DBX 166 Compressor

[Gazm]

Thinking of getting a DBX 166XL and I'm wondering the about best place to connect it?
FX loop or bass > DBX > amp.

I'm guessing the latter, but cable wise it would be nicer in the FX loop.

Any thoughts?

Pete.

[BOD2]

It can go in either place but there are some considerations and it could have a different effect depending on where you place it.

Firstly check that the compressor will adequately handle the two different signal levels. The bass signal might be much lower than the fx send signal. There may be input level switches on the compressor to allow for this., or it may handle these two levels with ease.

If your FX loop has a "level" control and you put the compressor in the fx loop then the level must be fully on, otherwise some of your bass signal will get through uncompressed, defeating the purpose of the compressor.

If you go bass > compressor > amp then the bass signal is compressed before it reaches the preamp (input gain and tone section of the amp). You could therefore use the compressor as a "limiter" to prevent overload of the preamp (possibly not necessary - just one option)

The fx loop, however, comes after the preamp so you couldn't use the compressor for limiting before the preamp.

If you use other fx then you might want to consider the placement of the compressor in the chain. Compressors are usually best first in the chain, unless you use "envelope triggered" fx (e.g. auto-wahs) that respond differently according to how hard you play. These type of fx must be placed before a compressor as the compressor will even out the dynamics of your playing and you'll lose the tiggering for these fx.

Other than that you can try out both placements to see what works best for you.

[Gazm]

Many thanks for the reply.

I've just downloaded the manual and found this bit:

OPERATING LEVEL Switch
This switch selects between a -10dBV and +4dBu nominal operating level. When the switch is in the in position, a
-10dBV operating level is selected. When it is in the out position +4dBu is selected. A -10dBV operating level should be
selected when interfacing with “semi-pro” or low level equipment, while a +4dBu level should be selected when interfacing
with “pro” equipment. The switch simultaneously changes the operating levels for both the input and output circuits.
Note that the switch is slightly recessed to prevent accidental switching of operating levels while plugging in or unplugging
cables.

Sounds like I'll be able to try either method of connection and see how it goes!

Pete.

[Toasted]

Put it where it sounds best to your ears. You can put it in the loop (Where it will probably be post EQ) or inbetween your bass and head.

Remember that if you connect it in the FX loop and you DI from your amp, then the effects loop could very well be post-DI.

[Dan_Nailed]

You can't plug your bass directly into the compressor as it doesn't have a proper Hi-Z guitar input. -10 and +4 are both line-level standards that are meant to be used with already line-level inputs and outputs, such as other effects gear, preamps and poweramps.

The best place is in the FX loop, or ideally between your preamp out and poweramp in(if you have one).

If you plug your bass straight into the dbx you'll either get stupidly low signal and very unusable compression, or nothing at all. If you have an active bass things might be slightly better but your signal to noise ratio will still be terrible. You could go Bass>DI box>dbx if you wanted though. I think it's always better to compress after the preamp as you compress any boosts in EQ that you've put in previously.

As for amp DI out, if your amp DI has a Pre EQ/Post EQ button, make it post-EQ and it should include everything in the FX loop. This is what I do when sending a DI to the soundguy and I want my out front sound gated. However, most engineers like to use their own compression and EQ so I wouldn't worry too much about sending all your signal to the soundguy.

[Dood]

[quote name='Dan_Nailed' post='11836' date='Jun 4 2007, 01:54 PM']You can't plug your bass directly into the compressor as it doesn't have a proper Hi-Z guitar input. -10 and +4 are both line-level standards that are meant to be used with already line-level inputs and outputs, such as other effects gear, preamps and poweramps.

The best place is in the FX loop, or ideally between your preamp out and poweramp in(if you have one).

If you plug your bass straight into the dbx you'll either get stupidly low signal and very unusable compression, or nothing at all. If you have an active bass things might be slightly better but your signal to noise ratio will still be terrible. You could go Bass>DI box>dbx if you wanted though. I think it's always better to compress after the preamp as you compress any boosts in EQ that you've put in previously.

As for amp DI out, if your amp DI has a Pre EQ/Post EQ button, make it post-EQ and it should include everything in the FX loop. This is what I do when sending a DI to the soundguy and I want my out front sound gated. However, most engineers like to use their own compression and EQ so I wouldn't worry too much about sending all your signal to the soundguy.[/quote]

I'm going to have to disagree Dan. pretty much every compressor rack that I have used has had a far higher input impedance than that of a passive bass and has worked fine IF as you say the pickups have enough output volume. Active pickups don't suffer to badly from from the impedance miss-match, having a far lower impedance. Low into high is fine. I do agree that if the bass is too quiet the s/n will be a bit grim. Pups like EMG for example are pretty hot and I find that I have to switch down to take care of the extra input gain.

