Sta Level Distortion, Grrrrr....

[emrr]

It makes sense that overloading the input would cause the splat but it seems like removing the input pad on the sta level is something most folks regularly do. The Redd47 only puts out a max of 48db i believe so not too hot of a signal going into it when testing with a mic.

Until input overload is definitively dismissed as a possible cause, we got nothin' reasonable to work from. 

48dB max from the Redd means nothing, think about it.  48dB from what? 

48dB from a Redd and then 60dB from a Stalevel. 

Subtract the full gain of the Stalevel from it's max output.  Off the top of my head, we're at -30dBm. 

No pad on the Sta, no way to avoid input transformer overload.  The MANUAL specifically states the input pad is used to "prevent overloading the input transformer with high level signals", which is what we feed Stalevels.  "An input level of -10dBm (WITH input pad) will give approximately 15dB gain reduction with +24dBm output level". 

I've seen a bunch of Stalevels straight out of radio stations.  Radio gain structure is no different from ours.  All of them had the input pad.  I never heard of a Stalevel without the input pad until the last 10 years, it's dubious info from unknown internet commentators. 

It's still 35dB gain even with all the pads installed.  Add 48dB to that.  subtract that from 30dBm (max output). 

Eliminate this question and then we can consider other problems.  Good luck!

 

[gridcurrent]

It makes sense that overloading the input would cause the splat but it seems like removing the input pad on the sta level is something most folks regularly do.

cannot speak for most folks, but some technicians in LA have been installing 1:1 transformers minus the pad. 
based on the gain structure notes, it appears a step-down coil could alleviate potential issues.

 

[emrr]

cannot speak for most folks, but some technicians in LA have been installing 1:1 transformers minus the pad. 
based on the gain structure notes, it appears a step-down coil could alleviate potential issues.

Yep; THIS makes sense. 

 

[CJ]

so that is not a line level box?  you know the 670 looks a lot like this but with higher headroom, which is what that old buzzard Rein Narma told me, he wanted something with higher input capabilities,

you can use any color for the voltages, just open it in a Paint type program and insert text.

 

[emrr]

it's sorta line level if it has the input pad installed, which this does not.....

 

[CJ]

here is the operating manual>

http://www.realoldiesradio.com/docs/StaLevel/Sta-Level_Manual.pdf



gain for pad or no pad on first page>

 

[CJ]

built a pad, used 220 ohms and 100 instead of 240 and 120, s/b about the same,

cuts signal from 1 volt to about 0.1 volts into a 600 ohm load,

so that looks like a minus 20 dB pad,

try a 100 mv signal input without the pad and see what happens,

60 dB gain without in/out pads means 1 volt in = 1000 volts out! is my math right?

if so, no wonder you have massive distortion.

35 dB gain with in/out pads means 1 volt in still gives 50 volts out,

no pads and 100 mv signal in still gives 100 volts out,


20 mv in at 60 dB gain will give 20 volts out,  (semi reasonable)

so this circuit has a ton of gain ,  if using input pad but no output pad, 60 dB minus 20 dB (pad) = 40 dB.

a 100 mv signal plus 40 dB amp = 10 volts,  so that machine wants an instrument level input even with the 20 dB pad.


why? maybe so they could plug a turntable into it at the radio station. 

 

[orangechili]

Ok,

I added the original input pad per the original schematic with 240 ohm resistors and 120ohm resistor and it sounds worse if that is possible.  Same nasty distortion just it takes a harder level to start compressing.

I'm going to those additional tests and to get that voltage chart soon.

 

[CJ]

how many milli volts were you putting into the pad?

 

[emrr]

OK!  It's something else then....one down.....

 

[orangechili]

Yep, I appreciate the ideas though!

CJ, it was me just testing with a mic through the unit with the pad attached. There is an output T pad on the unit as well.  Attached is a clip of that test, it's me just checking the unit with a mic out of a preamp... . Just remove .jpg from the extension to hear it. I tried lower gain into it as well and same issue. There is something clearly unhealthy with the unit. Initial voltages tests didn't indicate nothing amiss but I'm gonna try and get that full voltage chart. Work keeps in getting in the way of going thru this thing...

Also 100mv into the unit and it barely compresses with the pad, I have to crank the input control to get the needle to move. Maybe 5db of compression max.

 

[orangechili]

Ok, Attached is a schematic with the dc voltages written in Blue ink.

Also the B+  Voltage is 276V AC

 

[CJ]

how many millivolts were you injecting into the pad?

 

[mjrippe]

Ok, Attached is a schematic with the dc voltages written in Blue ink.

Also the B+  Voltage is 276V AC

If you have *AC* for the B+ then something is very wrong.

ASSuming you meant DC, I would check the coupling caps for all stages.  Leaky caps are common in Sta-Levels.

 

[orangechili]

I actually meant AC voltage coming off of the power transformer, not B+. Good catch! Just to explain some of my lower DC voltages compared to the schematic.

CJ these are just DC measurements on the attached schematic in blue with no signal being injected. If you want I can inject 100 millivolts and give those measurements?

 

[CJ]

yeah 0.1 volts into the pad then transformer at 1 K hz,

 

[groselicain]

Good luck chili, I'm following with baited breath.

 

[Andrewfrommontreal]

Hey there orangechili,

What ever happened with the Sta Level? I just received one and it seems to have a similar issue.

 

[Andrewfrommontreal]

In my case these are my findings:
- output level doesn't affect the distortion
- input level does
- if I lower the threshold of the compressor it can get rid of the distortion to a certain extent, therefore the distortion is occurring following the gain reduction of the compressor.
- it is an aggressive distortion (very ugly) and it doesn't seem to come in gradually like an overdrive, it comes in quite suddenly.

Should it make any difference, mine is a Drip build.

Any thoughts?

 

[emrr]

- if I lower the threshold of the compressor it can get rid of the distortion to a certain extent, therefore the distortion is occurring following the gain reduction of the compressor.

Don’t hold to that thought.  Threshold is ratio and it affects GR.