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Old 28th May 2002, 08:38 PM   #11
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Default feasibility and pricing

I just talked to BrownDog about feasibility and pricing. The estimated preliminary pricing for a fully populated FET cascode current source opamp adapter is ~$10-20 and an unpopulated version with press fit socketed pins is ~$5-10, depending on quantity.

The primary application is biasing opamps into class A in legacy circuits such as CD players and headphone amps. Let me know if you are interested in this adapter, and whether you want it unpopulated or fully assembled.
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Old 28th May 2002, 10:37 PM   #12
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Default Re: feasibility and pricing

Quote:
Originally posted by morsel
I just talked to BrownDog about feasibility and pricing. The estimated preliminary pricing for a fully populated FET cascode current source opamp adapter is ~$10-20 and an unpopulated version with press fit socketed pins is ~$5-10, depending on quantity.

The primary application is biasing opamps into class A in legacy circuits such as CD players and headphone amps. Let me know if you are interested in this adapter, and whether you want it unpopulated or fully assembled.
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I am interested both populated and upopulated Prefer them without pins so that I can solder two pins on top of existing adpator or opamp.
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Old 30th May 2002, 07:04 PM   #13
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There is not enough interest here to justify proceeding at this time. I will take the discussion over to Headwize and see what they think.
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Old 6th June 2002, 03:37 PM   #14
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CRD versus cascode

I am intrigued by the considerable sound quality difference between a buffered CRD 1k - Vishay J505 and a cascode system 2N5457-2N5457- 100R in three applications with moderate (10k) to high Mohm input impedances. The systems are; analogue out from a tuner; A/D buffer;
and D/A filter. in all cases the CRD sound coarser and with a different sound stage (more forward) than the fet CS. The latter is much more refined and the currents drawn are nearly identical at around 1 mA.

Why is this??
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Old 13th June 2002, 03:27 PM   #15
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Default CDRs vs cascoded fets vs cascode/crd

I dont know if you have read this section, but they talk about the advantages of each option and why one is better than the other.

http://tangentsoft.net/audio/meta42/tweaks.html

cheers
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Old 14th June 2002, 10:16 AM   #16
ppl is offline ppl  United States
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Default Casscode current dose sound better to me

I have used Current sources to load Opamp's for quite a while and current loading improves the sound of almost any opamp. Going to a cascode current source is evean futher Refinement and as fmak states the differences are dramitic enough to warrent the effort. BTW i now like High Value Buffer resistors evean for cascode current sources.
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Old 14th June 2002, 03:36 PM   #17
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Default Re: Casscode current dose sound better to me

[QUOTE]Originally posted by ppl
I have used Current sources to load Opamp's for quite a while and current loading improves the sound of almost any opamp. Going to a cascode current source is evean futher Refinement and as fmak states the differences are dramitic enough to warrent the effort. BTW i now like High Value Buffer resistors evean for cascode current sources. --------------------------------------------------------------------------

I have now established through making a lot of cascode and crd CSs that loading at 2mA is desirable. At 15V this is still only 0.03W . The headphone people like 1 mA but for fixed equipment one can go higher and further remove the 'opamp' sonic signmatures. I may try 3 and 4 mA in future. The best combination for mke in Uk is 12 mA Idss 2N5486 with 2 to 4 mA 2N5457. Both are cheap and lo noise. For some reason the J112 and 304 series seem very temperature dependent and regulation using thes not as good. I get about +-0.4% between 10, 15 and 20V.

The CRD-resistor combination sound significantly worse than the cascode. This is for three separate applications.
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Old 14th June 2002, 06:06 PM   #18
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Default opamp current loading

Hi,

I don't know how you decided that 2mA load was OK, but there is an easy way to determine that.
Assuming that the object is to run the opamp output stage in class A (we DO agree on that, don't we?), determine the max output voltage you expect and divide that by the lowest loading impedance you expect.
Example: 5VRMs, across 2kOhm load gives max load current of 2.5mA RMS which is about 3,5mA pk-to-pk (for a sine wave). Taking some reserve, in this case 4mA would be OK.
You could of course do a series of listening tests at 1, 1.1, 1.2 etc mA, but that seems rather primitive and tedious, and I wouldn't put money on the reliability of the outcome of such a process.

Cheers,

Jan Didden
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Old 14th June 2002, 08:52 PM   #19
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Default Re: opamp current loading

You could of course do a series of listening tests at 1, 1.1, 1.2 etc mA, but that seems rather primitive and tedious, and I wouldn't put money on the reliability of the outcome of such a process.
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Simple impedance and level matching considerations don't always count in audio. If this were the case, then there should be no difference in sound quality amongst resistor loading, crd/fet-resistor loadong and cascode loading, given suitably high input impedance. This is not the case by common agreement.

My point is that the 1 mA criterion usually adopted by the headphone guys does not necedssarily apply. In my cases, I found 2mA to further improve the sound for a variety of opamps. The basis is very simple. You are operating in different portion of the transfer curve. I would speculate that the middle portion ie. 0.25 of maximum current, could be even better.However, this would require heat sinking.

Why do you mistrust hearing to the point of calling it tedious and primitive, which it is???!!!
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Old 16th June 2002, 01:11 AM   #20
ppl is offline ppl  United States
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Default The Ear Brain is far more Accurate than Given credit

The ear can locate a sound to within 1.0% accuracy, the Ear-Brain and nural network is able to compute faster than large mainframe Computors. So i always trust my hearing and moswt times it is in trying to remove a sonic fault that i often find a technicaly Elagent solution to a Problem of the circuit that measurments and simulation failed to Show. Measurements are more Dependable than simulations, whitch only give a starting point.
Anyway regarding my View of the amount of current to Bias an opamp at then no more than 1/10 Th the opamps nominal Output Current. Alot less would Probaly be good in most high Impedance situations, However capacitive loading by long interconnect cables may require Opamps who's outputs will see the Outside world then 3-5 Ma of Constant current is a safe bet on covering any possible Load situations Excepting Low impedance loads within the Audio range like Headphones But It is my posistion that Opamps should be Buffered by a Dedicated Buffer IC like the BUF-634 or a Discreet component Alternative, However since the gain stage is Monolithic then why not Keep the concept similar in the output stage.
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