Official 33609 builder's tread. See 1st page for updates.

[promixe]

Yeah, the audio samples are night and day.   It only takes a second of each to hear the difference! NOT subtle.

Yep! I encourage everyone to check out these samples and write here what they think of the difference.

Just a dumb question, is it possible you were running the signal differently through the two units?  Different gain structure, anything?  Were they set up differently internally?

For example, I don't understand the two switches on the right on the original.  It says compress, In.  Then it says Bypass, In.  Does that mean the other position is Bypass, Off?  Meaning the bypass was "In," or active (in bypass)?  In other words, was the compressor in bypass on the original?  Can you absolutely be sure how those switches were set up?

Yes, I'm absolutely sure of the settings and signal feeds. The units were fed from a single stereo DAW source (swapping the XLRs in the back between units manually after recording each sample), and they were routed into the same stereo input into DAW (again, interchanging XLRs by hand once done capturing each unit's output). That means that the gains of insert send and return in the DAW were identical.

As far as the switches in the original: the "compress in" switch means exactly that. When it's in the upper position the compressor sidechain is OUT of the circuit, i.e. equivalent of Igor's "COMP. out" switch position on each channel.
The switch next to it (on the original) literally describes the global state of the whole unit - it's either "bypassed" (up) or it is "in" (down, the opposite of bypass). The bypass switch on our DIY units is actually incorrectly labeled as "COMP in/out", leading one into deception with three identical switches "COMP in/out" on the front panel. Two belong to each compressor channel's sidechain, the third one is the "bypass" one, but still labeled "COMP..."...

Does this make sense?

 

[kazper]

I have dropped my wad on a 33609 kit that is sans the 2 BA340 boards.

If anyone has built this 33609. and used another Amp block in it's place, do you happen to have the BA340 boards lying around, that I could purchase.

Thank You.

I have a original BA340 somewhere in the piles of stuff, I'll try and verify that it will fit in the layout as a option. if Igor can't help you then maybe Livingsound can do some from his graphic or from the 1081 project layout files.

 

[RuudNL]

I remember that when I still worked for an international radio station, we used to have a console with '2264 like' compressor/limiters in it (the meters were mounted on the front of the desk). I don't remember the exact typenumer, they had blue face plates.
They sounded excellent, but they were SLOW!
If you would set the limiter threshold for the maximum output level (@3 dB gain reduction, +9dB -> +6dB), you could see serious overshoots on a standard PPM on program material, such as voices.
So this means the attack time must have been VERY slow.
A lot of people thought the compressor/limiters sounded so good because they were slow!
I did have a look at the diagram at the time and saw that there was a note how to make the attack time faster, if I remember well it was a matter of bypassing or shunting a 3K3 resistor. In the documentation there was also a note NOT to use the fast setting on for example piano or other 'normal' program material, but only use it when needed, or when driving a transmitter.
In fact, when setting the compressor/limiter on a steady tone (1 KHz. 3 dB gain reduction), you could already hear some distortion, you could just notice it was not a clean sine wave anymore, however: the distortion was 'mild'.

I can image that if you use 330uF//10 uF (as shown on the pictures) the LF distortion is gone, but that would be the same as using a very slow release time!
I have matched the diodes in the attenuator within 1 mV (at the same temperature!), so I don't suspect the problem is in the attenuator.

Edit: the compressor/limiters I meant were 33314, the design is almost the same as the 33609.

 

[RuudNL]

@promixe: I used the same settings as on your photo, but with 100 mS release for the compressor and the limiter (fast attack). Then I played your FILE though my compressor, with this result. Gain reduction ca. 5 dB. This is without my mod!

 

[promixe]

@proxime: I used the same settings as on your photo, but with 100 mS release for the compressor and the limiter (fast attack). Then I played your FILE though my compressor, with this result. Gain reduction ca. 5 dB. This is without my mod!

That's interesting! The audible distortion is really subtle on your processed clip. Just to note, I was using a bit different of a preset for this particular example - look HERE for described settings. But nevertheless, your unit seems to be a lot closer to the original 33609 as far as how it handles LF distortion!

Hmm! There's something going on with my channels, but they appear fine on the scope and within specs on the analyzer, according to Igor's tests...

Could anyone else run my MP3 example through their unit and post here? This is very helpful to check out!

 

[Autophase]

I'm seriously considering this for my next project, ive just finished the GSSL which works perfectly, and I'm well under way with my Neumann summing box, based on Volkers thread.
How easy/hard is the 33609 build in comparison to the GSSL?

 

[radiance]

I'm seriously considering this for my next project, ive just finished the GSSL which works perfectly, and I'm well under way with my Neumann summing box, based on Volkers thread.
How easy/hard is the 33609 build in comparison to the GSSL?

It's more difficult I guess....also more work and way more expensive.

 

[Autophase]

Who's selling the boards for this?

