Doepfer

lately i've been using my system for processing external signals quite often 
and i've come to notice that my a119 degrades the sound more than i'd like.   
the studio environment i'm usually in is of a high standard, neve console, etc...  
unfortunately i'm sometimes limited to what i can send to the a119 due to 
lessened sound quality of the results.  especially w vocals and drums.   i'm 
very careful w gain-staging so i don't think it's me.

out of curiousity just  patched the a119 from a send and back to the desk, the 
quality drops considerably w vocals and drums, but the narrowed bandwidth 
is usually pleasing on synth and guitars.
 
was looking at the opamps inside the a119, i believe the one that handles 
audio duties is a TI tl064c, pretty run of the mill chip w low power draw and 
pretty low slew rate according to info i found on TI's site.

i imagine a chip upgrade would make a big difference here as long as it 
doesn't draw too much current.  not looking for anything fancy but an 
improvement in bandwidth and slew rate would be nice.  anyone have any 
knowledge of opamps enough to recommend a suitable upgrade?

anyone else feel this way about the a119?

thanks!
-psm

Hi psm,

Not much experience in this area, but a quick look at the 'audio' 
chapter in Jung's 'IC Op-Amp Cookbook' (1st edition *only*!) suggests 
that a key factor is 'gain bandwidth product' (you need large one), 
but also slew rate comes into play as well. Basically the more gain 
you want, the less bandwidth you get. Thus the gain stage on the 119 
acts as a low-pass filter, and as you crank the gain up, the lower 
the cut-off frequency gets. I probably won't have time to try any 
real measurements, but I did a quick simulation of the gain stage of 
the 119, and the results (very, very roughly) suggest that there 
shouldn't be much of a problem with the asymmetric input unless the 
gain is nearly max (8-9 perhaps), but with the symmetric input 
problems are likely to be noticed at much lower gain settings, 
perhaps around 4 or 5. (This is because the overall gain requirement 
for the symmetrical input is much greater.) Does this tie in with 
your use?

The book also shows how to improve standard op-amp set-ups for audio 
use (gets non-trivial very quickly - external compensation, extra 
bits 'n bobs everywhere!). As for a recommended chip, you could try 
searching the Synth DIY archives (www.buchi.de/sdiy) as I bet the 
question comes up there from time to time, or you could of course 
pose the question directly to that list (there's a link at the bottom 
of the archive page).

Tim


--- In Doepfer_a100@yahoogroups.com, "ps_minor" <pscottm@h...> wrote:
> lately i've been using my system for processing external signals 
quite often 
> and i've come to notice that my a119 degrades the sound more than 
i'd like.   
> the studio environment i'm usually in is of a high standard, neve 
console, etc...  
> unfortunately i'm sometimes limited to what i can send to the a119 
due to 
> lessened sound quality of the results.  especially w vocals and 
drums.   i'm 
> very careful w gain-staging so i don't think it's me.
> 
> out of curiousity just  patched the a119 from a send and back to 
the desk, the 
> quality drops considerably w vocals and drums, but the narrowed 
bandwidth 
> is usually pleasing on synth and guitars.
>  
> was looking at the opamps inside the a119, i believe the one that 
handles 
> audio duties is a TI tl064c, pretty run of the mill chip w low 
power draw and 
> pretty low slew rate according to info i found on TI's site.
> 
> i imagine a chip upgrade would make a big difference here as long 
as it 
> doesn't draw too much current.  not looking for anything fancy but 
an 
> improvement in bandwidth and slew rate would be nice.  anyone have 
any 

> knowledge of opamps enough to recommend a suitable upgrade?
> 
> anyone else feel this way about the a119?
> 
> thanks!
> -psm

hi tim, 
thanks for your reply.  that's useful info.  maybe  what i'm hearing is premature 
slew limiting (or something!) because i notice a loss of detail w pretty much 
any gain setting, especially hi ones, like you say.  i scrapped using the 
symmetrical early on due to noise and started using a high quality impedence 
transformer (reamp box) in front of the assym input instead, so the +4db signal 
from the console gets knocked down to instrument level.  that helps alot.

i'll pose the opamp upgrade question to the synth DIY group and see what 
they say..

also, seems that by the time i amplify the signal enough to get a healthy 
envelope signal from the a119 the audio on output is really dull.  maybe 
there's an adjustment for making the envelope follower more sensitive..(??)
thanks!
-psm



--- In Doepfer_a100@yahoogroups.com, "Tim Stinchcombe" <timothy@t...> 
wrote:

