Thanks for that info Prr,
I'm starting to understand the various types of attenuator and their effects on input and ouptut impedences.
I can see how high values of attenuation demand resistors which cause stray capacities to have increased effect.
I got a bag of 3200 resistors ,metal film 1%(ish) 20 of each value from a fraction of an ohm to 20Mohm, just a few dollars including postage from China.
I did one time make a resistor string att on a 12 way Lorlin ,It all added up to 1Mohm,I started off with around 250k resistor and gradually reduced the resistance of the sucessive ones, I didn't do any math whatsoever ,I simply adjusted each resistor along the chain up or down as needed to get what seemed to be an even step in volume with each click and a final mute position , absolutely 'on the button' db's of attenuation doesnt really matter so much for recording ,the simple repeatabillity of steps comes in handy though. It works great on a pickup output into a di to fine tune your levels, as I often found the usual 20/40db attenuation switches on di boxes are too much when say a hot pickup output is just clipping the input of the DI, you only need to shave off a handfull of db to be hitting it right on the money,a -20db pad dumps s/n , setting the guitar volume control at some arbitrary amount down from top means no repeatabillity in terms of level .I sometimes use the same attenuator in reverse as a load matcher after an input transformer ,1meg being the internally set value of input impedance of most of my stuff. Tuning the load on the transformer secondary allows me to set the amount 'magnetic core ' I get in the sound ,if you have several transformer coupled stages with carefully adjusted relative gains/impedences ,so only the peaks are just causing barely noticable distortion ,you have a handfull of db headroom in the digital domain ,so that by the time your hitting 0db digital your program material has already been limited by the action of the previous circuitry and transformers to a high degree. Any sibilant or plosive sounds your vocalist issues at full tilt hit the transformers a wallop and get eaten up ,where an op signal path to digital is going to need miles more headroom to reproduce the odd transient that comes along ,course you patch all that up in the mix by adding plugin dynamics later ,but your signal has already suffered bit munch at that stage anyway..
Im getting a better feel for the attenuators now thanks for all of your contributions once again , I can see something around 600 on the input ,with a chain of lower values in the ten of ohms range might suit my purposes.
I see some guys who have designed say 24 way attenuators , I see a range between -10 and -20 I like the look of,can I simply pluck that section of the attenuator out and build it on my own switch ? adding the combined value of the rest of the chain at the end to ground ?
Hi David,
Yes I noticed the abillity to calibrate impedence of the HP with external values of resistor as well , 28 dollars is a total steal ,even if it was to sit on the shelf as an ornament and only be used once in a while. Be a handy item in studio just to tweak your gain structure to get those last few Db signal/noise on special sources like vocals etc.
I guess this tread has some crossover with next doors DI post , loads of great info on impedence matching ,loading(or lack of) etc ,easily one of the most fundamental things to getting a good sound and the one of the most misunderstood. as well.
For me the LCR meter has made a huge difference ,for instance being able to look at your grid wirings stray capacitance directly ,normally your head would be boggled my math to figure it out approximately ,where you just hook up the LCR and bam you have it ,you can easily check how much neater shorter wiring impacts stray capacitance .
November 12, 2006, 10:27:11 PM