Rohde und Schwarz Begrenzungsverstärker ABR / U23

[Falk]

@Volker

great idea! A 470uF cap reduced 100Hz noise by 6dB. Gonna expand the psu by two of these and hope for the fuse to not blow

 

[gyraf]

Good one Volker!

Falk:

Perhaps try with C/R/C - two capacitors with a resistor in between? resistor value depending on how much voltage you have to spare - I often use 1K here, which looses me 1V per mA consumption on HT line

/Jakob E.

 

[Falk]

Hi Jacob,

I decided to use a π-Filter (CLC) with two 470uF caps and a 7H choke. Before and after the caps will be 390 ohms resistors.
For now its the easiest way to treat this hum issue. Once it works I will redesign the psu pcb again.
Thanks for your help.

Best regards,
Falk

 

[Erik2345]

Regarding the Braunbuch U23 schematic Jakob posted on page 1, the resistors are drawn with markings.
Do these markings reflect the wattage of the resistors? Or the tolerance?
Can anyone explain? Markings can be longitudinal, across, combined.

Cheers, Erik

 

[SKJGProject]

Subscribed

 

[mjrippe]

Regarding the Braunbuch U23 schematic Jakob posted on page 1, the resistors are drawn with markings.
Do these markings reflect the wattage of the resistors? Or the tolerance?
Can anyone explain? Markings can be longitudinal, across, combined.

Cheers, Erik

They indicate wattage.  There are a few different styles of markings that were used.  Neumann schematics usually had a legend explaining them.

 

[Erik2345]

Thanks mjrippe!

 

[gyraf]

Yes.

their insistent  emphasis on marketing and fluffy words scare me too

Is this such a bad thing to say?

I just got off the phone from a very unpleasant conversation with a guy claiming to be vacuvox

He basically told me that he thinks I am attacking and trying to damage his product. Mentioned several times that he is not the kind of person that talks badly about other companies. And btw that I use cheap and bad switches in my products (well, but I only ever had to replace power switches so far) where he uses expensive ones from *name* company. and so on.

I was pretty certain that I mainly commented on the marketing BS surroundings, not the product itself. Returning here to check, I don't see a big problem in what I wrote?.

Conversation got gradually more and more unpleasant and threatening, the guy working himself up to yelling at me in the phone - and I eventually had to hang up on him.

If I was a psychologist I'd say that with a defense like that, you have to have very little confidence in your own product. Makes me kinda hope he wasn't who he claimed to be.

Always freaks me out dealing with such dark sides of business - so I'm here to ask for your opinion and timestamp the incidence.

And should I now be scared about someone starting to talk badly about my products? I'm not big on marketing, my customer base builds very slowly from hands-on - could that be impacted?

/Jakob E.

 

[jarvis]

Is this such a bad thing to say?

Hey Jakob,
I have no idea, where that guy is coming from. What you said is not even remotely a comment on his products, merely the way he markets them. Sorry, you had to have such an unpleasant conversation.

If I was a psychologist I'd say that with a defense like that, you have to have very little confidence in your own product. Makes me kinda hope he wasn't who he claimed to be.

Haha, yes, if only you had a degree in psychology and were teaching at a renowned university...  ;D

And should I now be scared about someone starting to talk badly about my products? I'm not big on marketing, my customer base builds very slowly from hands-on - could that be impacted?

I'm not trying to be rude here but no one knows the guy and I doubt his opinion would influence anyone interested in buying your products. I mean, I can't image that anyone has had a bad encounter with you or your products so I wouldn't worry for a second about some random guy all of a sudden tarnishing the great reputation, that you've been building up over the years with great products and support.

Best
Jannis

 

[Heikki]

Is this such a bad thing to say?

Definitely not a bad thing to say. The guy is probably just frustrated. There's COVID going on and maybe his products aren't selling well and he just needed someone to vent his frustration to.

I used to work for a boutique guitar amp company and there were at least two times when somebody started going crazy and badmouthing the company on internet forums. I don't remember if these were real dissatisfied customers or just some crazy trolls but it probably did hurt the sales. Then there was one time that some guitar amp service shop did a complaint to the Finnish Safety and Chemicals Agency, so they came around checking that we had the S3 installation repair qualification that is needed to repair electronics.

People can make your life difficult if you're a small company in audio business, but in your case I wouldn't worry too much. Like jarvis said, you have excellent reputation and great products and it would be very difficult to tarnish your reputation.

 

[echoplex]

Hey Jakob,

I don't want to hijack this thread and go too far off-topic but the fact that someone from Vacouvox called you and yelled at you, just once again confirms my impression: this company is unattractive!

I don't like their marketing either .. and I think you said nothing wrong. A company like them should be able to take this kind of critics anyways..

Maybe at this stage they are shitting their pants because someone from the DIY community is working on proper U23 clone boards and shows this thing is not about magic but about decent electronic engineering.
For me personally Falk's project is the most interesting project on GDIY this year and I'm super excited to see this proceeding.
I guess and hope soon there will be no reason anymore to dump 15k€ on a stereo pair of Vacuvox U23.
Deal with that, Vacuvox!

 

[jensenmann]

First of all, Falk, that´s an impressive work!!! Congrats and big respect.

The 470uF PSU cap is a hefty load on the bridge rectifier as the charging current will be very high since it has to pass the rectifier in a very short time. That´s something diodes don´t like in the long run. It´d be more economical to lower the capacity to a point where you still have around the same amount of hum reduction than before but life is going to be easier on the rectifier. The other option of course is to use a high current HT bridge rectifier.