> Hi psm,
> 
> Not much experience in this area, but a quick look at the 'audio' 
> chapter in Jung's 'IC Op-Amp Cookbook' (1st edition *only*!) suggests 
> that a key factor is 'gain bandwidth product' (you need large one), 
> but also slew rate comes into play as well. Basically the more gain 
> you want, the less bandwidth you get. Thus the gain stage on the 119 
> acts as a low-pass filter, and as you crank the gain up, the lower 
> the cut-off frequency gets. I probably won't have time to try any 
> real measurements, but I did a quick simulation of the gain stage of 
> the 119, and the results (very, very roughly) suggest that there 
> shouldn't be much of a problem with the asymmetric input unless the 
> gain is nearly max (8-9 perhaps), but with the symmetric input 
> problems are likely to be noticed at much lower gain settings, 
> perhaps around 4 or 5. (This is because the overall gain requirement 
> for the symmetrical input is much greater.) Does this tie in with 
> your use?
> 
> The book also shows how to improve standard op-amp set-ups for audio 
> use (gets non-trivial very quickly - external compensation, extra 
> bits 'n bobs everywhere!). As for a recommended chip, you could try 
> searching the Synth DIY archives (www.buchi.de/sdiy) as I bet the 
> question comes up there from time to time, or you could of course 
> pose the question directly to that list (there's a link at the bottom 
> of the archive page).
> 
> Tim
> 
> 
> --- In Doepfer_a100@yahoogroups.com, "ps_minor" <pscottm@h...> wrote:
> > lately i've been using my system for processing external signals 
> quite often 
> > and i've come to notice that my a119 degrades the sound more than 
> i'd like.   
> > the studio environment i'm usually in is of a high standard, neve 
> console, etc...  
> > unfortunately i'm sometimes limited to what i can send to the a119 
> due to 
> > lessened sound quality of the results.  especially w vocals and 
> drums.   i'm 
> > very careful w gain-staging so i don't think it's me.
> > 
> > out of curiousity just  patched the a119 from a send and back to 
> the desk, the 
> > quality drops considerably w vocals and drums, but the narrowed 
> bandwidth 
> > is usually pleasing on synth and guitars.
> >  
> > was looking at the opamps inside the a119, i believe the one that 
> handles 
> > audio duties is a TI tl064c, pretty run of the mill chip w low 
> power draw and 
> > pretty low slew rate according to info i found on TI's site.
> > 
> > i imagine a chip upgrade would make a big difference here as long 
> as it 
> > doesn't draw too much current.  not looking for anything fancy but 
> an 
> > improvement in bandwidth and slew rate would be nice.  anyone have 
> any 
> > knowledge of opamps enough to recommend a suitable upgrade?
> > 
> > anyone else feel this way about the a119?
> > 
> > thanks!
> > -psm

Hi psm,
I'm now going to (very likely) display my lack of knowledge when it 
comes to audio engineering terms. (Well they do make life very hard 
by surrounding the whole arena with an aura of mystical terms 
like 'dBm', 'dBV', 'dBv', 'dBu', 'VU' and 'line level' etc., and you 
never, never, ever see these things defined with the appropriate 
mathematical formula given - you have to be 'in the know' (nudge-
nudge, wink-wink). I have a book which _attempts_ to explain, but as 
always, shies away from giving all the maths - if anyone knows of a 
good web resource, to save me working it out from scratch, then I'd 
love to know it!). Here goes:

> symmetrical early on due to noise and started using a high quality 
impedence 
> transformer (reamp box) in front of the assym input instead, so the 
+4db signal 
> from the console gets knocked down to instrument level.  that helps 
alot.

Why do you need to step the signal down at all? Just how big actually 
is it? If by '+4db' you mean '4dBm', then this equates to a couple of 
volts at most, which you could safely stick straight into the 119 
asymmetric input, and thus save having to turn the gain up so much?

> also, seems that by the time i amplify the signal enough to get a 
healthy 
> envelope signal from the a119 the audio on output is really dull.  
maybe 
> there's an adjustment for making the envelope follower more 
sensitive..(??)

Yes, its called the gain control! It seems to me that making the 
signal big enough to drive the envelope circuitry is its main 
purpose! The envelope is developed by precision full-wave rectifying 
the signal, then low pass filtering - by the sound of it, what you 
would ideally want is a second gain stage in front of this so that 
the signal is bumped up high enough for the envelope stage 
independently of the audio out.

