Pre Amp Out Pwr In and Buffered Effects

[talbany]

Found this on the whirlwind site thought it might be relevant....


The Low vs. High Difference
A high impedance microphone or guitar will usually output a greater signal (voltage) than a low impedance microphone. This high impedance signal works fine and even has some advantages in a sound system as the mixer or amplifier doesn't need to boost the signal as much. Therefore, any noise on the line is also not amplified as much and this results in an improved signal to noise ratio.

Keep in mind however, that the impedance of the transmission line (or cable) is affected by the impedances of the devices that are connected to it. A low impedance microphone will lower the impedance of the entire line connected to it. Similarly, if you connect a high impedance microphone, you will have a higher impedance line all the way from the microphone to the mixer. This can become a problem as the length of the cable increases.

High impedance lines are more adversely affected by the inherent capacitance that is present in the cable itself. This capacitance combines with the impedances of the source and destination to set up a filter. As the impedance increases and/or the capacitance per foot increases, the active frequency at which the filter comes into play gets lower. The frequencies above this point actually begin to "short out" across the cable's conductors before they ever get to their intended destination. Keeping impedance low and using quality cables can be important issues for maintaining wide frequency response in long lines.

A high impedance line that is interacting with outside electrical interference will act more like an "antenna" than a low impedance line. This problem can get worse as the cable gets longer. This effect is usually insignificant for a guitar or high-Z microphone plugged into an amp with a 15' cord but it can have a big effect if that same signal is sent 100' down a snake. These are reasons why a high impedance signal is almost always converted to low impedance with the use of a Direct Box (DI) before being sent long distances.

Another reason for the use of a DI is that it takes a two conductor unbalanced line and converts it to a three conductor balanced line. This is a separate issue, not to be confused with impedance. It is a common misconception that all lines that use regular tip/sleeve 1/4" guitar cord type connectors or RCA Phono connectors are high impedance. Not so. The output from a guitar that has a battery operated active preamplifier or pickup system will be low impedance in nature and so will the output of an electronic keyboard, guitar preamplifier, guitar effects processor. The same goes for the RCA phono output from CD players, tape decks, etc. The signals are unbalanced but LOW impedance in nature.

Low Feeds High
In order to preserve signal level and frequency response, it's important to drive equipment with a source signal that is lower in impedance than the destination equipment's input impedance. If the input impedance of a device is not significantly higher than the source impedance, the signal will be reduced or "loaded down" and its signal to noise ratio and frequency response will suffer.

Think of this as having a nozzle at the end of a garden hose. The garden hose is a low impedance source (there is little resistance to the flow of water) and the nozzle is the higher impedance of the input being fed by the hose.

[FUCHSAUDIO]

Sorry got em backwards.. Impedance is frequency dependent.. still you change one it still effects the other or am I wrong in assuming this..
Another words how does lowering the impedance effect frequency response

Tony VVT

I've found that (for example) using our Pure Gain (r) as a buffer (unity gain 1-Meg in 2-K out), everything sounds better....Clarify, less stray noise, more presence. Guitars now can overcome any cable capacitance, you don't need a hf shunt cap (if your guitar cord pre buffer is short enough). Not everyone will agree, but lower impedance certainly makes things sound better imho.

The Two Rock guys (Bill in particular I think) don't believe in CF's, and most of the amps I've seen don't have one in the loop. Those amps are very sensitive to what's plugged through the loop. Guys like Scottl swear the D-lator (or concept thereof) is an integral part of the D-sound. I built the loop into my amps for convenience, but the sonic benefit was nice too...

[talbany]

Andy

Thanks for the response.. That doesn't surprise me much.. engineers/Designers in general think cathode followers are pretty useless in guitar amp circuits...Maybe looking at it from there chair they are correct..However the players like Scott who have such a positive connection with there interments and amps seem to dig what they do with the tone and for me feel of an amp .. A certain type of compression, top end clarity a thicker tone at high volumes...Ive gotten to where I can tell if an amp has a CF driver in the amp.. This is sort of the inspiration behind my little rave here...

Best single channel amp design Tweed Bassman/ JTM 45 IMHO


Tony VVT

[FUCHSAUDIO]

CF's get a bad rap, not entirely justified imho. A properly designed CF can serve a valuable purpose in an amp.

[dobbhill]

Dug up an old thread.....

This boss pedal is pretty cool.. Ive used this with good results and am able to switch effects..
http://www.bossus.com/gear/productdetai ... arentId=95

I'd like to hear more about this pedal for use instead of a D'Lator. A friend has one I can try out. I plan to get a d'lator, but not in the card$ rite now. I looked at the specs but couldn't tell if it had the headroom and drive capability that I need. I have an Itellifex and a couple of Yamaha REV units (100 & 500) that I'd like to try in my clone.

[Bob-I]

I just recently bought a TC Electronics Nova Delay. It has 2 inputs, line and guitar. I find that is sounds damn good in the loop using the line level input and I really like the tap tempo. Hold the button down and strum, it'll match your tempo.

[dobbhill]

Looks like a cool delay! It's just that I already have 3 rack units and a Boss delay pedal. Maybe it's time to sell something! Thanks for the tip. I got a birthday coming up and the Arlington Guitar Show is in the schedule.
D

[odourboy]

True the Dumbleator is not a requirement with some FX units but even with those it adds to the tone in a positive way. Once used you never go back.

In my experience, it IS a requirement. At basement levels, things are usually fine, but when you start to crank these amps, the signal level on the pre-out of a D-clone can exceed 100V P-P. That's enough to toast an effects unit that doesn't have any input protection circuitry. Before I started using a loop buffer, I managed to cook two devices.

[dobbhill]

From another post Today by Funk:

The problem with the Solid state device is in the available voltage, ie, it clips because a 9v supply doesn't have enough of a swing to take the input voltage from the Preamp (capable of 200V), SO, at low level playing that two are virtually identical sound wise, but if you get it up to Gig levels the Solid state unit clips. You can sort of accomodate this with a 36v supply, but it will still clip on the clean side if you are playing kind of loud.

I guess that answers my question....Thanks, Brandon. Now I gotta build something else....
D