Question about Yamaha SPX90 input - output levels

[jimbomonjeau]

Hi! I salute you all from Argentina. Advise: I have no electronical knowledge, and my questions are pretty stupid.

 

I recently bought an old Yamaha SPX rack unit. I never owned a rack unit before. It has -20dB / +4dB level switches beside the input and output jacks, as you can see in unit's manual ( http://www.yamaha.com/yamahavgn/Docu...udio/SPX90.pdf ). My amp has no loop effects send/return on it. So, my question is: if I select -20dB (which is intrument level?) in the input level switch and -20dB in the output one's, i would be using my rack unit "as a pedal" and there would be no impedance/level issues? Or it would still be better if used in an effects loop amp chain (in terms of electrical logic -I mean, not in terms of "prefered musical sound"- and where to put spacial effects, etc.)? If I use it in the effect loop chain of an amp (not on mine's 'cause as I said I can't), should i use -20 or +4 db level for the input and for the output? in which case could i need to use a diferent switch level in the input-output? Thank you all for your collaboration!!

[WRGKMC]

What you do is set the unit so there's no volume dip or bump when you plug and unplug it from the loop.

The unit should have a gain control or even and input and output level.

 

Many times you can switch the db switches then adjust the gain knobs as well to get a balanced level.

In one instance you may have the DB setting on high, and with the gains set low, you may have a more presence but more noise. In another instance, you have just the opposite. You need to try them all using the zero gain test to find the optimum level and choose the one that sounds best for your rig. Some of it will have to do with how string your amps preamp is. If the signal gets overdriven or overly noisy with a High DB input then you obviously want to set it to the low setting. Just be sure you tweak the overall volume remains the same by using the gain knobs when its disconnected. You don't want to blow the guitar amps power transistors by pumping a signal that way to hot. A little bump isn't bad, but if its more then what the Guitar preamp provides, heating up your output transistors (and sound quality) becomes a factor.

 

I have a similar effects unit and I believe I set my volume on the front panel around 2~3:00 to get a 1:1 Gain using it in front of the amp. From there the individual effects have volume levels I need to adjust as well.