G9 and its frequency response ?? (impedance matching?)

[Peter Simonsen]

[quote author="matthias"]@ CJ:

I want to use the G9 to makeup the gain of my pair of passive pultecs..

if I process some drums or bass guitar I really need some bass

at 50hz the loss is at -4,5db ... no good for that purpose..[/quote]

Not that I do not agree with you regarding this.. a -4.5 db at 50 hz can be bad, but it depends on so many other factors of the signal itself and the total signal chain! and what you´re trying to do to the sound. I have more than once had to insert a 12dboct lowcut filter at 100hz or more (up) on both bass guitar and bass drum...due to not so great tracking ;-)...or other choices made...

Like I said before..how does the unit sound to your ears...??? did you at any point before seeing the missing lowend responce...miss lowend in your use of the pre ???..How does the pre sound/work in your studio ?? are peple satisfied with the sound they are getting ???

Maybe the designer can put some light on this...Is the freq responce as it where designed, or is something wrong jakob ???

Kind regards

Peter

 

[matthias]

thanks for your help...

the tests was done with a -8db frequency sweep

I really like the sound of the G9, but as I said, I'd like to use it to make up the gain of my passive pultec eqs...

I think it's interesting that "Neeno" has the same problems...

but in general is it ok, to connect the g9 directly to my RME converter
with an output impedance of 47 ohms??


@CJ: I don't use any special test gear, just my computer with some good rme converters and the rightmark audio analyzer tool...
I used this to test my ssl comp some time ago and it worked pretty well...

@peter: the idea to test the freq response came by some listening test in combination with my passive pultec eq... I had allways turned the bass knob full cw to get enough of bass...

 

[alk509]

To repeat what Kev said, could you please provide a sweep of your RME? Remember there's probably a capacitor at the input, which could account for some of the bad low-end performance...

Peace,
Al.l

 

[Neeno]

Hi Matthias...
Yes, it's seems that I'm not the only one...
Some weeks ago I've posted something about the freq.response of my G9... As I told you I have the same "behaviour" a kinda roll-off starting @ 300Hz.

The lack in the low end is audible when i connect the G9 as a make up gain in the master chain... even if I use the Hi-z input....

But I used it a lot of times to track voices and overheads, and it sounds good enough for me and my clients...

I wonder if Jakob can shed a light on this issue... maybe the G9 needs some modifications to be used as make-up stage :?:

Actually I'm in Zuerich for work (away from my sweet home) 'till friday, when I'm back at home i'll post my freq. response graphs... just to compare them to yours...

Maybe we can also compare the parts we used... ??!?!?

 

[matthias]

here's a sweep of my rme converter.. I connected the outputs directly to the input with balanced cables...

looks pretty good to me..

edit : sorry I don't have this pic anymore...

@Neeno:

I used oep for input, lundahls for output..
all capacitors are WIMA MKS4 and MKP10
tubes: JAN PHILLIPS 5184A
relais: finder 30.22
ht-voltage is 244 V
all other voltages are correct

 

[CJ]

I would borrow an analog scope and signal generator to backup what you are seeing with your current setup.
And try sweeping the transformers by themselves.

 

[matthias]

I used relays for hardbypass, if the g9 is switches off...
so I can hear immediately the change in sound...

mat

 

[Hulk]

My G9 has an "all" Lundahl channel (1528 and 5402) and an "all" OEP channel (A262A2E and A262A3E).
I tracked some bass (DI) throught the G9 Lundahl channel and into my RME converters and I think the low end is huge - I know this is not objective data and I do not have any tools to analyse the bass frequencies but I could put up a short wav-file with the bass track for you to compare with??

 

[mattnj]

I am seeing the same problem on my pre as well with the OEP Xfmrs. I measured it on an AP system one and a Soundtech. The knee is set exactly at 200 Hz, and it doesn't change with loading (with the AP input; 50, 150 and 600 ohms), it doesn't change with gain setting or anything. There is also a ring at the extreme high end which is to be expected. I'll post the pics tomorrow. When I test using the DI input, it is ruler flat. Has anyone swept the OEP trannies by themselves? I haven't gotten in the studio with a decent mic and headphones/monitors to notice a rolloff in the low end (I know, I know. I need to do this) so I can't verify if this actually is a problem, but I test loads of audio gear on the AP system by all kinds of manufacturers and I've never seen this.

