You will need to find an SG505 or SG502 signal generator, but there is a Tektronix DA4084 on EBay at the moment, and the initial price is dirt cheap. Note-- it comes with its own TM503 power supply and you CAN NOT put the sig gen in the left most compartment. The DA4084 is very much like the AA501, except it has SINAD instead of intermodulation.
here's a link -- someone should snatch this up:
http://cgi.ebay.com/Tektronix-DA408...ryZ25423QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
here's a link -- someone should snatch this up:
http://cgi.ebay.com/Tektronix-DA408...ryZ25423QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
anatech said:
I think that the problem with this is that folks like to look at that pretty image of the fundamental...but the residuals are where the story is at.
DA's have pretty much crashed in price...what the country needs instead is a good, stable signal generator like a Tektronix SG505 or AP-1 but at a cost of thirty or forty bucks. something like this would advance the progress of civilisation.
Hi Gaetan,
You have an excellent unit. The weak point will still be your sound card, however you will have more dynamic range by using the HP 333. Many people miss how good the older HP stuff is. I can only imagine how good the new stuff is!
Old stuff I would love to have : All HP, 3585A, 3562A, 8901B, 8903, a new 6000 series scope and some RF generators. An arbitrary waveform generator would be playing, but lovely to have.
I'll bet a simpler load of new gear would more than do the trick.
-Chris
You have an excellent unit. The weak point will still be your sound card, however you will have more dynamic range by using the HP 333. Many people miss how good the older HP stuff is. I can only imagine how good the new stuff is!
Old stuff I would love to have : All HP, 3585A, 3562A, 8901B, 8903, a new 6000 series scope and some RF generators. An arbitrary waveform generator would be playing, but lovely to have.
I'll bet a simpler load of new gear would more than do the trick.-Chris
From the software analysis side of things, check out BaudLine. It runs only in Linux, but has some extremely powerful signal analysis tools. One of its greatest features is that it can do very long term averaging of the frequency domain, allowing you to get extremely precise frequency measurements, average out noise and transient conditions etc. Of course, basic THD, SNR and other distortion measurements are built-in. While not automatic, it is easily capable of measuring other parameters as well, such as IMD and frequency response.
Very powerful tool.
Very powerful tool.
jackinnj said:
Just a small note on using the diodes as indicated:
there exists one problem with this topology in that the diodes will forward conduct at +/- 0.7 volt if the power supply powering this device were to be switched off.
Instead of the intended Vcc/Vee +/- 0.7 V
This will result in excessive current into the diodes if the source device could produce the required current.
So to clarify don't switch the device with the diodes off while still connected to the source.
A small relay right at the input which drop out when the supply voltage are interrupted will cure this problem
The other issue that may come up is the variable capacitance from the reverse biased diodes. Double them in series and drive the new junctions with a buffered version of the signal to eliminate that issue.
Hi nonoise,
A relay was mentioned by jackinnj and it was also mentioned that the diagram was simplified. I imagine this was for exactly the reason you brought up.
-Chris
Hi nonoise,
A relay was mentioned by jackinnj and it was also mentioned that the diagram was simplified. I imagine this was for exactly the reason you brought up.
-Chris
Hello
M. Renardson has an interesting way to measure very low distortions, here's the link;
http://www.angelfire.com/ab3/mjramp/golopid6.html
Gaetan
M. Renardson has an interesting way to measure very low distortions, here's the link;
http://www.angelfire.com/ab3/mjramp/golopid6.html
Gaetan
anatech said:The other issue that may come up is the variable capacitance from the reverse biased diodes. Double them in series and drive the new junctions with a buffered version of the signal to eliminate that issue.
Hi nonoise,
A relay was mentioned by jackinnj and it was also mentioned that the diagram was simplified. I imagine this was for exactly the reason you brought up.
-Chris
Hi Anatech, yes the relay were mentioned and were probably used as
recommended but I have seen this type of protection often being recommended in application notes (diodes only) and felt that the potential for miss understanding / inadequate protection should be clarified.
From experience I certainly agree on the potential coupling of noise into the input from the supply lines via the diodes, they could also rectify HF noise and perhaps create DC offset problems.
The addition of a small Common Mode choke might help
anatech said:
I think that the junction capacitance of a 1N4148 is about 2e-12.
Jung, I believe it's in "Op Amp Applications" recommended Schottkey diodes for even lower noise.
An externally hosted image should be here but it was not working when we last tested it.
Hi jackinnj,
I imagine it depends on what the impedances are. Certainly this type of issue can often be ignored, and sometimes it may be a surprise.
Your posted diagram should show people how much worth there is in having signal conditioning done for them. What to roll your own one of these people?
-Chris
I imagine it depends on what the impedances are. Certainly this type of issue can often be ignored, and sometimes it may be a surprise.
Your posted diagram should show people how much worth there is in having signal conditioning done for them. What to roll your own one of these people?
-Chris
and speaking of DA's
I have a HP 339A, in addition to a TEK AA501 and the Boonton 1120 -- the HP339 had gone a little wonky on range switching -- with the oscillator kicking out or taking a long time to stabilize -- here's a word of advise -- just a little DeOxit on the range switching wafers did the trick -- it now consistently gets down into the very low THD% of my SG505 sig gen.
I have a HP 339A, in addition to a TEK AA501 and the Boonton 1120 -- the HP339 had gone a little wonky on range switching -- with the oscillator kicking out or taking a long time to stabilize -- here's a word of advise -- just a little DeOxit on the range switching wafers did the trick -- it now consistently gets down into the very low THD% of my SG505 sig gen.
