Bypassing signal path coupling caps

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AusTex64 said:
I was not accurate regarding how Rupert Neve uses NE5534's in the Portico range:

<The circuitry is built almost entirely using conventional-sized components, with the old familiar NE5534 op-amps doing the bulk of the work, supplemented with separate transistors in appropriate places. Rupert Neve's designs traditionally employed single-sided class-A topologies, and it is hard to square that approach with these Portico circuit boards covered in op-amps. The secret missing ingredient is that he uses a circuit technique with the 5534 op-amps which offsets the DC point of their output stages, so that for signals below about 0dBu they are effectively running in a single-sided class-A mode. This removes crossover distortion artifacts completely and is a significant contributor to the sound of this preamp.>

Also read some info indicating Rupert Neve had a hand in the design of NE5534. True?

Ignore the man behind the curtain.

AFAIK the Signetics NE5534 fell out of a Phillips op amp (TDA1034).

I don't think Rupert had semiconductor design chops.  More likely an early customer.

JR
 
JohnRoberts said:
AusTex64 said:
Also read some info indicating Rupert Neve had a hand in the design of NE5534. True?

Ignore the man behind the curtain.

AFAIK the Signetics NE5534 fell out of a Phillips op amp (TDA1034).

I don't think Rupert had semiconductor design chops.  More likely an early customer.

JR

I am sure Rupert had no hand in the NE5534. I was at Neve in the mid 70s when the TDA1034 came out. I remember the R&D department. getting hold of some and doing extensive tests on them. I am sure there is a Neve Technical Report about them somewhere. Not long after they began to be used in Neve consoles.

Cheers

Ian
 
I don't know anything about the Portico range, but a former coworker of mine was running an Amek 9098 preamp through an audio precision once and we were impressed with it showing a ruler flat 70dB of gain across the entire band with a very low noise floor.  Nice performce on the meter.  We opened it up and chuckled to see it being almost entirely 553x opamps.  The other take away was that they put a lot of effort (and parts) into RFI protection and filtering.
 
There was a time when it was popular to bypass electrolytics with film caps (1990). At that time, however, there was not the wide variety of exotic film, PIO, and electrolytics available today.
And while I love all the lit that exists on the subject, really, it depends upon the application where it works and where it's a waste of time. Sorry, no generic generalized "yes" or "no" is valid. And when it comes down to the listening part, the listener can be swayed by fashion, audio ideology, mood and experience.
The fashion part makes it very difficult, as clearly some capacitor look very "cool", and some do not.
That said, I have removed many bypass caps from microphones, and installed an entire console full of them in a famous room in Hollywood.
 
bockaudio said:
That said, I have removed many bypass caps from microphones, and installed an entire console full of them in a famous room in Hollywood.

Do you have any measured results that compare the performance of the mics and console before and after the changes?

 
That section was actually how I found out about the Self book a while back while doing a google search.  It can be a useful book to have around as a general reference for all sorts of audio type things.  I just pulled my copy out to check a short section he has about a condenser mic head amp circuit as I was looking into condenser circuits beyond the typical Shcoeps  clone that everyone uses.
Interesting as Self talks about that circuit as if it's ubiquitous and it's not.
I found a few other discrepancies in that book.
 
bockaudio said:
That section was actually how I found out about the Self book a while back while doing a google search.  It can be a useful book to have around as a general reference for all sorts of audio type things.  I just pulled my copy out to check a short section he has about a condenser mic head amp circuit as I was looking into condenser circuits beyond the typical Shcoeps  clone that everyone uses.
Interesting as Self talks about that circuit as if it's ubiquitous and it's not.
I found a few other discrepancies in that book.

I found several typos in the figures for noise versus resistance. Doug is very happy to be contacted directly with corrections and comments.

Cheers

ian
 
JohnRoberts said:
Reminds me of the audio-phools who would complain about the sound degradation from passing through switch contacts...  8)

I was surprised when my rocket scientist uncle expressed shock that relays were used so often in audio. He said "what about the distortion"? He designed measurement instruments for the Pluto mission. He isn't an audiophool.
 
David Manley's old book addresses relays, and I recall the only ones they found acceptable for audio back in the late '80's were ones with tons of contact area, like 30A types, brute force.  I don't know what his legacy company thinks today. 
 