I also have to disagree with the placement of compression after the EQ. It isn't wrong as such to do this, but there is a good reason not too, unless it is the effect you are hoping to get. I'll do my best to explain!

ok.. lets get theoretical.

We'll take it that we have plugged a bass into a preamp and then into a compressor. We will assume for this example that the bass is a flat response across the frequency spectrum to make my life a little easier explaining.

we'll set the compressor to kick in at -10dB

ok, if you strike a note down the bottom end of the scale, the 'bassy' sounds will go over the threshold and pull the compressor output level down closer to the -dB level.
Also if you hit a high frequency note and it goes over the threshold level, the compressor then pulls the whole output level down to the -dB level.

How's that sound so far? and frequency that goes over the threshold volume level will make the compressor pull the total output level down toward the threshold.

ok, here's my problem with putting the EQ before the compressor. Remember we are assuming the bass is flat response. (most basses have a greater bass end than top end)

ok, lets play a bassy note and a trebly chord at the same time. because both are a similar velocity the compressor pulls down both by the same amount towards the threshold.. you can stil hear them both clearly. good.

now. lets wind the bass end up to +15dB at say 40 Hz.

this is where it gets difficult to explain!! if the threshold of the compressor is -10dB, the bass frequencies need a whole 15dB less to kick the threshold of the compressor and drag the output right down by an additional 15dB.

now play a chord (something high up) and then strike a bass note whilst the top notes are sound. you will notice that the extra 15dB boost on those low notes will tug that output level down by that extra 15dB. You'll hear your bass note at the right volume, but because the total output volume of the compressor has been forced down ward.. your high notes / chords whatever will just disappear. Too much bass boost and you will loose top end and the compressor will sound woolly.

The only way round this on a budget compressor is to ensure it has a side chain filter, or.. go out and grab yourself a dual band or multiband compressor.

Failing that, simply move the EQ after the compressor, so it has no effect on the compressors threshold.

I have tried and tested this on many amps to the same effect.

a nice cheap rack compressor with said side chain filter is the Behringer Autocom.

I'd finish off by saying, that if you want a woolly bass sound that pumps annoyingly, set a lower threshold say -20dB and crank the ratio nice and high.. 4:1 or higher then pile on the bottom end on your EQ!

I hope this makes sense. It'd be easier with pictures!

[The Funk]

I get what you're saying. I'm still to find the best place in the signal chain for my compressor. The trouble with shifting it from the Pre-out to the F/X loop is that it might be post-EQ there anyway.

Edited June 4, 2007 by The Funk

[Dood]

yup good point. I guess we need to know what the amp in question actually is! ;o)

[The Funk]

Ah, well it's an Aguilar DB680 preamp. It might actually say in the literature somewhere. I'll have a look when I get home.

[Dood]

[url="http://www.aguilaramp.com/pdf/support_manuals_db680.pdf"]http://www.aguilaramp.com/pdf/support_manuals_db680.pdf[/url]


I have had a very brief look.. it appears the Di can be post or pre EQ. I would make the assumption that the post EQ sections is also post FX as well. There isnt a block diagram to refer to and I cant be bothered to read the whole manual. The EQ section is pre FX loop.

[Dood]

On a related note, one of the very few preamps that I have seen that have an effects loop between the bass input and the input gain control (pre amplification, pre EQ) is the Trace Elliot V-type. Just a great design for simplicity!

[Gazm]

Thanks for the info guys, most helpful.
The DBX still hasn't arrived as yet but will update you on what I find when I get it. I've got a Behringer graphic in the rack so I'll have a play with the side chain settings via the eq. My amp is an SWR Working Pro 700.

Pete.

[Dan_Nailed]

[quote name='dood' post='11984' date='Jun 4 2007, 06:52 PM']I'm going to have to disagree Dan. pretty much every compressor rack that I have used has had a far higher input impedance than that of a passive bass and has worked fine IF as you say the pickups have enough output volume. Active pickups don't suffer to badly from from the impedance miss-match, having a far lower impedance. Low into high is fine. I do agree that if the bass is too quiet the s/n will be a bit grim. Pups like EMG for example are pretty hot and I find that I have to switch down to take care of the extra input gain.

I also have to disagree with the placement of compression after the EQ. It isn't wrong as such to do this, but there is a good reason not too, unless it is the effect you are hoping to get. I'll do my best to explain!

ok.. lets get theoretical.

