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Can Overloading/Clipping Damage a Mic Pre?
Old 2nd June 2006
  #1
Can Overloading/Clipping Damage a Mic Pre?

I use a GR and Phoenix Pre and was wondering if, for effect, you clipped the pre could damage it? I can't imagine ever doing this, but just in case. On the GR, you can actually hear the clipping coming from the box itself. What exactly is going on when clipping occurs? In solid state class A devices? Do they all clip the same way? If it isn't damaging the mic pre, are there any devices that could be damaged by clipping.?

Thanks,
swordinhand
Old 2nd June 2006
  #2
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Jeff16years's Avatar
 

i think this is a good question...
that i don't know the answer to

i have clipped a track on purpose before and wondered if it is bad for the pre.
Old 2nd June 2006
  #3


I doubt it (though the design could be funky somehow)

You are much more likely to dammage the tweeters on whatever you are using to monitor it.



-tINY

Old 3rd June 2006
  #4
Depends on what you're feeding in. Hard to imagine a conventional mic sending enough signal to damage a pre. But if the level of the signal you were sending in was hot enough, for sure. Question is, what's hot enough to damage a given pre?

Obviously, you wouldn't want to hook the speaker output of a power amp (with no parallel load on it) to a pre inuput (or even a line input).

I'll leave it to those with more experience with different gear to weigh in on whether a (say, very hot) line level signal could damage a mic pre. (I'm thinking it's not likely, and many of us have probably fed line level instruments like synths into the instrument input of various pres to "warm" the sound.) [OK... I think I'm getting to be done with the word, "warm," too.]

As noted, the resulting square waves from any of this could, indeed, be damaging to your ears and or your speakers.

Square waves tend to be not just violent but (particularly) low frequency squares attempt to keep the speaker in one place. And the thermodynamic physics of that business means what doesn't get turned into motion will be turned into heat, which can damage the core of the speaker in various ways. This is how using underpowered power amps (and overdriving them to "compensate") can damage speakers that would, by their handling capacity rating, appear to have plenty of "headroom." (Apologies for armchair pop science explanation.)
Old 3rd June 2006
  #5
Gear Head
 

Quote:
Originally Posted by Sword in Hand
I use a GR and Phoenix Pre and was wondering if, for effect, you clipped the pre could damage it? I can't imagine ever doing this, but just in case. On the GR, you can actually hear the clipping coming from the box itself. What exactly is going on when clipping occurs? In solid state class A devices? Do they all clip the same way? If it isn't damaging the mic pre, are there any devices that could be damaged by clipping.?

Thanks,
swordinhand
Hi,

Obviously I can't speak for the GR or any other manufacturer's equipment, but you would have a pretty hard time damaging the DRS (or any other Phoenix Audio (UK) input stage) by driving them into clipping under "normally hot" input conditions.

To over-simplify what's happening.......The power rails of the DRS are 24V and 0V, to prevent clipping the input signal needs to be kept swinging within these limits otherwise the peaks simply "hit their head" on the rails, and end up with everything that would normally go above the rail being "squared off".

The transistors used are more than capable of dealing with a "very hot" input, and usually recover from a drastic overload very quickly. This shouldn't be used as a guide, but the transistors used are rated at 45V (but I wouldn't want to put that sort of level into the input.)

It's very difficult to clip the output stage in Phoenix Audio (UK) equipment as the maximum levels fed to it are governed by what's coming out of the input stage.

I hope this helps a little.

Regards,


Shaun Leveque
Phoenix Audio (UK)
Old 3rd June 2006
  #6
Registered User
 

Quote:
Originally Posted by theblue1
Depends on what you're feeding in. Hard to imagine a conventional mic sending enough signal to damage a pre. But if the level of the signal you were sending in was hot enough, for sure. Question is, what's hot enough to damage a given pre?

Obviously, you wouldn't want to hook the speaker output of a power amp (with no parallel load on it) to a pre inuput (or even a line input).

