Siemens V276 Frequency Response

Dear Members,
I racked two V276 some time ago but wasn´t really pleased with their sound. So I decided to recap them in hope to turn them into those great pres everybody is raving about. Well, I ran them through my analyzing software using 7,5K resistors in series to + and - of the input of my soundcard and a 150R across. This is what I got:


What is going on, is this amp really this bad? Anyone out there having (good) experience with these boxes?
Thanks, Emre

Please wait a minute guys, I´m using Fuzzmeasure the first time (analyzing software) and maybe there is something wrong in my measurement, so please just ignore this topic in the meanwhile...
I tried to delete this topic but can´t....
Please moderators, could you do this for me?

Have you listened to it after the recap ? How does it sound ?

I have a pair of U274's (they're pretty similar to the V276), and IMO they sound great. But they're not clean at all.

No, not yet, because I didn´t bring them into my studio yet. Just wanted to check them with my new software "fuzzmeasure" but seems like I did something wrong. Anyway I did a new check with RMAA which looks way better. I made the filter switchable as in http://www.groupdiy.com/index.php?topic=29852.msg361348;topicseen#msg361348
So flat is flat and HP is with the Highpass-Section engaged.
Now I feel ready for the listening check  ;D
Thanks, Emre

That doesn't look right. Either your setup has an error or your V276 is f#cked. Your curve is *way* to jagged. You should get a fairly smooth curve that is essentially flat in the midband. I don't have a V276 but a couple of V272s, and they look fairly linear.

Genrerally speaking, the sound of a preamp is not really visible in the frequency response plot. They all look linear in the mid band, don't expect EQ-Curves or a wild, jagged response.

Hi Veermaster !

If you're using FuzzMeasure (great software by the way...) but sure to be methodical with it.

You need a soundcard with at least 2 inputs and 2 outputs. There's a window called Audio Capture Settings which allows you to choose input and output channels. Let's say you devote In 1 and Out 1 to send the test signal to and from the unit you're testing, and In 2 and Out 2 for what they call Device Correction Channels.

Now plug a cable from Out 2 to In 2 on your soundcard to create a correction loop. Uncheck Enable Correction. In the upper part choose Out 2 for Playback and In 2 in the Record On field. Click on Measure, you're sending the test signal through Out 2 to In 2 just as a test loop.  This allows FuzzMeasure to have a reference signal (for frequency response and signal delay of your soundcard) and use it to compensate for the irregularities of your soundcard when measure any given equipement. This is important for example for delay measures of a signal because you need to compensate for the computer induced delays (USB connection of your soundcard for example...) and conversion delay...

So your "correction loop" measure should look something like this, near flat frequency response... This for example is my MacBook Pro's Line In/Line Out loop.



Now set back Playback to Out 1 and Record to In 1, plug the I/O in the unit you're testing, set Out 2 and In 2 in the Device Correction Channels, check Enable Corrections. Now you're outputing the test signal through Out 1, you're recording it through In 1 and you're correcting your measure with the Out 2 and In 2 loop.

What might have happened with your initial measure is that you had the Enable Corrections box checked, no correction loop and you were then correcting your measure with a completely false or inexistent correction loop.

Check their forum, there's plenty of infos. I use FuzzMeasure all the time at work (live sound) and it's really a great tool !!!

Hope that helps, cheers, Piotr.