Gates Sta Level !! protoboards preorder !!

[kubi]

The needed bias voltage depends on the transformers. After having settled down on one set of transformers, you can actually set a fixed bias voltage and have one thing less to care about.

My recommendation is as follows:
Build a prototype with the set of transformers you have chosen for the final version of the limiter and a trimmer for the bias voltage after the regulator.
Adjust the desired threshold with the trimmer (probably +4dBu in your case), measure the trimmer and replace it with two resistors representing the same values. Release the project with the two resistors, not the trimmer.
Reason: Many of the builders that hang around at GroupDIY will be not be able to properly determine the right voltage for the threshold themselves. That will significantly increase your support overhead. Expect a lot of dump questions at GroupDIY.

For two or more channels one regulator is more than sufficient. Just make sure to have dedicated voltage divider resistors (the ones to replace the trimmer) for each channel. Using the same trimmer or the same resistors for more than one channel would cause a bleeding of gain reduction from one channel to another.
(Asymmetrical signals will load the capacitors attached to the "bias resistors" and slightly shift the threshold; ok on one channel, bad sucks if multiple channels influence each other.)

[zayance]

Hi Kubi,

Ok i hear you.
Will draw a clean Schematic for having something to show, and will get back here.

Thanks for your help and suggestions.


T.

[bernbrue]

A few questions before Tony starts to do the layout.
- is there maybe an easier solution for the voltage divider/rectifier part of the circuit? Maybe a simple 100V Zener diode?
- trimpots: would it be comfortable to have trimpots between R8/R9, R15/R16?
- should we make the input pad switchable as long as we do not know which input transformer we want to use? We don´t want to put the resistor values on the silkscreen because the values need to be adapted to the input transformer that will be used.
- sidechain: are there any disadvantages to put the resistor network for attack/release on an extra pcb soldered directly to the lorlin switch?
- are there any other changes that would be nice to have?

regards
Bernd

[bernbrue]

Here is a modified schematic with a few ideas

http://twin-x.com/groupdiy/albums/userp ... link~0.JPG

More questions:
1) Is the stereo link option correct the way I did it?
2) Are there any disadvantages when we put the whole sidechain (except the 6AL6) on a frontpanel pcb together with Lorlins for Mode and Recovery Time?
3) trimpots: would it be comfortable to have trimpots between R8/R9, R15/R16?
4) input pad switchable?
5) other changes?
......

Bernd

[kubi]

Two things I noticed at the first glance quickly before "Feierabend" in a few minutes...

R35b as low as 4700Ohm will increase distortion when the diodes conduct, because the 6V6s (which are quite powerful but not almighty) will be ac shorted with C10 which is loaded with a low voltage before the compression begins. Not too bad with 56kOhm in the way, but 4,7k will cause distortion during the attack phase. Unless you want the transients to be quashed on purpose...

Another thing: If the 20dB-Pad is really to be a 20dB-Pad, the primary of the input transformer must be Z=600Ohm. Simple calculation. That leads to two facts: a) the transformer is wound 1:10..12 or higher to reflect the 100kOhm of the secondary as 600Ohm on the primary. And b) when the 20dB-Pad is bypassed like drawn by you, the input's Z becomes 300Ohm, which is the transformer's primary's Z (=600Ohm) and the three resistors (240Ohm+240Ohm+120Ohm=600Ohm) in parallel. Just redesign the switch and you're fine.

And now: 7PM, which means "Feierabend" for today!!!

[bernbrue]

Thanks for your reply, Darius. For the 4K7 I just did what RETRO supposed to have done with their STA Level:

Ok, I started to modify the schematic and included the variable recovery time mod as done by DRIP and others. I found an interesting statement, supposed to be made by Phil from RETRO about how they implemented the triple mode:

The Retro Sta-Level has all the same circuitry and component values as an original Gates. The slowest setting of recovery is the original 4.7 Meg. The five faster settings are derived from a ladder of 330K resistors that are added in parallel with the 4.7 Meg. The added resistance values are 1.98 Meg, 1.65 Meg, 1.32 Meg, 990K, 660K (fastest CW).

In single mode, the release C is 1 uF + 0.5 uF or 1.5 uF. The double mode hangs the 1 uF capacitor from a 10 Meg resistor. This provides an intelligent dual time constant where the .5 uF gives the fast attack/fast recovery and the 1 uF sets a variable gain-riding plateau. The triple mode uses double recovery and decreases the 56K attack R to 4.7K.

Measured recovery time in seconds from 15 dB gain reduction back to 0 in single mode: 20 (CCW), 9, 7, 6, 5, 4(CW). In double and triple mode, recovery times are 70% faster, but exhibit a non-linear rate, with recovery slowing until fully recovered. This is mostly applicable to the full CCW setting.

