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Old 10th January 2013, 03:48 PM   #1521
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by 1audio View Post
You seem to have missed the discussion; essentially a lamp is a very linear positive tempco thermistor. David showed a really elegant solution for making a multiplier with a lamp and some dc voltage. The remaining task is a level detector to "steer" the level with higher precision that can be had from the lamps. SG suggested using a simple rectifier/integrator, which should be fine since the response time is slow anyway.

This could be used with either a Wein bridge or a state variable oscillator. I'm not sure how practical this would be for an HP339.
Thanks for putting it together... back into perspective.... appeared as just a bunch of ideas, at first. And, I start loosing focus. Hopefully, this will lead to a plan of action sometime along the way... or I loose interest. What further can be done with the 339A and what is, if anything, going to be done along these lines you outlined as discussed here?

Is there another existing product besides the 339A which has even greater potential for making a super source/analyzer. One which has built-in some of the techniques discussed here.

A QA400 will be here tomorrow for me to play with :-)

Changing the worn output level pot on the 339a reduced the 10KHz H3 a lot... leaving only H2. BUT at lower frequencies (1KHz) the H3 came back up to near H2 levels. Will try different pot material, later.

How is the CES? I decided not to go this year... first in 20 years or so. Thx-RNMarsh

Last edited by RNMarsh; 10th January 2013 at 04:05 PM.
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Old 10th January 2013, 03:56 PM   #1522
RNMarsh is offline RNMarsh  United States
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For 339A.... a dual opamp and a few needed parts could be mounted on an adapter/header and plug into U1 oscillator socket if the thd can be lowered with a series pair of super low noise/thd opamps. -RNM

Last edited by RNMarsh; 10th January 2013 at 04:02 PM.
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Old 10th January 2013, 05:49 PM   #1523
davada is offline davada  Canada
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Quote:
Originally Posted by RNMarsh View Post
For 339A.... a dual opamp and a few needed parts could be mounted on an adapter/header and plug into U1 oscillator socket if the thd can be lowered with a series pair of super low noise/thd opamps. -RNM
Hi Rick,

I working on my oscillator right now and I'm still waiting on parts for my Twin T(s).
I'm giving the 339A a rest for the time being but I will return to this later.

Cheers,
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Old 10th January 2013, 06:10 PM   #1524
RNMarsh is offline RNMarsh  United States
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Ok David -- sounds good to me. Its a good point in time for a pause on the 339A.

I am looking forward to your new oscillator design !
Thx for all the good help and work, ideas on the 339A that has been done to date.
Thx-RNMarsh

Last edited by RNMarsh; 10th January 2013 at 06:13 PM.
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Old 10th January 2013, 07:27 PM   #1525
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For all the discussion on the HP339 over the last month I am confused as to what mods have been done and which ones resulted in beneficial improvements. Before everyone abandons this part of the topic, can someone please outline these mods up to this point?

I have been looking for a deal on an HP339. When I finally land one I am sure I would like to make these improvements. Even though the theory behind some of the mods is over my head, I feel that I am capable of implementing any of the improvement modifications if they are clearly defined.

I do want to thank everyone for this discussion. I did pick up some knowledge and enjoyed following it.

Thanks!
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Old 10th January 2013, 08:01 PM   #1526
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Where is this phase shift of the harmonics coming from that cause cancellation?
It's a property of the distorting element. The harmonics it causes necessarily have a phase relation to the fundamental.

Samuel
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Old 10th January 2013, 11:31 PM   #1527
davada is offline davada  Canada
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Quote:
Originally Posted by RNMarsh View Post
Ok David -- sounds good to me. Its a good point in time for a pause on the 339A.

I am looking forward to your new oscillator design !
Thx for all the good help and work, ideas on the 339A that has been done to date.
Thx-RNMarsh
Hi Rick,

It's not necessarily going to be a long pause. I reached by measurement ability and so can't go further until I expand on that. Twin T etc. Secondly I have reevaluate some of the changes I did to the balanced modulator board. It seem I've lost the tracing ability when adjusting the frequency vernier. I might have tightened thing up a bit too much.
I also need to isolate each stage and evaluate them separately. There are some things happening that don't add up. Unfortunately all of the amplifiers operate with full common mode swing, non inverting, and so distortions rise/fall with signal levels.

There is nothing stopping you from continuing.
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Old 10th January 2013, 11:45 PM   #1528
davada is offline davada  Canada
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Quote:
Originally Posted by dennismiller55 View Post
For all the discussion on the HP339 over the last month I am confused as to what mods have been done and which ones resulted in beneficial improvements. Before everyone abandons this part of the topic, can someone please outline these mods up to this point?

I have been looking for a deal on an HP339. When I finally land one I am sure I would like to make these improvements. Even though the theory behind some of the mods is over my head, I feel that I am capable of implementing any of the improvement modifications if they are clearly defined.

I do want to thank everyone for this discussion. I did pick up some knowledge and enjoyed following it.

Thanks!
Hi Dennis,

What mods you do really depend on how you want to use your 339a. None of the modes I did really benefited the meter reading at all. Rick did find some things that helped a bit.
If you want to improve what you see on the monitor output with FFT then some of the mods will do this. If you want to tap the notch filter then those modes will serve you.
What I did with the balance modulator was to lower the noise and harmonics at it's outputs which helps with the FFT but it won't make the 339a analyzer work any better.
Improving the notch depth was redundant because it neither improved the 339a analyzer and is not needed for the FFT/notch method. We only need about a -60dB notch for that.

I would suggest that the mods be carried out one at a time and evaluated before moving on. there is nothing that can't be undone again if it doesn't work out.

Cheers,

David.
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Old 10th January 2013, 11:50 PM   #1529
davada is offline davada  Canada
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Originally Posted by Samuel Groner View Post
It's a property of the distorting element. The harmonics it causes necessarily have a phase relation to the fundamental.

Samuel

Do you mean 'The harmonics it causes don't necessarily have a phase relation to the fundamental.' Is this correct?.

Is this true in general that harmonics don't necessarily have a phase relation to the fundamental or is this particular to filters?
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Old 11th January 2013, 03:10 AM   #1530
RNMarsh is offline RNMarsh  United States
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Default strange buffer things -

Quote:
Originally Posted by davada View Post
Hi Rick,
I also need to isolate each stage and evaluate them separately. There are some things happening that don't add up. Unfortunately all of the amplifiers operate with full common mode swing, non inverting, and so distortions rise/fall with signal levels.

There is nothing stopping you from continuing.
One thing I have tried today was perplexing --- Changing the oscillator opamp (A1U1) to the lower noise and lower thd part was an improvement -- but the following opamp used as a buffer [A1U3) is a puzzel. No other alternative opamp I tried gave lower thd than the original ! Retuning after each opamp change never reached the null in thd that the original does. So, I havent changed that opamp.
But wonder why that one works so well... is the input Z of the other opamps a weird load/phase on the osc? If so, it has implications beyond this oscillator source.

Thx-RNmarsh
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