Rohde und Schwarz Begrenzungsverstärker ABR / U23

[studiosus]

Looks very interesting. I would be in for a var 2 pcb&powersupply with a bom.

 

[Falk]

@Falk do you think it's possible to build a dual mono version and fit two boards into one case?

power supply in the middle like in this Electronaut M63 for example?

Only depends on the size of the case and the shielding of the transformers. I personally have no motivation to do it put when using a 4 HE case it should be possible.

 

[Falk]

I am on my way to do the measurement in the original unit today. I thought of getting these values. Anything else you would recommend?
I want to measure all voltages on the tubes, all inductance and dcr of the primaries and secondaries of the transformers and inducutors, VBs and the resistance at the mode selector switch. Should I measure the inductance at 100Hz or 1kHz?

 

[Murdock]

I am on my way to do the measurement in the original unit today. I thought of getting these values. Anything else you would recommend?
I want to measure all voltages on the tubes, all inductance and dcr of the primaries and secondaries of the transformers and inducutors, VBs and the resistance at the mode selector switch. Should I measure the inductance at 100Hz or 1kHz?

100Hz is probably more interesting as this gives a clue about low frequency capability and impedance range. What kind of measuring device do you have?

 

[Falk]

100Hz is probably more interesting as this gives a clue about low frequency capability and impedance range. What kind of measuring device do you have?

I have a PeakTech 2170 LCR Meter

 

[Murdock]

Ok, that's one of the better ones. Test level is 0,6V / -2dBu, so a good level for representative measurements.
Thanks for doing this!

 

[Falk]

Good news is the everything is in the right ballpark. Voltages are more or less spot on. Whats really surprising because I was estimating most of the unknow component values from playing around with my spice simulation. I have a bit of a difference in the bias of the side chain diode but also the whole side chain is modded anyway and works. So I dont want to overthink this.

Voltages R+S U23:
V1 + V2: K 0.5V A 250V G2 47V
V3 K 13V A 143V
V4 K 3.7V A 230V
V5 K 20V A 250V
Diode: K 2.1V
Double Triode: K1 80V A1 250V K2 3.4V A2: 70V

Input TX is 1:1.5 (32mH : 48mH @100Hz) - I use 1:1
Interstage TX is: 1:1.2 (28.5H : 34H @100Hz) - I use 1:1
Output: made a failure here (I assume 2 : 1) - I use 1:1
Sidechain: 3 : 1 (135H : 50H @100Hz) - I use 5 : 1

L2: 100H 2k5 - I use 150H 3k7
L3: 60H 3k2 - I use 60H 2k7

 

[protools]

I thought a bit more of how to deliver the boards.

Var 1: The boards come without PSU - this would be very simple for me but everyone would need to invent a PSU and order their own power transformer.
I could also pre finance the whole project and you would need to pay just before the shipment. (I estimate 60€ excl. VAT per channel)

Var 2: The boards come with PSU and toroidal. This would be better for trouble shooting and the PSUs work stabile since two years. Also in summer.
This would mean that I would need at least a non refundable down payment to be able to pre finance 30 toroidals. (I have 15 people on the list for 2 units each - who hasnt wrote me a mail until now, please declare your unbinding interest and mail to [email protected]) (I estimate 175€ excl. VAT per channel)

Var 3: I provide boards, psu, toroidal, chokes (2) and transformers (4) - this would mean you would need to pay the whole package beforehand. After gathering the money I would order everything. After waiting for all the parts to arrive I would ship all the orders. (I esitmate 450€ excl. VAT per channel)

I will only offer one of the 3 options after we decided for one. So please let me know wich option you prefer. The price estimation are not very much based on real world prices so please dont be resentful if they change for the worse in the end. Its also possible that it will become less.

Best,
Falk

Option 2 or 3 is fine

 

[Falk]

As people keep asking, which I understand:
I know its tiring but I am not coming with the best news. Financially I have to prioritize some studio projects before I can dive into the U23 thing again. Since I use the U23 on a daily base for paying clients I need to build two main boards of the last revision to test them and finally set them free to the people that are on the list. Dumping two or three days and about 1000 Euro in a machine that is working is kind of not so appealing. As of right now I can need the money and time to get the studio in shape and work done. I will asap finish this build - thanks for your patience. Its going to be great. I promise.

 

[chet.d]

Among the chorus of folks that are so looking forward to this. Hoping I (a tech challenged Philly musician type) might be able to sort finding a tech to aid with this when it becomes available. Exciting.

 

[AnthonyBisset]

Hi @Falk ,

Totally empathize with work/life equations slowing projects down.

