Drip U73b

[delaymix]

Update:
Finally I got a proper working unit, really sounds great! It was a hell of a ride but finally this beast is alive.

Thanks to Walter who helped me out with most of the issues.

Bugs:
Psu
Main pcb-relay  comp/lim, plate choke (v72 is the wrong one, take 1377 ...sowter)
Some resistors to replace or take out the circuit (R60, R47).

I have followed the thread with interest. So I'm going to ask some questions.

What problems has the relay part caused you?

As for the problem of the comp / lim part of the circuit, I understand that it refers to the change of the plate choke. In the original schematic Telefunken shot it is a CTV 72/2 with a 10: 1 ratio; Could you be a little more explicit in your arguments about why the Sowter 1377 is better?

 

[Impulsstudio]

I have followed the thread with interest. So I'm going to ask some questions.

What problems has the relay part caused you?

As for the problem of the comp / lim part of the circuit, I understand that it refers to the change of the plate choke. In the original schematic Telefunken shot it is a CTV 72/2 with a 10: 1 ratio; Could you be a little more explicit in your arguments about why the Sowter 1377 is better?

Hi,
sure.

As far as I know the original choke was the BV514 , the right equivalent is the Sowter 1377. It got only half as many henries as the 9375.
value at the cathode resistor R47 was about 2.4V (should be 1.8V), what causes distortion on the output.
Replaced the choke with a 15K resistor and replaced R47 with a 390 resistor. Still not at 1.8V (now it´s around 2.0V) but distortion is gone. And I took of the R60 resistor (a tip from Walter) for more headroom.

Alex (also posted here) left the 9375 in the circuit and soldered a 10k resistor in line the the choke, but I don´t know if this worked out. But i think so.

I don´t know if current revision of the main pcb still have this bug, but on the first revision (bought mine almost 2 Years ago) the contact of lim and cmp on Relay SW78B was fliped...so you need to cross them. Otherwise you will not be able to calibrate the unit im Lim mode.



So far..hope this will help.

So far

 

[Sc]

Hi - just got into the forum …

The relay issue - only on the first Edition 2018 board - the switch lim/comp acts wrong on the R79 cathode bypass – R79 is open in comp mode instead of bypassed to ground. You can fix it by crossing two pins on the relay.
The issue with the anode-choke is technically quite difficult - the original BV514 (Haufe) choke is Sowters 1377. It has a lower DCR and about half inductance  compared to 9375E (the V72 choke).
I was not able to get the prescripted 1.8V at the cathode E88CC (actually I had around 2.5). But the 1.8V are absolutely essential, because at 2.5 one of the halfwaves goes into cutoff at lower signals already. You can see a flattened halvwave on the Scope. This gives a nasty distortion. Switched to 1377 and lowered the cathode resistor to 390R - fine. I dont think you will have to change the output transformer, unless you want to have 10:1 instead of 12:1. The parallel resistor over the primary  of the OT (R60 - 10k) was used to correct frequency response  and was aligned in the factory. Since the original OT probably has slightly different properties, the value of 10k might not be correct. In our case it works fine without parallel resistor - frequency response is perfect.
Finally the issue with the PSU. I can't verify this exactly, because we used the stronger 273EX from the beginning. But whenever B+ drops under load, the load is probably higher than it should be (or the transformer to weak to deliver).

Good luck and carry on - it's a fantastic compressor.

Regards Walter 

 

[chrisenglish]

I started this tread with the hope of others chiming in with their builds. Also the expense of the transformers. I have a very successful build using Edcor transformers ( LA2A) with great support from this forum. I am not seeing that with this build. I am already flush in great compressors and would like to make this build happen but not seeing much support from Drip makes me think I should cut bait and reinvest...

 

[boji]

Someone correct me if I'm wrong, but on the current Drip website while attempting to make sense of photo of the "mastering" U73 version, it appears (perhaps not) GL has made a single, stereo PCB to replace the dual mono PCB's that were first released-- can anyone confirm if this is true?

