Pad before microphone input transformer

[iampoor1]

Thanks guys, I think this has cleared up all of my questions. I deeply appreciate all of you!

 

[isophase]

Thanks guys, I think this has cleared up all of my questions. I deeply appreciate all of you!

+1

 

[nielsk]

It is likely if you consult the Gates literature for the module it will have detailed instructions for input attenuation pad implementation

 

[abbey road d enfer]

It is likely if you consult the Gates literature for the module it will have detailed instructions for input attenuation pad implementation

The document is in reply #8 above; no mention is made of how a pad should be designed. The installer is supposed to know.

 

[nielsk]

It is sure to be found in Gates literature somewhere, maybe for the console it was a part of. Most companies of the era (Collins, RCA and the like) covered this specific to their units in the manual.
I think there is merit to considering the manufacturers approach.

 

[MidnightArrakis]

Hi Nathan, not sure if I sent you this doc with the preamps. Sorry if I forgot to. Anyhow, the pre has a max input level of -40 and max out of +5. Designed to go to a 600 ohm Daven attenuator and then to a program amp. A pad on the input and a good output stage would make it much more useful.

GREETINGS!!! I realize that I am over 3-years late coming to this particular party, but circumstances on my end only have taken place within the last couple of days that would eventually lead me here anyway. So, I don't know if my contribution will make any difference and/or even matter!!! But, anyway.....

About 30-minutes before I discovered this thread and your response with the GATES M6034 Preamp circuit attached, through my own searching efforts, I came across another website that had the "GATES - M6034 Mic Pre-Amplifier Manual" and I downloaded it. As I compared the schematic I had downloaded and the schematic that you have provided, I noticed some disparaging differences between the 2 sets of the same schematic from the same company. Maybe the differences are due to improvements that had taken place over time, since the schematic I had downloaded was created in 1962.

In my GATES M6034 schematic, Q1 is a 2N422 and Q2 - Q4 are all 2N1414's. In your schematic, Q1 - Q3 are all 2N5087's and Q4 is an A30319 "Select". But, on Page-1 under the heading of "Theory Of Operation", it states there that Q1 is a 2N1307 low-noise transistor. I am only guessing that this inclusion has to be an error of some type that simply wasn't caught, because in the Parts List and everywhere else, Q1 is stated to be a 2N5087 type. What do you know about this? I will attach my version of the GATES M6034 schematic for your comparison and review. In addition, since the transistors shown in my version of this schematic are either hard-to-find or even obsolete, NTE Components shows that their "NTE102" replacement transistor is good for - both - types of transistors shown. So, that tells me (probably incorrectly) that in your version of this schematic, the 2N5087 could be used as Q1 thru Q4 and be OK.

Also, do you know what the secondary value of T1 might be? 600-Ohms??? I get that the primary is 150/250-Ohms, but I am not sure about the secondary. Also, would you happen to know who makes the AI-34678 T1 transformer? Is there a JENSEN Transformer equivalent? I would think that there would be.

I also found it quite surprising when I came across this "NOTE" within the documentation: "REMEMBER - In transistor circuitry B+ is ground, therefore, capacitors have the positive side connected to ground". Who in the heck dreamt that up??? Does everything really need to be connected to a power-supply "backwards" in order to operate? (i.e. +30VDC from the power-supply = M6034 GND and "GND" from the power-supply = "M6034 -30VDC"?). Confusing!!!

Anyway.....I hope that possibly you might find my version of the GATES M6034 Preamp to be interesting and useful and I am looking forward to receiving your comments and input. THANKS!!!

JBW

/

 

[abbey road d enfer]

I also found it quite surprising when I came across this "NOTE" within the documentation: "REMEMBER - In transistor circuitry B+ is ground, therefore, capacitors have the positive side connected to ground". Who in the heck dreamt that up??? Does everything really need to be connected to a power-supply "backwards" in order to operate? (i.e. +30VDC from the power-supply = M6034 GND and "GND" from the power-supply = "M6034 -30VDC"?). Confusing!!!

This clearly indicates this manual was written at a time where silicon transistors were not yet there, but rather the older germanium types, that were almost exclusively PNP types at the beginning.
Regarding the disparity in transistor references, it is obvious that this piece of gear started as germanium-based and evolved in a silicium-based version.
In order to make them compatible, Gates continued using PNP silicon transistors.
Indeed, a modern silicon-based circuit would probably use the more common negative ground arrangement that NPN transistors encourage.
Actually any circuit that has been designed with negative ground can easily be adapted to positive ground, by mirror effect.
In a well-designed product, transistors should be easily swappable between different but similar types.