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Old 27th November 2012, 02:34 AM   #30011
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John; I found 4558 adequate in channel strips of TOA console when biased each to + rail by 6K8 resistors. Did not find any reason to replace them by more modern and expensive opamps, if each channel is used by a microphone or musical instrument. However, it does not mean that I will use them in either my mic preamp, or power amp designs, where power amplification is maximal. But I see no reason to replace them by anything else in the console strips. However, I found economical to replace them by OPA1612 in summing amps, adding SOA/DIP adapters. I Don't enjoy very much that new fashion to build prototypes not designer-friendly. Initially TI guys on AES stand promised me to ship that BB samples in DIP cases, but did not keep that promise. Shame on them!

Scott, does AD make designer-friendly samples, or just SIM models for iKids with iPads only?
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Old 27th November 2012, 02:54 AM   #30012
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Originally Posted by Wavebourn View Post
Scott, does AD make designer-friendly samples, or just SIM models for iKids with iPads only?
At the time i was in concern with this kind of stuff, AD was the coolest company you can dream of. Samples, test boards, and help to find the parts you needed. The technician-Commercial i was in contact with, in Paris was near a friend of mine, after some time.
Pity, now, lot of my preferred products from them have disappeared.
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Old 27th November 2012, 03:15 AM   #30013
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Quote:
Originally Posted by Esperado View Post
At the time i was in concern with this kind of stuff, AD was the coolest company you can dream of. Samples, test boards, and help to find the parts you needed. The technician-Commercial i was in contact with, in Paris was near a friend of mine, after some time.
Pity, now, lot of my preferred products from them have disappeared.
Looks like marketing iKids took over guys with oScilloscopes and sOldering iRons..,... sAd...
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Old 27th November 2012, 02:44 PM   #30014
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4558, well that restrained the discussion, didn't it? Scott, are you not prepared to DEFEND the use of the 4558, even with serious audiophiles? '-)
The problem with the 4558 is that it is virtually an 'improved' 741, with just about 4 times the slew rate, due to improvements in processing, for what I can presume.
It is a CLASSIC example, (beyond the 741) of a design, PROVEN by Barrie Gilbert to generate PIM. This is what the PIM test was all about. This is why Matti Otala, Richard Sequerra, and Mitch Cotter recommended testing for it as long as 34 years ago.
Finally, somebody has made tests good enough to separate the bad from the better.
Unfortunately, even Ron Quan's tests still have a fairly high residual, that keeps us from evaluating the 'better' op amps completely, as their FM distortion (if any) lies below the residual of Ron's test equipment. Don't worry, improvements will be made. Maybe, a BIG company will address the issue and give us serious test equipment to measure this distortion. I sure would hope so.

Last edited by john curl; 27th November 2012 at 03:05 PM.
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Old 27th November 2012, 02:56 PM   #30015
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Quote:
Originally Posted by Wavebourn View Post
Here is one more unexplained phenomenon:

Click the image to open in full size.
The other socks go to mars. That's what the NASA announcement is going to be ..they found a mountain of single socks.

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Originally Posted by Esperado View Post
Occasion to ask to Jneutron how to build a cable with 6 ohms impedance from several 100 Ohms ones ?
Cat5e cables are 100 ohm impedance, and all four pairs are orthogonal to each other due to different twist pitches. Do not bother twisting the overall cables into any fancy braid pattern, it makes no difference. Just bundle the cables.

If you make a cable using all the stripes as negative and all the solids as positive, you create a cable impedance which will be 100 divided by n, n being the number of pairs. Number of pairs is simply 100/z, z being the final desired impedance.

For 6 ohm z, 100/6 is 16 pairs, or 4 full cat cables.

I made a roughly 4 ohm 15 foot long cable using 6 cat5e cables, 24 pair. It passed a 40 volt step in 10 microseconds to a 1 meter long copper foil stripline half inch wide separated by a 1 mil thick kapton layer, to a 4 ohm load in liquid helium. No overshoot or ringing. edit(please forgive my mixing of metric/english units..)

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Mike, once again regarding transient spikes at the output during light switch turn-on. As a cure, try:

- everything in class II.
- no ground loops. Especially protective earth loops must be avoided. This is assured when components in class II.
- shielding continuity must be fulfilled, everywhere and in every component. Audiophile signal link cables where shield is connected only at one end are not allowed if you fight with EMI/RFI.
- no signal transformers outside amplifier cases.
- properly shielded circuits with high HF PSRR.

In case you keep these recommendations, you would not need to use additional mains filters.
Or, select plan B or C from my pic, see below.
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Originally Posted by RNMarsh View Post
Other good sources of info are the IEEE standards and EU Directives on EMC.
IEEE-1050 was great, although retired.

Here's the pic. Option A is typical of small home systems with no powered sub. If you use a separate outlet for the source, you extend the ground loop to the service panel, worse.

Option B is very simple, wrap the source line cord around the IC's, then around the amp power cord to the outlet.

Option C is a small variation of B. I cannot guarantee it will work for long runs however, as I have only done if for 125 foot runs of unbalanced line level between the source and the amp, with 15 kW of scr based lights, a quarter million volt vandygraf, and a toro 700 leafblower. Houses typically are worse...

jn
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File Type: jpg system ground layout options.jpg (61.7 KB, 123 views)

Last edited by jneutron; 27th November 2012 at 03:26 PM.
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Old 27th November 2012, 03:01 PM   #30016
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Wavebourn, I agree that in mid fi applications, the 4558 is 'adequate' I have been listening through 4558's on an SACD player that I have had for the last 10 years or more. Without DIRECT COMPARISON with better equipment, it is difficult to find any problem. YET, Barrie Gilbert's analysis PREDICTS FM distortion, so we should note it, and perhaps avoid it with our 'best' designs.
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Old 27th November 2012, 03:15 PM   #30017
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4558 is quite poor, regarding sound quality....
It is always a candidate for exchange, in case we want to get somewhat better sound.
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Old 27th November 2012, 03:21 PM   #30018
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The other socks go to mars. That's what the NASA announcement is going to be ..they found a mountain of single socks.

jn
OT: a pretty close guess: Limmy's Show - Just be the dug. - YouTube
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Old 27th November 2012, 03:25 PM   #30019
bcarso is offline bcarso  United States
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Originally Posted by Wavebourn View Post
Here is one more unexplained phenomenon:

Click the image to open in full size.
Perhaps entangling the socks would help
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Old 27th November 2012, 03:31 PM   #30020
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Can everyone note the similarities in these two simplified schematics?
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