 

[radiance]

I might have a set for this...pm me if interested.

 

[promixe]

@promixe: I used the same settings as on your photo, but with 100 mS release for the compressor and the limiter (fast attack). Then I played your FILE though my compressor, with this result. Gain reduction ca. 5 dB. This is without my mod!

What transformers do you have on your unit? And did you use stock recovery resistor values (from the current AMS schematic)?

 

[RuudNL]

I used transformers from old broadcast equipment, I think they were made bij Haufe.
The output transformer can deliver +20 dBu @ 30 Hz. at a very low distortion.
For the input transformer I used a small Haufe transformer in a 'zero field' configuration, so no problems with high levels here.

I didn't use an intermediate transformer, but I used a differential amplifier instead.
I modified the audio path of the design a little, because I wanted a compressor and not a 'transformer distortion box'.
But the compressor and limiter side chains are exactly as in the original design, as is the attenuator circuit.
The amplifier circuits should not really contribute to the 'sound' of the 33609.
(IMHO an amplifier that has a specific 'sound', is a defective amplifier! ;D )

In fact, I even lowered(!) the values of the recovery resistors a bit, because my measurements showed that the release time was slightly longer than the markings on the frontpanel. So this should make the 'LF distortion' even higher!

 

[maxheadroom]

I modified the audio path of the design a little, because I wanted a compressor and not a 'transformer distortion box'.

what do you exactly mean with this?

 

[RuudNL]

what do you exactly mean with this?

I did not use an intermediate transformer. More transformers=more distortion.

 

[tommypiper]

I used transformers from old broadcast equipment, I think they were made bij Haufe.
The output transformer can deliver +20 dBu @ 30 Hz. at a very low distortion.
For the input transformer I used a small Haufe transformer in a 'zero field' configuration, so no problems with high levels here.

I didn't use an intermediate transformer, but I used a differential amplifier instead.
I modified the audio path of the design a little, because I wanted a compressor and not a 'transformer distortion box'.
...

OK, I am officially confused and lost by all your discussion of the LF distortion.  ???  First, you've been saying it's inherent in the design, but your tests don't reveal where/how/why... then when Promixe posts his files showing LF distortion you show that your build has no LF distortion with his file.... then you reveal that you haven't even built a stock build, with Neve or Carnhill transformers, and you claim removing the middle transformer reduces distortion....

It looks to me like you have lost total credibility here.  I mean, I'm totally confused.  Please explain.  How can you be complaining about your unit distorting, when it's not even a stock build like everyone else's?  How do you complain about it being an inherently distorting design, and then show that it doesn't distort like Promixe's build?  I'm totally confused and I don't understand where you are coming from.  These are self-contradicting statements.  There are too many variables which are being used that keep moving...

Your tests seem flawed to me.  As I mentioned in previous posts about the diode bridge.  I just don't see a coherent, logical discussion here anymore...  Please explain.

 

[RuudNL]

A short reaction:

As I stated before: the audio path of my compressor is exactly the same as the original 33609, with the exception of the intermediate transformer. I replaced the intermediate transformer by a differential amplifier. This should not have a significant influence on the sound quality; the only difference could be less (transformer) distortion.

Since more people experienced the 'LF distortion', I measured the distortion on my compressor. The conclusion was that as long as there is no 'modulation' on the control voltage (=a steady DC voltage), the distortion is not audible. This lead to the conclusion that the LF distortion was caused by an electrical component superimposed on the CV. To solve this, I designed a 'hold circuit’ that lowered the LF distortion significantly.
But even in the original state (without my addition), the LF distortion of my compressor is lower than the version of for example Promixe, as you can hear in the posted examples.

B.T.W: I posted the results of my investigations to help people solve a problem that apparently exists.
If you think it is useful: be my guest. If you think it is utter nonsense: that's also fine with me...

 

[rrs]

Help Wanted ???
--------------

Had a bit of a problem with by 33609 stereo build during a session yesterday and hoping someone can help me track down the problem.

What happened was I was adjusting the threshold on channel 1 and as I was turning the switch (Elma 04-1130) i saw a spark come from what looked like behind the meters/ power supply area.
Now I have no compressor or limiter control on either channel but gain switch does work. Same on both channels with link switch in or out.

I am still getting 24v to main board.

Any advice welcome.

 

[Igor]

Cool. Simplest thing is to pull link PCB and check what is shorts.
Maybe, a piece of wire, etc. Just check everything.
I don't think something blew out, but maybe something disconnected.
In any case, there are 10R resistors, they acts as fuses; check'em as well.
Good Luck!

 

[rrs]

Thanks I will check. Nothing looks burnt so thats a start.
I have a second link PCB I will substitute and report back.

 

[rrs]

replaced link/meter pcb and R43 10R was damaged , all working fine now

THANKS. :-*

 

[Igor]

Hurray!!!