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200 ohm or 600 ohm output impedance in DI Box?
Old 18th April 2017
  #1
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200 ohm or 600 ohm output impedance in DI Box?

Radial J48 has 600 ohm output impedance, but I chose another DI Box that has 200 ohm output impedance. I want to record electric guitar in my audio interface through DI box. Which impedance is better?
also, how it is that 20$ behringer DI box sounds exactly the same as 200$ Radial J48? Here is comparison test recordings:
https://www.youtube.com/watch?v=VcKvf6bKPbA
Old 18th April 2017
  #2

Well, the 200 ohm one should have just a little less noise (hiss). But, both are sufficiently low to work fine for guitar into nearly any modern mic pre-amp...

As for the quality of the cheaper unit: Guitars are easy. The bandwidth doesn't go very high or low and the inductive nature of the pickups combined with the low signal level are easy for transformers to deal with...

Try plugging a hot analog synth doing bass patches into each box - you'll probably hear a difference there.



-tINY

Old 18th April 2017
  #3
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Quote:
Originally Posted by tINY View Post

Well, the 200 ohm one should have just a little less noise (hiss). But, both are sufficiently low to work fine for guitar into nearly any modern mic pre-amp...

As for the quality of the cheaper unit: Guitars are easy. The bandwidth doesn't go very high or low and the inductive nature of the pickups combined with the low signal level are easy for transformers to deal with...

Try plugging a hot analog synth doing bass patches into each box - you'll probably hear a difference there.



-tINY

Thanks for answer. So there is no such thing as too low output impedance? First I thought that 200 ohm are worse than 600 ohm, since most DI boxes have 600 ohm output.
Also is it true that if I connect DI box to my interface with phantom power on, then I wil not be able to use Ground Lift knob?
Old 18th April 2017
  #4

IT depends. On the good one, there is a coupling cap on the secondaries which will prevent DC current from flowing. The cheap one... maybe.

But, the DC resistance of the secondaries is not 200/600 ohms. Those ratings are the reflected AC impedance if the primary is loaded as indicated. So, a typical 10k/600ohm DI transformer is 300 ohms output impedance with 5k source on the other end. Additionally, the phantom power should have limiting resistors and most mic pre-amps are designed to survive a direct short....

Finally, the ground lift should only dis/connect the 'low" side of the primary to ground (pin 1 on the XLR). So, it won't make any difference on the output side.



-tINY

Old 18th April 2017
  #5
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Quote:
Originally Posted by tINY View Post

IT depends. On the good one, there is a coupling cap on the secondaries which will prevent DC current from flowing. The cheap one... maybe.

But, the DC resistance of the secondaries is not 200/600 ohms. Those ratings are the reflected AC impedance if the primary is loaded as indicated. So, a typical 10k/600ohm DI transformer is 300 ohms output impedance with 5k source on the other end. Additionally, the phantom power should have limiting resistors and most mic pre-amps are designed to survive a direct short....

Finally, the ground lift should only dis/connect the 'low" side of the primary to ground (pin 1 on the XLR). So, it won't make any difference on the output side.



-tINY

My audio intreface Steinberg ur242 actually has one input that has Hi-Z knob, specially for guitars and bases. But I still find my guitar sounding very noisy. That means that there is not as good convertion of Hi-Z impedance as in separate DI box?
Will DI box help to clean DI signal of my guitar? even if my interface has build in Hi-Z knob?
Old 19th April 2017
  #6

Depends how good that Hi-Z input is... I'd start with the cheap DI - it probably has a more limited frequency response - which helps keep noise down.

The other trick to try with that Hi-Z input is to roll your tone knob back slightly....




-tINY

Old 19th April 2017
  #7
Quote:
Originally Posted by KenjiMax View Post
Radial J48 has 600 ohm output impedance, but I chose another DI Box that has 200 ohm output impedance. I want to record electric guitar in my audio interface through DI box. Which impedance is better?
also, how it is that 20$ behringer DI box sounds exactly the same as 200$ Radial J48? Here is comparison test recordings:
https://www.youtube.com/watch?v=VcKvf6bKPbA
It depends on the input impedance of the mic input you're using and whether it's transformer or transformerless. It also depends on the true impedance (NOT DC resistance) of the pickup.The 200 ohm box might work better with some transformer inputs.

