prism barrell limiters.. make a 8 channel model with meters?

[trubac]

to sum up , its a very simple (oversimple ) circuitry, but nobody wants to make a drawing to explain it ...
unwanted thread ?

 

[craptical]

http://headwize.com/projects/showfile.php?file=limiter_prj.htm

Back-to-back zener diodes; see figure 5a.

/Dave

 

[trubac]

Ah thanks !
Nice weather in Sweden i suppose !  ;D
So Barclaycon, your turn now !

G

 

[tv]

I don't think it was mentioned here, but the back-to-back design must be

- either floated (one more resistor) or
- doubled, i.e. two "headwise 5a" circuits (both referenced to ground), one for positive and the other for negative signal.

one question remains: exact part values (maybe the makers tested for most oomph?)

 

[barclaycon]

So Barclaycon, your turn now !

Well, very useful contributions from craptical and tv.
Thank you for those.
Replies that actually helped us find answers rather than talking down to people.

one question remains: exact part values (maybe the makers tested for most oomph?)

Coudn't have said it better myself.
I'm sure it is all very simple - but can't we save ourselves a lot of practical research by just finding out what they used?
Then we can try it out for ourselves.

 

[strangeandbouncy]

Hi


  Apogee softlim is actually a That's 2180 vca chip NOT diodes, zener or otherwise. i know 'cos I've just taken my Mini-Me apart to adjust the sensitivity. Oh, and I dislike softlim intensely. Just use lower gain, esp at 24bit, and sort it out afterwards. I can never understand the point of risking overloading squeezing the last bar out of the meters, only to have to lower the gain in the mix. you'll end up with the same no of bits, won't you? Just record with your faders as near to unity as you can, and adjust the input gain accordingly, (like we used to in the olden days . . . . ). Otherwise you'll only lose on the swings that which you've gained on the roundabouts.



    Kindest regards,



    ANdyP

 

[barclaycon]

Depends on which Apogee converter you are talking about Andy.
The original AD500 had an excellent Soft Limit (and also Soft Saturate) circuit that was based on transistors.
It was one of the main reasons for the popularity of this unit (as well as the linear phase filters).
I bought one straight away after hearing it and was extremely pleased with it.
When the next version came out (AD1000) I considered buying it but after listening, decided on keeping the original unit - which sounded better. It's still great for rock stuff etc.
They never bettered that original soft limit design in my opinion, and yes with 24 bit it's just as well not to try and pin the endstop but maybe record a little lower and do all the gain stuff later.

 

[craptical]

The SoftLims I switch off is on the AD8000´s; haven´t opened it up so I don´t know what´s inside... Works fine on (some) drums IMHO.

/Dave

 

[AMZ-FX]

Try this:

http://www.muzique.com/tmp/zclip.gif

-Jack

 

[barclaycon]

Yep. That looks like the kind of thing.
Values ?

 

[Sleeper]

Sorry but I'm not sure how to quote across several topics, but here's what NewYorkDave says regarding the values. 

First of all, if we're trying to emulate the Prism gadget, it's supposed to start clamping at 18dBU, not 18dBV. 18dBU is 17.4 volts peak-peak. Since each zener in the back-to-back pair clamps one half of the waveform, we're interested in the PEAK voltage, which is 8.7V. Subtract from this the FORWARD drop (0.6V) of the other zener diode that's in series with the one that's "zenering" at any given signal peak and that leaves 8.1V. 8.2V seems to be the closest standard zener value.

The clamp should go between hot and cold, not between hot and ground and cold and ground. For reference, we're talking about the sort of circuit shown in figure 5A of that Headwize link. For balanced use, you'd split the value of the current-limiting resistor R1 and place half in series with hot and half in series with cold. As for the value of R1, that would be chosen to pass the desired current through the zeners at the point they begin clamping (thus affecting the "knee" characteristic) without presenting an excessive load to the driving device. It's not a good idea to run a clamp like this without current-limiting resistance since when it's limiting, it's essentially shorting out the output of the device driving it  :?

As an aside, I wonder about their choice of 18dBU since a system should usually be set up with 20dB of headroom above nominal operating level, which would mean a clip point of greater than +24dBU in a "+4" system. Perhaps they made the knee so soft that they needed to set the initial limiting point several decibels lower than that to ensure effective suppression of +24dBU peaks.

with Jacks circuit in mind and the following information, all that's left to fill in is the level your converters clip at. We don't know this do we (unless its in the post at the beginning of the thread.)

Once you get the voltages set it does seem like you may want to check out a few different current limiting resistor values either by scope or by ear to see how you want the knee to behave.

Sleeper

 

[barclaycon]

Excellent reply sleeper.
A very useful reference point - especially as it was posted some 4 years ago. I wasn't aware of this before.

 

[Sleeper]

Glad to help Barclay, I'm thinking about making a couple of these... I never got around to it in the past and I have to have a think and explore a bit to figure out the calculations for R1.
I can only guess what the answer might be.
        As has been mentioned I think there's something similar on the green pre.
and more info in Jack Ormans pages.
For starters I don't know what the voltage or current requirements are for my converters...
then how to plug those into a calculation
then to get the scope set up.
It's not so much to do really...

I find that often the answer to a question is posted and then the thread keeps moving and pretty soon the answer is really hard to locate. I'm really helping myself out here by combining the information in one place.