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

[Curtis]

I had my audio interface adjusted so that the test tone was within 1dB of clipping the converters, so in this case all the tests RMAA did were referenced to 0dBFS.  From what I can gather of how RMAA works, it expects it's reference to be at 0dBFS, and the software asks you to adjust the levels as such when you start the test.

 

[maxheadroom]

I had my audio interface adjusted so that the test tone was within 1dB of clipping the converters, so in this case all the tests RMAA did were referenced to 0dBFS.  From what I can gather of how RMAA works, it expects it's reference to be at 0dBFS, and the software asks you to adjust the levels as such when you start the test.

try to connect 0.775VAC (0dBu) to your audio interface input and read the level from your computer

 

[rob_gould]

Hi All,

I'm trying to follow the simplified calibration procedure and have run into a problem early on.

Here's what happens:

output of PS is 23.9v

voltage drop over R44 is 260mV

The CV point next to the opamp on the PSU is 3.00v to ground.

So all the first part of the procedure is OK

Comp is set to out, overall comp out, link out.

I am feeding a 1kHz sine wave from soundforge out of my Echo Audiofire 12 soundcard.  The output of the soundcard is set to +4dB

With the unit bypassed, I can see a 0dB signal coming back into the soundcard

BUT...

When I try to follow this step:

4.1. APPLY 0DB TO INPUT. COM OFF, LIM OFF, BYPASS IN, MEASURE OUTPUT IS 0 DB,
CONNECT LINK TO CV 3.00V WITH CROCODILE CABLE. ADJUST RV2 TO GET -8 DB AT OUTPUT.
LET UNIT HEAT-UP 5 MIN, REPEAT.

Nothing happens to the output signal when I adjust RV2.  I currently have the crocodile cable connected from +CV on the PS board to the LNK pad next to C13.  This is correct right?

Also, when I connect the croc cable, it slams the meter right over to the right too.

Here are my test voltages:

TPA - 4.02V
TPB - 3.70V
TPC - 0V
TPD - 11.64V
TPE - starts at around 1/2 1 volt when I probe and then starts to fall.
TPF - 0V

Any ideas anyone?

Cheers,

Rob

 

[Curtis]

Currently out of town and don't have the unit in front of me, so I can't comment on the measurements there but:

With the unit bypassed, I can see a 0dB signal coming back into the soundcard

The unit needs to be UN-bypassed to calibrate the sidechain, signal going thru the unit, but with Limi and Comp for each channel set to Off.  The description of Bypass In/Out can be a litle confusing at times 

Nothing happens to the output signal when I adjust RV2.  I currently have the crocodile cable connected from +CV on the PS board to the LNK pad next to C13.  This is correct right?

Pretty sure, that's how I did mine and it seemed to work fine.

Also, when I connect the croc cable, it slams the meter right over to the right too.

The meter will move when you apply the 3V signal (how much depends on how badly out of calibration the meter is, but you adjust that out further thru the procedure).  By adding 3V to the sidechain signal you're effectively forcing the gain reduction element to start working, hence the meter showing gain reduction.

HTH.

 

[rob_gould]

Thanks Curtis.  I see now how it should work.

I think that the issues I'm seeing now are all related to not having my soundcard set up right.

I have got a sine wave which I created at 0dB in Soundforge.  It's looping now in Cubase and the output meters are showing 0dB.

On my Echo Audiofire soundcard, I can pick -10 or +4 as the output level, but when I use my DMM to check the values of these signals, I either get 5.1V between ground and hot and 0V between ground and cold when set to +4, and 1.0V between ground and hot and 0V between ground and cold when set to -10.

Edit - just realised that the reason I'm only seeing a signal on the hot line is because the Audiofire is impedance balanced rather than differentially balanced.  Cheapskates!

I was expecting to see 0.7V for 0dBU somewhere, but this isn't the case.

Can anyone suggest what's happening here?  It's so frustrating to not be able to get this sorted because it appears that the 1st channel is pretty much calibrating as it should.  I just need to be sure I'm using the correct level going in.

Cheers,

Rob

 

[Curtis]

0dB in the PC is probably +18dB or +12dB in the outside world (see my previous conversation with maxheadroom).  Just generate a sinewave loop in your DAW and adjust the master fader level until you measure 0.775VRMS on the output of the soundcard, irrespective of what the meters in the DAW say.

If you're using the DAW to monitor the signal coming back out of the unit as well you'll need to account for the fact that 0.775VRMS coming into the soundcard will only be -18dB (or whatever) on the DAW meters.  Just add 18dB to the results you get from the test procedure.  Run the test tone through the unit in bypass to establish your reference levels before you start.

