Camcorder with Line Input

Terfyn

Whereas I won't disagree with you, direct feed from my keyboard worked fine for me, I use a simple "pad" , a SESCOM attenuator cable.

rogs

I'm guessing then that both aspects that can cause problems are OK with your camcorder?

• You were able to defeat the AGC for this task...

•Your actual camcorder mic preamp is of good quality...

The problem with using mic pramps and pads (attenuators) is that your are still having to deal with  the noise floor limitations of a mic  level preamp, which - by definition - will be quite a lot noisier than a more appropriate line level input.

But in most cases - for consumer level recordings anyway - an 'attenuated' camcorder mic pramp will produce pretty satisfactory results...

12harry

This thread started 2013 and OP doesn't appear to be replying....
If OP gets in touch with a Movie-Making club, there may be someone there willing to make-up such an attenuator...and maybe a few for other club members; as I guess they might be useful. However, the Movie-Making Club may also be interested in a Keyboard player, esp. if OP is writing music material - which may suit films, etc.

Good Luck.

BTW - my own Keyboard  ( With DIN-style MIDI ) has only headphone o/p - so that is relatively low impedance . . . can't say impedance-matching has ever been an issue in Audio,  since most o/p are Low and inputs High.  This is done to make leads less sensitive to pick-up and the make loading the output as little as possible. In HF circuits I will agree "matching" is very important; to avoid reflections for aerials . . . and maximum power transfer ( that's why cars have gears! ). Hope that helps . . . but OP has "gone away" it seems.

wakerickman

hi rogs, i do stand slightly corrected, point of contention is as you say/i aggree hf can only be lost going from hi to low impediance, the point is, in actual fact, a keyboard has a medium impedance output typicly around 10 K ohms, and since  a mic input is low  typicly 1 K [ for a standerd 600 ohm mic ] there is still a diferance of a factor of 10 so some slight loss of hf might accure without impediance matching, also note a [ much ] higher impedance of 1 M ohms is the norm for a guiter [ picup ] ok cheers

rogs

I'm surprised to read that keyboard line level outputs are that hi-Z?...I always tend to think of 'line level' output impedances as being around a nominal 600R.....
Rather surprisingly, I can't find the rated 'aux out' impedances listed in the spec sheets for either of my keyboards  (Yamaha P105 and MOX6). I may have just missed it of course.

As I mentioned in my earlier posts, I don't think using a camcorder mic input is an ideal input for recording a  keyboard anyway, but assuming that is the required option... and that the output impedance of the keyboard is 10k... then a 3 resistor T pad attenuator would solve the situation. 10K series input resistor, 1K output and 220R shunt.  An impedance matching 30dB attenuator for less than 10p (plus connectors of course )

The values in the model quoted by Terfyn seems to be about 10 times lower than that, so for Hi-Z keyboard outputs that might still present a small problem.

Or solve it completely by using the headphone output from the keyboard instead!

The very  Hi-Z inputs required for passive guitar circuitry is a whole different ball game of course...

wakerickman

hi rogs, just saying, i cant remember where i got the 1o K figure for output impedance for a keyboard [ which i do/think believe is correct ? ] but/as like you i, now cant find it listed in any of the manuals for all of my 5 keyboards, so will have to chase up other sources to confirm. also i do aggree that idealy you shouldnt put a keyboard directly into a camera mic input.[ perticuarly because of the AGC, other  point to note, a good way to record/sync music/video and hi quality audio is just use a cheap DAW [ digital audio workstation ] [ there are dozens of makes/versions ] & a cheap small hard ware mixer with usb, you can get a cheap DAW with video capabilitys for £80  [ cubase elements 9 ] and a cheap mini usb mixer [ beringer ] for around £60. [ i have both ] so you just plug the keboard into the mini mixer and its usb conection will take it to the computer, there are all sorts of featues you can do with the cubase, of cubase do , do more up market DAW for £400, but that is way more than what you would need , the buget modal ive quoted will easerly do the job   more. [ ie 64 midi track recording/48 audio track recording , so i beleve the above would be a more cost effective solution to the audio/vidio recording, then buying an exspensive "pro" camera perticuarly as you can do all the "pro" overdubing/recording  etc with the DAW as well ok cheers

