[HerbertR]

Outside

[HerbertR]

Inside

[JMan]

Congrats, Herbert!

[Murdock]

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?

[fripholm]

When we take the "normal" 600 Ohm input, the secondary Impedance is 150 ohms. Isn't that to low?

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'.

[Murdock]

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'.

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?

[fripholm]

Absolutely! I meant 'meaningless' in the sense that the transformer can be used only at this particular impedance.

[Murdock]

Absolutely! I meant 'meaningless' in the sense that the transformer can be used only at this particular impedance.

Thanks! So it's safe to say, that a 600:150 Ohm transformer is not suitable for this circuit, right? 10k:2k5 would be better.

[fripholm]

So it's safe to say, that a 600:150 Ohm transformer is not suitable for this circuit, right? 10k:2k5 would be better.

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...

[BerndVP]

finally came to the point where I wired everything.
Now when playing sound thru the unit even in Bypass I'm getting distorted noise ?
When in active mode, nothing is happening on the VU

[octavez]

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.

[fripholm]

The datasheet only mentions wiring options for 4:1 and 1:1 ratios but if you wire both the primary and secondary in parallel or both in series you should be getting 2:1 as well.

[BerndVP]

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.

[fripholm]

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.

[octavez]

The datasheet only mentions wiring options for 4:1 and 1:1 ratios but if you wire both the primary and secondary in parallel or both in series you should be getting 2:1 as well.

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]

ok, will check this today,
On the audio pad that you give, is this directly coming from the audio interface or first thru the input transformer ?

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.

[fripholm]

On the audio pad that you give, is this directly coming from the audio interface or first thru the input transformer ?

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.

Would you recommend waiting on the VTB 9046 to be back in stock?

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. 

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