The calibration is a gimmick. Yes, it only needs some sine voltage to be fed to the input tx secondaries center tap to check for matching of the ef83s. This way one calibrates for maximum cancelation. One could also calibrate for maximum voltage before the first gain stage. I put A LOT of test points all over the board. No need to worry too much about the 12V for calibration.
Rohde und Schwarz Begrenzungsverstärker ABR / U23
- Thread starter Falk
- Start date
Help Support GroupDIY Audio Forum:
Ich found this one:
https://www.don-audio.com/Audio-Toroidal-Transformer-Pri-2x115v-Sec-240V-50V-2-x-12V
This should work.
https://www.don-audio.com/Audio-Toroidal-Transformer-Pri-2x115v-Sec-240V-50V-2-x-12V
This should work.
Hey Folks,
is anyone here quick and good in designing frontpanels?
Maybe someone could design a panel for this particular built we all can use.
Maybe even a group buy of panels is possible.
Me personally I'd like a design which is reminiscent of the Vacouvox design or Thermionic Culture Phoenix and the likes.
is anyone here quick and good in designing frontpanels?
Maybe someone could design a panel for this particular built we all can use.
Maybe even a group buy of panels is possible.
Me personally I'd like a design which is reminiscent of the Vacouvox design or Thermionic Culture Phoenix and the likes.
Would you or somebody else be so kind to explain how to propperly simulate a compressor in Spice?
I've simulated a few vari mu circuits and frequency response, gain and voltages seem to be good but when trying to somehow plot the compression I get weird results. I tried it with stiff supplies e.g. batterie supplies but also with "normal" power supplies. What puzzles me is that the controlls somehow work but the gain is always way to high at the output... So when feeding something like 1Vpeak I get the amplification of the whole amp at the output and the waveform is severely distorted.
What exactly are you plotting? I would assume the transient response, right?
Edit: just found this interesting thread and will try to grasp it all: https://gearspace.com/board/geekzone/1184274-gyraf-ssl-ltspice-simulation.html
I've simulated a few vari mu circuits and frequency response, gain and voltages seem to be good but when trying to somehow plot the compression I get weird results. I tried it with stiff supplies e.g. batterie supplies but also with "normal" power supplies. What puzzles me is that the controlls somehow work but the gain is always way to high at the output... So when feeding something like 1Vpeak I get the amplification of the whole amp at the output and the waveform is severely distorted.
What exactly are you plotting? I would assume the transient response, right?
Edit: just found this interesting thread and will try to grasp it all: https://gearspace.com/board/geekzone/1184274-gyraf-ssl-ltspice-simulation.html
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I don’t know if I missed it in this thread but can somebody please explain what’s exactly going on with the screen grids and cathodes of the varimu tubes? Is that some kind of feedback?
When simulating and comparing to other more "simple" circuits it seems as if the plate and screen voltage pretty much stay constant while in the other circuits they vary quite much with gain reduction.
I just realized that the RCA BA-6A has a quite similar arrangement.
When simulating and comparing to other more "simple" circuits it seems as if the plate and screen voltage pretty much stay constant while in the other circuits they vary quite much with gain reduction.
I just realized that the RCA BA-6A has a quite similar arrangement.
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@echoplex Sorry only read this message now.
A couple of days ago a few sound samples of the dutch units showed up at vintage king so I made samples of this audio too.
Here you can find sound samples of the original recording, the dutch unit, my first unit and my second unit.
Btw: I use the units almost daily and they are fine. BUT I am still not happy enough to release them. This project was delayed again and again but is now top on the list and I will do everything to make it happen this year. Its only details but they must be done before printing boards for the community.
Best,
Falk
A couple of days ago a few sound samples of the dutch units showed up at vintage king so I made samples of this audio too.
Here you can find sound samples of the original recording, the dutch unit, my first unit and my second unit.
Btw: I use the units almost daily and they are fine. BUT I am still not happy enough to release them. This project was delayed again and again but is now top on the list and I will do everything to make it happen this year. Its only details but they must be done before printing boards for the community.
Best,
Falk
scott2000
Well-known member
Levels are a bit different, especially with the LA-23...
I usually get confused as to what I'm listening for in some comparisons if it's not obvious like attack and release... so maybe no big deal...
I usually get confused as to what I'm listening for in some comparisons if it's not obvious like attack and release... so maybe no big deal...
Ordered
Thanks @scott2000 for the feedback and sorry for that. I actually level matched all files but the files from vintage king were stereo and mine mono. So google drive converted them to stereo files which caused levels to shift. I matched all files to -25.7 LUFS and reuploaded them.
Today, a couple of transformers from UTM arrived. They have a much higher inductance than the Edcors, and I want to try them as interstage transformers. The reason for this is that I had to lower the anode resistors of the Vari-Mu stage to preserve bass response. I assume this is causing some low-frequency distortion. While the distortion isn’t always unpleasant, it is higher than stated in the original manual.
Connected to this issue is the metering circuit, which will need some adjustments then.
Additionally, the layout of the output gain requires slight modifications.
Once these three issues are resolved—hopefully by next week—I can order the V3 PCBs, assemble and test them. Since these are minor changes, I don’t expect any issues with the new PCBs. The main task will be updating the Mouser basket.
If everything works as expected with the V3 PCBs, I’ll reach out to all of you to check if you’re still interested.
Best,
Falk
Connected to this issue is the metering circuit, which will need some adjustments then.
Additionally, the layout of the output gain requires slight modifications.
Once these three issues are resolved—hopefully by next week—I can order the V3 PCBs, assemble and test them. Since these are minor changes, I don’t expect any issues with the new PCBs. The main task will be updating the Mouser basket.
If everything works as expected with the V3 PCBs, I’ll reach out to all of you to check if you’re still interested.
Best,
Falk
