[BUILD] fripholm's TG1 Zener Limiter boards - support thread

[JMan]

As far as I understand, current wants to return the same (and shortest possible) way it came, so it seemed logical to return the power supply rails through the GND wire to the PSU board first and then tie it all together at chassis ground.

Would this also apply to the ground connection from the bypass relays?  The guide has a symbol that I interpreted as "chassis ground," but I suppose that one should also connect back to the PSU board first?

 

[fripholm]

Would this also apply to the ground connection from the bypass relays?  The guide has a symbol that I interpreted as "chassis ground," but I suppose that one should also connect back to the PSU board first?

Theoretically you're right but I think the relay's ground connection could really go everywhere because most of the time they are in either of two steady states which shouldn't mess with your clean signal ground. The actual switching event is short enough to not cause any disturbance either. As you can see from the sketch I posted earlier, my relays share the GND pad from the output connector and it's never been a problem.

However, the voltage for the relays comes directly from the PSU (through a switch), so make sure they can handle 28 Volts.

 

[JMan]

Theoretically you're right but I think the relay's ground connection could really go everywhere because most of the time they are in either of two steady states which shouldn't mess with your clean signal ground. The actual switching event is short enough to not cause any disturbance either. As you can see from the sketch I posted earlier, my relays share the GND pad from the output connector and it's never been a problem.

However, the voltage for the relays comes directly from the PSU (through a switch), so make sure they can handle 28 Volts.

Thanks for the explanation!  I think that for the sake of simplicity, I will take the relays' ground connection back to the PSU along with everything else (LEDs, STROM, etc). 

I have some 24v relays that I plan to use, like is recommended in the guide. 

But actually, the voltage rating issue does raise another question that I have.  I'm intending to pick up a few of those square LED switches from Don Audio or Frank at frontpanels.de to use as the bypass and link switches, but it looks like the LED in those is 2v.  The datasheet is pretty much just a drawing of the dimensions and doesn't provide any other info, so I'm wondering how I go about calculating the value of resistor that I need to use to keep the +28v from the PSU from burning out the LED...

I actually had the same question about my meters, but I *think* I'm good on those.  I have some Sifams with a 24v LED and an 820r resistor (looks to be 1 watt or higher, nice and fat, but I can't tell exactly), and this seems to me like it should be fine to take the +28v, right?

 

[fripholm]

I'm wondering how I go about calculating the value of resistor that I need to use to keep the +28v from the PSU from burning out the LED...

You take the supply voltage and subtract the LED voltage from that = 26 Volts. The rest is Ohm's law I = V / R

I'm using 10k for the LEDs in my switches which calculate to 2.6mA. I didn't even bother to calculate this at the time - just popped the resistors in and liked the brightness of the LEDs (or lack thereof)...  8)

I actually had the same question about my meters, but I *think* I'm good on those.  I have some Sifams with a 24v LED and an 820r resistor (looks to be 1 watt or higher, nice and fat, but I can't tell exactly), and this seems to me like it should be fine to take the +28v, right?

26 Volts divided by 820r is 31mA which is pretty high and will make your LEDs age more quickly. Other than that, it just might be too bright, especially in a dim studio environment. You don't want your meters to hurt your eyes every time you look at them, do you? 

Replace it with anything from 3k to 10k, or put it in series with the internal resistor. 250mW resistors are fine.

 

[JMan]

You take the supply voltage and subtract the LED voltage from that = 26 Volts. The rest is Ohm's law I = V / R

I'm using 10k for the LEDs in my switches which calculate to 2.6mA. I didn't even bother to calculate this at the time - just popped the resistors in and liked the brightness of the LEDs (or lack thereof)...  8)

26 Volts divided by 820r is 31mA which is pretty high and will make your LEDs age more quickly. Other than that, it just might be too bright, especially in a dim studio environment. You don't want your meters to hurt your eyes every time you look at them, do you? 

Replace it with anything from 3k to 10k, or put it in series with the internal resistor. 250mW resistors are fine.

This all makes good sense!  I suppose my confusion was coming from the current draw, since I have no idea what number is good for an LED (this is one of many blind spots for me).  I looked to see if there was anything in the data sheets that would give me a hint, but the sheets for both the meters and the switches are just technical drawings showing the measurements, no other info!   But if I understand correctly, low single digits mA is probably what I want, eh?  The calculation is easy enough, and from there, it's "adjust to taste" based on the brightness?

Thanks, by the way, for continuing to patiently answer these questions.  I'm sure a lot of this stuff is common knowledge, and I've been doing lots of reading, but the phrase "you don't know what you don't know" really applies to me here!

EDIT:

On review, I think that the meter calculation that you did (which I know was just a quick scratch calculation, so no worries) used the Bypass LED voltage instead of the meter LED.  My meter LEDs say that they are 24v, so I think it would look like this:

28v-24v=4v

4v=(I)(820r) ---> I=4.88mA

So maybe I will try this out first, and if it's still too bright, perhaps I'll add another 500-1k resistor in series to bring it down to ~2-3mA.  Unless I've missed something...?

 

[fripholm]

The forward voltage of an LED is usually from 1.5 to 4 Volts max so I assumed that your meter LED including the resistor was designed to work with a 24V supply. I haven't heard of an LED that drops 24 Volts on its own  ???

The rated current of standard LEDs is around 20 to 30mA but IMHO they end up being too bright and the limiting resistors getting unnecessarily hot.

