SSL 9K D.C. coupled or not?

[volta]

On the SSL web site the overview of the 9k board states it's channels are dc coupled.
http://www.solid-state-logic.com/music/products/sl9000j/

Doesn't dc coupled mean there are no capacitors in the audio path?

The 9k pre that has been floating around here has capacitors in the audio path at several places. :?
Are my newb eyes missing something or am I misunderstanding the meaning of DC coupled?

 

[Svart]

well.. usually DC coupled does mean the lack of capacitors in the audio chain...

 

[gyraf]

DC coupled means use of servos in stead of coupling caps.

 

[volta]

The ssl 9k schematic shows C69,C55 and C84,C68 in the audio path.

I take it this is just a circuit that is close to the real SSL 9k but not the real thing.

 

[gyraf]

Well, the "real" 9K would include EQ, dynamics, grouping, several sends and a mixbus with compressor. It's quite heavy too.

So yes, you're right. This is only a part of the 9K - that is, the mic amp.

Jakob E.

 

[volta]

So yes, you're right. This is only a part of the 9K - that is, the mic amp

I'm refering to the 9k schematic http://www.beatbazar.com/guests/ssltech/9k/9k-schem.pdf


If that is the real mic pre of the 9k why does it have coupling caps when they(SSL) claim dc coupled.
The ssl 9k schematic shows C69,C55 and C84,C68 in the audio path.That doesn't look like dc coupled to me.Am I missing something?

 

[Svart]

C55/69 are assumed to be phantom blocking caps, not much you can do to get rid of these easily(cheaply) IMHO. the others look like interstage DC blockers, you may be able to get rid of these, but I don't have time to do the math.. maybe someone can chime in?

:thumb:

 

[NewYorkDave]

DC-coupled does not necessarily mean servos. Many direct-coupled circuits do not use servos.

 

[DrFrankencopter]

It's probably a matter of semantics, but I would not consider a servo'd circuit to be DC-coupled. I would call it servo coupled, because it will not pass DC.

To me, a DC coupled system will pass DC. In audio, a DC coupled system will require devices with very low offset voltages.

A servo coupled system uses a servo (integrator) circuit to null out the low frequency components. I.e. it will not pass DC (until the DC is greater than the authority of the servo circuit).

A capacitively coupled system uses caps to block DC.

That's how I see it...

Cheers,

Kris

 

[volta]

That's exactly how I see it.

But what SSL are trying to say is: where they can avoid using caps they have done and gone with servos instead.
And off the top of my head they have done on the 9k - where possible

I see the logic in the replies,but if you are going to claim something like d.c. coupling or servo coupling it needs to be just that.

When I look at something like the John Hardy M1,M2 that looks like a non-capacitively coupled(Servo Coupled) circuit.
No caps directly in the audio path.

Even this circuit from Jensen is a true NON-CAPACITAVELY coupled pre or not:
http://www.jensen-transformers.com/as/as019.pdf

I have just made a pre that works very well using a servo coupled method like the hardy pre.

All I'm asking is why is SSL claiming dc coupled boards if the so called cloned pre doesn't represent the real thing.

The clone is wrong or SSL is.or...........

 

[PRR]

> am I misunderstanding the meaning of DC coupled?

What did Humpty Dumpty say? "A word means what I want it to mean!"? {edit} Ah----

As Humpty says to Alice in Through the Looking Glass: `When I use a word,' Humpty Dumpty said, in rather a scornful tone, `it means just what I choose it to mean -- neither more nor less.'

`The question is,' said Alice, `whether you can make words mean so many different things.'

`The question is,' said Humpty Dumpty, `{who} is to be master -- that's all.'

 

[volta]

and then........
is ego in the way?
leggo

 

[volta]

It's probably a matter of semantics

Most logical approach I guess.
Nothing is as it is unless you believe it is.

 

[SSLtech]

I believe that SSL quoted the signal path from LINE INPUT TO BUSS OUTPUT as being free from in-line capacitors. They deliberately omitted the mic pre, and sensibly too.

Without a transformer, youd have to be a giggling genius or insane or both to try to eliminate the phantom blocking caps. If you're not using phantom, you can eliminate them and feel better (if that helps you to sleep at night! :wink: )

The only caps that are there are non-electrolytic so Mr. David Mate has done a splendid job of working the design.