Note the emphasis on "might" and "some".

I have no interest in your Youtube "comparison". as YT's lossy encoding and other processing makes any real comparison impossible.
Old 19th April 2017
  #8
Quote:
Originally Posted by KenjiMax View Post
Thanks for answer. So there is no such thing as too low output impedance? First I thought that 200 ohm are worse than 600 ohm, since most DI boxes have 600 ohm output.
Also is it true that if I connect DI box to my interface with phantom power on, then I wil not be able to use Ground Lift knob?
If it's an active box running on phantom you'll probably need the ground, yes. It depends on how sophisticated the powering circuit is.

As to the rest of it - it's a pretty complicated subject. I'm considering copying a post from another site I'm on where some real heavies hang out, but it would likely just increase your confusion.
Old 21st April 2017
  #9
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Thread Starter
Quote:
Originally Posted by tINY View Post

Well, the 200 ohm one should have just a little less noise (hiss). But, both are sufficiently low to work fine for guitar into nearly any modern mic pre-amp...

As for the quality of the cheaper unit: Guitars are easy. The bandwidth doesn't go very high or low and the inductive nature of the pickups combined with the low signal level are easy for transformers to deal with...

Try plugging a hot analog synth doing bass patches into each box - you'll probably hear a difference there.



-tINY

So if my goal is just to record guitars and basses with passive pickups direcly to audio interface then any DI Box will make job done well? I was choosing between expensive Radial j48 (200$) or cheap Samson MDA1 for 40$. I want as cleanest signal as possible to record and put plugins on it. Or somehow more expensive DI box will have cleaner signal?
Old 21st April 2017
  #10
Quote:
Originally Posted by KenjiMax View Post
So if my goal is just to record guitars and basses with passive pickups direcly to audio interface then any DI Box will make job done well? I was choosing between expensive Radial j48 (200$) or cheap Samson MDA1 for 40$. I want as cleanest signal as possible to record and put plugins on it. Or somehow more expensive DI box will have cleaner signal?

The more expensive passive DI will generally have a better transformer. For bass or for harsh electrical environments (like factory floors and aircraft), the better transformers often work better. You need the low-end and the isolation.

For guitar, the limited bandwidth doesn't require as good a transformer - and the studio is usually a noise-free electrical environment.



-tINY

Old 21st April 2017
  #11
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Thread Starter
Quote:
Originally Posted by tINY View Post

The more expensive passive DI will generally have a better transformer. For bass or for harsh electrical environments (like factory floors and aircraft), the better transformers often work better. You need the low-end and the isolation.

For guitar, the limited bandwidth doesn't require as good a transformer - and the studio is usually a noise-free electrical environment.



-tINY

But for passive pickups it is better to get an active DI box right?
Old 22nd April 2017
  #12
Quote:
Originally Posted by KenjiMax View Post
So if my goal is just to record guitars and basses with passive pickups direcly to audio interface then any DI Box will make job done well? I was choosing between expensive Radial j48 (200$) or cheap Samson MDA1 for 40$. I want as cleanest signal as possible to record and put plugins on it. Or somehow more expensive DI box will have cleaner signal?
To begin with, the Radial j48 is not a passive DI, it's active. As such it's suitable for use with pretty much any type of pickup or electronic instrument without any adverse effects on the tone, level, or pickup loading.

The Samson MDA-1 is also an active box. It boasts most of the same general "features" as the Radial. This just goes to show how much good the "feature" lists in sales literature are.

Both boxes use an output transformer for isolation from ground loops and providing a balanced signal. However you could buy two of the Samson boxes for the cost of one of the transformers in the Radial. Good transformers are expensive and they make all the difference to sound quality. Also, the Samson runs on 9 volts internally, while the Radial uses a special internal power supply to boost the rail voltage, which provides much greater headroom. The Radial also uses much higher quality circuitry in general.

If you're actually interested in a passive box, I'd suggest the Radial JDI, which runs around $100.
Old 22nd April 2017
  #13
Quote:
Originally Posted by KenjiMax View Post
But for passive pickups it is better to get an active DI box right?
With cheap-ass boxes, yes. For quality boxes it's less cut and dried. High quality passive boxes can be very good indeed, and some players prefer them tonally. Low quality passive boxes are fraught with problems.