I'll leave it to those with more experience with different gear to weigh in on whether a (say, very hot) line level signal could damage a mic pre. (I'm thinking it's not likely, and many of us have probably fed line level instruments like synths into the instrument input of various pres to "warm" the sound.) [OK... I think I'm getting to be done with the word, "warm," too.]

As noted, the resulting square waves from any of this could, indeed, be damaging to your ears and or your speakers.

Square waves tend to be not just violent but (particularly) low frequency squares attempt to keep the speaker in one place. And the thermodynamic physics of that business means what doesn't get turned into motion will be turned into heat, which can damage the core of the speaker in various ways. This is how using underpowered power amps (and overdriving them to "compensate") can damage speakers that would, by their handling capacity rating, appear to have plenty of "headroom." (Apologies for armchair pop science explanation.)
no apology needed....i'd forgotten the point you made about square waves....thanks
Old 3rd June 2006
  #7
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the charm of a lot of the pre's we have in the studio is finding the sweetspot in pushing the pre and attenuating accordingly.

we do this all the time w/ JLM's, and Chandlers especially.

great on vocals and guitars especially.

so it's the squarewave created that gives that vintage charm.thumbsup
Old 3rd June 2006
  #8
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Quote:
Originally Posted by Sword in Hand
I use a GR and Phoenix Pre and was wondering if, for effect, you clipped the pre could damage it? I can't imagine ever doing this, but just in case. On the GR, you can actually hear the clipping coming from the box itself. What exactly is going on when clipping occurs? In solid state class A devices? Do they all clip the same way? If it isn't damaging the mic pre, are there any devices that could be damaged by clipping.?

Thanks,
swordinhand
It is very unlikely you will damage the mic pre when clipping, provided that it is the output thats clipping and you're not simply roasting the input with ridiculous levels in DI sitations or direct connections to instrument amps etc... Most good mic amps have input protection regimes to handle extremely large input levels that might otherwise damage or degrade the delicate input stages or cause the amp to misbehave for long periods after the event..

In some less well designed mic pres it may be possible to find gain settings where the internal circuits clip prematurely before the output reaches max - or you may be able to make the output 'fold over' rather than limit at max etc.. This kind of behaviour generally sounds awful (splats, farts and such like) so one should avoid overdriving such units..

The kind of sonic result you get will depend heavily on the design of mic pre you are using and the way it is actually being clipped. In particular - winding up the gain to clip the output may produce a very different result from sending loads of level in the first place and keeping the gain relatively low (as in DI situations).. And obviously direct coupled types may behave differently from transformer input types where the transformer itself may produce complex premature LF distortion and other artefacts etc..

Another important factor if you are looking for a sound effect from overdriving, is the behaviour of the amp in the immediate aftermath of the overdrive (refering to ripper's previous post). Much of the character of the distortion is provided by the often complex and longer term recovery periods after the overload, rather than the actual clipping itself. This produces a period of complex distortion in the tails of the sound that varies over time depending on how big the overload was and how long it lasted (much like instrument amps) and it's possible to 'play into' this behaviour artistically during the performance to produce textured grunge, characterful sustains or 'glassy' riffs for instruments or some softer 'raspiness' and 'bite' in vocals. This is caused by disturbances in the amps operating conditions due to the overload and is very delicately dependent on gain settings and input levels (a bit of a black art). This kind of behaviour is much more interesting artistically than simple clipping and is more likely with vintage tube types and single rail solid state types (i.e. running from a single +ve supply rather than a balanced +ve and -ve supply). Therefore vintage and earlier designs are likely to produce more interesting artistic results than more recent designs.
Old 3rd June 2006
  #9
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Paul is exactly right, for instance the MP-2MH is a discrete opamp, running off of bipolar 24 volt rails, it sounds great right up to the point that it clips. It clips fast, hard, and not particularly musically, but it recovers instantly and goes on.

The NV on the other hand is a single rail supply, with large coupling, decoupling and bypass caps that all swing around as you push things hard, and they bounce around back to the correct operating point over time, causing the interesting overload characteristics the box is known for.

The sound you are hearing from the box are the windings in the output transformer "singing". Normal, some are a little worse than others.
Old 3rd June 2006
  #10
Really informative answer, Paul!
Old 3rd June 2006
  #11
Let me clarify a couple things.

