| Author |
 Topic  |
|
|
Laurie
Double Platinum Member
Canada
4854 Posts |
 Posted - 03/06/2010 : 16:11:08
|
SG-1 pedals are expensive because they are rare, not because they are �vintage-and-awesome�. They are rare because nobody bought them way back when they were made because they were� �different�.
So what does that mean?
Technically, the SG-1 looks like this:
The heart of the swell effect is the FET.
Imagine things start out with no signal coming into the pedal, and everything sitting at �zero�. In this state the FET is turned fully on - the FET is set up ("biased") so that with no signal into the pedal the correct voltage is applied to the gate of FET to turn it fully on. With the FET "on" the input signal is shorted to ground. No sound will come out of the pedal.
If a note is plucked on the guitar, the following things happen:
1) The input buffer passes signal, but the signal can�t pass to the output buffer because the FET is shorted to ground.
2) The amplifier and rectifier take the input signal and turn it into a DC voltage that it proportional to the strength of the input signal. The attack control circuit then applies a �ramp� voltage to the FET which slowly turns the FET off. As the FET turns off, it allows more and more signal to pass to the output buffer and we have a swell. Technically, the attack control contains an RC filter and the attack knob adjusts the �R� part of the filter � which changes the time-constant and hence time taken for the output to swell.
3) The signal decays and eventually the voltage coming out of the rectifier goes back to the bias voltage turning the FET fully on again which mutes the sound and the system is ready for the next swell.
The sensitivity knob is used to control the gain of the amplifier. Modern guitar pickups have high output and they drive the gating amplifier properly with very little gain needed � usually setting the sensitivity control to around 9 o�clock is about right. Increasing the sensitivity will eventually saturate the gating amplifier and the swell effect will be lost.
There are quite a few implications from this design.
Only one of the knobs changes the sound of the pedal. Only the �attack� knob is designed to change the sound of the pedal. The �sensitivity� knob is used to match the pedal to the output level of the instrument connected � it is essentially a set-once-then-forget kind of control, it is not a control that you would use dynamically to change the character of the sound.
The attack control is somewhat limited. The attack only goes out to about 300ms which gives a nice bit of a swell, but not as much as you might expect (300ms is about the time it takes to say the word "and" if you say it quickly). Also, it is hard for the ear to tell the difference between 300ms (knob fully clockwise) and 150ms (knob at 12 o'clock) - so the attack control seems like it doesn't do much.
Held notes decay �strangely�. If you hold a note, the decay of the note gets �lumpy� when it starts to tail off. This is because the amplifier/rectifier pair does not produce a smooth output at low drive levels.
The tracking might not be as good as you expect. Longer attack times will require slower picking, possibly with gaps between the notes. When using longer attack times, careful adjustment of the sensitivity will be required to get the best results. Strong, even picking will be required.
The pedal is slightly noisy � there is a hint of fizz or �hash� that can be heard along with the decaying note. In the Boss design, the amplifier is driven �to the rails� and every time output voltage of the opamp is hits a rail it puts a tiny noise into the power supply. Add up all these tiny bits of noise and you get just that hint of �fizz� in the audio in this pedal. This is completely normal and unavoidable with the Boss design.
|
Edited by - Laurie on 03/06/2010 16:14:46 |
|
|
Pedal Dan
Silver Member
USA
419 Posts |
Posted - 03/06/2010 : 21:02:23
|
I agree, it's not perfect. And yeah, it's pretty much a one trick pony. But it does that trick very well, and ya gotta get one if you want The Holy Trinity! |
 |
|
|
Dr. Bob
Moderator
Australia
6593 Posts |
Posted - 03/07/2010 : 04:13:29
|
Excellent write up Laurie.
These pedals have gained mythical status - (urban legend status).
For no other reason than the fact, that very few people bought, wanted or understood,
what they could do with a swell pedal, back in the 70's-80's.
Excluding perhaps the experimentalists.
Regards Dr. Bob 
|
Edited by - Dr. Bob on 03/07/2010 04:15:15 |
|
|
|
Pedal Dan
Silver Member
USA
419 Posts |
Posted - 03/07/2010 : 04:19:43
|
quote:
Originally posted by Dr. Bob
Excellent write up Laurie.
These pedals have gained mythical status - (urban legend status).
For no other reason than the fact, that very few people bought, wanted or understood,
what they could do with a swell pedal, back in the 70's-80's.
Excluding perhaps the experimentalists.
Regards Dr. Bob
Have you ever tried one with an Ebow and slide? Mr. Gilmour would blush. |
Edited by - Pedal Dan on 03/07/2010 04:21:07 |
|
|
|
red_riviera
Bronze Member
United Kingdom
111 Posts |
|
|
Dirk
Platinum Member
Netherlands
1309 Posts |
|
|
Pepe
Silver Member
Germany
230 Posts |
Posted - 03/08/2010 : 20:39:50
|
| In the BOSS Book the BOSS people explained, that they have used the noise filter as a basis for the SG-1. So it's not surprising to me that a simple and rather cheap NF-1 can be modified to work as a Slow Gear. |
|
|
|
fabs
Silver Member
France
213 Posts |
Posted - 03/11/2010 : 18:35:41
|
I wonder if there is a mod to use a SG-1 as a NF-1  |
|
|
|
Pepe
Silver Member
Germany
230 Posts |
Posted - 03/11/2010 : 18:43:00
|
quote:
Originally posted by fabs
I wonder if there is a mod to use a SG-1 as a NF-1
Who'd be THAT dumb?  |
Edited by - Pepe on 03/11/2010 21:04:59 |
|
|
| |
Topic |
|
The SG-1 demystified
