signal is being changed by the device under test.  It would be nice if the generator had a stable output level and accurate frequency, but I sure don't need a lot of bells and whistles.

I know I could use a laptop and the audio output, but there are some hassles with that:

1) I only use Macs, and software is harder to locate (I'm not buying yet another computer!)
2) Setting up the computer for a quick measurement (which often involves retrieving it from elsewhere in the house) takes longer than the measurement
3) I need flat frequency response up to about 100KHz and I'm sure that's harder to do on a computer

Thoughts?
 

Offline montemcguire

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Re: waveform generator advice
« Reply #11 on: May 25, 2018, 06:32:49 am »
VMware Fusion will let you run a virtual machine with Windows or whatever you need to run. It provides a separate machine in a Mac window, and you can cut and paste between the Windows box and the Mac, share files, etc. It might not work with all possible hardware, but when you plug something in, you can tell it to attach the device to the Mac or Windows, and I have used it with a bunch of different Windows utilities, some of which drive test gear, and it works very well. VMware creates a very faithful PC inside of a Mac, so there's no need to do dual boot or any such nonsense. It's well worth considering if you need to use Windows software and you have a nice Mac.
 

Offline Performa01

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Re: waveform generator advice
« Reply #12 on: May 25, 2018, 10:59:19 am »
Always some good recommendations on here!

I'm also looking for an arbitrary waveform generator with sweep functions in the audio range (10Hz-100KHz).

However, I don't need low distortion or noise, necessarily.  I have a modified Heathkit IG5218 which I'll actually be using for a measurement signal source - but I need something to provide a swept signal, tone burst, etc. in order to get a quick visual indication of how the signal is being changed by the device under test.  It would be nice if the generator had a stable output level and accurate frequency, but I sure don't need a lot of bells and whistles.

I know I could use a laptop and the audio output, but there are some hassles with that:

1) I only use Macs, and software is harder to locate (I'm not buying yet another computer!)
2) Setting up the computer for a quick measurement (which often involves retrieving it from elsewhere in the house) takes longer than the measurement
3) I need flat frequency response up to about 100KHz and I'm sure that's harder to do on a computer

Thoughts?


For your application, the combination of the SDS1104X-E DSO and SAG1021 AWG option might be worth considering.

The AWG has a THD well below 0.1% up to 2MHz and together with the scope can provide a nice (up to) 3-channel bode plot without a computer. Yet the scope can be remote controlled from a PC with any OS via its webserver and you even get a pretty fast real time display with the latest firmware.

A (still incomplete) review can be found here:
https://www.eevblog.com/forum/testgear/siglent-sds1104x-e-in-depth-review/50/

The review of the SAG1021 is in replies #48 and #49 and a brief demonstration of the bode plotter can be found in reply #67
 
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Offline David Hess

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Re: waveform generator advice
« Reply #13 on: May 25, 2018, 11:14:54 am »
Are there any advantages going with an analog function generator for audio work these days? I'm guessing they have a continuous rotary dial while changing parameters like frequency and voltage? I see Aim-TTi still make the TG300, perhaps others.

An analog function generator would be more useful if you need triggered sweeps for network analysis.  Many have the option of being triggered, generating the trigger, or providing the ramp output.  The same analog function generators also often allow phase continuous AM and FM modulation.  To give a concrete example, what DDS would replace a Tektronix FG504 or FG507?

For distortion analysis you need something better than a DDS or analog function generator.  Some digital audio cards and adapters are suitable up to a point but how do you think they verify the performance of the digital audio cards themselves?  Sine sources with distortion low enough to test audio ADCs do not come from audio DACs.
 