I completely understand the idea of 'pushing' the input on a pre for more color, and finding the sweet spot. But the idea of clipping a solid state amp, for a nasty tone, (like I said, I probably would never do this) has never really been discussed. Also, I'm only using regular instrument outputs and mics, and I certainly would never hook up a power amp speaker output to the pre (but thanks theblue1 for that info anyway).

Keep this thread going, I love the info.


Thanks to everyone for the great responses. Special thanks to Shaun and Dan for sharing about their great pre-amps.

swordinhand
Old 5th June 2006
  #12
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Quote:
Originally Posted by Dan Kennedy
Paul is exactly right, for instance the MP-2MH is a discrete opamp, running off of bipolar 24 volt rails, it sounds great right up to the point that it clips. It clips fast, hard, and not particularly musically, but it recovers instantly and goes on.

The NV on the other hand is a single rail supply, with large coupling, decoupling and bypass caps that all swing around as you push things hard, and they bounce around back to the correct operating point over time, causing the interesting overload characteristics the box is known for.
Yes - exactly :-)

The issue is that designers of mic amps aiming for maximum purity and fidelity would avoid the kinds of circuit arrangement that produce this sort of complex (some would say unpredictable) behaviour and would aim for the max flexibility and tolerance to suboptimal settings and usage, whilst staying within the specified performance parameters. This means minimal distortion over the maximum possible range of use and setting - and the fastest possible recovery from adverse conditions. Not at all what you need for subtle artistic sound effects :-(

The point is that philosophically speaking mic amps are not really intended for sound effects of this kind - and it would be far better to produce the distortions and harmonic behaviour you need from a dedicated process, where the parameters you actually want can be varied with confidence and getting your sound is no longer a hit and miss affair..

However - with everyone chasing purity, cost/profit ratios, or the latest 'must have fad', the processes you need are often not available - not least of all because few modern designers understand them anymore and understand even less why you would actually need them. This means that you must resort to whatever works in search of your artistic goals - even if that does mean deliberately overdriving a susceptible bit of kit :-)

The trouble with 'progress' is that it's specific and exclusive - and therefore selective in what gets carried forward into the new domain. People who must replace the 'old hacks' and weald the new technologies are necessarily (for no fault of their own) lacking in the depth of knowledge acquired by the many decades of cultural/artistic feedback and related technologies they are leaving behind.. Sadly they have little appreciation for the amazing complexity of behaviour often produced by seemingly simple (often viewed as flawed) circuit arrangements used in the past (as is evident by claims made from the proponents of convolution emulators etc.). This is why each new technical revolution brings with it a degree of sanitisation and dissatisfaction, as it tends to remove dimensions of artistic subtlety from your creative pallete.
Old 5th June 2006
  #13
84K
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84K's Avatar
Isn't clipping the Neve's the sound of hard rock?

If it hurts them, mine would have died years ago.
Old 5th June 2006
  #14
I'm really not looking to clip these pres for artistic reasons (a distortion box would be much better). I do like pushing the amps for effect, though. Mainly I just wanted to know if clipping the pre, say because of a sudden, accidently prolonged OVERLOAD, could damage it, or even shorten the life on some of the components.

It sounds to me like this should be avoided. But in all likely hood it probably would be fine.

Thanks for all the great insight.

Swordinhand
Old 5th June 2006
  #15
84K
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From my experience, Nothing distorts as nicely in a rude way as a Neve pre.
Old 5th June 2006
  #16
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Quote:
Originally Posted by Sword in Hand
I'm really not looking to clip these pres for artistic reasons (a distortion box would be much better). I do like pushing the amps for effect, though. Mainly I just wanted to know if clipping the pre, say because of a sudden, accidently prolonged OVERLOAD, could damage it, or even shorten the life on some of the components.

It sounds to me like this should be avoided. But in all likely hood it probably would be fine.

Thanks for all the great insight.

Swordinhand
Sorry if this thread seems to have gone off track for you :-( The answer is potentially yes - you could at the limit damage your amp.

