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

[nielsk]

Strapped a resistor across the meter terminals, got adjustment range.....2k seems about the best
Has anyone else had to do this?

 

[Igor]

Yes, 10k pot should bring meter to nothing. If pot is good and nothing happens
(meter still reacts when there's GR signal) check all connections going to meter, bypass board.
Meter should be 1mA FS.

 

[maxheadroom]

Some audio examples:

Can some one run the unprocessed file through their unit AND/OR the original 33609(C/J/JD)?

Original: http://dev.ax-design.com/electronics/33609/33609-test4a.mp3

Compressor IN (THD -4dBu / 100ms RECOVERY / +6 GAIN / 4:1 RATIO): http://dev.ax-design.com/electronics/33609/33609-test4b.mp3 - the 100ms problem was fixed by replacing R10 with 24k

Limiter IN (THD +4dBu / 100ms RECOVERY / FAST attack): http://dev.ax-design.com/electronics/33609/33609-test4c.mp3 - you can hear the distortion. I don't know what it would be attributed to (see next link)

Limiter IN + Compressor IN (setting are as above): http://dev.ax-design.com/electronics/33609/33609-test4d.mp3 - really distorted signal. Compressor smoothes the track, adds gain makeup, and then the limiter freaks out. It sounds like there is an overload somewhere along the limiter sidechain. Where would I look? It calibrated fine though...

Examples C & D sound pretty horrible if you ask me =)
Example B on the other hand really remind me of the classic neve-ish mixing desk sound. That one gives me hope =)

I would really appreciate if someone replicated same settings on their unit (DIY or original) and posted audio. I can provide space for it on my server if needed. Thanks!

hello promixe,

have you found a solution regarding your problem with the distortion of the limiter?
i have the same problem. especially on limiting the bass as single signal i hear great distortion when i turn the limiter on.
anyone else have this problem?

 

[Curtis]

Strapped a resistor across the meter terminals, got adjustment range.....2k seems about the best
Has anyone else had to do this?

I had to do the same.  I used a Sifam AL19W that was actually a VU meter (can't remember the exact model number).  The problem is that unless the meter is 1mA full scale deflection it won't respond properly, and the Sifam VU model is more sensitive.  You need to slug it by installing some shunt resistance across the meter terminals.

 

[promixe]

hello promixe,

have you found a solution regarding your problem with the distortion of the limiter?
i have the same problem. especially on limiting the bass as single signal i hear great distortion when i turn the limiter on.
anyone else have this problem?

I have never figured out what is going on with this. But... I'm about to finish the second 33609 unit (I was building two simultaneously) and see if I have the same issue. Don't get me wrong, but I'm actually glad someone else has the same issue =) It makes me feel not as lonely in searching for a solution as before =) Also, statistically speaking, now the two of us have a better chance figuring it out than just me on my own. =)

When I talked to Igor last time (Hi Igor BTW, sorry for dropping out for like months...), he suggested some modifications that didn't eliminate the issue, but overall he was thinking it might also be a mismatch component or two somewhere. It becomes tricky to troubleshoot without intimate knowledge of how the entire circuit works and plenty of experience.

The bottom line is: going to finish the second unit ASAP, and if it works I'm going to investigate HOW (because components are identical) and if it doesn't - I have two dead 33609s sitting here. That's a lot of dead $$$ value =) And two dead units should motivate me more to figure it out than just one. =)

Cheers!

Promixe

 

[rrs]

I am about to start this project and ordering parts.
Looking through the threads the Sifam meter AL19wf seems the preffered meter and fits Pursua's case.

I have found the meter on the canford site but it looks different so can someone confirm if this is the right meter to use .
http://www.canford.co.uk/Products/58-381-SIFAM-AUDIO-LEVEL-METER-AL19WF
http://www.canford.co.uk/Products/58-384-SIFAM-ILLUMINATION-KIT-Festoon-lamp-type-for-AL19WF-meters-with-12V-lamp

 

[Curtis]

That's the same one I used.  You'll need to print a new scale for it and stick it over the front of the VU scale, and also fit some shunt resistance across the meter terminals to make it work properly (as was mentioned a couple of posts up).

I could mail you the scale I used if you like, although some of the gain reduction markings were a little off.

 

[rrs]

That's the same one I used.  You'll need to print a new scale for it and stick it over the front of the VU scale, and also fit some shunt resistance across the meter terminals to make it work properly (as was mentioned a couple of posts up).

I could mail you the scale I used if you like, although some of the gain reduction markings were a little off.

That would be great.

How do you open up and replace the cutout ? I'm sure theres a thread on here somewhere if I could type the right thinng into the serch engine.

 

[Curtis]

The clear plastic front just unclips from the meter assembly.  Do it carefully otherwise you'll damage the meter movement.  After that the cream VU insert just slides upwards out of some retaining guides.

All I did with mine was print a new scale on some white self-adhesive labels, cut them roughly to size, and stuck them on the back of the VU insert.  Once stuck on the insert they can be trimmed exactly to size with a sharp knife and slipped back into the meter.

 

[ultra-alex]

in search of the threshold switches i just talked to elma germany and the told me that the elma 04-1130-20 is NOT in production anymore.
substitute is ELMA 04-1133-20. don´t know if this has already been mentioned before...
cheers, alex

 

[nielsk]

Same distortion on low end here, lots in limiting. Could this have something to do with using the 340 instead of the 640 that the actual 33609 uses?
Has anyone tried one of these with a 640 in it?
I will try to find some time to compare the 2264 (it uses the 340) and the 33609 schematics and try to find any other differences that could contribute.

