john12ax7
Well-known member
Try a XLR to TS cable.
Impedance Issue between preamp out (EZ1290) and Audio Interface Line IN (Prism).....Help!
- Thread starter PatchDog
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Voyager10
Well-known member
Stupid question: does anything else work properly when plugged into your Prims's line in?
If so, what sort of plug is it?
If you're wiring the secondaries in parallel, promise me faithfully that you haven't reversed the connections to one of them inadvertently, meaning that they are in antiphase and therefore fighting each other terribly.
If so, what sort of plug is it?
If you're wiring the secondaries in parallel, promise me faithfully that you haven't reversed the connections to one of them inadvertently, meaning that they are in antiphase and therefore fighting each other terribly.
ruffrecords
Well-known member
You do not need the 600 ohm resistor across the output. The original Neve circuit has an output impedance of about 75 ohms and will drive any load from 600 ohms upwards. Your problem is definitely not an impedance problem.
As others have said, this is either an cable issue or a design error in the interface which is probably trying to cater for both balanced and unbalanced inputs
Cheers
Ian
That does indicate that at minimum gain the microphone input will have 7dB more gain than the line input in -10dBV mode. You will have to compensate for that somewhere.
Not relevant, you are concerned about the line level inputs of the Prism.
No, that is completely opposite, a higher input impedance will cause less reduction in level due to the output impedance of the driving stage.
According to the specs you pasted above it is not possible to apply less than 10dB gain to the mic input. Minimum gain is -1 dBu for full scale digital, line input in low voltage (-10dBV mode) is +6 dBu for full scale. In +4 mode it takes +18 dBu to reach full scale digital.
However, the EZ1290 manual says it has over 70dB of gain available, so there should be no reason to use -10 dBV mode. I have never heard of a Neve design which could not hit 18 dBu, so something else is going on.
You do mean the 1/4" input in the center of the XLR connector on the rear panel, or the 1/4" only line inputs next to those on the rear panel, and not the 1/4" inputs on the front panel, correct?
Can you describe exactly the cable connections on each end, XLR and TRS? The symptoms all point to a cable problem.
Thank you every one for your super helpful knowledge and suggestions, this forum truly has the best of the bunch on here.
It looks like I made a really dumb error in my XLR wiring on the male pins (output), as most of you suspected (holds head in shame). Humble apologies. Looks like I didn't take into account the 'mirrored' factor of my diagram when I wired this up years ago. I'm re-wiring now so haven't tested but it's got to be that. Rookie error.
It looks like I made a really dumb error in my XLR wiring on the male pins (output), as most of you suspected (holds head in shame). Humble apologies. Looks like I didn't take into account the 'mirrored' factor of my diagram when I wired this up years ago. I'm re-wiring now so haven't tested but it's got to be that. Rookie error.
Brian Roth
Well-known member
Yes, it was exactly that, Pin 1 & 2 swapped on the XLR outs. Doh!! I've had it like this for over 10 years lol. Very weird that in most situations with my interfaces and mixers over the years it wasn't an issue, at least not audibly.
That's really interesting. ~Would you say it would be better to add that 650 ohm over not having it? 20Khz seems like it would be a noticeable difference in comparison. Do you or anyone know how if they had it on the original Neve?
It depends on the characteristics of the specific transformer model you used. You have it connected to your audio interface, I would suggest just measuring the frequency response, that will tell you if an addtional loading resistor is needed or not.
Brian Roth
Well-known member
"Modern" equipment almost always has some sort of electronically balanced inputs and outputs vs. transformers. Depending on the design of those circuits, a mis-wired cable may (or may not) create an obvious failure. There are a variety of circuit designs and wiring combinations, so there is no "rule of thumb" if a mis-wired cable will cause any particular type of malfunction.
Many years ago, one of my studio clients introduced me to the Behringer CT-100 box. It tests a variety of cable combinations. One really cool feature is that it will detect an intermittent connection. I sometimes have had a funky problem at the end(s) of a cable with RCA plugs I soldered on. I can plug the cable in, wiggle the cable at the RCA connector and the box detects the fault....typically an intermittent short circuit. Those can be very tricky to detect with just a simple multimeter.
It also has a very basic tone generator function as well. It's FAR from being even close to a lab-grade device, but is quite handy when "toning out" an audio line in a studio or PA application. Here in the USA, Sweetwater has it for $29.00 with free shipping. UK dealers should have it for a low price as well.
https://www.sweetwater.com/store/detail/CT100--behringer-ct100-6-in-1-cable-tester
Bri
That's a cool little box for the money, I know it well, I ran Behringer tech support for 5 years. I make all their synth videos these days though.
Well cheers for the help again everyone. Success, it's all working perfectly now. Still can't believe I had it wired like that for 10 years oh boy.
Brian Roth
Well-known member
So glad you have it sorted out! The big clue for me was the very low signal level that sound thin/tinny. I recall my first part-time gig in a "real" studio (2" 16 track Ampex and a MCI desk) 50+ years ago. I was maybe 19 years old, and already had some skills after working with garage bands when in high school.
Anyway, one day I was micing up a band and one mic on the drums sounded....very weak and tinny! My studio mentor immediately recognized the sound and he quickly traced it down to a pin 2 (3?) open circuit in the mic cable. THAT sound was permanently etched into my brain...lol.
Bri
Anyway, one day I was micing up a band and one mic on the drums sounded....very weak and tinny! My studio mentor immediately recognized the sound and he quickly traced it down to a pin 2 (3?) open circuit in the mic cable. THAT sound was permanently etched into my brain...lol.
