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

[Vito Janeiro]

Thanks guys for the support!

Unit is working and it sounds amazing!

The only problem is that left cahnnel gets really distorted about 8db´s before right channel. What would be the best method to trace the fault?

Wbr,

Vito

 

[Rob Flinn]

The only problem is that left cahnnel gets really distorted about 8db´s before right channel. What would be the best method to trace the fault?

Vito

What I would do is switch the compresion in, but have the controls set so that neither the limit or compression is in.   Send a sine wave through the channel at a reasonable level that you know causes distortion, checking with a scope for distortion, probably before & after the BA640 first.  This will eliminate  or tell you that it is the BA640. If it's not the BA640 trace through the circuit to see if you can find that bad area.

If you have no scope then you could check the voltages that you have on the test points on Igors diagram, to see if there is anything out there.

 

[maxheadroom]

ulta-alex, Nice unit! Congrats! How does it sound? =)

Update on my LF distortion saga:

I finally got a minute to plug in the second set of the boards (I was building two 33609s at the same time) into the first unit chassis (all switches+PSU remained from the first unit, just the channel boards are the new ones). After calibrating one of them I ran the same music test through it as I did with the original problematic boards - this one behaved in EXACTLY the same way, i.e. had the same character LF distortion at the same settings etc. So, the conclusion is - all four channels that I built act identically and all have the distortion issue.

RuudNL, have you been successful with your LF distortion mod overtime? Have you compared it to the original 33609 units in terms of how it sounds and how similar its response is? I'm thinking this is my last resort is to implement your mod on all four boards that I have.

Igor, since I have four boards that all have the "mystery LF distortion" problem, that at least 4 more people beside me on this thread have experienced, would you be interested in checking one of my boards if I send it to you?

Thanks for the support! =)

any news about the LF distortion?

 

[RuudNL]

Did you get in touch with Igor in the meantime about checking a board?
It seems the distortion is in the design...
As you know I experienced the same distortion. To my surprise a lot of people say: "it sounds great", but I think they are using less critical material to do the tests with.
(Or our ears might be better...)

 

[radiance]

Did you get in touch with Igor in the meantime about checking a board?

As in: you've made a layout for your design and want Igor to have a look at it?

 

[RuudNL]

I had the impression that maxheadroom had the intention to send one of his boards to Igor, to have them checked for the LF distortion problem.

 

[radiance]

Ah...I see..maybe someone should rent a real 33609 and check for the same distortion...

 

[tommypiper]

I'm also still waiting for the verdict on the LF distortion before I build mine.  I thought Igor was going to investigate it.  But we haven't heard anything from him about it.

 

[tommypiper]

Ah...I see..maybe someone should rent a real 33609 and check for the same distortion...

As I mentioned some posts back, I can't imagine this LF distortion would exist in a commercial product from Neve.  Particularly from that era, when things were all hand built and hand designed, etc.  Testing a design in those days was pretty thorough. 

Additionally, if this LF distortion IS in the original design, then wouldn't it also be in the 2254 line of compressors, (as they have a similar diode compression mechanism AFAIK)?

Therefore, we'd be talking about ALL the famous Neve compressors having this same LF distortion flaw!  :  I find that hard to believe is the case...

 

[radiance]

Still strange that Ruud, who build his own 33609 "interpretation" , has the same distortion  :-\

 

[tommypiper]

Still strange that Ruud, who build his own 33609 "interpretation" , has the same distortion  :-\

I know.  I agree.  It's troublesome!  Are there any differences between the original and Igor's?

 

[kambo]

http://www.auroraaudio.net/dcforum/DCForumID1/792.html

 

[RuudNL]

So what's the answer?  "The distortion should be there" or "I don't know"... (In fact I know the person who asked this question!)

 

[kambo]

so, was it a genuine rev_j or a clone ?

 

[RuudNL]

It was a second hand genuine rev_j !

 

[Igor]

Makes some sence

 

[tommypiper]

Makes some sence

Igor, do you think it's in the original design? 

Do you think it's the diodes or the time control like Ruud is saying? 

Have you tested YOURS for LF distortion?!

 

[Igor]

My friend who have original 33609 (old one, without any mods/recap
and miscalibrated about up to 2db difference in compression between 2 channels)
has checked it and compared during mix session.
Mine was with Beclare in/interstage and homebrewed outputs(Hi-B C-core iron).
It was about 2 years ago, and I asked him about LF distortion....He liked the sound and
can't remember anything strage in limiter's behaviour. This was the reason all this discussion
about LF distortion seemed strange for me. I still not get "distorting" channel from Alexey (Promixie).... IMHO LF distortion guys talked about exists in both (original and mine),
this is the way it works with fast time constant on lows. Anyway, I'd like to check
"distorting" unit with "strange" behavior

 

[promixe]

Hey everybody, I'm back! =)

Reading the last couple of pages on this thread about the LF distortion here is what I can say:

1) The LF distortion IS in the original units and I COULD hear it when comparing my unit with the original unit (see my pics and posts on page #19). However, you can barely hear the LF distortion on the original and it blends with the compression effect of the unit so many people are not going to perceive it. It is, however, of THE SAME character/quality that we have on the replicas, just is very subtle. On my unit the distortion is so severe that the unit becomes unusable in professional applications. Therefore I conclude that the distortion issue IS in the original design, but is masked by component choice. (??)

2) As far as I know there are no schematic difference between the original and Igor's version, as he did use the original schematic to generate PCB layout from (Am I correct, Igor?). There are a few resistor value mismatches that were all found and corrected in this thread and with the exception of R10 mod (see page #28 my post) are not presenting significant difference in sound.

3) Igor, can I still send the boards to you? Would you look at them? I packed them in the box many months ago and it's been sitting here all this time, since I didn't have time to work out the shipping. I can ship the package as early as the end of this week.

4) NONE of the people who built the unit on this forum ever posted audio examples of how their units perform. It almost seems to me that people are building them to run a sine wave through, look at the scope, note some distortion and SNR numbers and be happy about their engineering skills. I mean, c'mon people, we build these things to CREATE MUSIC at the end of the day. Real music should be fed through these units and the only final verdict and evaluation benchmark is how the unit SOUNDS when listening with your EARS! =) The scope or analyzer program could say anything it wants, but the ear is the final judge!

Thanks to all!

 

[jdiamantis]

My friend who have original 33609 (old one, without any mods/recap
and miscalibrated about up to 2db difference in compression between 2 channels)
has checked it and compared during mix session.
Mine was with Beclare in/interstage and homebrewed outputs(Hi-B C-core iron).
It was about 2 years ago, and I asked him about LF distortion....He liked the sound and
can't remember anything strage in limiter's behaviour. This was the reason all this discussion
about LF distortion seemed strange for me. I still not get "distorting" channel from Alexey (Promixie).... IMHO LF distortion guys talked about exists in both (original and mine),
this is the way it works with fast time constant on lows. Anyway, I'd like to check
"distorting" unit with "strange" behavior

I'm wondering if tighter matching of the "bridge diodes" or variolosser would reduce the LF distortion? In my own experience with other limiters using the dynamic diode resistance of rectifiers to implement gain reduction has shown that matching of these elements at stratigic bias points reduces distortion (and feed-through thump).

jDiamantis