It depends entirely on how the amp was designed and I can't speak for your particular unit. But for instance, in some insufficiently protected direct coupled designs using discrete input transistors (i.e those without transformers) persistant overloading (or one great big blast) can degrade the front end transistors and lead to increased noise. This may be difficult to detect because the amp may apparently carry on working in other respects.

One common situation that used to cause this with a particular design I was familiar with was when you accidentally hot plugged a dynamic mic into an input that had phantom power switched on. The sudden drop in the phantom voltage as the mic shorted it out sometimes used to degrade the input transistors. Each time this happened the transistors could further degrade until the input noise got bad enough for people to notice :-(

But please note - any potential damage is caused by excessive input level only. Turning the gain up on a legal input should not cause damage, however hard the output clips.
Old 5th June 2006
  #17
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lucey's Avatar
Quote:
Originally Posted by Sword in Hand
I do like pushing the amps for effect, though. Mainly I just wanted to know if clipping the pre, say because of a sudden, accidently prolonged OVERLOAD, could damage it, or even shorten the life on some of the components.
Guitar amps never tire of clipping
Old 5th June 2006
  #18
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Quote:
Originally Posted by 84K
Isn't clipping the Neve's the sound of hard rock?

If it hurts them, mine would have died years ago.
The biggest source of the heavily driven Neve sound was the strangely designed transformer output stages. These were driven essentially single ended (rather than push-pull) with a current source to balance the the standing current in the transformer. This meant that in overdrive conditions the output became assymetrical and complex because the transformer could be driven harder one way than the other. This produced some 'interesting' distortion - but it's character was load dependent (i.e. depending on what was down line) and therefore unpredictable.
Old 5th June 2006
  #19
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lofi's Avatar
 

well i killed one dbx minipre driving it hard with vocal on sm58..the tube is still ok..but pre never recovered... lesson learned....
Old 5th June 2006
  #20
So Paul, let me completely understand what you're saying... by asking more questions.

Example 1:

Let's say I sent a keyboard signal, that was extremely hot going into the pre, and I turned the pre input and output levels to a nice level. The pre in and out meters are comfortably in the green, but I still hear distortion. Is this potentially damaging the pre/transistors?

or

Example 2:

Let's say that the keyboard's output is lowered to a comfortable level. I then turn the input gain to where the input meter is pegging the red, and the output trim is still metering in the green. Is this potentially damaging the pre/transistors?

or

Example 3:

Same as #2 except, the pre's input gain is in the green and the output is pegging the red. Is this potentially damaging the pre/transistors?


Is there any difference between #1 and #2, if damage could occur?

I hope these examples makes sense.

swordinhand
Old 5th June 2006
  #21
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Ruphus's Avatar
 

Once I asked the same question to two tube gear manufacturers. Both said that I couldn´t damage their pres with line level voltage.

Don´t know about convertors e.g. though ... As a precaution I try to not overload them too much.

Ruphus
Old 5th June 2006
  #22
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Quote:
Originally Posted by Sword in Hand
So Paul, let me completely understand what you're saying... by asking more questions.

Example 1:

Let's say I sent a keyboard signal, that was extremely hot going into the pre, and I turned the pre input and output levels to a nice level. The pre in and out meters are comfortably in the green, but I still hear distortion. Is this potentially damaging the pre/transistors?
If the input and output meters are not showing red - there shouldn't be distortion. If there is distortion then this isn't a great amp and/or it's being overloaded internally without telling you on the meters? If you have reduced the input level to a legal value (i.e. meters show green), then normally it shouldn't do damage - however with the distortion you describe, something somewhere is suspiciously unhappy. I would worry about this :-(

The only way to be sure if you are damaging the amp is to compare the output level from the keyboard with the specified max input level quoted for the mic amp.