Bri
Matt Syson
Well-known member
The resistor plus capacitor across the transformer secondary corrects the frequency response to a fair degree and then the 604 OHM or whichever value close to 600 Ohms corrects bot frequency and lEVEL 'errors' when that is in circuit. Having that switchable woulmd allow you to hear bother versions of 'compromise' as in or out the true original response depends on the external gear you are connecting it to. the response also changes when feeding LONG lengths of cable (300 Feet or more) so when the gear is used in a fixed unstallation values might need adjusting to get an overall response thqat meets the full requirements. The definition of 'right or wrong' is variable so the 'best compromise' values are used. This of course makes a mockery of all those determined to be 'authentic' when gear is taken out of the original design parameters.
I think you are essentially picking the damping for a RLC circuit. The capacitance is distributed across the windings, so probably a bit difficult to measure independently or calculate from geometry, but easy enough to put a variable resistor across the output and measure the frequency or step response at various loading values.
Hi!
I agree with others that this is not an impedance issue. It seems like a missing or wrong connection issue. The xlr to 1/4" cable is miswired (like socket 1 and 3 swapped or some other swappage, or a wire is broke. Or a connection in the to or from gear is broken.
Troubleshooting so far seems incomplete. You must do these testes:
1) check cable wiring with ohm meter and make sure socket 1 of xlr goes to shield (aka sleeve) of 1/4" plug, socket 2 of xlr goes to tip of 1/4" plug and socket 3 of xlr goes to ring of 1/4" plug.
Or if 1/4" plug is unbalanced type then socket 1 and 3 of xlr should go to 1/4" plug shield and socket 2 of xlr to 1/4" plug tip.
2) test that cable(s) additionally be plugging from/to other equipment.
If the cables pass tests 1 & 2 then the cable is not the problem. Then problem is with with sending or receiving unit, possible the connectors on those units themselves. It seems you can visually inspect the wiring of the sending unit..any wire broken? Jankily soldered? xlr polarity and sheld correct?
On the receiving unit you can do a gerry-rigged test by, with 1/4" cable plugged into that unit and it's gain turned up (but be careful of speakers...keep speaker level low at first) touching with finger/hand, alternately to cable female xlr socket 2 & 3. Obviously you will need a small screwdriver or paperclip or something like that to make contact in the xlr female connector. You should hear a buzz or hum when touching, and should sound the same on both xlr 2 and 3. That's if the 1/4" input is balanced.
If 1/4" input is unbalanced then you should only hear finger hum/buzz when touching xlr socket 2 if cable is correctly wired, and socket 3 if wired out of phase.
If, with balanced 1/4" plug you hear hum/buzz with touch test on only xlr socket 2 or 3 then there is a broken connection in the receiving unit on tip or ring.
Cheers
I agree with others that this is not an impedance issue. It seems like a missing or wrong connection issue. The xlr to 1/4" cable is miswired (like socket 1 and 3 swapped or some other swappage, or a wire is broke. Or a connection in the to or from gear is broken.
Troubleshooting so far seems incomplete. You must do these testes:
1) check cable wiring with ohm meter and make sure socket 1 of xlr goes to shield (aka sleeve) of 1/4" plug, socket 2 of xlr goes to tip of 1/4" plug and socket 3 of xlr goes to ring of 1/4" plug.
Or if 1/4" plug is unbalanced type then socket 1 and 3 of xlr should go to 1/4" plug shield and socket 2 of xlr to 1/4" plug tip.
2) test that cable(s) additionally be plugging from/to other equipment.
If the cables pass tests 1 & 2 then the cable is not the problem. Then problem is with with sending or receiving unit, possible the connectors on those units themselves. It seems you can visually inspect the wiring of the sending unit..any wire broken? Jankily soldered? xlr polarity and sheld correct?
On the receiving unit you can do a gerry-rigged test by, with 1/4" cable plugged into that unit and it's gain turned up (but be careful of speakers...keep speaker level low at first) touching with finger/hand, alternately to cable female xlr socket 2 & 3. Obviously you will need a small screwdriver or paperclip or something like that to make contact in the xlr female connector. You should hear a buzz or hum when touching, and should sound the same on both xlr 2 and 3. That's if the 1/4" input is balanced.
If 1/4" input is unbalanced then you should only hear finger hum/buzz when touching xlr socket 2 if cable is correctly wired, and socket 3 if wired out of phase.
If, with balanced 1/4" plug you hear hum/buzz with touch test on only xlr socket 2 or 3 then there is a broken connection in the receiving unit on tip or ring.
Cheers
Graham Nystrom
Transformers and transistors for me please!
It’s really nice to have the option. Put the load resistor on a switch if you can. Otherwise leave it out and build a cable that has the load resistor in the barrel across pin 2+3.
With it you get flat response and tamer overall gain. Without it you get an aggressive hf boost way up at like 20k. Both are nice depending on your mic and your source.
In the old days, the next circuit in line (eq etc) would probably present the 600 ohm load, so while it didn’t necessarily have the resistor, it also didn’t need it.
What’s even more fun to is to put 3 or 4 load resistors on a switch so you can have options from flat to full HF boost (caused by the unloaded output transformer “ringing“).
Last edited:
ruffrecords
Well-known member
Neve output stages we designed to drive any load from 600 ohms upwards. Peaks in the response are caused more by driving source impedance rather than load impedance. The Neve class A output stage has a source impedance of about 30 ohms and the Zobel network across the transformer tames any HF peaks caused by transformer interaction with this source impedance. With or without a 600 ohm load, a Neve should be essentially flat out to about 75KHz.
Cheers
Ian
Cheers
Ian
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