rogs

Further to the posts above, I was intrigued to find out just what the output impedance of my Yamaha MOX keyboard actually is.
I can't find the value listed anywhere in the specs... so I measured it myself.
It comes out as a fraction under 700 Ohms - about 690 Ohms in fact - Which is pretty much what I expected to find.
I think it's reasonable to assume that figure is fairly typical (most line level impedances are traditionally around 600 Ohms - although some are a bit lower these days) and explains why Terfyn has had no problems using his SESCOM attenuator cable,( which has a 1.5K input impedance)..

12harry

FWIW and IMHO -  The only time impedances really matter are in "matching" items like HiZ electret mic capsules ( which already have a semiconductor to match the electret element to the outside world )..... these need care because of the way the DC is supplied.
For 99% of mic-users, this isn't likely to concern them...as someone else has done all the work.

As rogs and others have mentioned Pro Mics are usually balanced 600 ohm - there being no reason to deviate from this, any alternative "matching" isn't really worth much time discussing. Also, most Pro-matching involves a small audio transformer to isolate potential differences, thereby practically eliminating "ground-loops" which can be a huge issue where long low-level cables are concerned.
By contrast I've used a 20ft extension on my camcorder ( not 600 ohm)- but because the mic was moving-coil and the location miles from electricity, there appeared to be no downside.​
The other critical matching is ( or rather "was" ), matching the record pick-up cartridge which needs both resistive and capacitive loading.  Getting this badly wrong will affect high frequencies -and- low-output may affect the whole audio spectrum.

Cheers.

wakerickman

hi rogs, i do stand corrected, an thanx for letting me know the true situation, as i said i couldnt quite remember where i got my impedance rating from, so somewhere they must have been something ive seen/read but proberly refers to some other electronic device ? [ im going to try and investigate where i got my information from ]. but i still believe a passive [ transformer based ] DI bax with attenuater switches is still a good idea  for those people who dont feel comfortable diy , just buying/useing a ready built [ cheap] box to plug into will be there best option. but of course if you are handy with a soldering iron then of course save some money and diy. but note best methord is a potential devider with 2 resisters [ or even - but bulky- varable potentiomitor ] and not just one rester in seriers . but again biggist problem is as you rightly  say tis he AGC which has to someway be disabled, if thats not possable then its very doubtfull that you will succeed in getting a good sound [quality ] from that camcorder ok thanx cheers

12harry

DIY using a transformer is difficult - these are not mainstream parts and any I've seen are mighty expensive . . . obviously DI-Box Makers have "trade sources"  - or maybe wind their own.
Resistive potential-divider may perform well, but provides no isolation, so it is "risky" if you don't know the venue ( ie trial-tried it prior) as there is no protection against "ground-loops" ( or worse!)...
"Disabling the AGC"  is usually done in the ( recording device) SET-UP - it's not something you can do by external DIY means.... AFAIK.

Variable resistors are to be avoided. They are notorious for introducing noise, whereas a 3-way switch,  using a 3w 4-pole "make-before-break" rotary-switch will cost you about the same as the stereo potentiometer and is almost certain to outlive the pot, while introducing zero noise. The same price-point would provide a 4-way switch, or if you desire a whole range of Attenuation values, then a 6-way 2-pole rotary switch is commonplace in Electronic Suppliers......

However, as with many things it's not what you do - rather the way you do it - and if you want an "Easy-peasy" solution: then spend  ~£35 on a modest DI-box, is by far the easiest fix.... & giving you isolation at the same time.

EDIT _ wakerickman reminded me that for a small extra cost, DI box can be 2-channel Stereo. Probably easier to mislay two units, so a single Stereo box is "better" IMHO. As to cheapness ( ealier Post ) I'd hope that the more-expensive models would have better isolating transformers ( with extended LF performance?)- and would be useful in other situations where music is involved - e.g. an electronic church organ - where very complex waveforms may be present....FWOW