Sorry if this has been answered, it is really hard to use the search function. (I've been using Google to find this thread)

 

[gec]

I posted the same question in the g9 thread but I didn't get an answer. I thought the problem was with the OEP but looking at Neeno having the same issue with Lundhals make me think the problem is somewhere else...
I tried using mine with Apogee AD and DA 16x chain for mixing and mastering purpose (just to put some tube sound), but I gave up and now I'm using it only for tracking.

 

[mattnj]

It looks like Neeno has the problem even when he uses the DI input which isn't happening with mine. I have a great frequency response when using the DI. I think perhaps it has something to due with the input section before the DI, or else for some reason we all made the same wiring mistake (mine's point to point) and created an RC filter with the 220 nf cap. I still haven't uploaded the graphs.

 

[mattnj]

These are my results from the AP tests. What do you think? Notice the vertical scale. It really isn't that bad. If you were to assign a value to the high pass filter that is created when testing it would be around 10 hz. No big deal. And same thing with the ring of the input xfmr it's around 30 khz. So I am still really satisifed with my results.

The second graph shows three sweeps, one with no high pass, one set at 80 hz and the other at 160 hz.

 

[radiance]

I've had the same problem...When using the DI the low end roll off was slightly better (meaning more bass) but still noticable.
Here a quote from a post I made in the official G9 help thread with some roll off numbers...(not very acurate I guess)

[quote author="radiance"]Ok, I did some meassurments and although they're not really acurate I think they will give an idea of the lack of low-end I'm talking about.

G9 inserted

Hz____dB
10___-14,3
16___-10,2
21___-7,3
26___-5,5
32___-4,4
37___-4,0
43___-3,8
48___-3,5
53___-4,3
59___-3,5
64___-4,8
69___-4,4

G9 Bypassed
Hz_____dB
10___-2,5
16___-2,4
21___-2,5
26___-2,4
32___-2,6
37___-2,5
43___-2,6
48___-2,6
53___-3,7
59___-2,8
64___-4,2
69___-4,4

It's all done with a sine sweep recorded through the G9 into my DAW...
Maybe it's just the frequentie characteristics of the Oep transformers I've used.[/quote]

 

[jensenmann]

I have two Version of the G9, one with OEP and one with Haufe input trannies. The Haufe sounds even a little thinner than the OEP input. But both versions are still acceptable for me since it´s just a little bass that´s missing. I´d rather describe it as the character of the preamp than an error.

....and the DI ROCKS bigtime!

 

[mattnj]

Has anyone done sweeps of the OEP transformers? Since I am back at school I no longer have access to the AP or Soundtech and I can't find anything by searching the boards.

 

[okgb]

Perhaps the designer will pipe up ?

i have one in the pipes too and would like to know
if there is something i should avoid .

 

[mattnj]

Anyone have any comment?

 

[stanz]

I too have seen this problem and have seen nothing about what to do to solve it. Is it possible that this is the normal frequency response of the design?



My observations:

Using just my ears, it sounds lacking in the low end. If I record bass using the DI, it does not have the same bottom end as when I am using the pre on my Mackie mixer.

I tried running a signal generator with a sine wave into the G9 and measured the output with a tektronix scope. I do not have the measurements at hand, but the voltage started to drop around 400Hz and by the time I was down to 100Hz, it was significant.



The unit sounds great, and even with the roll off, it still can be used for vocals and possibly guitar.

Looking for suggestions about where to start. Someone suggested the 220n cap feeding the first stage. Doing some calculations, a 220n cap with a 2k4 resistor has a roll off of 301Hz.

 

[stanz]

double post

 

[rodabod]

Have you guys measured the response prior to the output transformer? Say via a cap into a 30K line input.