Since Radial owns Jensen Transformers they are able to sell the JDI for approximately the same money that the transformer in it sells for separately.

It is very tricky to design and build a good passive DI transformer.
Old 22nd April 2017
  #14
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Just from my experience with microphones, lower is better.
Old 27th April 2017
  #15
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Thread Starter
Quote:
Originally Posted by tINY View Post

The more expensive passive DI will generally have a better transformer. For bass or for harsh electrical environments (like factory floors and aircraft), the better transformers often work better. You need the low-end and the isolation.

For guitar, the limited bandwidth doesn't require as good a transformer - and the studio is usually a noise-free electrical environment.



-tINY

Got a DI box today. ZERO difference to guitar sound(
Old 27th April 2017
  #16
Quote:
Originally Posted by KenjiMax View Post
My audio intreface Steinberg ur242 actually has one input that has Hi-Z knob, specially for guitars and bases. But I still find my guitar sounding very noisy. That means that there is not as good convertion of Hi-Z impedance as in separate DI box?
Will DI box help to clean DI signal of my guitar? even if my interface has build in Hi-Z knob?

Time to start looking for noisy power circuits and shielding your guitar....



-tINY

Old 27th April 2017
  #17
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Thread Starter
Quote:
Originally Posted by tINY View Post

Time to start looking for noisy power circuits and shielding your guitar....



-tINY

Is that consider noisy guitar? First one is direct to interface, second do DI box. NO difference, but is it noisy or is just me?
Old 27th April 2017
  #18
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Thread Starter
Quote:
Originally Posted by tINY View Post

Time to start looking for noisy power circuits and shielding your guitar....



-tINY

/////
Attached Files

DI box Steinberg.wav (8.59 MB, 144 views)

Old 27th April 2017
  #19

That seems pretty quiet for such a high gain.... I'd live with that.



-tINY

Old 27th April 2017
  #20
Gear Head
 

Thread Starter
Quote:
Originally Posted by tINY View Post

That seems pretty quiet for such a high gain.... I'd live with that.



-tINY

But is it any difference to you? because first part is interface only, second is DI box.
How can DI box make ZERO difference?
Old 27th April 2017
  #21

It can make zero difference when it faithfully passes the signal to the converter in your little digital box....

If there is no connection to ground at the guitar, this is not surprising. Where transformers make a big difference is when there are ground loops.

If you are looking to degrade the signal with a transformer, you need to hit it harder (like a clean boost pedal) or load the secondaries heavily.... say, 50 ohms across pins 2-3 of the XLR connector.




-tINY

Old 4th May 2017
  #22
Quote:
Originally Posted by BarcelonaMusic View Post
Just from my experience with microphones, lower is better.
No.

You can't generalize like that.

With microphones it depends not only on the type of microphone it is, it also depends on whether or not the mic uses an output transformer and what the impedance of the secondary of that transformer is - and since the impedance of the secondary is not fixed but is determined by a ratio between primary and secondary and the primary impedance is determined by its source the whole matter gets pretty complicated.

Then there's the matter of the type on input the mic is connected to - transformer or transformerless, bridging or matching, etc.

Furthermore impedance is a curve, not a single fixed number.

Maybe lower is better for a particular microphone, but how much lower?

This is something that I've been learning about for years and I still haven't got it all. I think I've got a handle on one aspect of it and then I get in a conversation with somebody like Dr. Mark Fouxman or (the late) Oliver Archut (may he rest in peace) and my head starts spinning trying to understand how it all fits together.

With guitar pickups and passive DIs it depends a LOT on the real impedance of the pickup, which is actually a drastically different thing from the DC Resistance spec quoted by pickup manufacturers.

I've asked Mark if I can post a quote or two from him - we shall see.
Old 4th May 2017
  #23
Quote:
Originally Posted by tINY View Post


For guitar, the limited bandwidth doesn't require as good a transformer - and the studio is usually a noise-free electrical environment.



-tINY

That's not entirely true, as the bandwidth limitation of the guitar is mostly on the high end and the first place that the deficiencies of a cheap transformer will show up is the low end, both in bandwidth and headroom.
Old 4th May 2017
  #24
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Quote:
Originally Posted by John Eppstein View Post
No.

You can't generalize like that.

