Help with SPX90 and ADA MP1

[carv]

Hello guys,

I am new to rack effects and basically need someone to explain me the following:

I bought a Yamaha SPX90 and put it in the FX Loop of my Marshall Silver Jubilee 20W Studio Head and Cab. I connected the Marshall's Fx "Send" to the SPX90's "Input", and the SPX90's "Output" to the Marshall's "Return".

Both the Input Jack and the Output Jack on the SPX90 have a -20db/+4db switch, each of them.

Combo 1: both input & output jack at -20db = low volume

Combo 2: both input & output jack at +4db = again low volume

Combo 3: input @+4db & output at -20db = again...low volume

Combo 4: input @-20db & output jack at +4db = BINGO!!! = Proper tone!

Why is it that Combo 4 only works? The FX Loop of the Jubilee according to Marshall is @-10db, i.e. for stompboxes / instrument level, like a guitar signal. So I would expect that both input and output jacks should be set to -20db for that reason, or both at +4db (line level, IF the FX Loop was designed like that, but apparently is not, is ar -10db according to Marshall). So why does it only work with Input Jack at -20db but Output Jack at +4db??? Is as if the "Send" and "Return" of the Amp are different...


Finally, can someone tell me if I want to bypass the Marsall's own preamp and use the ADA MP1, then connect the SPX90, then use the Marshall's power amp stage, what exact steps do I follow and where do I set that switch on the rear of the ADA next to the output jacks? Also, where do I set the -20/+4 switch on the SPX90 when it goes after the ADA and before the amp's return?

thank you all

[rnolan]

Hey Carv, I replied to your other post first before I saw this one.  The results you get are a little strange, the amp loop is trying to accommodate either inst or line level devices.  Seems they have the loop send set low so it works with pedals (inst lv) and if you used a line level device (like the SPX) you need to turn the SPX input up.  What I find a little confusing is that the return works better with line level and not inst level as if you used a pedal the output would be inst level and it "should" accommodate it.

Combo 1: both input & output jack at -20db = low volume - Should be fine as it's what a pedal would want/do, turn the SPX input up

Combo 2: both input & output jack at +4db = again low volume - again should be fine but you need to turn up the SPX input as the amp send is low (inst level) or set it as you did in Combo 4

Combo 3: input @+4db & output at -20db = again...low volume - was never going to work well because of the gain miss match but turning up the SPX input (as amp send is low level) "should" work

Combo 4: input @-20db & output jack at +4db = BINGO!!! = Proper tone! - so this indicates that the amp send is low (inst level) for pedals and the return can tolerate line level and thus is the one to use (obviously) as it works.

The MP-1 loop has a knob to adjust for line/inst level devices so you increase the send level for line (+4) or decrease it for inst level -20).  However it's a single knob for a dual ganged opposing pot,  as you increase the send level it decreases the return and vis versa.  You still have to tweak the Fx input and output to fine tune it.

So my SPX90 only has an input level control, no output level control.  As the amps send is set at inst level, you can use the SPX input level to adjust and set SPX input to -20db (inst level).

As in my other post, I suspect the best setup will be with SPX in MP-1 loop, you have much better control of the gain and you can switch it in/out per patch.