You'll be fine with 2 to 6mA, maybe 10...

 

[JMan]

The forward voltage of an LED is usually from 1.5 to 4 Volts max so I assumed that your meter LED including the resistor was designed to work with a 24V supply. I haven't heard of an LED that drops 24 Volts on its own  ???

The rated current of standard LEDs is around 20 to 30mA but IMHO they end up being too bright and the limiting resistors getting unnecessarily hot.

You'll be fine with 2 to 6mA, maybe 10...

Ah, that makes sense.  Again, I don’t have much information on the meters, which is ironic since they came directly from Sifam as a custom order — I couldn’t remember if there was ever a consensus about the Don Audio mirrored pair, so just to be sure I contacted Sifam directly about making a 1mA version. 

They didn’t say anything about the LED assembly (and I didn’t have the forethought to ask), but they did put a sticker on it that says 24v.  When I just touched the leads to a 9v battery, the meter lit up nice and bright, so I guess you are right!  For connecting to the +28, I will try putting a 4.7k resistor in series with the 820r, which will put me a little under the 5mA mark, and see how that goes.

 

[tommia]

So who uses it in mono and who in stereo or in %?

 

[electrisizer]

So who uses it in mono and who in stereo or in %?

100% stereo - its the best overhead or drum room comp ive heard

 

[tommia]

Ok so for Andow and electrisizer: 100% stereo. More opinions?

 

[fripholm]

My stereo unit is used mostly on the mix or rear (google 'Andrew Scheps rear bus technique') bus UNLINKED and in parallel (about 20 to 50% wet).

The mono unit lives on close mic'ed snares. Nothing else is able to liven up a wimpy snare sound as this beast does. Depending on the track and the original dry sound it's also in parallel from 50 to 80%. I hardly ever use 100% compression these days.

So, for me it's (dual) mono and in parallel.

 

[meantimedude]

Hi sorry for the newbie question! I'm currently looking at the ELMA switches for wiring. Does anybody have any pictures of their ELMA switches wired up for the TG1? (i'm struggling to confirm where im leaving the gap in the resistors and where wiring to them goes)

Like I said apologies for the stupid question, any help really appreciated

 

[tommia]

Thanks for the replies.
So I'm going for a stereo unit that can be unlinked.
This wil also work for snare.

 

[BerndVP]

Hi, just a last question, the output transfo's how do I need to wire them ? 600 ohm / 600 ohm or 150 ohm / 150 ohm or a other way ?

 

[andow]

Hi, just a last question, the output transfo's how do I need to wire them ? 600 ohm / 600 ohm or 150 ohm / 150 ohm or a other way ?

Either way will work, but for the lowest output impedance wire them in parallel.

Wasn't it you who asked the same question on FB already?  ???

 

[BerndVP]

yeah, it was me.

 

[JMan]

On the various switches (hpf, attack, mode, input/output gain), is there a preference for shorting or non-shorting, or does it not matter so much in those applications?

 

[fripholm]

It shouldn't matter for HPF, attack or mode as these only affect what's going into the sidechain. For input and output shorting is preferred.

 

[HerbertR]

Hi, my Zener is also working. Yeaaah 
And it sounds pretty well... I want to share in my opinion the most important Startup settings:

-One Problem I had was a shorted Inputtransformer through a soldering blob. Rest works perfekt now.
I am using the Carnhills VTB 9046 Input 2:1 serial primary and secondary and the VTB 2291 Output 1:1 -parallel primary and secondary. I recognised that issue by feeding a 0dBU / 0.775 V signal into the bypassed Unit. One Board has given after the Outputtransformer about 0.79 V,  the other only 0.4 Volts - measured between XLR Pin 2 and 3. As far as an Amateur I can say this is the easiest test you can do to check the correct wiring of I/O Transformer and the Output/Makeup Stage / Bd139/140. All other Mistakes should be between the Compressingsignalpath when not bypassed the Unit. Correct me if I am wrong.
-For the two boards I used 4 Pairs of SAME matched Fairchild Diodes, as this are the recommanded sorts of Diodes. Noise is only noticeable at highest Input/Output and Mixersettings. But its defintily more than I know from a G1176,.... but also really low. Hum is no Issue.
-I have used shielded Cabels from XLRs to the transformers and also to the PCBs/Switches. The shields are connected to PCB 0V->Starground, and between XLRs and Transformers directly to the Chassis/ XLRs.
-The resistors I have used are the recommanded ones: R86 820 Ohms, R87 3.3kOhm, R22 12kOhm - Omit / shorted FT2A Trimmer, Omit R56 and using the FT2B Trimmer - pretrimmed to 1K as starting Point. By adjusting this trimmer the Compression begann to work. I ve adjusted all Panelknobs and Pots similar in both two Units, measuerd the omited Parallelresistance R56 and adjusted the FT2B in second Unit to the same resistance. Sound is completly similar the same way. All measuring point of booth boards are showing nearly the same Voltage.  Cool.
Its really a heavy punchy Compressor. Not suitable for all Signals but on Drums and Bass its a Killer. THD Mode and High Compression Distortion is also really cool. Wow. I think on Vocals I will not use it so much because this Compressor is really a heavyweight. Or you are Axel Rose ..
Thank you Thomas "Fripholm" for this Genius PCBs...

 

[HerbertR]

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