Online nctnico

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Re: waveform generator advice
« Reply #14 on: May 25, 2018, 10:03:35 pm »
Are there any advantages going with an analog function generator for audio work these days? I'm guessing they have a continuous rotary dial while changing parameters like frequency and voltage? I see Aim-TTi still make the TG300, perhaps others.
An analog function generator would be more useful if you need triggered sweeps for network analysis.  Many have the option of being triggered, generating the trigger, or providing the ramp output.  The same analog function generators also often allow phase continuous AM and FM modulation.  To give a concrete example, what DDS would replace a Tektronix FG504 or FG507?
All these functions you list are standard on modern AWGs and probably can do these function even better. Even the cheap Chinese ones from Rigol or Siglent can do what you describe.
« Last Edit: May 25, 2018, 10:06:27 pm by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline GregDunn

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Re: waveform generator advice
« Reply #15 on: May 26, 2018, 04:56:01 am »
Well, VMWare is either $80 or $160 by itself.  Add the $250 for the SAG1021 and PC-only software (required), and we're nearing (or over) $400 already - plus it ties up my laptop while using it.  I could buy a nice simple standalone AWG for a lot less and not have to futz around with a laptop, cables and dongle.  It's just more effort for something that adds features I don't need.  I was hoping there might be a decent no-frills signal generator for considerably less money...  Maybe one of the low-end Siglent models isn't so expensive given the alternatives.
 

Offline RoGeorge

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Re: waveform generator advice
« Reply #16 on: May 26, 2018, 05:22:14 am »
Well, VMWare is either $80 or $160 by itself.

VMWare Player is free for personal or non commercial use. VMWare Workstation is not free. To create and run virtual machines, VMWare Player is enough.

An alternative to VMWare Player is VirtualBox, which have all the functionality of VMWare Player and Workstation (and maybe more) for free (non commercial use). Even more, VirtualBox is not only free, but also Open Source.
 
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Offline Performa01

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Re: waveform generator advice
« Reply #17 on: May 26, 2018, 06:39:26 am »
Well, VMWare is either $80 or $160 by itself.  Add the $250 for the SAG1021 and PC-only software (required), and we're nearing (or over) $400 already - plus it ties up my laptop while using it.  I could buy a nice simple standalone AWG for a lot less and not have to futz around with a laptop, cables and dongle.  It's just more effort for something that adds features I don't need.  I was hoping there might be a decent no-frills signal generator for considerably less money...  Maybe one of the low-end Siglent models isn't so expensive given the alternatives.

The SAG1021 is an option for the SDS1004X-E DSO series and cannot be operated standalone. I'm not aware of any software for a PC that could replace the scope for operating the AWG.

I just figured you might be interested in a solution that can do frequency response analysis without a PC. As stated in my review, the SDG1000X AWG series appears way more attractive anyway (at a higher price that is) and could serve both purposes: a fully featured standalone AWG and the required signal source for the bode plotter in an SDS1004X-E DSO.

The SDG1000X is not dirt cheap, yet the cheapest modern AWG (that isn't a toy and doesn't come from a C-brand) that I'm aware of.
There are a few cheaper ones, like Rigol DG1022 or Siglent SDG805, SDG1025, but they are older designs with considerably less capabilities and inferior signal quality.
 

Offline David Hess

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Re: waveform generator advice
« Reply #18 on: May 26, 2018, 01:15:31 pm »
Are there any advantages going with an analog function generator for audio work these days? I'm guessing they have a continuous rotary dial while changing parameters like frequency and voltage? I see Aim-TTi still make the TG300, perhaps others.
An analog function generator would be more useful if you need triggered sweeps for network analysis.  Many have the option of being triggered, generating the trigger, or providing the ramp output.  The same analog function generators also often allow phase continuous AM and FM modulation.  To give a concrete example, what DDS would replace a Tektronix FG504 or FG507?

All these functions you list are standard on modern AWGs and probably can do these function even better. Even the cheap Chinese ones from Rigol or Siglent can do what you describe.

On arbitrary waveform generators maybe but not on DDS function generators and no AWG I have seen supports external modulation.

Did you have any specific models in mind?