With microphones it depends not only on the type of microphone it is, it also depends on whether or not the mic uses an output transformer and what the impedance of the secondary of that transformer is - and since the impedance of the secondary is not fixed but is determined by a ratio between primary and secondary and the primary impedance is determined by its source the whole matter gets pretty complicated.

Then there's the matter of the type on input the mic is connected to - transformer or transformerless, bridging or matching, etc.

Furthermore impedance is a curve, not a single fixed number.

Maybe lower is better for a particular microphone, but how much lower?

This is something that I've been learning about for years and I still haven't got it all. I think I've got a handle on one aspect of it and then I get in a conversation with somebody like Dr. Mark Fouxman or (the late) Oliver Archut (may he rest in peace) and my head starts spinning trying to understand how it all fits together.

With guitar pickups and passive DIs it depends a LOT on the real impedance of the pickup, which is actually a drastically different thing from the DC Resistance spec quoted by pickup manufacturers.

I've asked Mark if I can post a quote or two from him - we shall see.
Now I agree with you. That was kind of an old post, but I have a new microphone I built that just works betther at HIGHER ohms. I`ve built several and I`m not sure why some work better on different ohms than others since I generally use the same FET capacitor for all. The only thing a CAN`T control are the diaphragms.
Old 5th May 2017
  #25
Here are excerpts from a conversation I recently had with Dr. Mark Fouxman of Samar Microphones on another site, which I found quite educational.



Quote:
Originally Posted by Mark Fouxman

markfouxman Avatar


Apr 10, 2017 at 1:49pm monkeyxx likes this

Post by markfouxman on Apr 10, 2017 at 1:49pm
The main problem with pickups is they are all different and there is no standard to their parameters... It very much reminds me older moving coil cartridges for LP players--they all were all over the place and each one required a well matched transformer.

Usually, all DI boxes I saw use 1:12 transformer (IOW, "one size fits it all"). While works for some pickups it is often totally wrong ratio for others. For example, DiMarzio Angel Series pickups have much lower impedance and with 1:12 you'll lose quite a bit of gain besides of obvious impedance mismatch and severe sonic degradation. Ideally, for the best results you'd want to have the transformer matched to your particular pickup.

Another problem is the higher ratio the transformer the more it is sensitive to the quality of winding topology and lamination. Understandably, the "dollar store" transformers do not have any "fancy" winding techniques and have very poor lamination choice (a quality High Nickel lamination alone would cost more than the entire $.99 transformer)--indeed, you get exactly what you pay for.
Quote:
With an acoustic DiMarzio pickup we have here (Angel series) I measured its impedance at 1kHz as 3.08kOhm (from memory listed DCR 1.66kOhm as most of their other acoustic ones). Assuming bridged operation for max voltage transfer we want load impedance of about 10 times of source. Most of the mic inputs are in the 1.5--3kOhm range. A 4:1 transformer should be quite sufficient, giving over 6dB gain increase in comparison to 12:1 transformer. This is beside the point it is much easier task to make a good 4:1 transformer than 12:1.

Best, M
Quote:

Apr 11, 2017 at 9:39am

Post by markfouxman on Apr 11, 2017 at 9:39am

markfouxman Avatar
Apr 10, 2017 at 4:07pm markfouxman said:
With an acoustic DiMarzio pickup we have here (Angel series) I measured its impedance at 1kHz as 3.08kOhm (from memory listed DCR 1.66kOhm as most of their other acoustic ones). Assuming bridged operation for max voltage transfer we want load impedance of about 10 times of source. Most of the mic inputs are in the 1.5--3kOhm range. A 4:1 transformer should be quite sufficient, giving over 6dB gain increase in comparison to 12:1 transformer. This is beside the point it is much easier task to make a good 4:1 transformer than 12:1.

Best, M
Quote:
Originally Posted by JE
You said "DiMarzio pickups", not one specific and anomalous model. Not that that really makes a whole lot of difference, given that your premise is flawed.(Edit: The above lines were written before Dr. Fouxman edited his previous post for clarity.)

"Assuming bridged operation for max voltage transfer we want load impedance of about 10 times of source."

Why would you want that? A typical magnetic pickup on an electric guitar has a DC resistance somewhere between 4K and 11K ( up to 15 k in cases of extreme overwind - like many DiMarzios) and is intended to operate into a load impedance of around 1 megohm or more. That's ONE HELL OF A LOT MORE than 10 times the source. A lower impedance pickup will have a much more efficient voltage (gain) transfer. Again, we're not driving a Telco transmission line here.