It needs to be highlighted again what Jakob said about the orientation of transformers. You can get rid of crosstalk and hum by turning trannies in all 3 dimensions. The 50Hz peak in your FFT will benefit from that. Distance and shielding is another option and probably the best of all is to use an external PSU. If you don´t want that for some reason then get a well shielded toroidal mains trannsformer for internal use. I´m using Müller-Rondo for my tube projects as well as for gear modifications. They will wind whatever you want for you, including static and magnetic shield, even with shielded wire.

@Jakob
I haven´t found any offence against vacuvox in your posts. Let´s forget about that crap and make Falk´s U23 better than every other U23 on earth.  8)

 

[gyraf]

Thanks guys. I'll worry less about the episode. I wonder if Falk gets a dose of it as well for his interest?

Jens - very good point on the peak-charge-current and how to limit it. I had a problem once with too big electrolytics for heaters, injecting rectifier switching currents everywhere. Can often be helped with a small-ish power resistor in series with transformer secondary..

/Jakob E.

 

[Falk]

Good evening, gents!

@Jakob - My phone rang too. But that was at least two weeks ago. I understand his worry about a DIY approach on the U23 but he has a product on the market which is high end and aims on a totally different group of users than my approach could ever do. I am sorry for the discomfort that arises from your great and highly appreciated support here. I did not perceive your comment as offensive. A technical product needs marketing that evokes emotions to sell. Every good marketing campaign needs exaggeration to be vivid. Thats normal but also makes (DIY-) engineers and technicians as we are suspicious. One needs to deal with this.

I do not plan to build a historically correct replica of the Rohde und Schwarz U23. Neither do I want to build something like the dutch high end recreation. For me its just a piece of gear that shall facilitate my work. Furthermore its a feasibility study and a personal challenge. I rather have a bread and butter approach than needing a silver spoon to eat.

I really hope emotions calm down again.

@jensenmann Thank you for the nice words on my build. I really appreciate it. I still use my Jensamps pretty often and love them every single time. I will consider hi current diodes for the next revision of the power supply. I am using 1N4007 now. I will see how much I can lower the capacity to still have enough hum suppression.

@echoplex Thanks for your interest. I ll keep documenting every step I take.


Shall I maybe close this thread and give it a name that is not directly connected to the U23? Would that prevent any more discomfort?

Back on the thing:
The π-Filter boards arrived and I will implement them tomorrow and see if there is the desired benefit on the 100Hz hum.

Furthermore I optimized some resistor values to have a better reading for the meter when in calibration mode. Also the threshold has a wider range now and the ratio works like a charm. I am constantly updating the boards for the second and hopefully final revision. Finally I found out a sweet solution for the heater wiring. I do not think this project will be finalized before mid / end of next year. I really want to build this machine to be secure and down to LVD standard.

Thanks for hanging in here. Your support and interest is priceless.
Falk

 

[echoplex]

Shall I maybe close this thread and give it a name that is not directly connected to the U23? Would that prevent any more discomfort?

Absolutely not! .. I think it's a cheek that Vacuvox called you guys at all!
Rhode&Schwarz are still operating.. so Vacuvox clones a unit by a company who's still in business and then freak out when some else is cloning it? Crazy !

 

[JMan]

...Vacuvox clones a unit by a company who's still in business and then freak out when some else is cloning it? Crazy !

Right???  I guess they were upset at what they perceived as a slight toward them directly.  Still, if they had any worry that Gyraf’s comment was going to ding their reputation or sales among the people here, being aggressive and making a**es out of themselves has surely put the final nail in that coffin.

Falk, I agree with the earlier statement that this is one of the most exciting threads of the year (for the build, not the drama).  Keep going!  I just wish I had more to contribute.

 

[Falk]

Hey everybody. I hope you are having a nice moody sunday as it is here in Berlin.

News from the workbench: The pi-filter does its job. 100Hz hum disappeared somewhere in the noisefloor.
The machine has a SNR of 92dB at unity gain now and I will stop to further improve the noise issue for now.

The dB scale in the plot attached equals a dB(u) reading.

@jensenmann: I put a 1k resistor between the diode bridge and the big capacitors. The voltage rises quite slowly now and the simulation looks well too. So now the time has to show how the diodes pair up with the caps.

Gotta work the next days so I wont be able to make progress. I ll kepp you posted.
Falk

 

[volker]

I would make the first capacitor 100-200µF, and then increase the subsequent ones after the choke and the following resistor. There you already have enough isolation from the rectifier, and you don't need to introduce more voltage drop.

 

[Falk]

Hi Volker,

I will try this as soon as I order new parts. I dont have any caps at hand to do so. Thank you for your advice. I am not too concerned because even the 100mA fuse (right before the diode bridge ) in the Vb circuit works well when powering up. I designed the pi Filter to have a cutoff frequency below 3 Hz. When I lower the capacitance the frequency will rise. I will keep an eye on the PSU but for now its works.

Thank you.
Falk

 

[gyraf]

Supply ok, now the interesting part starts - figuring out what parameters to put under user control, user interface, and usable control ranges.

I do not plan to build a historically correct replica of the Rohde und Schwarz U23.

;D nor did they actually, if you read through their marketing blurps: It's claimed to be "built upon" the U23, then lists a loong list of "upgrades", "modifications" and "improvements". Think of it for a second: trying to "improve" something made by R&S in the 50'es.. I'm 100% with the modification(s) and even additions, these are very welcome for modern-day use

modification of the output gain and the thresholds and 2 extra gain stages

I wonder how much u23 is really left in there at a closer look?

/Jakob E.