Drip Sta-Level build complete - noise troubleshooting help needed

[bsconz]

I have completed a Drip Sta-Level on the large Drip PCB from 2012.

It's all together now but I'm fighting noise issues. Even at idle with both input and output turned all the way down, there's quite a loud noise floor.

All Sowter transformers, JJ tubes except the 6AL5 and 0B2 which are NOS.

I'm testing it at home by just connecting an SM57 to the input and running the output to Logic through my interface.

It does have the ouput pad built per the schematic but no input pad at the moment. I am thinking I will build one.

I fought through some PCB silkscreen/print errors...mainly the potentiometer terminal labeling was backwards from standard convention.

I think I may need to move the hookup wire shield drains to different spots too.

The PT is grounded to the chassis and hard mounted directly. I do have some rubber grommets that I could use to isolate it from the chassis ground.

The 6.3VAC center tap is just lifted and isolated right now but I may try  grounding it through a cap per the schem.

I am reworking the 3 main ground  wires that come off the PCB and the H.V. 0V wire to all go to a star ground.

At this point I'm thinking there's a grounding error somehow so I'm in a listing ideas, reworking, and testing mode.

I'd love to get some feedback and help on this issue.

 

[rock soderstrom]

I have completed a Drip Sta-Level on the large Drip PCB from 2012.

It's all together now but I'm fighting noise issues. Even at idle with both input and output turned all the way down, there's quite a loud noise floor.

The PT is grounded to the chassis and hard mounted directly. I do have some rubber grommets that I could use to isolate it from the chassis ground.

The 6.3VAC center tap is just lifted and isolated right now but I may try  grounding it through a cap per the schem.

I am reworking the 3 main ground  wires that come off the PCB and the H.V. 0V wire to all go to a star ground.

At this point I'm thinking there's a grounding error somehow so I'm in a listing ideas, reworking, and testing mode.

You have to ground the heater. It´s a good idea to connect all grounds to a central ground and than connect this point to the chassis. 

 

[Bowie]

Mine is super-quiet.  Follow the grounds laid out in the guide (which includes grounding the heater CT) and you should be ok. 

 

[bsconz]

Yep, it's quiet now! Definitely have to have the heater grounded. Thanks for the advice and guidance!

I reworked the whole ground scheme and put everything to a common star ground. I isolated the PT too and actually have its case ground floating from the chassis.

I also built the input pad per the schematic and popped that inline. Now both input and output XLR's measure about 600 Ohms across pins 2 and 3.

However, I am having the following issues still:

1) The VU meter barely moves when singing loudly directly into an SM57. I have to have the input turned way up and basically shout into the mic to see the VU meter needle move. I also have the output all the way down and it's still overdriving the input on my converter. Not sure where to go from here. Maybe my test method is not a good way to judge this?

2) I bought a new JJ 6386 and it seems to be highly microphonic. Just barely tapping on the chassis of the unit is getting picked up and coming through the output. If I lightly tap on the tube itself it produces a loud metallic clanking through the output. I know with guitar amps this is a sign of bad preamp tubes. Is this similar to your Sta-Level units? Is it potentially a bad tube or damaged during shipping? I have no way to test this tube.

 

[Bowie]

Yep, it's quiet now! Definitely have to have the heater grounded. Thanks for the advice and guidance!

I reworked the whole ground scheme and put everything to a common star ground. I isolated the PT too and actually have its case ground floating from the chassis.

I also built the input pad per the schematic and popped that inline. Now both input and output XLR's measure about 600 Ohms across pins 2 and 3.

However, I am having the following issues still:

1) The VU meter barely moves when singing loudly directly into an SM57. I have to have the input turned way up and basically shout into the mic to see the VU meter needle move. I also have the output all the way down and it's still overdriving the input on my converter. Not sure where to go from here. Maybe my test method is not a good way to judge this?

2) I bought a new JJ 6386 and it seems to be highly microphonic. Just barely tapping on the chassis of the unit is getting picked up and coming through the output. If I lightly tap on the tube itself it produces a loud metallic clanking through the output. I know with guitar amps this is a sign of bad preamp tubes. Is this similar to your Sta-Level units? Is it potentially a bad tube or damaged during shipping? I have no way to test this tube.

1) It's not great as a mic pre.  Drive it with a line-level source and see where you're at.
2)  I've heard of numerous problems with the jj 6386.  I'm a tube dealer and I won't carry them because of all the negative feedback customers have shared with me about those.  They don't seem to last long either based on the one I had here.  The Sta-Level's 6386 section is fairly sensitive to noise and microphonics in the 6386 tube.  Not all tubes are going to be quiet enough for that spot, even the GEs.  You have to take it on a tube-by-tube basis.