Note: recheck the amplitude of the signal going into the unit if you run it bypassed with a 600ohm load on the output tranny (I think it's mentioned in the procedure to load the output with 600ohms).  I found that the output of my sig gen was slugged quite a bit because of the loading through the OP transformer with the unit in bypass.  Taking the unit out of bypass removes the 600ohm loading seen by the sig gen and the input level will shoot back up again.

 

[rob_gould]

Thanks for that info Curtis

One final noob question:

Is loading the output tranny with 600 ohms a simple matter of putting a 600 ohm resistor across the output tranny secondaries?

Cheers

 

[Curtis]

Yep, across pins 2 and 3 of the output XLR.

 

[rob_gould]

Thanks for the help dude  ;D

 

[rob_gould]

OK - still having some problems here...

I've procured a swanky Fluke multimeter from ebay so I now know that my soundcard is outputting exactly 775mV

With bypass out, the signal passes straight through with no problem, but when I switch bypass in, the most I can get at the output is 583 - 584mV when I turn RV1

I'm measuring directly across pins 1 and 2 of the output XLR to get this value.

I'm sure that there's still a problem with the way I'm measuring though, because both boards are exactly the same with RV1 at maximum:  583 - 584 mV.  Too much of a coincidence to be a bad component or something I'd say.

The thing I'm slightly concerned by is discovering that my soundcard is not differentially balanced, just impedance balanced, so there's no negative signal on pin 3.  Will this influence what's happening in the 1st input transformer?

Man I'm confused over this.  I just can't seem to get to a point where I'm certain what I'm doing is correct.

Can anyone take a guess at what's happening here?

Cheers,

Rob

 

[Rob Flinn]

Rob

Take a look at the diagram.  It has the level changes in dB at the different stages as the signal travels through the audio chain.   It could be worth your while just seeing if you have the relevant changes in level happening.  Then, if you are losing some gain somewhere you will know where it is happening.

Also some DMM's have limited frequency range in ac mode........ even older flukes I believe !  I always use an ac millivolt meter for this stuff, & check for obvious anormalities with a scope.

 

[Igor]

Hi Rob! Please write which transformers are you using in your unit and how do they connected. (ratios).
All db measures related to transformer's windings, so, it does not matter if souncard is unbalanced.
Let's start from this point:
Trafo ratios:
input: 2:1 (-6db)
interstage: 1:2 (+6dB)
output: 1:2.5 (+8dB)
If no GR signal, i.e. no compression, all voltages and dB measures on schem should be correct (within 2%).
Mesure voltages and DB's with Fluke on trafo windings and TP's.
Please read previous posts, there was some good stuff from Promixe regarding measures etc.

 

[Curtis]

I'm measuring directly across pins 1 and 2 of the output XLR to get this value.

Fairly sure you should be measuring across 2 and 3 (hot and cold), not 1 and 2 (shield and hot).  You'll be 6dB down otherwise (or half volts).  What happens if you max out RV1 and measure 2 to 3?  My guess is that you'll see 2x 584mV = 1.168V.

 

[rob_gould]

Thanks for the replies.

[quote author=Curtis]

Fairly sure you should be measuring across 2 and 3 (hot and cold), not 1 and 2 (shield and hot).  You'll be 6dB down otherwise (or half volts).  What happens if you max out RV1 and measure 2 to 3?  My guess is that you'll see 2x 584mV = 1.168V.
[/quote]

Yes - that's exactly what happens.  When I measure across pins 2 and 3 at the output, I can easily adjust RV1 for 775mV

Can anyone confirm whether what Curtis suggests is correct?  This would make sense in terms of me getting the right values...

[quote author=Igor]

Hi Rob! Please write which transformers are you using in your unit and how do they connected. (ratios).
[/quote]

It's the 9045, 9046, 9056 combo.  9045 and 9046 are wired in series same as other people's 33609s

[quote author=Igor]

Mesure voltages and DB's with Fluke on trafo windings and TP's.
[/quote]

OK - just one channel to begin with (bypass in, everything else out):

TPA - 4.03V
TPB - 3.72V
TPC - 0V
TPD - 11.76V
TPE - 0.58V and dropping very slowly
TPF - 0V

TR3 emitter - 18.01V
TR3 base - 17.39V

TR4 emitter - 18.04V
TR4 base - 17.4V

On the VTB9046 (tranny 1)

Pri +  775mV
Pri -  0V (remember this is connected to ground on my soundcard)
Sec + 177mV (-12.8 dBu)
Sec - 147mV (-14.4 dBu)


[quote author=Rob Flinn]

Also some DMM's have limited frequency range in ac mode........ even older flukes I believe !