I'm about to start building Heikki's Vari-Mu and u73bt/u273/u373/rn2254 inspired diode comp. (Thanks @scott2000)

Also have a DRIP u73B board sitting here begging for attention.

Even worse, I can't get my mind off the u23 or Vacuvox, but they're both ridiculously expensive. All I really know is I've joined the Uxx tribe and have a lot of populating ahead of me. Whenever your take on the U23 happens, i'd love to be included in the PCB list if that might be possible? Cheers, /A

 

[Falk]

Could you write a mail to [email protected] - I ll put you on my list then. The price was the only reason I got into this endeavor. The wait will be worth it. I also have the U73 boards and transformers in the drawer. Since I have the U23 I dont feel like needing something else. I also have a Stamchild 670 and in 95% of the cases I prefer the U23 on the stereo bus.

 

[Falk]

I updated the BOM today and changed my plan a bit to get on track faster. I wanted to check transformers from Igor but I will skip this. Maybe someone of you people might do this. So this build will be recommended to use Edcor transformers and Hammond chokes.

Per Channel:
2 x 15k:15k EDCOR XSM (Input and Interstage)
1 x 10k:10K EDCOR WSM (Output)
1 x 15k:600r EDCOR WSM (Sidechain - 600r side only using half of the winding)
1 x Hammond 156c (First Gain Stage)
1 x Hammond 155c (Output Stage)

I will do the following. I will order REV 3 boards next week. This is the revision I want to give to you. I will order the exact BOM for the signal board and build two of the signal boards. I will put these in place of my REV 2 boards and see how it goes. When everything goes fine I ll do some calculations and contact everybody from the list and take orders. I hope all this will happen until end of June 2024.

The PSU is fine. It works very stabile in the U23s since almost 2 years and in my stereo V76 since a couple of months.
I used custom transformers with electrostatic and magnetic shield. The power TX will need to deliver:

Secondary 1 HV: 225V 150mA (200V is the absolute minimum)
Secondary 2 Filament: 12V 4A (should not have less than 3A)
Secondary 3 Calibration: 12V 100mA or more

So if you want to start gathering some stuff. Here you go.

The boards need the following tubes:
2 x EF83 (I can provide some of you with those)
3 x EF86 or PF86 (I can provide some of you with those)
1 x 6SN7
1 x 6AL5

Best,
Falk

 

[Rob Flinn]

Hi Falk. I have been following this thread from the beginning. This project interests me. What price do you estimate the boards to cost ?

 

[Falk]

Hi Falk. I have been following this thread from the beginning. This project interests me. What price do you estimate the boards to cost ?

I think 75€ without PSU Board and 100€ with PSU Board. But I cant really make the calculation before I know how many people will order.

I think the cost per channel will be like:
electrical components 200€
transformers 200€
case 200€
tubes 120€
PCBs 100€
misc 100€
power tx 75€
cable and hardware 50€
-----------------------------
1045€ per channel

 

[Rob Flinn]

I think 75€ without PSU Board and 100€ with PSU Board. But I cant really make the calculation before I know how many people will order.

I think the cost per channel will be like:
electrical components 200€
transformers 200€
case 200€
tubes 120€
PCBs 100€
misc 100€
power tx 75€
cable and hardware 50€
-----------------------------
1045€ per channel

Count me in for a set of pcbs please. Can you give more details of the mains transformer so I can work out if I have something suitable lying around here ?

 

[rock soderstrom]

Count me in for a set of pcbs please. Can you give more details of the mains transformer so I can work out if I have something suitable lying around here ?

Secondary 1 HV: 225V 150mA (200V is the absolute minimum)
Secondary 2 Filament: 12V 4A (should not have less than 3A)
Secondary 3 Calibration: 12V 100mA or more

So if you want to start gathering some stuff. Here you go.

The boards need the following tubes:
2 x EF83 (I can provide some of you with those)
3 x EF86 or PF86 (I can provide some of you with those)
1 x 6SN7
1 x 6AL5

 

[Falk]

Count me in for a set of pcbs please. Can you give more details of the mains transformer so I can work out if I have something suitable lying around here ?

Secondary 1 HV: 225V 150mA (200V is the absolute minimum)
Secondary 2 Filament: 12V 4A (should not have less than 3A)
Secondary 3 Calibration: 12V (100mA or more)

Could you please write a mail to [email protected] I ll get back to you as soon as I plan the orders.

 

[Rob Flinn]

Presumably one doesn't actually need the calibration voltage in the box. Does this unit need calibrating a lot ? Could one use a bench PSU ?

 

[Rob Flinn]

Looks like the Hammond 369HX could be a good candidate for the mains transformer.