 

[bsconz]

Ok, I brought it in to the recording studio today so I could test with line level signal (the studio owner happened to be there too so we took a listen together with some source from a DI bass track).

1) The 6386 quieted down a lot but still not enough for my tastes. Any suggestions on NOS tubes to try?

2) Driving the input pretty hard now the VU meter is definitely acting like it should. Guess it won't be a great mic pre. I sort of knew it's a 1-trick pony anyway.

3) With the output knob all the way to the left, the output does not go completely to zero. It's wired according to the schematic and Sta-Level Micro manual. There appears to have been some errors on the silkscreen and terminal labelling for the pots. The standard convention, as I know it, for potentiometer terminals is with the shaft pointing up and the terminals facing you, left to right is 1, 2, and 3. In order to connect the output pot so that turning to left turns the volume down, I had to reverse terminals 1 and 3. The schematic and Sta-Level Micro manual show terminal 1 (normally 3) and 2 joined. Terminal 3 (normally 1) is connected to the 200R resistor from the high side of the output pad. Pin 2 is connected between the 2x 270R resistors on the low side of the output pad. Obviously with no terminal of this pot connected to ground, there is no way to turn the output fully to zero. Am I losing my mind or is this how it should be? (I can try to clarify this with photos if needed.)

4) Tone on the bass is great but usable output range is not what I expected. Turning to the right, it just has crazy amounts of output, even with the output pad. Not sure if the other attenuator options offer more attenuation or if this is normal too?

 

[Bowie]

Sta-Levels have a hot, no, HOT output.  I used a pot at first with an output pad and that proved worthless.  Then, I had to implement a Mallory T-600 in addition to a resistor pad.  That got things under control.

 

[bsconz]

Ok, this is reassuring. I ordered a Mallory T-600 to install.

Can you tell me if you wired it in the same way as the schematic shows for the 1k pot? Or did you do it a different way?

 

[Bowie]

Ok, this is reassuring. I ordered a Mallory T-600 to install.

Can you tell me if you wired it in the same way as the schematic shows for the 1k pot? Or did you do it a different way?

I did this;
https://www.dropbox.com/s/mxjhxubhaqwgys4/Mallory600OhmT-PadWiring.jpg?dl=0
You'll still need a resistor pad as the T-600 will have a super-hot signal at only 15% open.

 

[bsconz]

Awesome sauce! Thanks a million for your help Bowie...you are a gentlemen and a scholar.

 

[bsconz]

Here's a little sketch of what I did to modify the output section of the Drip Sta-Level in order to get the output level and knob range into a usable state.

I took the output transformer leads to a Mallory T600, then to U-pad with 2x 270R resistors and 1x 68R resistor, then to output XLR.

I have yet to test this but wanted to get some feedback just in case this refreshes anyone's memory. A lot of you seem to have built theirs quite a while ago and have forgot exactly what they did.

 

[bsconz]

Just a follow for anyone else who may come across this thread.

Everything is working tip-top and sounding GREAT!

With the stock schematic input pad and pot and the modified output pad (shown above on hand sketch) and Mallory T600 pot, the output levels are very useable if not slightly low.

This unit is now in service at Saint Cecilia Studios in Tucson, AZ.

Thank you all for your help/advice!

 

[jcoutu1]

Just a follow for anyone else who may come across this thread.

Everything is working tip-top and sounding GREAT!

With the stock schematic input pad and pot and the modified output pad (shown above on hand sketch) and Mallory T600 pot, the output levels are very useable if not slightly low.

This unit is now in service at Saint Cecilia Studios in Tucson, AZ.

Thank you all for your help/advice!

Got any pics of the newly installed T-Pad? I purchased a used unit and I'm trying to get it up and running. It looks like the transformer leads go to the underside of the PCB, is that correct? I need to desolder those leads and send them to the T-Pad? Then the T-pad goes to the resistor network on the breadboard? Here's some pics of my unit...

http://imgur.com/a/q7s3a

...ps, I'm a total beginner and really have no idea what I'm doing other than soldering/unsoldering.

 

[jcoutu1]

Ok, this is reassuring. I ordered a Mallory T-600 to install.

Can you tell me if you wired it in the same way as the schematic shows for the 1k pot? Or did you do it a different way?