Quote:

or

Example 2:

Let's say that the keyboard's output is lowered to a comfortable level. I then turn the input gain to where the input meter is pegging the red, and the output trim is still metering in the green. Is this potentially damaging the pre/transistors?
No this should be ok. It is now clear that what you call an input meter is in fact an internal intermediate level (maybe the output level of the front end amp). In other words you can clip the output of the actual mic amp (within the box) and then reduce it with the trim after the event and end up with a distorted signal even though the final output is not overdriven? I despair - what is the use of an output trim after the mic amp if the mic amp itself has already saturated?! If this is so it's a bad and confusing design, but you shouldn't be able to damage the amp by clipping the output of the first mic amp stage. The key here is that you have had to increase the gain to get the input red light(?) - so the input level must be within the expected legal range?


Quote:

or

Example 3:

Same as #2 except, the pre's input gain is in the green and the output is pegging the red. Is this potentially damaging the pre/transistors?
No - this definitely should be ok. It shouldn't be possible to damage the amp by clipping it's final output.

A word of advice - with this amp leave the output trim flat out (and never reduce it) and adjust the mic amp gain to get the required output level. If the amp had a proper gain trim (rather then just a volume control after the mic amp before the output), none of this confusion would have ever occured.
Old 5th June 2006
  #23
I think I'm making a big deal about something that.

A: I will never do

and

B: Is getting way more confusing then it needs to.


I'm also sure that every pre amp has different issues concerning clipping, and that it is best left alone by someone like me. I'm just interested in how stuff works and wondered, because it sounds so bad, if clipping a class A pre damages the input?

Paul when I'm talking about the meters, I'm referring to meters on the Great River ME-1NV. This amp has two stages and they both have meters (one is labelled IN and the other OUT), I think. This is also an extremely high quality pre amp, so I don't think bad design is coming into play here. It's probably me just doing something wrong.


Thanks for everyone's input (no pun intended).

swordinhand
Old 6th June 2006
  #24
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Quote:
Originally Posted by Sword in Hand
I think I'm making a big deal about something that.

A: I will never do

and

B: Is getting way more confusing then it needs to.


I'm also sure that every pre amp has different issues concerning clipping, and that it is best left alone by someone like me. I'm just interested in how stuff works and wondered, because it sounds so bad, if clipping a class A pre damages the input?

Paul when I'm talking about the meters, I'm referring to meters on the Great River ME-1NV. This amp has two stages and they both have meters (one is labelled IN and the other OUT), I think. This is also an extremely high quality pre amp, so I don't think bad design is coming into play here. It's probably me just doing something wrong.


Thanks for everyone's input (no pun intended).

swordinhand

I have had a look at the site for your amp (thanks for the model ref) and indeed it IS a multistage design that (as I suspected) does allow and even actually encourage the overdriving of the input section to obtain distortion.. The 'input' meter is not measuring the input level at all, it's actually monitoring the output of the first gain stage - and the output control section (and meter) is after the input amp to allow you to reduce the level so you can overdrive the input stage at will without having to blast out unmanageably high levels from the output that might otherwise overdrive equipment down line.

So no - it's not you doing something wrong at all, very far from it - and this could indeed be a big deal (certainly for me it would be). You might want to reconsider whether this device is really what you are searching for, given your stated intentions above and in previous posts?

From the link below:

http://www.greatriverelectronics.com...GuideWeb04.pdf

"Generally the signal will be affected least by keeping the large knob turned down and the small one up"

This is necessary to avoid inadvertantly overdriving the first stage before you reach full output capability (as I surmised before in a previous post). It goes on:

"More coloration occurs when the input stage does most of the work, so cranking the large knob and trimming back the output control will tend towards a thicker sound."

I.e. the input stage deliberately and intentionally adds distortion and you get to control the amount by cranking up the input gain and bringing down the output level to compensate. (E.g. exactly what you said you wouldn't want to do). This amp is intended to bring a character to the sound by coloration. But it goes on to warn you:

"When the input stage clips, it get's ugly, so keep an eye on it"

Hmm.. Enough said.....

However - since this amp is actually designed with the intention of overdriving the input stages (as per other posts in this thread about artistic effects) and playing off this distortion against that caused by the output stages, it's very unlikely that they would allow this very action to cause any damage. So the complex behaviour you may be experiencing is not being caused because it's broken :-)
Old 6th June 2006
  #25
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Yep, it will get ugly if you drive the FET buffer hard.

