I get the same on this 339a but only in certain settings. I wonder why. Try this in the overlapped next multiplier range. Like x100 at 10 on the left dial for 1 KHz and see if you.
get the same. Also try stepping the input range down 10dB and see if you get the same.
To have 1Vrms into the input of the notch filter you need to input -10dB of oscillator level.
Remember the input amp of the analyzer kicks everything up 10dB.
Noisy IC
Yes, i believe this is so, also. We had noticed this early on. i have the replacement quad IC ready to go into it. in fact, I'll do it now. Thx-RNM
Last edited:
Possibly requiring ac/cap coupling to the LDR (?) if it is dc sensitive (THD).
Rudolph the red nosed oscillator
Cleaned up my supply and added trims on the notch (>70dB). First the AD797 and second the AD844 just in case you thought a CFA would not work here. I suspect the thirds are down to the lightbulb's residual. This is a great find for anyone that simply want's to spot check a design, 30dB better than the 327 lamp oscillators that I built 20 yr. ago. There are two spurs left from my display drivers (easily ignored). It does take 10 or more seconds to settle, this goes hand in hand with the distortion. The correction is add 10dB to seconds and 5dB to thirds.
Cleaned up my supply and added trims on the notch (>70dB). First the AD797 and second the AD844 just in case you thought a CFA would not work here. I suspect the thirds are down to the lightbulb's residual. This is a great find for anyone that simply want's to spot check a design, 30dB better than the 327 lamp oscillators that I built 20 yr. ago. There are two spurs left from my display drivers (easily ignored). It does take 10 or more seconds to settle, this goes hand in hand with the distortion. The correction is add 10dB to seconds and 5dB to thirds.
Attachments
ocillator
Have a close look at where the 2nd H is now. This is at the expense of higher frequency performance. The distortion at it's best at 1KHz and 1Vrms into the notch filter.
I forgot to mention, in the list of what's been done, I put a 50k trim across A3R48 and trimmed the total R to 10k. This forces the LDR to operate at a lower resistance much the same as putting a trim in series with the LDR. It has the same effect.
New stuff.
I removed capacitor A1C46. Cut the trace at right at the pin5 of A1U1 and added a 33 ohm
cheapo $0.06 carbon composite resistor in series with pin 6 and the output trace.
Tweaked the Jfet distortion trim and this.
I'll see if I can fix the high frequency performance with out losing the 1KHz.
Cheers,
Have a close look at where the 2nd H is now. This is at the expense of higher frequency performance. The distortion at it's best at 1KHz and 1Vrms into the notch filter.
I forgot to mention, in the list of what's been done, I put a 50k trim across A3R48 and trimmed the total R to 10k. This forces the LDR to operate at a lower resistance much the same as putting a trim in series with the LDR. It has the same effect.
New stuff.
I removed capacitor A1C46. Cut the trace at right at the pin5 of A1U1 and added a 33 ohm
cheapo $0.06 carbon composite resistor in series with pin 6 and the output trace.
Tweaked the Jfet distortion trim and this.
I'll see if I can fix the high frequency performance with out losing the 1KHz.
Cheers,
Attachments
The Goal is close -- low THD and variable freq -
Cut trace at pin 5? whats on pin 5?
[I did the 50K trim.]
Got that second down there quit aways. I hope the high freq THD are not much different. Then, we'll have a nice flexible, variable freq source.
I have been focused over on the analyzer... Its can be useful for general purpose (?) stand alone bench meter that will work down well below -120. Just a few IC and parts upgrades are all that is needed.
The lower THD limit for a working amp is about .00001%..... plus, external parts and contacts and the like are also at these numbers and you cant make anything real without such external parts.
Thx - RNMarsh [I too am very interested in the QA400.... esp if it is at least as good as this mod 339A]
Cut trace at pin 5? whats on pin 5?
[I did the 50K trim.]
Got that second down there quit aways. I hope the high freq THD are not much different. Then, we'll have a nice flexible, variable freq source.
I have been focused over on the analyzer... Its can be useful for general purpose (?) stand alone bench meter that will work down well below -120. Just a few IC and parts upgrades are all that is needed.
