Rohde und Schwarz Begrenzungsverstärker ABR / U23

[Falk]

@Jakob

thanks for the hint. The price is actually great but I can not afford to store stuff I dont need. My studio is unfortunately too small for such an approach right now.

I couldnt make sound samples yet since there is too much work to do in the studio. The LA-23 got somewhat cued BUT! I revisioned the frontpanel and will include the Moogish knobs Jacob sent. What do you think?

Best,
Falk

 

[gyraf]

Darn, that one looks really fine imo!

If I should change anything now, it would probably be details like there perhaps being too much coloring going on in the meter scale - the red/yel/blu dots at the meter 15/12/8dB are possibly visually disturbing (unless they serve a necessary technical purpose in calibration, where you need to identify working area quickly and "out of the corner of your eye")

totally get you on the storing-stuff-for-niceness thing, this I'm so very not good at myself

Jakob E.

 

[Falk]

Hi Jacob,

thanks for the super fast feedback. I get your point on the meter scale. I will make a redesign at some point. When I colored the scale it looked great but together with the final layout it looks somewhat childish. I agree.

I am super thankful you motivated me to get rid of the chicken heads and emphasized your point by sending your favorite knobs. Those look really timeless and cool. I totally into them.

I will make another dummy plate from wood to see if everything fits now. If so, I will give Frank from frontpanels.de a call and order two sets. I cant wait to build a second unit.

In the near future I will start to write a documentation of the machine. I think in spring or early summer we can have a round table to see what features need to be included to make this comp ready for the community.

Best,
Falk

 

[Winston OBoogie]

I like your new panel layout Falk.

Another opinion from me    I understand where Jakob is coming from on the meter's colour markings but, looking at the photo you posted of your actual R&S meters, I  think they look nice.  Maybe because the actual colours are more pastel than on the drawing, dunno?

Anyway, whichever way you do it, I like it   

 

[Falk]

Hi Winston,

thanks for the encouraging words. I will take a photo once the unit is assembled and we ll see how it fits. Actually I thought the color scheme of the meter would help to read it since the digits are really small.

I hope for everything to get together until Christmas.
I ll keep this channel updated.

Speak soon,
Falk

 

[SKJGProject]

i'm short of rack space....really hoping for a stereo version

 

[echoplex]

i'm short of rack space....really hoping for a stereo version

This is a DIY forum, right?! 
No one will deter your from cluttering a 2U case with 2 pcbs, a bunch of transformers and tubes.
Make a stereo-unit if you want to!
Welcome do groupDIY !

 

[Falk]

@skjg project - I am not sure of what will happen once the both prototypes I am woking on are up and running. This means I can not promise at this time that there will be anything more than a documentation which could be used as a solid base to work from. What I can promise is that I will not design a stereo unit.
This has several reasons. Most are technical but also there are personal reasons, such as time and of course money. To stick two units in one case will need to look at this project from a totally different angle to make it work. This basically means to start all over again. Buying or building a beautiful 6 HE is so much cheaper.

I decided to build the second unit as fast as possible. So I made another front plate dummy to check for the drilling and printing again. With minor changes I am ready to order them.

@Jacob - thank you again for your feedbacks regarding the front panel. Experience is priceless and you really nailed it. See attached. I am super happy. Some of the printing will be yellowish what will look even better and less cool as now when monochrome.

Thanks for your interest anyone.

 

[Falk]

Good evening Gentlemen,

I almost finished the second unit. It misses the input transformer since it was not shipped with the order I placed but it should be here Wednesday. I transplanted the input tx from unit one and did a first measurement. The units measure almost the same. There is some difference in the high end which I will tame soon but I want to have everything in place and measure again.

I will also do sound samples this week with stereo program material. I hope you are doing fine. Have a nice 2021.

Falk

 

[Falk]

And some more pictures.. the link button needs some tiny pcb to light up. Its needs 12V DC and I only have 12V AC right now.

 

[Erik2345]

That really looks very, very nice!!
That old VU meter does not look dated at all.
Is that a strat switch for the ratio?

 

[Falk]

Hi Erik, thank you. I am glad you like it too. Yes this is a five way switch known from guitars. It was on my mind from the very first scratch of the front panel and I like it a lot. I will make a video of the VUs sooner or later. They are really great.

 

[warpie]

Good evening Gentlemen,

I almost finished the second unit. It misses the input transformer since it was not shipped with the order I placed but it should be here Wednesday. I transplanted the input tx from unit one and did a first measurement. The units measure almost the same. There is some difference in the high end which I will tame soon but I want to have everything in place and measure again.

I will also do sound samples this week with stereo program material. I hope you are doing fine. Have a nice 2021.

Falk

Do you have a zobel network? Looks like there's some ringing on the red trace.

 

[Falk]

Hi Warpie,

yes there is a damping network right with the interstage. I am not really worried about it. Should be easy to fix. When I did this measurement there was also a tube with some out of spec behavior involved. I only figured that later. So I will do it again once everything works as supposed.

Best,
Falk

 

[Falk]

The guts:

 

[Falk]

and the two of them:

 

[gyraf]

And now the really important question:

Can you get them tracking well regarding gain reduction? This seems to be a weak spot in some other "versions" of these.

/Jakob E.

 

[Falk]

Hi Jakob,

interesting. I didnt know that.

The missing input tx arrives tomorrow. I will extensively test stereo processing then and update here with full transparency.

I ll keep you posted.
Best,
Falk

 

[mjrippe]

Beautiful inside and out!

 

[Falk]

Thank you mjrippe. I appreciate it. Still waiting for the input transformer to come. I ordered a small pcb to light up the Link-LED button and switch a relay. 7 month have passed and there is still stuff that I didnt think about yet. Engineering at its best.