Purchased a dual set with varicom last year as well, but I've bigger fish to fry right now -- Thanks Chris & Impulse for starting a thread on this- eventually I'll take the plunge as well-- (hoping the choke issue gets worked out).

/Cheers
-Boji

 

[Impulsstudio]

Someone correct me if I'm wrong, but on the current Drip website while attempting to make sense of photo of the "mastering" U73 version, it appears (perhaps not) GL has made a single, stereo PCB to replace the dual mono PCB's that were first released-- can anyone confirm if this is true?

Purchased a dual set with varicom last year as well, but I've bigger fish to fry right now -- Thanks Chris & Impulse for starting a thread on this- eventually I'll take the plunge as well-- (hoping the choke issue gets worked out).

/Cheers
-Boji

As far as I know there’s nothing like a stereo pcb set...just the varicom. Gregory build a mono channel, that’s what the pictures show.  And so far I didn’t  hear about a build that is working with a  varicom. My Dual mono is working like it should and sounds amazing, still waiting for sowters 1377 choke to arrive.  But the choke issue seems to be fixable...like Walter said.

 

[chrisenglish]

I am throwing in the towel here, I have listed the U73b PCB's on the Black Market.

 

[JMan]

I am throwing in the towel here, I have listed the U73b PCB's on the Black Market.

Sorry to hear. 

I am still (perhaps naively) optimistic that I will eventually tackle this, but given the investments in time, energy, and money that are needed, it really is a journey project that I have not yet had the fortitude to begin. 

On the plus side, I did email Gregory a couple times recently with technical questions about one of his other builds, and he actually responded with answers!  (First time I've experienced that since I first purchased something from him a year and a half ago, so...)

 

[oldskool1]

I'm just starting this build (2020 boards) and I don't see the links to the Digikey carts anywhere in the documentation. I really don't want to spend a few days entering all these parts manually, does anyone happen to have the links to the Digikey carts for the U73b panel, main, and transformer boards that they can share here?

 

[oldskool1]

I happened to find a fellow who was selling his set of the boards on Reverb and he was kind enough to forward the complete docs including BOMs. I was able to make a complete BOM, and if anyone needs it, hit me up and I'll forward you the .xlsx file.

 

[jasavoy]

Update:
Finally I got a proper working unit, really sounds great! It was a hell of a ride but finally this beast is alive.

Thanks to Walter who helped me out with most of the issues.

Bugs:
Psu
Main pcb-relay comp/lim, plate choke (v72 is the wrong one, take 1377 ...sowter)
Some resistors to replace or take out the circuit (R60, R47).

HI- I've just finished populating my PCBs for the dual u73. I have the varicom as well but waiting to get this working before messing with that. I've been in touch with Greg at Drip, but could you please tell m a little more about waht you had to do to get the voltage up to spec? You used Sowter 1377 choke instead of the V72 choke (#9375)? Could you tell me what values you used for R60 and R47? Anyone moved onto the Varicom yet? Thanks!

 

[Sc]

Hi
The issue with B+ too low: Several builders out there solved this problem with the next stronger Hammond 273EX. Maybe you could skip the GZ34 and HT-Regulation as described in the errata to the STA-Level and stay with the BX - but I don't know. And you can reduce capacity of the B+ Caps on PSU and mainboard by up to 70% - it leaves still more than original. In my build I have 3 separate, unregulated B+ PSU's for each channel and the varicom with only 6.3V regulated. I had distortion on one half wave with the 9375 and 500R Cathode resistor - changed to 1377 and R47 390R. R60 skipped. Just recieved case and frontplate for my working varicom - post some pic's soon. It's an extraordinary compressor and worth the pain.

 

[jasavoy]

Update:
Finally I got a proper working unit, really sounds great! It was a hell of a ride but finally this beast is alive.

Thanks to Walter who helped me out with most of the issues.