The lower THD limit for a working amp is about .00001%..... plus, external parts and contacts and the like are also at these numbers and you cant make anything real without such external parts.
Thx - RNMarsh [I too am very interested in the QA400.... esp if it is at least as good as this mod 339A]
Last edited:
Rick, I think David meant pin 6, to add a small isolating resistance between the output of the amp and the load of the rest of the circuitry. This has worked well for me a couple of times -- I used 47 ohms recently on the output of an LT1468. But I haven't done anything to my 339 as yet -- still have a few other fish to fry first.
We are far from the initial topic of this thread now -- time to make a thread on modding the HP 339A?
We are far from the initial topic of this thread now -- time to make a thread on modding the HP 339A?
Hi Dick,
Yes I meant pin 6. Sorry. I worked late into the evening got tired.
It is the isolation resistor.
Well we can a have a moderator move all this to a new thread. But I forgot what the topic is. Is this really not fitting? Maybe it's evolved this way.
What does everyone say?
Cheers,
Hi Dirkwright,
At the least it would be incredibly expensive. I not convinced, for the total analyzer performance, it would be worth it. But who knows what will become of this greening.
Cheers,
Well, maybe just the oscillator board(s)? Power supply? I dunno, just throwing ideas out there.
Well, as the opening poster it does not matter to me. I like the conversation. Even though I have contributed little past my intitial question, I have faithfully followed this thread. I have learned a lot and serveral members have been very helpful and generous helping me when I did not understand something.
One good point about starting a separate thread is providing an easier search for members in the future specifically looking for HP 339A information.
I recently purchased an HP 339A that was supposed to be fully functional. Unfortunately, it came to me not functioning. I have read the manuals circuit descriptions and studied the schematic and started trouble shooting. I think I have narrowed it down but I am not sure.
Anyone familiar with the HP 339A and willing to provide me a little mentoring on the side via email please PM me.
Regarding my opening post, I have an oscillator that I am quite happy with for my work. It is the HP 239A (which is very similar to the oscillator in the HP 339A Analyzer). And should I need a lower distortion oscillator I have the Victor 1 KHz Oscillator.
Thanks to all!
One good point about starting a separate thread is providing an easier search for members in the future specifically looking for HP 339A information.
I recently purchased an HP 339A that was supposed to be fully functional. Unfortunately, it came to me not functioning. I have read the manuals circuit descriptions and studied the schematic and started trouble shooting. I think I have narrowed it down but I am not sure.
Anyone familiar with the HP 339A and willing to provide me a little mentoring on the side via email please PM me.
Regarding my opening post, I have an oscillator that I am quite happy with for my work. It is the HP 239A (which is very similar to the oscillator in the HP 339A Analyzer). And should I need a lower distortion oscillator I have the Victor 1 KHz Oscillator.
Thanks to all!
Test Equipment forum --
I think just changing the title of the forum to cover low thd oscillator and analyzer mods - Test and Measurment forum; Hardware and software.
So far we have several oscillators to choose from - Victor and Scotts and there are several HP models which could be in the running for upgrades.. like the HP239A. And, there are several measurment products which could be reviewed and discussed. In other words, the full spectrum of sources and analyzers for audio test and measurment. Right now such hard/software is scattered all over the place... speaker builders and thier hard/software etc. Put all the test equipment in a forum (with sub groups) to discuss them and any DIY mods et al and help in using them. Might even include SIM programs (?) Thx-RNMarsh
I think just changing the title of the forum to cover low thd oscillator and analyzer mods - Test and Measurment forum; Hardware and software.
So far we have several oscillators to choose from - Victor and Scotts and there are several HP models which could be in the running for upgrades.. like the HP239A. And, there are several measurment products which could be reviewed and discussed. In other words, the full spectrum of sources and analyzers for audio test and measurment. Right now such hard/software is scattered all over the place... speaker builders and thier hard/software etc. Put all the test equipment in a forum (with sub groups) to discuss them and any DIY mods et al and help in using them. Might even include SIM programs (?) Thx-RNMarsh
Last edited: