DIY Mic Pre Kits, Lunchbox Mic Preamp Kits, Power Supply Kits

I recently completed my two kits an X12 and an sc1MkII which I mounted in the same case. The preamps seem to work well with one exception; the x12 sound has very little bass, as If the bass had been rolled off around 100hz. It has a clear sound but no bass. Any idea whats happening here or is this the sound of the preamp?

Scott Alger

Scott, I'm not doing any roll off on the X-12. Can you run a line-in level signal and see if you're still having that problem?

Also, when soldering the input transformer, make sure you don't use too much solder so much so that melted solder flows out of the other side of the hole. If it does, you'll create a short between the metal case of the transformer and the solder pad. i.e. creating a short to Ground.

IF this happens, you'd get either no signal or weak signal, and it will sound like the low freq has been cutoff or filtered out.

On this page, http://fivefishstudios.com/index.php/Audio-Samples.html you can hear a complete song recorded only using X12 preamps on everything, drums, bass, guitar, etc.

Certainly no rolling off of bass on the X12.

_________________

Thanks for your reply, I didn't mean to question whether the preamp was good-- I just dont have anything to compare it to. Sent in sine waves at
1000 200 and 70 Hz. and there is a 13db drop at 200 and a 21db drop at 70 hz. I will check the transformer as you said and get back to you.
Scott Alger

Scott, that doesn't sound right.

I did a comparison of a SC1 and X12 here, fed both the same 30Hz signal (from a transformer splitter) and both the SC1 and X12 have similar freq response.

In fact, the X12 was a bit louder/hotter. But definitely no loss of low end.

_________________

I did the same test with the sc1 and no problem. Funny though I was using the two preamps together to record an acoustic guitar in stereo and got a real nice sound.I got the two because I wanted some color in the sound and the x12 definately has color.
Anyway I Will check the transformer as soon as I get near my tools.

Thank again. Scott

Maybe it's out of phase? (speakers, output)?

_________________

O.K. so I took your suggestion. Can't see any solder under the transformer but... several adjoining pins are connected to ground and therefore to each other. Unfortunately the schematic is in indiana and I'm
in chicago right now . Looking at the assembly pictures you have the input transformer in the upper right corner. If I numbered the pins like this: 1 5

2 6



3 7

4 8 2,3 and 4 are connected to ground

Does this sound right?

Yes. looking at PCB top view, the left side pins (bottom 3 pins) are all connected to ground.

_________________

I'm having trouble making a diagram!!!! 1,2,3,4 going down from the top left 5,6,7,8 going down from the top on the right

Sorry for all this confusion.

Ok I'll have to get back to this later I must work now

Thanks

You know, its funny. I noticed the same thing before Scott posted his issue.
I placed the X12 on my kick drum thinking it would be ideal, but its definitely more mid aggressive and lacking on the lower end. Both my sc1 and the pres on my MR816 have more bass content with the same kick and microphone placement.
This was assembled by Owel....500 format.

I did some tests so we all can see what might be going on. Tested using a MOTU828mk2 audio interface, upper limit of 20Khz.

Scott, from graphs below, you can see the X12 response and SC1 response are about exactly the same. Very flat too. It doesn't roll off until about 30-35Hz.

SC1 with trafo. The SC1 does a slight uphill before it starts rolling down.


X12 with trafo.


This is the interesting part. If you use the Input Pad on the X12, for example: to attenuate the signal (say you're micing a very loud signal), notice the change in freq. response. Now it starts rolling off earlier starting at about 65Hz - 70Hz


So there is a difference in low end freq response if you turn on the PAD. Since the purpose of a PAD is to attenuate loud signals, (and most of the energy are in the low frequencies anyway), it doesn't hurt that the lower end is attenuated more.

_________________

I'm not getting a 13dB drop at 200Hz or 21db at 70Hz. See graph below.

From my testing, both the SC-1 and X-12 have almost identical low end (-3dB @ 22Hz).

But with the PAD engaged on the X-12, the low end is (-3dB @ 41Hz)

_________________

Hello again and I have discovered the problem.

I installed unbalanced outputs on the two preamps,using output from

pins 1 and 2 to phone jacks. The sc1MkII unbalanced out works fine.

The X12 for some reason does not. Hooking up the X12 balanced works

fine!!! So nothing wrong with the preamp, sorry for any confusion here.

I'll keep keep poking around and let you know what I find.

I can see that you went to a lot of trouble here...My apologies