Bugs:
Psu
Main pcb-relay comp/lim, plate choke (v72 is the wrong one, take 1377 ...sowter)
Some resistors to replace or take out the circuit (R60, R47).

Wondering if anyone can help me here- I also finished and calibrated my dual u73b from Drip but my meter does not track accurately at all in compression mode- and it does move at all in limit mode. I've removed the resistors and diodes in the hairball meter. Only showing a few dB in gain reduction even when it's heavily compressing (as per metering the output). Thanks! Haven't even tried to hook up the varicom yet

 

[jasavoy]

Hi
The issue with B+ too low: Several builders out there solved this problem with the next stronger Hammond 273EX. Maybe you could skip the GZ34 and HT-Regulation as described in the errata to the STA-Level and stay with the BX - but I don't know. And you can reduce capacity of the B+ Caps on PSU and mainboard by up to 70% - it leaves still more than original. In my build I have 3 separate, unregulated B+ PSU's for each channel and the varicom with only 6.3V regulated. I had distortion on one half wave with the 9375 and 500R Cathode resistor - changed to 1377 and R47 390R. R60 skipped. Just recieved case and frontplate for my working varicom - post some pic's soon. It's an extraordinary compressor and worth the pain.

Very cool thanks! I've got it all working well and voltages all to spec except my meter isn't tracking correctly and it's not track at all in limit mode. See my post above. Don't know what to do. Haven't tried to hook up varicom yet but I've got it built. Would love to see your varicom faceplate!

 

[Sc]

Hi Jasavoy
I don't know the fs specs of your meter, but probably a VU reading AC line voltage. Without rectifier and resistors it might not be sensitive enough. In Drip's Design the Instrument reads DC current over the 50 ohm cathode resistor of the two E99F - the zero-set pot in series. This reflects compression.
To work correctly it must be a 200uA (or less with mods) DC Meter. The Simpsons from IMS (thanks Jason) 3/12" round or rectangular have a U73b custom made calibrated compression scale. During construction I had a cheap 100uA DC - Meter for tests - apart from weak ballistics it worked fine.
Cheers Walter

 

[L091c]

next stronger Hammond 273EX

Hi Sc, did you mean 270EX? Can't find the 273EX, the 273 series seems to have a 700V secondary (instead of the needed 550V)

 

[Sc]

Hi Sc, did you mean 270EX? Can't find the 273EX, the 273 series seems to have a 700V secondary (instead of the needed 550V)

You are perfectly right - sorry. 270EX or 370EX with international primary. Today I use two torroidals (250 V @ 0,12 A; 6,3 V @ 3 A) for one channel each built to original schematics.
In general to these Drip universal PSU issues - I think a good regulated and stabilized DC supply for the heaters makes sense. But imho keep the B+ supply of (originaly tube rectified/regulated or not) vintage clones close to the original. Maybe just add a bit higher B+ cap values and a decent choke. Due to switch/load peaks etc. it's safe to have 150 - 200% of the working current availiable. P2P or if possible modify the board to it. Less heat, less noise, often even simpler and cheeper ... .

Cheers and thanks for pointing out this mistake.

 

[L091c]

I happened to find a fellow who was selling his set of the boards on Reverb and he was kind enough to forward the complete docs including BOMs. I was able to make a complete BOM, and if anyone needs it, hit me up and I'll forward you the .xlsx file.

Hi Oldskool, I started ordering iron, almost complete, going to start ordering the other parts, could you by any chance share your BOM?

 

[jasavoy]

Hey guys, went back to this stereo Drip u73 after it sat on a shelf for over a year. When I go through Greg's calibration procedure I keep having the same issue- in limit mode I get a big reduction in output with no visible gain reduction on the meter. Anyone have any ideas what this could be??? Quite happy with the build and sound otherwise although getting the input/output attenuation dialed in is a little different from what I'm used to. I assume that the input and output attenuation controls should be set for 0dB (max CW) during calibration, right?

 

[jasavoy]

Here's my build