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Home Theater Guide webboard => มุม Thai DIY Audio => ข้อความที่เริ่มโดย: Frank R. ที่ 20 พฤษภาคม, 2023, 12:52:08 pm
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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.
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Looking forward to seeing your work!
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Picture:
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Close up:
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Phenolic spider:
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The first step was to remove the OPTs and add solid terminals.
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Here the terminals, I build them from 2 mm aluminum with spacers.
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Here the Speakers with the terminals.
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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.
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Here Sachsenwerk on center panel.
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Here the finished open baffle.
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Wow! Very impressive! How do you like the sound?
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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
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Here both supplies finished.
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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.
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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.
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Very nice! d_d :drunk c) c) :clap
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Thank you!
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Cool. Thanks for sharing this project. :clap :clap
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.
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:headphone
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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.
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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.
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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.
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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.
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Here a close up of the Horn.
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Here the full set up.
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The horn is to high in the moment.
Here I made a computer picture, how I like to place the horn.
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Very nice! like
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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.
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Beautiful! d_d
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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.
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Here some more pictures.
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How will you paint the baffle - hand paint or spray? Will it be black or some other colors? c)
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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.
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Nice! Looking forward to seeing your finished masterpiece! d_d
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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 like to hear this speakers, let me know.
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I sure do like to hear the speakers. c) :clap like
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Let me know when you have time!
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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 like 3,9 to 4,7 uF.
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I sure do like to hear the speakers. c) :clap like
Please count on me too.