[BUILD] fripholm's TG1 Zener Limiter boards - support thread
- Thread starter fripholm
- Start date
Help Support GroupDIY Audio Forum:
Congrats, Herbert!
I don't know, if it was already covered. But what Impedance specs should the input Transformer have?
You recommend ratio of 2:1.
When we take the "normal" 600 Ohm input, the secondary Impedance is 150 ohms. Isn't that to low?
You recommend ratio of 2:1.
When we take the "normal" 600 Ohm input, the secondary Impedance is 150 ohms. Isn't that to low?
Murdock said:
You are right in that a transformer with a 2:1 winding ratio has a 4:1 impedance ratio. But in the case of an input transformer, the load that is connected across its secondary is 'reflected' with that ratio to the primary winding. It means that the input stage of the compressor with its input impedance of about 3 kOhms is 4 times that seen from the outside world through the transformer - about 12kOhms - which is in the ballpark of any line input.
'600 ohms' is just a meaningless rating for what a transformer is designed to work with - in this case, 'if it had a 150 ohms load across the secondary, the primary would see 600 ohms'.
fripholm said:
Thanks for the fast answer! The 3k Ohm information was what I needed. Thanks!
I know, what you mean with "600 Ohm is a meaningless rating". But it's not 100% true I think. It gives a clue about what inductance you can expect the transformer to have, which is important. Right?
Murdock said:
No. I guess that was lost in translation.
Trying again: the label '600:150' does NOT mean that the transformer can only be used at this particular impedance of 600:150 ohms. Hence, it's 'meaningless' if you're trying to figure out at which circuit impedance the transformer will work. It may very well work fine.
I'm using Haufe transformers (labeled 90436) in my builds and I don't even know, what these were originally made for. When I asked Haufe about them, they also had no clue what those were - but as long as they sound fine, they are fine to me.
When I built my first 1073 clone with MIC/LINE switch, I had Carnhill 9045 (mic level) and 9046 (line level) transformers which I accidentally swapped without noticing. I somehow even managed to wire them backwards so that at least the ratios were correct. When I looked at the labels a year later, I realized my mistake and swapped them to their correct positions. Although they're clearly designed for different purposes, I didn't notice a difference in sound before or after the swap...
octavez
Active member
I'm wondering if the Carnhill VTB 9071 input transformer would be suitable instead of the VTB 9046 (not available at the moment)? They both seem to have fairly similar specs.
Hi,
So, I rechecked all my wiring of my transfo's to my relays and to the BYP pins...
If I send audio thru the unit around +4dBu I need to set the input pot to max to get the VU showing a reduction of 4dB.
The unit in THD is directly distorting...
Any way I need to look at the unit ?
Also have one channel not passing audio thru it, but when bypassed it gives audio.
So, I rechecked all my wiring of my transfo's to my relays and to the BYP pins...
If I send audio thru the unit around +4dBu I need to set the input pot to max to get the VU showing a reduction of 4dB.
The unit in THD is directly distorting...
Any way I need to look at the unit ?
Also have one channel not passing audio thru it, but when bypassed it gives audio.
The meters will not show anything useful before there is some clean audio passing from input to output. Did you do any of the audio calibration steps (not the meters)?
Please check one board at a time, block by block, step by step. Carefully read (and follow) the guide and this thread. For example, see this post on how to inject a test signal directly to the output stage to confirm that it's working correctly. Or check your voltages against the chart from this post.
Please check one board at a time, block by block, step by step. Carefully read (and follow) the guide and this thread. For example, see this post on how to inject a test signal directly to the output stage to confirm that it's working correctly. Or check your voltages against the chart from this post.
octavez
Active member
fripholm said:
That's what I thought too. It looks like the main difference is the optimal load impedances (seems higher on the VTB 9071). Would you recommend waiting on the VTB 9046 to be back in stock?
BerndVP said:
Yes, directly from the signal generator/interface. Start with a low signal level. There shouldn't be any DC on this pad that could harm an interface output. Measure it first against GND - to be safe.
octavez said:
Depends on how long you're willing to wait. If you're not, go for it
Note that I don't have any experience with either of them in the Zener but I'm pretty sure the 9071 will be fine. 8)
Hi all, after shelving this for a while, I'm back to working on it. I have a few issues, but I'll start with the audio transformers I picked. I wanted to get some second opinions on how to wire these.
I went with Sowter 9165 for input and 3292 for output.
https://www.sowter.co.uk/colours/9165.pdf
for 9165 I have something that doesn't make any sense to me now:
Primaries:
yellow to xlr 3
pink connected to green
blue to xlr 2
black to xlr 1
Secondaries:
Red to audio gnd
Brown to white
Orange to audio +
(black to gnd)
https://www.sowter.co.uk/colours/3292.pdf
for 3292 I went:
Primaries:
orange xlr 2
white xlr 3
yellow xlr 1 (gnd)
black xlr 1 (gnd)
Secondaries:
Grey: audio +
Blue: audio gnd
I don't think I did this correctly :-\
I went with Sowter 9165 for input and 3292 for output.
https://www.sowter.co.uk/colours/9165.pdf
for 9165 I have something that doesn't make any sense to me now:
Primaries:
yellow to xlr 3
pink connected to green
blue to xlr 2
black to xlr 1
Secondaries:
Red to audio gnd
Brown to white
Orange to audio +
(black to gnd)
https://www.sowter.co.uk/colours/3292.pdf
for 3292 I went:
Primaries:
orange xlr 2
white xlr 3
yellow xlr 1 (gnd)
black xlr 1 (gnd)
Secondaries:
Grey: audio +
Blue: audio gnd
I don't think I did this correctly :-\
brewbacca said:
On a quick glance (anyone feel free to correct me or fill in any gaps), the output transformer looks like the issue.
The problem that I see is the yellow lead (the center tap on the primary side). I think you'll want to isolate this lead, not connect it to your xlr pin 1.
As for the black leads and where those should be grounded, someone else will have to tell you if that's in the right spot, as I'm not sure.
It does look like you adjusted correctly for the phase inversion in the output stage, if I'm reading those wire colors correctly.
Anybody want to confirm/correct me here?
From what I can see, the output transformer is wired backwards (but it should still work). The 'primary' is the INPUT of the transformer which connects to the circuit. Leave the center tap unconnected, orange to signal, white (and black) to GND, Grey and blue to XLR.
XLR pin 1 is NOT your audio ground connection - it connects to the chassis first. A few pages back there should be a diagram that shows proper ground wiring.
XLR pin 1 is NOT your audio ground connection - it connects to the chassis first. A few pages back there should be a diagram that shows proper ground wiring.
ok, cool. Thanks guys!
It looks like I had the ground figured out correctly and just labeled in wrong in my post (audio gnd is only connected to chassis gnd in one place). I think the next thing is the calibration, but I have the V2 board which required switching out resistors. I'm wondering if it would be worth it to get a par of the newer boards and stuff those?
It looks like I had the ground figured out correctly and just labeled in wrong in my post (audio gnd is only connected to chassis gnd in one place). I think the next thing is the calibration, but I have the V2 board which required switching out resistors. I'm wondering if it would be worth it to get a par of the newer boards and stuff those?
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