หัวข้อ: Sachsenwerk GR 3777 Field Coil Speaker

[Mr. Tube]

I sure do to hear the speakers.   

Please count on me too.

[Frank R.]

Here a small update on my network for the tweeter.


It is a simple 6 dB first order network, contain only a capacitor.


I have use alligator clips for connecting the capacitor, so it is easy to change the value of the cap.


So you can choose how much treble you need.


For me, I 3,9 to 4,7 uF.

[Frank R.]

Let me know when you have time!

[Diy Project Seeker ©]

I sure do to hear the speakers.   

[Frank R.]

It is not a masterpiece, but for this old speaker it sounds fantastic!


The problem with this old speakers is deep bass.


This speakers were mostly designed for voices, as use in radios.


But if someone to hear this speakers, let me know.

[Diy Project Seeker ©]

Nice!  Looking forward to seeing your finished masterpiece! 

[Frank R.]

I think, I will use a roller to paint the baffle.
A roller is better than spray paint, but more work!
For the color I am not sure.
But black, is to dark for me.
I am thinking about white, light grey or ivory color.
But not sure in the moment.

[Diy Project Seeker ©]

How will you paint the baffle - hand paint or spray?  Will it be black or some other colors?   

[Frank R.]

Here some more pictures.

[Frank R.]

Now, I have cut the open baffle to mount the HM 10 tweeters.
Actual, it looks not bad, too.
Normally, I was looking for field coil tweeters, but they were much too expensive!
I think, the Isophon are a very good choice.
As I said before, the sound is amazing, if you think how old the Sachsenwerk speaker is!
Very open, deep and detailed sound stage.
Only the bass is not that deep, but nearly all old speakers face this problem.
Now, I am thinking, to paint the baffle in a new color.

[Diy Project Seeker ©]

Beautiful!   

[Frank R.]

Today, I tested my Sachsenwerk GR 3777 Speakers with Isophon HM 10 tweeters.
This tweeters fit the Sachsenwerk very well.
With this combination I am very happy now.
The sound stage is very pleasant and very smooth.
Even the bass is acceptable for a speaker of this age.

[Diy Project Seeker ©]

Very nice!

[Frank R.]

The horn is to high in the moment.
Here I made a computer picture, how I to place the horn.

[Frank R.]

Here the full set up.

[Frank R.]

Here a close up of the Horn.

[Frank R.]

This weekend, I worked on the tweeter for the Sachsenwerk GR3777.
First, I tried Saba Green Cone Tweeter, but not loud enough!
I think, even the Isophon HM 10 will not loud enough!
So, I used my Flo Horn T1040 with BMS 4524 compression driver!
This driver deliver 113 dB with 1 Watts!
For test, I mount the horn on the top of the baffle.
Now, the speaker sounds so nice with Jazz Music.

[Mr. Tube]

Hi Mr. Tube,

What is the advantage of using a high voltage for making the fieldcoil?  Frank is using around 90-100V.

If I remember correctly, our systems use only 12V.

Sawasdee krab,
Mostly, the vintage FC Spk use high voltage / low current for field coil. The main reason is the power supply in those days used tube rectifier, and it can't supply high current. So, high DCR (High Volt / Low Amp) of FC is more suitable. They can even put the FC as filter choke for amplifier circuit and get advantage of hum cancellation from the FC to voice coil.


By the way, the low DCR FC have advantage over high DCR in 2 things.
1. Lower loss, when the signal coupling from VC to FC.
2. Easy to control the magnetic strengh by adjust the FC regulator.

[Diy Project Seeker ©]

Hi Mr. Tube,


What is the advantage of using a high voltage for making the fieldcoil?  Frank is using around 90-100V.


If I remember correctly, our systems use only 12V.

[Frank R.]

Yes, I have 2 OPTs from those speakers.


I will keep them, no rewinding!


They are 7 K primary to 3 Ohm secondary.


I think the OPT was made for AL1 Tube.

[ออดิโอแมน]

 

[Mr. Tube]

Cool. Thanks for sharing this project. 


By the way, Do you have plan with the matching transformers those had been removed from speaker? The core is very good. You can rewinding it to small OPT or interstage trans.

[Frank R.]

Thank you!

[Diy Project Seeker ©]

Very nice!

[Frank R.]

Here a closer look of my 6E5P-EV SE Stereo Amplifier.


Using only 1 tube per channel!


I am using James OPTs, and Saengthong toridal power transformers.


This amp sounds very open and natural.


But you need high efficient speakers.

[Frank R.]

Here the full set up of the open baffles with the Sachsenwerk speakers.


This speakers are very sensitive, so my 6E5P Stereo SE Amp with only 1,2 Watts RMS is nearly too much for the speakers.


If you listen to acoustic music and voices, the quality is good, even the bass is there.


Midrange is very nice.


On the other hand the trebble are not that great.


I guess, this speaker goes only to 10 Khz.


But I think, I will not add an tweeter, as there are no suitable speakers from this time periode.


There is a 13 cm tweeter from Sachsenwerk, but it is with Alnico magnet.

[Frank R.]

Here both supplies finished.

[Frank R.]

Here my Field Coil Power Supplies for the speakers.


I modified the supplies, I added a voltmeter and Speakon plugs.


The Speakon plugs are much safer than banana plugs, especially at higher voltages

[Diy Project Seeker ©]

Wow!  Very impressive!  How do you the sound?

[Frank R.]

Here the finished open baffle.

[Frank R.]

 
Here Sachsenwerk on center panel.

[Frank R.]

My plan is, to build this speakers on an open baffle.


I will use 15 mm plywood for the baffles.


To connect the baffles I use piano hinges.


The piano hinges comes rolled up, each hinge is 3,50 meters long.

[Frank R.]

Here the Speakers with the terminals.

[Frank R.]

Here the terminals, I build them from 2 mm aluminum with spacers.

[Frank R.]

 
The first step was to remove the OPTs and add solid terminals.

[Frank R.]

Phenolic spider:

[Frank R.]

Close up:

[Frank R.]

 Picture:

[Diy Project Seeker ©]

Looking forward to seeing your work!

[Frank R.]

Long time ago, I think in 2009, I bought a pair Sachsenwerk GR 3777 Field Coil Speakers.


The design of this speakers dates back to 1935.


In East Germany this speaker was manufactured until 1955.



This speakers have phenolic spiders.


The field coil voltage is about 90 - 100 Volt DC at arround 65mA.


So, now in 2023 I will start this project.