 

[radiance]

in search of the threshold switches i just talked to elma germany and the told me that the elma 04-1130-20 is NOT in production anymore.
substitute is ELMA 04-1133-20. don´t know if this has already been mentioned before...
cheers, alex

So, that's "gold 3 μm" instead of "gold flash". More durable and more expensive.

 

[promixe]

Same distortion on low end here, lots in limiting. Could this have something to do with using the 340 instead of the 640 that the actual 33609 uses?
Has anyone tried one of these with a 640 in it?
I will try to find some time to compare the 2264 (it uses the 340) and the 33609 schematics and try to find any other differences that could contribute.

The original 33609 actually used BA340 (and then BA440, which only differed by not having a trimpot, but a fixed resistor instead) and BA640 uses IC instead of discreet transistors (I think). All 3 modules are interchangeable and shouldn't contribute to the sound in a major way.

I think the audio path of my 33609 is fine (where BAx40 is concerned). The distortion has more to do with CV and time constants of the limiter/compressor. I actually hear the same distortion on the compressor, not just the limiter. But it's a lot less apparent and I could live with it eventually, eventhough when compared my unit with the original 33609 the latter had "smoother" distortion of the same kind on fast compressor settings (a lot more musical, transparent, shall I say, but still a distortion).

FIY: Igor's suggestions to relax timing of attack/recovery only made the whole distortion issue a lot more apparent... I'll post some mp3s of the modded timing unit so you can hear what I'm talking about.

PS: already 3 people in the "low end distortion camp" - even better =)

Cheers!

Promixe

 

[nielsk]

Looking a bit deeper, the schematic I have (version dated 4/7/89) R23 is 150, R31 is 680, the R28/R30 is done different (both attached to the E of TR7 then R30/3k3 feeds"LIM 6" and R28/3k3 feeds the B of TR13), there is no C24, and C13 &14 and the ones on the recovery switches are tants
It does show a 6k8 on both recovery switches between wafer A pos 3 and wafer B pos 7, is this the one some have tried as a 27k?

 

[Igor]

Hi Promixe, we have to work this out.
I will have more time to do this next month, sorry, way busy now with my stuff.

 

[RuudNL]

Hi,
I am trying to measure and compare the attack times of my reproduced '33609'.
Is there anybody who has the original 33609 at hand and is willing to replay en record my MP3 file with 10 dB compression (6:1) and 10 dB limiting (fast and/or slow) with 800 mS. release?
The file consists of 10 seconds 5 KHz. at 0 dB (to adjust the amount of GR), 10 seconds of silence, a short (100 mS.) 'blip' of 5 KHz./0 dB and 10 seconds silence. Any help would be appreciated!
This is the file with the burst: www.ljfaahw.nl/testburst.mp3
Many thanks in advance!

 

[RuudNL]

Same distortion on low end here, lots in limiting..
.....
PS: already 3 people in the "low end distortion camp" - even better =)

Add number four here!  ;D Although the first impression was good, I also get serious distortion on LF signals!
I don't think it has anything to do with the audio circuit, but I suspect the limit sidechain.
Tomorrow I wil try to check some of the waveforms in the sidechains.
A limited sinewave of 40 Hz. looks like anything but a sinewave after > 4 dB limiting (fast, 100 mS)

 

[RuudNL]

This is what causes the LF distortion:

Upper trace: input signal, lower trace: control voltage to diode bridge (magnified).

There is a sawtooth superimposed on the control voltage to the diode bridge. (ca. 10 mV. at 40 Hz, 6 dB limiting)
This is because the capacitor has to be recharged, to compensate the discharge during the past half period of the sinewave.
The leading edges of the sawtooth occur at the moment the limit point is reached, so this is at the top of the sinewave at steady signals. The shorter the release time, the higher the amplitude of the superimposed sawtooth, because the capacitor is discharged more.
The effect is more disturbing at low frequencies, because the capacitor has more time to discharge between two cycles at a low frequency than at a higher frequency. At higher frequencies, the amplitude of the sawtooth is less.
It would be interesting to know if this effect if also present in the original 33609!.

 

[promixe]

As far as I recall, this is how my CV looks too. As you limit more, harmonics of CV sawtooth become more apparent distorting source signal even more. As I said before, I also hear the same _tendency_ (or character) to distort on the original 33609 unit. I haven't looked at the original CV with the scope though, but I suspect it should look somewhat similar. This weekend I should finally have some time freed up to look into this whole issue once again and post new mp3s and scope pics.

PS: Igor, no problem man, all of us here would be thankful for your input once you have more time.

PPS: To sum up: maxheadroom, nielsk, RuudNL, and me are having the same distortion, which is most apparent when using the limiter side chain, even though is still present in the compressor side chain as well, but can be noticeably reduced by swapping R10 to 24k instead of 6k8. Look at my post http://www.groupdiy.com/index.php?topic=26218.msg366121#msg366121 for this info.

To clarify even more: the reason we call it "low-end distortion" is because it gets triggered by LF energy the most, but the actual result is a wide spectrum distortion affecting the entire bandwidth of the unit.

 

[radiance]

Just curious,...are there ANY people who finished this project who don't have this distortion promixe and some others have?

For instance...Igor, does one of your units have this distortion?









....I've most of the parts....still waiting for some time to arrive....