Update: The SDG1000X documentation says it has a trigger input and output although not at the same time and supports external modulation.  Siglent's other function generators apparently also have trigger inputs and outputs; I am not going to read through every one.
« Last Edit: May 26, 2018, 01:29:28 pm by David Hess »
 

Offline RoGeorge

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Re: waveform generator advice
« Reply #19 on: May 26, 2018, 01:52:21 pm »
My Rigol DG4102 have 2 BNC inputs on the back that can be used to feed external modulator signals into the DDS. Never used them, but the functionality is there.

From the Rigol DG4102 User Manual:

Quote
6. CH1: Mod/FSK/Trig
BNC female connector with 50Ω nominal impedance. Its function is determined by the current working mode of CH1.
 Mod:
If AM, FM, PM, PWM or OSK is enabled for CH1 and external modulation source is used, this connector accepts an external modulation signal.
 FSK:
If ASK, FSK or PSK is enabled for CH1 and external modulation source is used, this connector accepts an external modulation signal (users can set the polarity of the signal).
 Trig In:
If CH1 is in sweep or burst mode and external trigger source is used, this connector accepts an external trigger signal (users can set the polarity of the signal).
 Trig Out:
If CH1 is in sweep or burst mode and internal or manual trigger source is used, this connector outputs a trigger signal with specified edge.
7. CH2: Mod/FSK/Trig
BNC female connector with 50Ω nominal impedance. Its function is determined by the current working mode of CH2.
Chapter 1 Quick Start RIGOL
DG4000 Series User’s Guide 1-15
 Mod:
If AM, FM, PM, PWM or OSK is enabled for CH2 and external modulation source is used, this connector accepts an external modulation signal.
 FSK:
If ASK, FSK or PSK is enabled for CH2 and external modulation source is used, this connector accepts an external modulation signal (users can set the polarity of the signal).
 Trig In:
If CH2 is in sweep or burst mode and external trigger source is used, this connector accepts an external trigger signal (users can set the polarity of the signal).
 Trig Out:
If CH2 is in sweep or burst mode and internal or manual trigger source is used, this connector outputs a trigger signal with specified edge.
« Last Edit: May 26, 2018, 04:17:16 pm by RoGeorge »
 

Offline toli

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Re: waveform generator advice
« Reply #20 on: May 26, 2018, 02:21:35 pm »
Just a couple of notes on generation of clean sin wave from my limited experience.
There are a few methods on generating high purity signal with equipment that isn't good enough. There are a few papers on this topic which you can find using google, but most solutions are too complicated IMO with much calibration, so I would not go there unless there's no other way.

Harmonic distortion is something you can typically solve using filters. Getting very good filters can be expensive though, anywhere from 10's of $ a piece to a few 1000's. They will also only give you a limited frequency coverage obviously, so you'll need a few if you want to measure a few frequencies. There are various filter types depending on the frequency of interest and the tolerance, 3dB BW you are looking for, and signal power as well as the impedance of the line.
For audio use, you can probably roll your own filter without too much effort or cost. You can verify its transfer function vs. frequency to make sure it meets your needs to get a sufficiently clean signal at the output.

One thing which is often overlooked but can be an issue is non-harmonic spurs.As part of building a test setup for something at the office, I've made a few measurements a couple of months ago testing the spurs of the SDG2082X we have there. The measurement is done at 15Mhz due to the old HP generator I've used for comparison in the measurements I'm attaching, but I've seen similar results at the higher frequency too. Harmonics weren't too important for this use case since we have a very sharp LC filter placed after the generator which cuts it all done, its the spurs that are within the pass-band of the filter that I wanted to measure here, therefore the limited span.
Measurement is 5Vpk-pk sine-wave at 15MHz into 50ohm termination of the Siglent SA. The figure is attached below, green line is the SDG2082X, in blue is the SDG1020 I have at home, and in pink is my old HP 33120A. In this case both Siglent generators show spurs of similar level (the SDG1020 is a tad lower, but closer to the center frequency), but the HP is much cleaner which is very disappointing considering how old (and slow) it is compared with these more modern instruments. I've assumed that the 2082X will be significantly cleaner in this regard.
BTW, I did measure distortion of the generators too, but didn't compare. They were all within spec, but I didn't keep the results unfortunately.