And average 5K Strat pickup operating into a 1 meg input on a typical Fender amplifier would have a ratio of about 200:1.

Most passive DIs load magnetic pickups much more than optimum as it is, I don't see why you'd want to increase the loading even more - it would tend to kill the voltage transfer (gain).

Some people prefer passives, as the extra loading causes some high frequency loss which some people find euphonic. Such people find active DIs too bright and too detailed. Me, I've got 4 Countryman Type 85s. If they're too bright I turn the treble down.

Generally speaking, one wants as high a load impedance as is practical on a guitar pickup, the limiting factor being HF rolloff due to cable capacitance. Many active DIs have an input impedance in the 5 meg range.

I think you're making some assumptions that simply are not valid. (Edit: That's what I get for "thinking"!)

Best,

JE

Sorry, I have hard time following you. We are not talking about slapping a 1meg resistor into input of Fender amplifier and feeding it with 5k Strat. The topic is passive DI's and their transformers, i.e. by far more complicated devices, which have totally different design parameters and compromises. We are talking about step down transformer going into 1.5-3kOhm microphone input. We are not discussing DiMarzio pickups--rather, my point was a low output low impedance pickup will have different ratio transformer than high output high impedance one. The point I was making it is easier to make a high quality lower ratio transformer than high ratio one. The point was the lower ratio transformer will have less signal drop and thus higher output. Did you read it? Or do you propose to make a 200:1 transformer and then desperately try to recover some signal out of that?

While we are on that, please note we do not mix DCR and impedance in the same equation. While indeed, some sources do have their impedance purely resistive (notably ribbon microphones, where it is safe to assume DCR as an impedance--it changes only on the frequency of resonance, where there is impedance peak), the guitar pickups have a lot of reactance component due to its inductance and winding capacitance--their impedance is quite a bit higher than DCR, so please check your math.

Thanks, M
Quote:
Originally Posted by JE
So your point is that we need a different passive DI for every guitar?

The pickup you chose as an example is an outlier - very, very few guitar pickups have an impedance that low. If you're building a general purpose box it should cover the middle region of the bell curve well, not something stuck way out on the end of one leg.
Quote:
Originally Posted by MF
No, not different for every guitar, but definitely low impedance pickups require lower ratio.
Actually, the low impedance pickups are quite popular for their clean sound and many prefer them working with passive DI's, so using them with 12:1 just defeats the purpose...

A good solution would be using a transformer connected whether for 12:1, or 6:1 ratios, depending on pickup.

Best, M
Quote:
Originally Posted by JE
So what you're saying is that passive DI boxes should have specially made multitap transformers that should be rewired to match the particular pickup used in a given session according to what impedance one measures the pickup at (since the vast majority of pickup manufacturers do not state actual impedance (at which frequency?), they only spec DCR.)? And how many studios have the necessary equipment to measure true impedance, anyway?
Quote:
Originally Posted by MF
It is actually, not the best idea to use multitap transformers. That is, unloaded parts of turns can make problems like ringing, etc. The good way is a double bobbin transformers, so the primary can be switched in series for 12:1 and 6:1 operations (and yes, we make one like this).

Good point about true impedance measure and it is impossible to tell it from DCR, as reactance depends on pickup capacitance and inductance, so there will be a lot variables, including style of pickup, humbuckers, wire diameter, etc... However, if you see DCR of some 1-2kOhm then most likely it is a low impedance pickup and a lower ratio might be preferable... but as always, the final judge is our ears...
Quote:
Originally Posted by JE
Have you ever seen such a multiimpedance DI box?
Quote:
Originally Posted by MF
No, I have not. It does not necessarily mean that it would not be useful, esp. for the folks who use both pickup styles
Quote:
Originally Posted by JE
Wouldn't a good active box be a better choice for anomalously low impedance sources?
Quote:
Originally Posted by MF
It always depends on personal preferences of performer, but definitely is a viable option
Quote:
Quote:
Originally Posted by JE
First, the 1 meg resistor on a Fender or similar amp is not there to increase the impedance/input resistance - it's in PARALLEL with the grid input and it's there to REDUCE the input impedance, as the input impedance of a tube is nearly infinite. The series resistoers are 68k, which are there as mixer resistors between the two input jacks. The 1 meg resistor also reduces the sensitivity of input 2 when input 1 is unused.