Keith

 

[volta]

I believe that SSL quoted the signal path from LINE INPUT TO BUSS OUTPUT as being free from in-line capacitors. They deliberately omitted the mic pre, and sensibly too

That's what we needed to hear.At least me,myself,and I.
Thanks for the input guys.

 

[PRR]

> To me, a DC coupled system will pass DC.

The classic DC-coupled amplifier is the oscilloscope, which has flat response all the way to DC. Put in some DC, get DC out. That has major impact on the design. And it is a Bad Idea in audio, because we don't hear and don't try to reproduce static air pressure.

Those servos subtract the DC component. To my mind, DC is de-coupled. Same as a coupling cap, just done different, with capacitor flaws showing up a different way, maybe less.

> I believe that SSL quoted the signal path from LINE INPUT TO BUSS OUTPUT as being free from in-line capacitors.

OK. But if I can't trim it to unity gain, put a 1.5V battery on the input, come back a week later and still find 1.5V DC on the output, it isn't to me "DC-coupled". The DC has gone away. That's a Good Thing in audio, but isn't what I would expect from a "DC coupled" amplifier.

But Humpty Dumpty had a point (not about ego). In English, words very often mean what we want them to mean. Some folks would say that english isn't a language but a motley collection of borrowed words. Even inside English, we borrow words from one use and apply them to another use. "coupled" has several meanings older then electronics: what does it mean here? "DC train connections"? "DC Sexual Intercourse"?? If you think about English too much, you have to either stop talking or adopt Humpty Dumpty's point of view, except with "we" instead of "I". But who is "we" when English has no Language Police (like French has a Bureau) and the experts are observers not dictators?

 

[volta]

If you think about English too much, you have to either stop talking or adopt Humpty Dumpty's point of view

I'll dig up my fairy tale book and curl up to a good point of view tonight.

 

[SSLtech]

[quote author="PRR"]> I believe that SSL quoted the signal path from LINE INPUT TO BUSS OUTPUT as being free from in-line capacitors.

OK. But if I can't trim it to unity gain, put a 1.5V battery on the input, come back a week later and still find 1.5V DC on the output, it isn't to me "DC-coupled".[/quote]
Which is exactly why I didn't say "DC coupled". -Neither did SSL. The 'DC coupled' assumption is a paraphrasing which has led to the misapprehension that the SSL is DC coupled. -My definition of DC coupling is very much in line with PRR's.

There's an old (probably apocryphal) tale of a front-of-house sound engineer (working for AC/DC when I head the tale) whos console power supply died 20 minutes before the show. One rail went no-output, and the console wouldn't pass signal. The story goes that the engineer knew enough to fetch a 9-volt battery, wire a battery clip to a male XLR, and plug the battery into a crown DC300A. He then turned up the 'volume' control until his meter read 17Volts (or whatever) across the speaker terminals, then hurriedly rigged the output to the console power input with some speaker cable.

In my book, *THAT'S* DC-coupling. Servos would have ruined the job.

Keith

 

[volta]

Which is exactly why I didn't say "DC coupled". -Neither did SSL. The 'DC coupled' assumption is a paraphrasing which has led to the misapprehension that the SSL is DC coupled.

The exact quote from SSL's web page is

Advanced DC-coupled analogue technology offered a new high in audio performance, designed to complement the latest digital recording media, whilst the signal routing options provided unparalleled levels of flexibility.

http://www.solid-state-logic.com/music/products/sl9000j/

 

[SSLtech]

Ah. Looks like they've tripped over their own attempt to market their product!

When we bought our first 9K about a decade ago, Don Wershba told me that there were no caps in the audio path from the line input to the output. That agreed with what I read at the time. Apparently -presumably during a re-work of the blurb- that has been 'updated' to "DC-coupled"

Not something I agree with. To me, there is a difference. DC coupled circuits -at least the only ones which I've ever encountered- have no in-line capacitors. However, other circuits can have no in-line capacitors and yet not be able to pass DC... they are NOT DC coupled to my way of thinking.

A postman delivers letters. A postman wears a uniform. Not all men who wear uniforms deliver letters! :grin:

Keith