I did this;
https://www.dropbox.com/s/mxjhxubhaqwgys4/Mallory600OhmT-PadWiring.jpg?dl=0
You'll still need a resistor pad as the T-600 will have a super-hot signal at only 15% open.

Hey Christian,

I'm trying to figure out how to wire this T-Pad in. I have the Mallory that you suggested, but I'm confused about where I can get the + and - transformer leads from to wire it up. Also, the BOM says that the T-Pad should go before the resistor network attenuator, but the hand drawn pic posted above shows the resistors after. Any thoughts there?

Thanks man!

-Jesse

 

[emrr]

Here's a little sketch of what I did to modify the output section of the Drip Sta-Level in order to get the output level and knob range into a usable state.

I took the output transformer leads to a Mallory T600, then to U-pad with 2x 270R resistors and 1x 68R resistor, then to output XLR.

This is incorrect.  You are loading the 600 ohm output winding with 68 ohms, or less depending on T pad position.  You are presenting 600 to the outside world, which could care less.  At very least, the 68 should be on the XLR side. 

But really, you don't want a U pad here at all, AND you want the fixed pad between transformer and variable T pad, to take power load off of the variable T.  You want a 10dB fixed T pad.  Look at the output of the Collins 26U-2.  Copy that. 

The Mallory is overkill.  The typical modern T as sold by Hairball and CAPI is just fine.

 

[jcoutu1]

Here's a little sketch of what I did to modify the output section of the Drip Sta-Level in order to get the output level and knob range into a usable state.

I took the output transformer leads to a Mallory T600, then to U-pad with 2x 270R resistors and 1x 68R resistor, then to output XLR.

This is incorrect.  You are loading the 600 ohm output winding with 68 ohms, or less depending on T pad position.  You are presenting 600 to the outside world, which could care less.  At very least, the 68 should be on the XLR side. 

But really, you don't want a U pad here at all, AND you want the fixed pad between transformer and variable T pad, to take power load off of the variable T.  You want a 10dB fixed T pad.  Look at the output of the Collins 26U-2.  Copy that. 

The Mallory is overkill.  The typical modern T as sold by Hairball and CAPI is just fine.

Hey Doug, the drip manual says to use the Mallory and specifically not one from Hairball.

Does anyone have decent pics of this thing wired up properly? Or a build guide even?

 

[bsconz]

emrr, if you look at the sketch i posted, the output transformer is wired directly to the T600 and so I should think it would be seeing an impedance of roughly 600Ohms (depending on frequency). The 2x270R and 1x65R resistors in U-pad are wired after the T600 output pot and are acting like a simple attenuator pad. Without this U-pad, the output was insanely loud. It was an iterative process getting to this final product. First I completed the unit with just the 1kOhm output pot and no pad. It was off the effing charts loud...completely unusable. Then I popped the Mallory T600 in place of the 1K pot and it was still pretty loud. Then came the output pad.

The unit sounds incredible to me and the other engineers using it on a daily basis...BUT we don't really have a basis for direct comparison. The studio owner commissioned me to build it for him because he had used one for years when he worked for a different studio...so he's the only one with some sort of comparison basis. However, another local studio has a Sta-Level replica too but we haven't gotten around to doing a side by side. I will ask about it again. 

I'm all ears if you think I should rethink my output wiring scenario though. I admittedly am actually a mechanical engineer who knows just barely enough about electronics to keep myself from getting hurt. Sometimes I get lucky with my results though!

 

[jchudyk]

Mine is super-quiet.  Follow the grounds laid out in the guide (which includes grounding the heater CT) and you should be ok.

Does anyone have the grounding guide?  I just bought one assembled but it has some noise.

How did you ground the heater? Just an anditional wire from F- to chassis ground? Thanks!

 

[emrr]

emrr, if you look at the sketch i posted, the output transformer is wired directly to the T600 and so I should think it would be seeing an impedance of roughly 600Ohms (depending on frequency). 

Just now saw this.  A T-pad is not 600 ohms.  It's to be placed in a 600 ohm circuit.  Measure it.  At full volume there is no series resistance, it takes itself out of circuit, so sees your 65R as the load.  As it is turned down series resistance comes into play, giving some isolation from the load, but to do what it's supposed to do that load should be roughly 600R. 

 

[frederickalonso]

For what it's worth, i changed the pcb cables in a DIY unit that had too much noise with coax (TV) cable. The isolation does a good job and gives a lot more defenition in the stereo field. It's just not a really handy job to do.