The spur level in the figure is quite low and is within the spec of the instrument obviously. But the emphasis here is that this is something you can't filter out as easily as harmonic distortion. If relevant for you, non-harmonic spurs can be more of a problem than harmonic distortion. These can be very close to the signal of interest, so filtering them out will be more difficult. You would typically need a spectrum-analyzer to find them, but for audio you can use a sound card as a spectrum analyzer, there are plenty of great programs out there to help you.
« Last Edit: May 26, 2018, 02:24:37 pm by toli »
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Offline David Hess

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Re: waveform generator advice
« Reply #21 on: May 26, 2018, 03:43:36 pm »
Or you can build a two operational amplifier Wien bridge oscillator (1) which will deliver better performance than any analog or digital function generator and most digital audio sources.  If you want to verify the performance of the best audio ADCs, then something better than even this will be required.  If you do not want to build anything, then there are some suitable sound cards and USB connected audio interfaces which can be used.

If you are just testing audio power amplifiers, then you might get away with an analog or digital function generator and in practice, this is probably sufficient for most consumer level audio anyway.  It is certainly sufficient to learn the theory.

(1) One operational amplifier for amplification and one for common mode suppression.  http://www.analog.com/media/en/technical-documentation/application-notes/an43f.pdf
 

Offline RoGeorge

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Re: waveform generator advice
« Reply #22 on: May 26, 2018, 04:31:15 pm »
The spur level in the figure is quite low and is within the spec of the instrument obviously. But the emphasis here is that this is something you can't filter out as easily as harmonic distortion. If relevant for you, non-harmonic spurs can be more of a problem than harmonic distortion. These can be very close to the signal of interest, so filtering them out will be more difficult. You would typically need a spectrum-analyzer to find them, but for audio you can use a sound card as a spectrum analyzer, there are plenty of great programs out there to help you.

I think the "non-harmonic spurs" is phase noise (in rare cases specified as jitter instead of phase noise). Good generators specify the maximum expected phase noise. In DDS type of generators, the phase noise is caused mainly by the PLL and the crystal oscillator.

As a side note, my Rigol DG4102 have an unexpectedly good phase noise specifications:
Quote
Phase Noise Typical (0dBm, 10kHz deviation) 10MHz: ≤-115dBc/Hz

Offline David Hess

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Re: waveform generator advice
« Reply #23 on: May 26, 2018, 05:03:20 pm »
I think the "non-harmonic spurs" is phase noise (in rare cases specified as jitter instead of phase noise). Good generators specify the maximum expected phase noise. In DDS type of generators, the phase noise is caused mainly by the PLL and the crystal oscillator.

They are intermodulation between the sample clock and frequency content of the waveform produced by the non-linearity of the DAC and everything following it.  If the output waveform is synchronous to the sample clock, then only harmonic distortion remains.
 
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Offline RoGeorge

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Re: waveform generator advice
« Reply #24 on: May 26, 2018, 05:10:47 pm »
I just noticed that apart from the phase noise specifications, my generator has also a spec for spurious (non-harmonic) http://beyondmeasure.rigoltech.com/acton/attachment/1579/f-0167/0/-/-/-/-/file.pdf

Page 224 of 238
Quote
Spurious (non-harmonic)
Typical (0dBm) ≤10MHz <-65dBc >10MHz <-65dBc+6dB/octave

I thought non harmonic was directly related with the phase noise, now I'm puzzled  :-//

Later edit: @David Hess
I was looking for specs while posting, and didn't saw your post. Now it makes sense, thank you!
« Last Edit: May 26, 2018, 05:15:00 pm by RoGeorge »
 


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