Tim

hi tim, 
thanks for your thoughts on this..

the reason i use a transformer is because the output of the console's send is 
too hot (or too dynamic), it distorts the input of the a119.  also, the sends are 
balanced and the 'reamp' box is designed to do just this, take a hot line-level 
signal (often as much as +20db), unbalance it and present it to instrument 
amps or guitar pedals at the same impedence as a guitar output or synth 
output.

i think tomorrow i'll try some light compression in front of the a119 to see if i 
can smooth it out and attenuate it enough to get things to work in a more 
pleasing manner w/o the step-down transformer..

thanks again,
-psm  


--- In Doepfer_a100@yahoogroups.com, "Tim Stinchcombe" <timothy@t...> 
wrote:

> Hi psm,
> I'm now going to (very likely) display my lack of knowledge when it 
> comes to audio engineering terms. (Well they do make life very hard 
> by surrounding the whole arena with an aura of mystical terms 
> like 'dBm', 'dBV', 'dBv', 'dBu', 'VU' and 'line level' etc., and you 
> never, never, ever see these things defined with the appropriate 
> mathematical formula given - you have to be 'in the know' (nudge-
> nudge, wink-wink). I have a book which _attempts_ to explain, but as 
> always, shies away from giving all the maths - if anyone knows of a 
> good web resource, to save me working it out from scratch, then I'd 
> love to know it!). Here goes:
> 
> > symmetrical early on due to noise and started using a high quality 
> impedence 
> > transformer (reamp box) in front of the assym input instead, so the 
> +4db signal 
> > from the console gets knocked down to instrument level.  that helps 
> alot.
> 
> Why do you need to step the signal down at all? Just how big actually 
> is it? If by '+4db' you mean '4dBm', then this equates to a couple of 
> volts at most, which you could safely stick straight into the 119 
> asymmetric input, and thus save having to turn the gain up so much?
> 
> > also, seems that by the time i amplify the signal enough to get a 
> healthy 
> > envelope signal from the a119 the audio on output is really dull.  
> maybe 
> > there's an adjustment for making the envelope follower more 
> sensitive..(??)
> 
> Yes, its called the gain control! It seems to me that making the 
> signal big enough to drive the envelope circuitry is its main 
> purpose! The envelope is developed by precision full-wave rectifying 
> the signal, then low pass filtering - by the sound of it, what you 
> would ideally want is a second gain stage in front of this so that 
> the signal is bumped up high enough for the envelope stage 
> independently of the audio out.
> 
> Tim

> the reason i use a transformer is because the output of the 
console's send is 
> too hot (or too dynamic), it distorts the input of the a119.  also, 
the sends are 
> balanced and the 'reamp' box is designed to do just this, take a 
hot line-level 
> signal (often as much as +20db), unbalance it and present it to 
instrument 
> amps or guitar pedals at the same impedence as a guitar output or 
synth 
> output.

OK, I think I get the dBm, dBV, dBu etc. thing now. But of course 
this still leaves the question of _peak_ voltages (obviously if too 
big the 119 would clip them), and hence into the realm of VU meters 
and PPM meters, which seems just as confused as the dB situation. 
(yeuch). Which do you use by the way?

> i think tomorrow i'll try some light compression in front of the 
a119 to see if i 
> can smooth it out and attenuate it enough to get things to work in 
a more 
> pleasing manner w/o the step-down transformer..

I'll be interested to hear how you make out!

Tim

Hi Tim 

> like 'dBm', 'dBV', 'dBv', 'dBu', 'VU' and 'line level' etc., and you
You can simply avoid this stuff, by using an oscilloscope. Meters are nice,
but of no worth compared to a two channel scope, which is used to compare
the signal before and after any audio processing stage (not to mention,
that most times your ears will be the best measurement equipment you can
find...).

Florian

Hi ps_minor 

> lately i've been using my system for processing external signals quite often
> and i've come to notice that my a119 degrades the sound more than i'd like.
> the studio environment i'm usually in is of a high standard, neve console, 
Though I do not live in a Neve-like luxury as you ;-) I always preprocess
external audiosignals with a Compressor/Limiter. The only crux is if you
would like to use the A-100 for dynamical sound effects (like
compression/expansion with signals handled by different filtertypes).
Meanwhile I tend more to use the Nord Modular for processing audio signals.

Florian

i started using a comp/limiter in front of the a119 and it helps alot.  adds 
another clean gain stage for finding a spot where the a119 is happy, keeps 
the peaks from distorting, etc.  it's also nice for manipulating the overall 
contour of the envelope produced by the incoming audio.  great tip!

i'm still less than thrilled w the sound quality of the audio chip in the a119 but 
can work around it.  
-psm



--- In Doepfer_a100@yahoogroups.com, Florian Anwander <
Florian.Anwander@c...> wrote:
> Hi ps_minor 
> 
> > lately i've been using my system for processing external signals quite 
often
> > and i've come to notice that my a119 degrades the sound more than i'd 
like.
> > the studio environment i'm usually in is of a high standard, neve console, 
> Though I do not live in a Neve-like luxury as you ;-) I always preprocess
> external audiosignals with a Compressor/Limiter. The only crux is if you
> would like to use the A-100 for dynamical sound effects (like
> compression/expansion with signals handled by different filtertypes).
> Meanwhile I tend more to use the Nord Modular for processing audio 
signals.
> 
> Florian