Gold said:
JohnRoberts said:
Reminds me of the audio-phools who would complain about the sound degradation from passing through switch contacts...  8)

I was surprised when my rocket scientist uncle expressed shock that relays were used so often in audio. He said "what about the distortion"? He designed measurement instruments for the Pluto mission. He isn't an audiophool.

My answer today is the same as it was decades ago.. If you can hear a switch contact (relay?)  in your audio path, you have a faulty switch, so replace it.

I am not aware of a distortion mechanism inherent to relays, but like any switch contact, oxidation, or contamination of the switch contacts with foreign matter can degrade contact resistance. .

Some relays are designed specifically for audio (dry switching), many more for switching power. I was never a big fan of relays because of the cost but have used a few, when they were the right part for the task.  I don't think I ever experienced a relay that introduced distortion while just like bad switches I'm sure it happens.

JR 

PS: I have experienced way too many intermittent (dirty?) switching jack contacts, typically used in console insert points.
 
Gareth Connor said:
bockaudio said:
That said, I have removed many bypass caps from microphones, and installed an entire console full of them in a famous room in Hollywood.

Do you have any measured results that compare the performance of the mics and console before and after the changes?
Re: mics: no all done by ear, but not without attempting meaningful measurements.
re: console: no, mods were judged by the studio owner (famous engineer) and clients by ear only.
 
My dayjob is teaching audio in a professional school (dunno what equals that in other country´s educational systems, I guess it´s college).
One day some students asked me if it´s true that all mixing consoles sound the same. Obviously my collegue who is Tonmeister claimed that in his classes. At that time I a had a desk in my workshop for refurb and decided to prepare it for some listening tests with him. I refurbished the master and prepared 12 channels in very different ways. From original state (25yrs old, never recapped) in various permutations to recapped, bypass caps added, chip upgrades + opening up BW limits and input filters. After that I invited him to some blind listening tests. To make it short, every single improvement was audible, some things more obvious, some less. The biggest improvement was recapping OR adding bypass caps to the original electrolytics. The difference between these two version was the low end, but both improved the highend detail. The difference between recapped and recapped plus bypasscaps  was small but still audible. Remember that was a blind test and the judgements came from my collegue!
My interpretation of that result is that bypasscaps in a freshly recapped desk don´t make a huge difference. But since electrolytics deteriorate with age while foil caps don´t, it makes sense to add bypasscaps. They prevent loss in highend detail due to ageing electrolytics.
Sorry guys, we didn´t measure anything.
 
jensenmann said:
My dayjob is teaching audio in a professional school (dunno what equals that in other country´s educational systems, I guess it´s college).
One day some students asked me if it´s true that all mixing consoles sound the same.
Consoles routinely sound different but for easily explainable differences. Console EQ are rarely voiced the same, using different center frequencies and Q for boost/cut sections.
Obviously my collegue who is Tonmeister claimed that in his classes. At that time I a had a desk in my workshop for refurb and decided to prepare it for some listening tests with him. I refurbished the master and prepared 12 channels in very different ways. From original state (25yrs old, never recapped) in various permutations to recapped, bypass caps added, chip upgrades + opening up BW limits and input filters. After that I invited him to some blind listening tests. To make it short, every single improvement was audible, some things more obvious, some less. The biggest improvement was recapping OR adding bypass caps to the original electrolytics. The difference between these two version was the low end, but both improved the highend detail. The difference between recapped and recapped plus bypasscaps  was small but still audible. Remember that was a blind test and the judgements came from my collegue!
My interpretation of that result is that bypasscaps in a freshly recapped desk don´t make a huge difference. But since electrolytics deteriorate with age while foil caps don´t, it makes sense to add bypasscaps. They prevent loss in highend detail due to ageing electrolytics.
Sorry guys, we didn´t measure anything.
The scientific method benefits from measurement. Human perception can be easily influenced by external factors.

Your test screamed out for null testing, where you could compare modified channels to each other and by listening to the null product,quantify, and qualify what the differences were. Of course the weakness in null testing is you don't know which input is causing the difference, only how and how much they differ.

I find numbers very useful in such pursuits,

JR
 

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