In addition to our model, Retro has modded over a hundred original Sta-Levels this way.

So the recovery mod was done slightly different as DRIP did but basicly with the same result. I posted the modified schematic in the first thread.
Bernd

Well, maybe he just ment 47K. Anyway, I noted "tbd" on the schematic. Changed the bypass switch as well.
Enjoy your well deserved "Feierabend". I´m on holiday in France right now.
Bernd

[kubi]

I'm not saying it won't work with 4,7kohm. It will just increase distortion. Be aware of that. On the other hand, maybe you want to have your transients flattened on purpose. A fast limiter always distorts more than a slow one.

[bernbrue]

Hi,

http://twin-x.com/groupdiy/albums/userp ... link~0.JPG

schematic updated with further details for tubes being used and capacitor values (7abc). Can anyone confirm?
Bernd

[creativeblue]

Hi, i would like to join the party with the sta level project. This compressor was always one of my favs that I wanted to build. I builded a VK-1 (with my own mods), a pm670, La2a, 1176, SSLEQ, pultec, some preamps etc. I noticed that most people who are offering kits, boms, mods for these projects either dont know a lot about electronics or just dont mind about things like "noisefloor" or "beeing as close as possible to the original". For example, i dont understand how you could placa a big Power transformer on the PSU --> drip? It will create a lot of hum. For this project, I prefer building hand-wired, (eventhough this will be one of my first "handwired" project - all other stuff I did on PCB boards which I either made by myself or ordered from the forums). I probably have someone who can build the case, that will need a middle layer to place the tubes. I dont want the tubes "outside" on the backpanel, I would want to build a stereo unit, putting a middle aluminium layer to place the tubes, and wire direct from there. I think 3 HE would be fine. As for the powersupply i dont want to use tubes. Just diodes and zeners. And parallel wiring for left and right. I would want to try the mods on the release-time too. As for audio-transformers (in and out) it's necessarry to do a research which transformers can do the job. Probably the ones that Retro used? As for power transformer, definitelly will use a ringcore (Ringkern) trafo, because all others will produce hum (even if this hum will be only at -75 dB) but it will be definitelly there. Did anyone mearure the noise in the RETRO? They also didnt use a ringcore? I also want Tube shield covers for the audio tubes. This also makes the unit more "noise-free". I'm courious and excited about this project, and wanted this to be my "best build"

[bernbrue]

Hi,
welcome on board. This project is going to be on pcb with separate solid state psu for B+, bias voltage, optional AC heater and extra rail for relays, leds etc. So all tube will be mounted with tube sockets on pcb. We haven´t thought about the transformers for input and power yet. We are going to try the hammond output transformer, Kubi mentioned in one of the threads before. There is also an option for the Edcor output transformer. The recovery mod and triple mode (shorter attack) will be included as shown in the schematic. Don´t forget to enter your location in your profile.
Bernd

[DerEber]

@creativeblue:
Well, I am still thinking about making one point to point.
But too many things on my bench at the moment.
Maybe I´ll join in for transformers or at least this discussions are very interesting.
I did Vary-mu PTP twice, so if you are having a question feel free to ask.

I did SS Power supply. You can easyly calculate by yourselfe..... And it´s fun
I had the tubes outside..... It worked fine. It´s no Mic pre

best,
Stephan

[creativeblue]

Thanks! If the PCB isn't too large to fit for a stereo unit, and if it doesnt contain the PSU transformer, i'd probably would do it too with PCB, but actually I wanted to try something P2P!

[creativeblue]

About the Edcor transformers I had some bad experience. In my PM670 the output edcor just distorted the signal. I replaced it with a vintage Marinair and the distortion was gone and it sounded much better.

[bernbrue]

Hi,
all transformers will be mounted externally, i.e not on the pcb. So it´s up to you which transformer you want to use. The pcbs won´t be too large so that a stereo version basicly will be possible, provided that your power transformer is beefy enough. By the way, you noticed that the 6V6 will be replaced by EL90 tubes and the adapter for the 6386 will be included on the main pcb. So you can choose between a single 6386 or two 6BJ6 (E99F)/6BA6 (EF93) et al.
There is a stripboard layout somewhere for people who want to go P2P.
Bernd

[bernbrue]

Hi,
I´ve got a few questions (Volker, Darius ?):
AC heater: would it make sense to have the 100 Ohm to ground resistors, as Volker did in his Dual LA2a? What is the advantage?
Stereo Link: Is the stereo link correct as shown in the schematic?
regards
Bernd