Unfortunately, the meters indicate the overload point of the first gain stage after the transformer, but that doesn't clip first, the buffer will.

After messing around with it for a long time, I decided I liked the tone of the buffer when it was in moderate distress with hot guitar signals, relatively hot bass signals, and fairly low keyboard levels.

It is meant to color the sound to a moderate degree, not to be a universal throw anything at it input.

My other pre, the MP-2MH does that, but it's strangely unlovely as a DI, no feeling, just clean. Who wants that? :-)

It will crap out on really hot levels, there just isn't enough current running in the buffer to really swing the input transformer around a lot, kind of like an old U87.

It's not perfect, but it was put together 6 years ago, and so far most people like it, and realize the limitations and work with it.
Old 6th June 2006
  #26
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Oh, yeah, regarding damage, you can pretty much throw anything you want at it, things are current limited, and clamped and filtered, pretty much bullet-proof.
Old 6th June 2006
  #27
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Quote:
Originally Posted by Dan Kennedy
Yep, it will get ugly if you drive the FET buffer hard.

Unfortunately, the meters indicate the overload point of the first gain stage after the transformer, but that doesn't clip first, the buffer will.

After messing around with it for a long time, I decided I liked the tone of the buffer when it was in moderate distress with hot guitar signals, relatively hot bass signals, and fairly low keyboard levels.

It is meant to color the sound to a moderate degree, not to be a universal throw anything at it input.

My other pre, the MP-2MH does that, but it's strangely unlovely as a DI, no feeling, just clean. Who wants that? :-)

It will crap out on really hot levels, there just isn't enough current running in the buffer to really swing the input transformer around a lot, kind of like an old U87.

It's not perfect, but it was put together 6 years ago, and so far most people like it, and realize the limitations and work with it.
Since the buffer precedes the transformer you must rely on actual output level control from the instrument to control the distortion from the buffer stage - i.e. you cannot control it with any of the gain controls on the unit itself. This is a limitation since you cannot use the buffer distortion properly with inherantly low output (or quiet) instruments.

However the distortion (of a different kind) from the amp itself can be controlled by the gain and output controls, so this should be available for a wider range of instrument types..

One way to get the buffer distortion with quieter sources would be to actually drive this amp from another mic amp to bump up the level..
Old 6th June 2006
  #28
Dan and Paul thanks for the responses.

I'm getting how this works a lot better now. I also want Dan to know that the ME-1NV is absolutely awesome and that it works perfectly.

thanks,
swordinhand
Old 6th June 2006
  #29
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Quote:
Originally Posted by Sword in Hand
Dan and Paul thanks for the responses.

I'm getting how this works a lot better now. I also want Dan to know that the ME-1NV is absolutely awesome and that it works perfectly.

thanks,
swordinhand
This is great :-) It sometimes takes a while for these threads to get around to the precise issues people are actually dealing with - but with patience we generally get there in the end.

Apologies if I have spent too much time on wider detail, guessing what's in your box (and why it was apparently designed that way) and trying to understand why you were worried - before I finally had it all confirmed by looking up the model number.. I could have asked for the model details sooner and got there quicker...

But perhaps the details of some of these replies have helped other people as well?
Old 8th April 2009
  #30
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Quote:
Originally Posted by Paul Frindle View Post
If the input and output meters are not showing red - there shouldn't be distortion. If there is distortion then this isn't a great amp and/or it's being overloaded internally without telling you on the meters?
I can easily get gross distortion (to the point of the pre being unuseable) on my Great River running an active bass (especially if it has EMG's) into the instrument input with all the meters still in the green. In fact, I even had to email Dan Kennedy about it when I first got it and tried to record my buddy's EMG loaded Stingray with it.

By the way, after doing some reasearch I realized I don't have to have the volume all the way up on an active bass to retain proper tone like with passive pickups and electronics... in fact, according to Sterling Ball, not "diming" the volume on an active bass is the proper way to use it.

EDIT...
I hadn't read the entire thread when I posted this... I see Mr. Kennedy has already elaborated on it (wink)
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