We'll take it that we have plugged a bass into a preamp and then into a compressor. We will assume for this example that the bass is a flat response across the frequency spectrum to make my life a little easier explaining.

we'll set the compressor to kick in at -10dB

ok, if you strike a note down the bottom end of the scale, the 'bassy' sounds will go over the threshold and pull the compressor output level down closer to the -dB level.
Also if you hit a high frequency note and it goes over the threshold level, the compressor then pulls the whole output level down to the -dB level.

How's that sound so far? and frequency that goes over the threshold volume level will make the compressor pull the total output level down toward the threshold.

ok, here's my problem with putting the EQ before the compressor. Remember we are assuming the bass is flat response. (most basses have a greater bass end than top end)

ok, lets play a bassy note and a trebly chord at the same time. because both are a similar velocity the compressor pulls down both by the same amount towards the threshold.. you can stil hear them both clearly. good.

now. lets wind the bass end up to +15dB at say 40 Hz.

this is where it gets difficult to explain!! if the threshold of the compressor is -10dB, the bass frequencies need a whole 15dB less to kick the threshold of the compressor and drag the output right down by an additional 15dB.

now play a chord (something high up) and then strike a bass note whilst the top notes are sound. you will notice that the extra 15dB boost on those low notes will tug that output level down by that extra 15dB. You'll hear your bass note at the right volume, but because the total output volume of the compressor has been forced down ward.. your high notes / chords whatever will just disappear. Too much bass boost and you will loose top end and the compressor will sound woolly.

The only way round this on a budget compressor is to ensure it has a side chain filter, or.. go out and grab yourself a dual band or multiband compressor.

Failing that, simply move the EQ after the compressor, so it has no effect on the compressors threshold.

I have tried and tested this on many amps to the same effect.

a nice cheap rack compressor with said side chain filter is the Behringer Autocom.

I'd finish off by saying, that if you want a woolly bass sound that pumps annoyingly, set a lower threshold say -20dB and crank the ratio nice and high.. 4:1 or higher then pile on the bottom end on your EQ!

I hope this makes sense. It'd be easier with pictures![/quote]

Well, with [b]my[/b] dbx166 when I plug my EMG'ed Spectors in the level is basically pathetic, even running at 18V. The inputs on the 166xl are line level inputs, switchable between consumer -10db and professional +4db and the outputs of passive bass guitars are not line level(otherwise we wouldn't need DI boxes), now whether the compressor manufacturers manage to make their inputs high z is not the point - it is bad practice to go around plugging instruments straight into line level inputs without a preamp. I can plug my basses right into my PC soundcard line inputs at -10db and the level is not strong, and doesn't convey a very accurate portrayal of the tone. Hence I wouldn't go plugging straight into a line input on anything.

As for compression placement, you're right, but it's what your ears say sounds good whether you EQ the compression or compress the EQ. But unless you're boosting around 15db(which is pretty irresponsible let's face it) you won't encounter the limitations of none-multiband compressors very often!

[The Funk]

[quote name='Dan_Nailed' post='12259' date='Jun 5 2007, 01:22 AM']Well, with [b]my[/b] dbx166 when I plug my EMG'ed Spectors in the level is basically pathetic, even running at 18V. The inputs on the 166xl are line level inputs, switchable between consumer -10db and professional +4db and the outputs of passive bass guitars are not line level(otherwise we wouldn't need DI boxes)[/quote]

So, in theory, you could go from a DI box into channel 1 of your rack compressor then into a reamping box back into the preamp input of your amp through to your amp's EQ then into the other channel on your dual mono compressor?

Edited June 5, 2007 by The Funk

[Dan_Nailed]

You could but you'd be compressing the signal twice, pre EQ and post EQ and would need a lot of cables haha!

[Gazm]

[quote name='The Funk' post='12472' date='Jun 5 2007, 12:41 PM']So, in theory, you could go from a DI box into channel 1 of your rack compressor then into a reamping box back into the preamp input of your amp through to your amp's EQ then into the other channel on your dual mono compressor? [/quote]

That's what I'm gonna try when I eventually get it, obviously I'll different settings for each channel. It will also mean I can bypass each compressor channel and perhaps get some different sounds?
I will try the bass straight in to one channel and if it's pants go via the DHA VT2RM first.

Pete.

[The Funk]

Bloody hell, I was kidding. Still, I reckon that would be the easiest way (for the ears) to decide where in the signal chain the compression and EQ should go.

[Toasted]

Those tubes should give you nicer compression than a comp ever will