GSSL HELP THREAD!!!

[nwsoundman]

I am wondering if anyone who uses the Modultec 541-ME-DMA-001 meter from Mouser has verified the meter track GR properly?

I bought two of the and they both behave the same in my GSSL. The problem is that when there is 6 dB of reduction happening the meter only presents 2 dB. I measure just over 600 mvdc on the meter driver IC and at the meter itself. If I remove the meter sensitivity resistor and replace it with a jumper the meter presents a bit over 4 dB of GR.

I think the problem is that the meter resistance (internal) is 2300 ohms according to the data sheet.

I have corrected the ratios and the box sounds good. I just need to correct the meter issue. Can I just leave the jumper in place and change the gain of the meter amp to maybe .2 or .3 volts / db instead of the.1?

Also I have found a way to light these meters. I drilled a hole in the bottom of the meter case and inserted a blue LED powered from the control PCB. If you line the top inside the meter case wih foil the LED has no hot spots and very even distribution.

Thanks for any ideas on the GR tracking.

Kirk

 

[khstudio]

I did the same thing with the LED. One is the newer VCA's (218x's) = Blue LED & the other one is the older/dirtier VCA's(215x's) = Red LED.

I'm still a little concerned about the difference in voltage/current from the stock LED connected to that pad. It seems the Blue LEDs I'm using want 5 volts :shock: & more amps. I wonder if it will create any problems :?:
I asked a few weeks ago & don't remember getting an answer. O well, I'll be posting some pics soon... they turned out great!

This site & the people here are KILLER! :thumb:

 

[gyraf]

If you mis-track, then use a trimmer pot instead of the 2K meter resistor..

Jakob E.

 

[khstudio]

Roger,
I tried the 120k mix res. you talked about & it didn't seem to fix the ratio's or have much of an effect on the performance. Changing the 100k to 120k worked very well. I also liked all three being the same = 2180's... I tried the 2151 for just the sidchain & although it was cool, the 2180 seemed to track better & clearer. My other unit has all 2151's & has its own thing. Do you think it would be safe to run a wire from that 100k to a switch on the front & back to make it either 100k or 120k? I like the effects (ratio) of both, especially on drums.

Thanks,
Kevin

 

[nwsoundman]

Gyraf,

I installed a 5K trimmer already. I am (was) using a 1K meter resistor for a 10db FSD. If I up the value the meter drops, if I remove the resistor or trimmer all together I can get the meter to show me about 4db of reduction when it should show 6 db.

If I measure 600mvdc at the meter shouldn't it present about 6 db of reduction? I verfified that I do have 6 db of reduction by measureing the input voltage vs the output voltage.

Strange.

Kirk

 

[gyraf]

6 db of reduction by measureing the input voltage vs the output voltage.

Counting in the makeup gain?

You should have something like 2V at TL074pin8 (meter drive) when gain-reducing 20dB

Your meter may need a higher voltage (to drive 1mA through the coil) than the 2V that the circuit outputs at 20dB GR.

Jakob E.

 

[nwsoundman]

Ok. I am now at the studio so I was able to take a few measurements.

I have inputed a balanced signal and measure .775 volts on the output. My box is set up for unity gain when running balanced. I actually measure a plus .9 db when the conrols are set for no makeup and the threshold fully clockwise (no compression). So since I have .775 on the output I then start reducing gain untill the output measures .062 volts, gain is reduced from 0 db to -20 db. I now see negative 3.080 volts on pin 8 of the 074, negative 2.183 on the meter itself. I have the 1K meter resistor loaded now also. The meer shows about 9 db of reduction.

Thanks for the help,

Kirk

 

[gyraf]

20dB under 775mV would be 1/10 - that is 77.5mV, not 62mV

I have the 1K meter resistor loaded now also.

Does not compute... What do you mean?

 

[nwsoundman]

[quote author="gyraf"]20dB under 775mV would be 1/10 - that is 77.5mV, not 62mV

I have the 1K meter resistor loaded now also.

Does not compute... What do you mean?[/quote]

Yes. I accidently looked a the -22 db voltage on my db reference sheet and read -20 as .062 volts.

As for the 1K resistor you ask about. That is the meter sensitivity resistor that should be 1k for a 10 db scale on the meter.

