Siemens Mic-Preamp

[sahib]

I am in Istanbul at the moment. A friend of mine gave me this what appears to be a two channel stereo microphone preamplifier made by Siemens. There is no production ID label on it, so all of my google searches did not return any info. Would anybody know anything about this?

It has two transformer coupled microphone input channels. Gain control for both channel is through 10 position stepped switches. Master volume is a single potentiometer. Bass and treble controls uses dual concentric potentiometers. I have not yet worked out what the push button switches do other than the one on the right which is for checking the battery level.

It is powered by both internal battery and external 9V DC power supply. It is a solid state equipment and has very high built quality. I am taking it with me (to Glasgow) to first work out how it works and then modify the inputs/outputs with XLRs for pro-use.

 

[Walrus]

AVC, Automatic Volume Control?
The left input on the back appears to be a Gramophone or Tape input, maybe one of the switches will select that.

 

[TwentyTrees]

What an interesting bit of kit! I look forward to hearing how you get on with it.

Some creative googling has led to a Reverb listing and an eBay listing that both refer to this (or an identical unit with an orange case) as a "Siemens Einzeltrainer H 0901", though as Google Translate renders that as an "Individual trainer" I don't know how helpful that is! The eBay listing still has the ID label in the later photos.

The little pictographs that Siemens gear of this era uses are both clear and not entirely helpful. Could that left hand socket be the output for a tape machine or power amp?

On the switches, if I was speculating I might guess that the leftmost would be power, and the AVC might be some kind of limiter (similar to the Shure SE-30?) - but that really is guesswork. Maybe the circles could be a pad? Probably not going to know for certain until you get the chance to test it fully.

Please keep us posted!

 

[sahib]

AVC, Automatic Volume Control?
The left input on the back appears to be a Gramophone or Tape input, maybe one of the switches will select that.

That's what I thought about the AVC but I am not sure about the gramophone or tape input. The unit has headphone output. If it is only a headphone amp having microphone inputs would not make sense. Perhaps the headphone output doubles as line output. But I'll work it out once I start the investigation.

Some creative googling has led to a Reverb listing and an eBay listing that both refer to this (or an identical unit with an orange case) as a "Siemens Einzeltrainer H 0901", though as Google Translate renders that as an "Individual trainer" I don't know how helpful that is! The eBay listing still has the ID label in the later photos.

Thank you for these. It is sahame they have no info either.

Please keep us posted!

Absolutely. Stay tuned.

 

[ruffrecords]

The unit is vaguely reminiscent of the old 'language laboratory' set up where you listened to a tape of a foreign language and then spoke ( and recorded) your rendering of it.

Cheers

Ian

 

[rock soderstrom]

This unit seems to be a dual microphone preamp (into a headphone amp) with an additional input for a external source (tape machine/record player) that can be mixed in. No outputs are visible except for the headphone output, which to me suggests a speech or other language learning environment.

This is also indicated by the name Siemens Einzeltrainer H 0901...I would translate it with personal trainer.

Edit: I agree with Ian

 

[sahib]

Ian / Rock, thank you both. Never thought about it. Let's see what I can do with it. Stay tuned.

 

[MidnightArrakis]

I am in Istanbul at the moment. A friend of mine gave me this what appears to be a two channel stereo microphone preamplifier made by Siemens. There is no production ID label on it, so all of my google searches did not return any info. Would anybody know anything about this?

It has two transformer coupled microphone input channels. Gain control for both channel is through 10 position stepped switches. Master volume is a single potentiometer. Bass and treble controls uses dual concentric potentiometers. I have not yet worked out what the push button switches do other than the one on the right which is for checking the battery level.

It is powered by both internal battery and external 9V DC power supply. It is a solid state equipment and has very high built quality. I am taking it with me (to Glasgow) to first work out how it works and then modify the inputs/outputs with XLRs for pro-use.

View attachment 115047
View attachment 115048

However the circuit of this device has been assembled (i.e., either a PCB or Point-To-Point wiring), I am fairly certain that the circuitry for this is not too complicated. Therefore, it may be easy enough for you to "Reverse-Engineer" its circuitry and come up with an accurate schematic. Once you are able to accomplish that, then you could post your schematic on this thread and have everybody --- like Ian -- analyze and review your circuit. Then, more than likely, someone could provide you with a good conclusion of what this device does/is.

Sound like a plan?

/

 

[sahib]

Opened the unit. Here is inside.


Removing the chassis was a bit fiddly. Anyhow, after some inspection it did not seem to be open to modification. So, I have decided to dismantle everything.

First thing was the headphone jack socket. A very unusual thing. Definitely a custom component as I have never seen anything like this before.


Below are the headphone amp bards.



Below are the stepped, 10 position attenuators. These are really high quality components. However, they were wired at the output of the headphone amps. Appropriately old style.



These are the preamps (larger boards) and ( I think) the tone control boards.



This is the odd inductor board. It was not wired on the input of the preamp boards, so I am assuming they are part of the tone control circuitry.

This is the selector switch board.



This is the main/mother board.



Now here are the gems, the input transformers. I have not checked the ratio yet but these seem very high quality. A rocket would not get through those shields.


When I have a bit of time I'll do the schematic for the preamp module(s) and test to see if they are worth doing something with.

 

[rock soderstrom]

Opened the unit. Here is inside.

Thank you for the beautiful photos.
Definitely professional device built with high quality components. That was not cheap in its days. (early 70ies, see date stamps on the golden caps)

 

[sahib]

Thank you for the beautiful photos.
Definitely professional device built with high quality components. That was not cheap in its days. (early 70ies, see date stamps on the golden caps)

Thank you too.

This is what I love about this forum. Eye for the detail (re-the cap date stamps).

No doubt about the build quality. If only they would manufacture even the selector switches like that.

 

[cyrano]

The "Siemens Einzeltrainer H 0901" is a medical device, a hearing aid. It was used to train people with hearing or speech problems, especially children, so the headphone output is higher than usual.

I found this in an old pdf in Dutch, about the experiences of parents with kids with a hearing problem. That also mentioned it didn't use a pair of headphones, but a single earpiece.

Source: Orgaan van de vereniging voor doofstommen onderwijs, juni 1966, jubileumnummer. FENAC - Federatie van Nederlandse Audiologische Centra.

PS I'm not providing a link, as the server it's on might crumble under the load. It's also not linked from their website.

If anyone wants to read it, I'll upload it here.

 

[MidnightArrakis]

I will take a wild guess and guess that the "headphone jack" is a combined -- microphone/headphone -- jack. The top 3 connections "might" be for a balanced microphone (TRS) and the bottom two connections being for the earpiece. Again.....just a wild guess.

Should you have any desire to have new PCB's for this device, as the current ones look rather gunky, PM me about having these old PCB's "Reverse-Engineered", so you can have new PCB's fabricated. I have done this for a 1974 API mixing console and for U.S. fighter jets. Glad to help out if I can.

/