Having just acquired a new distortion analyzer I started poking around to see what are the current thoughts on them. I have an extensive collection including the Boonton in the schematic.
Re the Boonton input circuit- you will notice that the diodes are isolated from the input by the resistors so its not possible to zap them with any input signal. However that fuse in the chain to the ground relay gets zapped all the time- when you reset the instrument that relay closes so the balanced amp you attached is now driving through the relay and fuse to ground. Otherwise the input circuit can reliably deliver .0007% THD performance.
The HP voltmeter's analog output has a big distortion bump in it since its got the meter rectifiers in the feedback loop.
I just got a Shibasoku oscillator and analyzer to see if they are as good as claimed. They seem to be- a residual system distortion at 10V 1 KHz of around .00006% and a built in harmonic analyzer. I will play with it some more to see if the numbers are real. However for daily use the Boonton is still the easiest and fastest.
My collection includes ST1700B, ST1710, KH6810 (& matching programmable oscillator and a KH 4400 oscillator), Boonton 1120, 1121 & 1130, Radiometer Automatic analyzer (all analog sweeping tracking analyzer) and an HP 8903. The ST's are nice but fragile and showing their age. The KH is good but not as good as the Boonton's. The Radiometer is really neat but more of a collectors item than a daily user. I have access to some AP's but they are so computer centric they are slower to use for circuit optimization. The R&S is a neat idea using passive notch filters in front of an FFT, but expensive.
I liked the cancellation solution, but its far from original. RCA made an instrument with passive networks to do the same thing in the '50s, which I'd love to get for my collection. Peter Walker used the same technique to prove to himself that most amplifiers have inaudibly low distortion and its the speaker that matters.
I think distortion products less than 100 dB below program are just not important but chasing them is still an interesting intellectual pursuit. Getting the other stuff right is easily as important
Re the Boonton input circuit- you will notice that the diodes are isolated from the input by the resistors so its not possible to zap them with any input signal. However that fuse in the chain to the ground relay gets zapped all the time- when you reset the instrument that relay closes so the balanced amp you attached is now driving through the relay and fuse to ground. Otherwise the input circuit can reliably deliver .0007% THD performance.
The HP voltmeter's analog output has a big distortion bump in it since its got the meter rectifiers in the feedback loop.
I just got a Shibasoku oscillator and analyzer to see if they are as good as claimed. They seem to be- a residual system distortion at 10V 1 KHz of around .00006% and a built in harmonic analyzer. I will play with it some more to see if the numbers are real. However for daily use the Boonton is still the easiest and fastest.
My collection includes ST1700B, ST1710, KH6810 (& matching programmable oscillator and a KH 4400 oscillator), Boonton 1120, 1121 & 1130, Radiometer Automatic analyzer (all analog sweeping tracking analyzer) and an HP 8903. The ST's are nice but fragile and showing their age. The KH is good but not as good as the Boonton's. The Radiometer is really neat but more of a collectors item than a daily user. I have access to some AP's but they are so computer centric they are slower to use for circuit optimization. The R&S is a neat idea using passive notch filters in front of an FFT, but expensive.
I liked the cancellation solution, but its far from original. RCA made an instrument with passive networks to do the same thing in the '50s, which I'd love to get for my collection. Peter Walker used the same technique to prove to himself that most amplifiers have inaudibly low distortion and its the speaker that matters.
I think distortion products less than 100 dB below program are just not important but chasing them is still an interesting intellectual pursuit. Getting the other stuff right is easily as important
As far as I understand most amplifiers distort audibly even before clipping. Put thru a solid test this shows that only a few amplifiers are audibly transparent. This could indicate that those who have tested and claim transparency among most amplifiers have choosen a less than optimum method.
Also most CD players distort audibly.
My referencs on this matter is LTS, the Swedish "sound technologicall society". As far as I remember of hundreds of amps tested only one have passed the test as audibly transparent on all lewels, a big bridged Bryston amp.
For what it's worth.
/Peter
Also most CD players distort audibly.
My referencs on this matter is LTS, the Swedish "sound technologicall society". As far as I remember of hundreds of amps tested only one have passed the test as audibly transparent on all lewels, a big bridged Bryston amp.
For what it's worth.
/Peter
Demian --
Since we last saw you on the board I acquired the innards of another Boonton 1120 and one with the usual power supply issues. I also bought a ProLogix USB based GPIB controller, recommended by Conrad.
On the AP2 the Boonton 1120 measures 0.0007% THD with 14V balanced output. The SG505 oscillator measures a tad better than this -- 0.00022%
The most useful test (to my way of thinking) is to look at the distortion residuals with a good spectrum analyzer. The spectrum analyzer will also tell you if your distortion analyzer is actually telling the truth.
The 1/16th amp fuses do blow all the time --
Jack
Since we last saw you on the board I acquired the innards of another Boonton 1120 and one with the usual power supply issues. I also bought a ProLogix USB based GPIB controller, recommended by Conrad.
On the AP2 the Boonton 1120 measures 0.0007% THD with 14V balanced output. The SG505 oscillator measures a tad better than this -- 0.00022%
The most useful test (to my way of thinking) is to look at the distortion residuals with a good spectrum analyzer. The spectrum analyzer will also tell you if your distortion analyzer is actually telling the truth.
The 1/16th amp fuses do blow all the time --
Jack
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