That's fine. That resistor with all other parallel and series resistances/impedances defines input impedance. That's not the point. What we want in a passive DI is to get the impedance of the pickup matched to the input impedance of mic input of the preamp. For simplicity let's take round numbers of 3kOhm (pickup source) working into mic input of 3kOhm. As always, any design is all about compromises. For the best compromise between maximum voltage transfer and parameters of the transformer we take a universally accepted value of the load being 10 times of the source. Needless to say, for the very same reason it is a universally accepted output impedance of the microphones being 200 Ohm and input of the pre 1.2--3kOhm. Here is a little, but important detail--1.2kOhm input will work fine with solid state output microphones (usually, their output impedance can be as low as some 30 ohm). The transformer coupled outputs, however, would rather want to see more like 200-->2kOhm ratio and be much more sensitive to variations. Indeed, try to wire some Neumann older transformer coupled mics (with 50 Ohm and 200 Ohm options) for 50 Ohm and feed into 3kOhm input and you will find they sound like crap, with low output and poor freq. response.

What we have in guitar pickup and passive DI box is exactly the same, but instead of step up, going step down (in terms of impedance matching it really doesn't matter). We do not want to get too much of the step down for the reason--the transformer primary 'wants' to see just the max number of turns for given inductance (=low end output). At the same time, the more turns--the more winding capacitance. That capacitance can become considerable and together with that of the cables can severely affect the sound. On the other hand, lower impedance source for the same bass response requires less input inductance (i.e. less wire turns and less capacitance--this is another reason the multitapped transformer would not be a good option here). There are ways to reduce that capacitance, but they require much 'fancier' winding techniques--the main reason good transformers are always by far more expensive. That's why it is much easier (and cheaper) to make lower ratio transformers.

Back to our numbers: with 3kOhm (pickup source) working into mic input of 3kOhm we want a source of 10 times higher (i.e. 30kOhm). What we have is an impedance ratio of 10:1. Since the voltage ratio (that's how transformers ratios defined) is square root of impedance we would like a transformer of some ~3:1. Since there is a lot of deviation of the mic input impedances the lower range would be 1.2kOhm. We have here 30,000/1,200=25:1, i.e. 5:1 transformer should fit here. Overall we are quite close to 6:1 (which would be a good compromise, as it is easy to wire from 12:1).

Now let's see what happens with gain if we use different transformer ratios. While it is true 12:1 transformer would load the same source signal less (maybe by a dB, or so), on the other hand, 6:1 step down would have twice (or 6dB) lower signal loss. Overall we have about 5dB higher output in comparison if we used a 12:1 ratio. Together with the fact 6:1 transformer ratio has much less sonic compromises that would be preferable... but as always, our ears decide everything...

Surely, in a real life things are quite a bit more complicated and there are much more details, however, just wanted in a simplest way to touch main points so less experienced and technically inclined folks could follow.

Best, M
Quote:
Originally Posted by MF
Apr 17, 2017 at 6:26pm

Post by markfouxman on Apr 17, 2017 at 6:26pm
Quote:
Originally Posted by JE
johneppstein Avatar
Apr 14, 2017 at 11:43pm johneppstein said:


As I'm reading it right now the choice of transformer in the DI should probably be dependent on the type of mic input involved as much as on pickup impedance, right? You probably wouldn't want the same transformer with a transformerless mic pre that you would with a classic transformer coupled input, right?
Indeed, there is no set standard for input impedances. For example Mackie 1202 mixer has mic input of 2.5kOhm, while say, Grace Design Felix 8kOhm. That is one of the reasons many pres sound so different and there is no general 'rule of thumb' here.

The transformer coupled gear in general is more sensitive to the impedance matching because inductance and winding capacitance create resonances, which often define sonics. Exactly the same with the pickups. In both the peaks can be considerable, so the loading will effectively suppress them (again, affecting the sonics). Since the transformer is a "two way" device, meaning it passes the load both ways in a passive DI the peaks of the pickup itself will also be smoothed. Sometimes it works very nicely, sometimes not. That would probably be the main difference between passive and active DI box, you mentioned earlier.

Best, M
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