Now I am seeing negative 2.8 volts on pin 8 of the 074 when reducing gain -20 db. Should this voltage be positive relative to the center tap on power transformer secondaries?

 

[mathflan]

Hi,

I have a question about the disrtotion trimmer.

I use VCA 2181LB with the modifications :

- Remove 68 R.

- Change 1M ohm resistor to 220 K.

I keep 10 K but, apparently, I have to change it with a jumper, I'm not sure...

As I have to Keep this distortion trimmer with the 2181LB, How I have to set this?
Someone have a method?

 

[khstudio]

I found this great link & wanted to share it but have a few questions?

http://groupdiy.silentarts.net/martthie_08/gssl/calibration.html

From member silentarts website:

CALIBRATION:

Compression ratio adjustment
Replace 100K between pin 8 of TL074 and pin 2 of TL072 with 120K for correct compression ratio behaviour (2:1 / 4:1 / 10:1). I found this value experimentally by measuring the ratio's using a method suggested by "the lab" member SSLTech, you can look here: http://www.groupdiy.com/index.php?topic=944 if you would like to read the original thread.

This is great & worked for me as well.:thumb:

meter adjustment
use 2K resistor for 0-10dB range or 1K resistor for 0-20dB range of gain reduction indication, when using a 1mA meter. I have the meter set up for 0-20dB range, because if you are sqeezing the shit out of a drum room track, you can easily peak on 20dB of compression. For more delicate work, you might prefer a smaller range.

OK, this confussed me. I have a 1mA meter & I'm using a 2k resistor... :?
I though the 2k was for 20db. Which one is correct :?:

modifications for the use of THAT 2181LA VCA in Jakob's "DBX 2150 to DBX202C emulation" circuit
1. remove the 68k resistor from pin 4 to ground.
2. replace the 10k resistor from pin4 to distortion trim pot with a piece of wire (short it out)
3. change the 1M resistor from 50K trim pot to the THD connection of the DBX202C circuit to 680K.

1. OK

2. Why short out where the 10k was... I just pulled mine like I read here was the way to go :?:

3. Why does the 1m get reduced to 680k... I never read that one either? Can someone explain what these changes do :?: :?:

Thanks,
Kevin

 

[mathflan]

For the Replacement of the resistor 1M by a 680 K:

See here

http://www.thatcorp.com/datashts/dn137.pdf

2181LA : Change 1M by 680K
2181LB : Change 1M by 220K
2121LC : change 1M by 130K

I know this page for calibration, but It doesn't talk About Distortion trimmer calibration??

 

[enthalpystudios]

I tried searching for asterisk, and star, and some other things, but couldn't quite find what I'm after.....

The places on the board with asterisks (and one with **), are they optional? and what are the options for?

I'm off board power trannie, so I know which bridge rectifier spot to use.....

I'm using 2181lc's btw..... seems I need to follow the above instructions for those....

Thanks

billy

 

[nwsoundman]

The ** at the 2K resistor located by the 10 pin connector means that when using a 2K your GR meter will have a 0 - 20 db scale. If you install a 1K resistor your meter scale will be 0 - 10 db. This info is on the PCB PDF's.

The * at the 1K's in the channel VCA's was just a note when Jakob was designing.

 

[enthalpystudios]

awesome, thanks man!

should be able to finish the insides of this puppy pretty soon, it'll be the first thing for me, so it's time to feel antsy....


I have to tape mud and paint my basement so I can move down there, or I'll never get a single thing done.... all this crap is in my office along with a bunch of instruments computers and CRAP


very soon, obey-wan

 

[Purusha]

I have a question regarding the W04 - 1.5A 400V Bridge Rectifier.

I got only 1.5A 250V Bridge Rectifier (B250C) as closest match. Would this be OK or should I get the W04?

 

[gyraf]

How high voltage do you have across it?

 

[Purusha]

[quote author="gyraf"]How high voltage do you have across it?[/quote]

I ordered torid 2x15V 35VA. Is this answering your question?

 

[khstudio]

Why short out where the 10k was ?

 

[Purusha]

Hey Greg,

I found 10 places for 100pF monolitic capacitors on the PCB and not 9 like you mentioned in your part's list PDF. Maybe you can add this in META thread.