Hi,
I made a passive, 2 channel dual transformer box ( 2 transformers per channel) and I have a question about how reflected impedances work with transformers.
The box is designed as a color box for tracking or during the mixing stage. Each channel consists of a 600/600 ohm 1:1 transformer wired to the xlr input then the secondary of that transformer is wired to the primary of another transformer that is 1:1 with a 20k ohm input impedance and the secondary of that transformer is wired to the output xlr.
The first transformer is being fed 150 ohms from the line output of a pre amp. I understand that it will see a 600 ohm input impedance or load but what will the reflected output impedance after that first transformer be? Also, based on that output impedance which will feed the second transformer, what will the output impedance after the 20k second transformer be?
Trying to wrap my head around this so I know the load for each stage.
Thanks,
Matt
I made a passive, 2 channel dual transformer box ( 2 transformers per channel) and I have a question about how reflected impedances work with transformers.
The box is designed as a color box for tracking or during the mixing stage. Each channel consists of a 600/600 ohm 1:1 transformer wired to the xlr input then the secondary of that transformer is wired to the primary of another transformer that is 1:1 with a 20k ohm input impedance and the secondary of that transformer is wired to the output xlr.
The first transformer is being fed 150 ohms from the line output of a pre amp. I understand that it will see a 600 ohm input impedance or load but what will the reflected output impedance after that first transformer be? Also, based on that output impedance which will feed the second transformer, what will the output impedance after the 20k second transformer be?
Trying to wrap my head around this so I know the load for each stage.
Thanks,
Matt
When used within its normal impedance and frequency range, a transformer does not have an impedance but simply reflects what impedance it sees on its two sides. Normally, if you cascade two 1:1 transformers then the result you get is basically another 1:1 transformer although perhaps with a narrower bandwidth and slightly more distortion.
That is not what you have. By cascading a '600 ohm' transfomer with a '20k' transformer you have ensured that at least one of them will be operating well outside its design parameters. Why use two transformers when using one will be cheaper, and will actually work?
That is not what you have. By cascading a '600 ohm' transfomer with a '20k' transformer you have ensured that at least one of them will be operating well outside its design parameters. Why use two transformers when using one will be cheaper, and will actually work?
A 20k:20k transformer has an inductance so high that it can only sensibly be used directly at an input. Otherwise any non-negligible amount of cable capacitance will cause severe frequency response peaking issues. Hence something like this generally has no business being in a passive transformer box.
As a rule of thumb, a passive 1:1 transformer will present a source impedance of at least the signal source's output, plus the wire resistance of both primary and secondary winding added, plus some more to account for imperfect coupling. 1:n is a bit more complicated because the loss impedances, too, are transformed.
As a rule of thumb, a passive 1:1 transformer will present a source impedance of at least the signal source's output, plus the wire resistance of both primary and secondary winding added, plus some more to account for imperfect coupling. 1:n is a bit more complicated because the loss impedances, too, are transformed.
Thanks for the responses and the information. I have done several diy audio mods and projects but I am still learning about circuit theory and electronics.
This project came about because I had an old ampex 440 reel to reel deck that needed too much work and would cost more than I would like to spend to restore it. However, I read that the input and output transformers are responsible for a lot of the color of that machine and so I thought I'd try to wire them passively to salvage something.
Would it be possible to have the 20k transformer first and the 600 ohm after and get a reasonably flat response or should I just use the 600 ohm transformer only? And in either of these implementations, do I need any coupling/decoupling capacitors? I thought since it is purely passive I would not.
Thanks again
This project came about because I had an old ampex 440 reel to reel deck that needed too much work and would cost more than I would like to spend to restore it. However, I read that the input and output transformers are responsible for a lot of the color of that machine and so I thought I'd try to wire them passively to salvage something.
Would it be possible to have the 20k transformer first and the 600 ohm after and get a reasonably flat response or should I just use the 600 ohm transformer only? And in either of these implementations, do I need any coupling/decoupling capacitors? I thought since it is purely passive I would not.
Thanks again
A couple of comments from a former tapehead. The colorations you refer to were the cumulative effect of all of the passive and active components in the recording path as well as the process of recording and playback.
I think you will find that pulling these transformers and using them as proposed is not going to result in anything close to the effect you are looking for. These are high quality transformers and the 440 wasn't actually designed as an effects box at all, the fact that people find the distortions of analog tape pleasant is largely an artifact of the tape and process.
These are also worth a substantial amount of money, might actually be nice to pass them along (or maybe the whole deck) to someone who will use them appropriately. You could then use the money to purchase something more likely to achieve the goal. YMMV and I could be off base here. Just thought I would say my piece.. 😀
I think you will find that pulling these transformers and using them as proposed is not going to result in anything close to the effect you are looking for. These are high quality transformers and the 440 wasn't actually designed as an effects box at all, the fact that people find the distortions of analog tape pleasant is largely an artifact of the tape and process.
These are also worth a substantial amount of money, might actually be nice to pass them along (or maybe the whole deck) to someone who will use them appropriately. You could then use the money to purchase something more likely to achieve the goal. YMMV and I could be off base here. Just thought I would say my piece.. 😀
I totally agree! And I know this first hand because I own a Studer/Revox B77 that I bought at a consignment store and restored. Even the passive components on it can really affect the sound.
Because I already own the B77 reel to reel, I figured it would be cool to track through the ampex transformed into the revox to get a blend of the color from both machines. Before I actually got any response on this thread I went ahead and wired the transformers together in the configuration I mentioned in my first post. I definitely hear some of the unique coloration of the ampex after using them.
I did notice some high frequency peaking and weirdness like others are saying. However, I read that the 20k transformer must have its secondary pins jumpered with a 22k resistor or the high frequencies will be 3db too hot. So, I soldered a 22k old carbon comp resistor I had lying around across those pins and it definitely is flatter now. The carbon comp is old and has drifted to 24k already so I imagine it will get better with a much more precise resistor. But this configuration may still not be fully workable. I don't know enough yet to be sure so that is why I am asking you guys.
carbon film produces a lot more noise and distortion that good resistors.
Carbon composition is even worse than carbon film.
Carbon composition is ultra low inductance and that is based on the physical size of the resistor. Keep them for duties that need ultra low inductance, cheaply. There are some special ultra low inductance resistors that cost many decades more than C comp.
Carbon composition is even worse than carbon film.
Carbon composition is ultra low inductance and that is based on the physical size of the resistor. Keep them for duties that need ultra low inductance, cheaply. There are some special ultra low inductance resistors that cost many decades more than C comp.
Carbon comp resistors may be necessary for those desiring the old sounds of the 1950s: noise, popping, distortion, replacement every 5-10 years.
- Status
- Not open for further replies.