[/quote]

This is a newish Fluke 177 so I think it should be OK, though I did notice that resolution changes depending on AC frequency which is interesting.  Unfortunately my previous multimeter only measured AC to 0.1V accuracy, hence the need for the upgrade...

Unfortunately I have to stop there as I have to leave for work, but at first glance, it's clear that the voltages look OK, but the first transformer is decreasing the signal by double what it should isn't it?  Around 12 dB instead of 6dB?

Cheers,

Rob

 

[Igor]

When I measure across pins 2 and 3 at the output, I can easily adjust RV1 for 775mV

HUH. Fine.

It's the 9045, 9046, 9056 combo.  9045 and 9046 are wired in series same as other people's 33609s

I not good in remembering numbers, but I suggest the ratios are exactly 2:1, 1:2 and 1:2.5.
Anyway, see prev. quote, if you got unity gain fixed, trafo ratios are OK.

OK - just one channel to begin with (bypass in, everything else out):

TPA - 4.03V
TPB - 3.72V
TPC - 0V
TPD - 11.76V

OK

TPE - 0.58V and dropping very slowly

OK, should be in this range

TPF - 0V

TR3 emitter - 18.01V
TR3 base - 17.39V

TR4 emitter - 18.04V
TR4 base - 17.4V

Fine

On the VTB9046 (tranny 1)

Pri +   775mV
Pri -   0V (remember this is connected to ground on my soundcard)

OK

Sec + 177mV (-12.8 dBu)
Sec - 147mV (-14.4 dBu)

Measure not to gnd, but between sec+/-, people, WTF, read some posts ago, this stuff was explained!!!!!
Anyway, it is fine

Quote from: Rob Flinn

Also some DMM's have limited frequency range in ac mode........ even older flukes I believe !

Yup. I luv my old good Boonton 1120 (hardly modyfied). Worth $300 I paid and hours passed to modify

Saves time and V->dB conversion table.

Unfortunately I have to stop there as I have to leave for work, but at first glance, it's clear that the voltages look OK, but the first transformer is decreasing the signal by double what it should isn't it?  Around 12 dB instead of 6dB?

AAARRRRGGGHHH!!!!! Rob!!! Please, go ahead this thread and read Promixe posts and my answers!!!
Your intelligence seems way higher than mine, at least by level of your English.
Just mind, for you it will take less time to read 20 posts back than for me explain it again
using every 10th word English-Russian Babylon

Pass the testproc and tell if everything is OK.
Good luck with your 33609!!!

 

[Igor]

Very helpfull:
http://www.groupdiy.com/index.php?topic=26218.360
Please read!!!!

 

[rob_gould]

[quote author=Igor]
AAARRRRGGGHHH!!!!! Rob!!! Please, go ahead this thread and read Promixe posts and my answers!!!
Your intelligence seems way higher than mine, at least by level of your English.
Just mind, for you it will take less time to read 20 posts back than for me explain it again
using every 10th word English-Russian Babylon

Pass the testproc and tell if everything is OK.
Good luck with your 33609!!!

[/quote]

Thanks Igor. It's not that I have not read this whole thread several times (including Promixe's posts), but I lack the confidence to know for sure if my problem is exactly the same as his.  I appreciate how annoying it is to keep repeating yourself.  These concepts are very new to me but I am learning with your and everyone's help.

Anyway, my English may be good (I am British though), but your electronics is better

I'm back at home on Thursday, so hopefully my next report will be of the 33609 working

Edit: Just spotted your big red writing.  Thanks dude 

 

[Igor]

Great. Will be happy to see another working 33609!
Good luck, dude!

 

[promixe]

Alright! I'm back! =) My 33609 still has the same issue, even after the 0.22uF parallel poly cap mod that Igor suggested. I'm gonna post some audio examples so people can hear what I'm referring to. Also, gonna catch up with the thread and follow up on question people have here in the next little bit.

 

[rob_gould]

It works!  ;D ;D ;D

After a few hiccups, I have everything calibrated and the 33609 sounds fantastic

Many thanks to Igor for this project and your help over the last week or so.  But also thanks to everyone else on the forum who has offered advice on getting this project finished.  I've learned a load making this!

Pics to follow tomorrow when it's light.

One word to fellow DIYers who have not yet started this project:

It really pays to match the gains of the BC441s in position TR15.  I spent a while trying to establish why the compressor was not compressing equally on both channels until I stumbled over this info earlier in the thread.  I desoldered the unmatched transistors I had originally, put in a much closer matched pair and suddenly compression between channels equaled out nicely...

Cheers,

Rob