U73b (drip) - 3 questions

[Sc]

Hi

You can use two relay sockets, cut off the two pins at the upper one and cross by wire. Another possibility is scraping the laquer of the board, scrape the ground connection of one pin off, and connect the other one to ground. Works fine. But be aware - I have a 2019 board with this bug fixed …..

good luck
Walter   

 

[hugo]

Hi

You can use two relay sockets, cut off the two pins at the upper one and cross by wire. Another possibility is scraping the laquer of the board, scrape the ground connection of one pin off, and connect the other one to ground. Works fine. But be aware - I have a 2019 board with this bug fixed …..

good luck
Walter 

I checked the connection and it looks to be the 2018 edition, regarding the fact i have the same connections as your draw

 

[hugo]

I don’t want to create multiple posts for a single unit so here is an other question. I replaced the 10k resistor of attack with a potentiometer of 100k. It seems to not have any effect..is there anything to do to have this potentiometer operational ?

Also, the freq resp in Comp mode is strange, is it normal ? pic attached

 

[hugo]

Just in case your boards have the same bug, flipped lim and cmp at the relay, here´s a pic that shows where you should cross the contacts.

PS. again, thanks Walter!

Regarding the relay, and your picture : Is your picture showing a good or a bad board ? I have same connections as appearing on the picture.

 

[Sc]

Hi Hugo

The pic shows the old version of the board. You have to interrupt lim - ground and connect comp - ground.

 

[Sc]

I don’t want to create multiple posts for a single unit so here is an other question. I replaced the 10k resistor of attack with a potentiometer of 100k. It seems to not have any effect..is there anything to do to have this potentiometer operational ?

Yes - I believe an attack resistance could only be placed directly at the center tap of the side-chain transformer.  But it interferes with the release and even more with the eventual varicom connection. We changed to the original release and are now figuring  the varicom integration. So I can't help with a working attack.

Also, the freq resp in Comp mode is strange, is it normal ? pic attached

Compared to my (analog) measurements you seem to have a little more and a bit uneven loss beyond 100Hz, but not much. And it changes quite a bit with the input level.  IMHO it's still a very nice response - it's a vintage tube unit (and you know, how  speaker responses are .... :. Any comparison out there ?
regards Walter

 

[hugo]

Hi Hugo

The pic shows the old version of the board. You have to interrupt lim - ground and connect comp - ground.

I cut a leg and put some hard wire to modify the relays, I do have a « bad board » and it’s a shame to not tell this on the doc. 
Thank you for all infos

 

[hugo]

Thanks a lot for the support, the unit now seems to completely work, or almost.
This 100k pot in place of attack resistor does not affect the attack of the comp..is that normal ?  How to make it effective ?
Also, is there a way to make a mod to not have this low end loss ?
Thanks again

 

[Sc]

Thanks a lot for the support, the unit now seems to completely work, or almost.
This 100k pot in place of attack resistor does not affect the attack of the comp..is that normal ?  How to make it effective ?
Also, is there a way to make a mod to not have this low end loss ?
Thanks again

Hi
just in case you want to experiment with attack - try a pot at the point shown on the schematics . This will work, but interferes with standard calibration and fixed attack settings of the U73b (as well as the use of the 670 time constant - with the missing 800k the circuit has a much lower impedance). Both makes it a bit more complicated when you want to integrate a varicom. So we decided to quit this option and will use the original release setup.
Regards Walter
 

 

[hugo]

Hi
just in case you want to experiment with attack - try a pot at the point shown on the schematics . This will work, but interferes with standard calibration and fixed attack settings of the U73b (as well as the use of the 670 time constant - with the missing 800k the circuit has a much lower impedance). Both makes it a bit more complicated when you want to integrate a varicom. So we decided to quit this option and will use the original release setup.
Regards Walter

Hi, I am also building the varicom so I will make it just as you.  I hope it’s not too difficult. So I have to remove this 220k and to find original values for the boards.. right ?

 

[leeksoup]

Hi all,

Just chiming in!

I have a major Varicom issue - see below, would love to break the back of this and have it fully functioning.

I've had my unit up and running for over a year and have been dropping into this thread from time to time to see if I can solve any of my issues,, for one I finally got the comp/lim issue sorted so thanks to the people who have posted here about that. 1377's on order and will look into the resistor changes/cuts. Thank you everybody.

Now for my VARICOM issue (and Walter (Sc) I think I have emailed you about this but not sure if you have my email). First up, anyone who is installing the Sowter transformer on to the board there is a colour code error on the board, you need to switch two of the wires - I will confirm exactly what these are next time I open up the unit but its something to watch out for, please speak up if you are desperate/need this info asap and I'll open it up.

My varicom links the two channels but I am positive that the 10meg resistor I have on a switch does not aloow the varicom to 'take control' of the attack or release time parameters as the controls "fet bias, sensitivity, release, frequency" seem to have no impact. This ties up with somebody's earlier message on here regarding placing a 100K potentiometer in place of the 10K attack resistor and it having no impact because that is where I have my 10M resistor which is activated once the varicom is engaged. Earlier in this thread Sc has kindly drawn a position on the schematic a better place to put it...

1. Sc could you be more specific and suggest a place to put the varicom 10M resistor but on a diagram of Drip's PCB instead of the schematic? I can figure it out but would be interested to know where you have put yours or how you have implemented the varicom.

2. Does anyone have the varicom working? At this stage I don't know if having the FC time constants prevent the varicom controls from doing anything, if so then...

2. Would anyone be able to propose the correct position and values of the original u73b time constants for Drip's board.

Sorry to be pain but I'm so close to having a badass unit fully working, I do actually use this a lot and it would be great to have full functionality, check out the photo of my front panel.... hope you like

Lee

 

[leeksoup]

Ok, an update-

Major breakthrough, I have the varicom working, its not pretty and its a long task to get it working I have to admit but I got there in the end.

FYI it sounds amazing so well worth persevering those who have bought this board, and whilst there may be discussion in the group about reverting to the original release time settings this works fine with the FC time constants and rocks. Will be making a video over the coming days and will post here.

Firstly, as promised - if you are using the Sowter transformer on the main board switch red and orange wires they are the wrong way round, fairly sure it's them

So - in order to get the varicom to take over control it is imperative to insert 10meg resistors into BOTH the attack (R80) and somewhere into the release path (I have inserted mine between the 'time' sma's from the main board to the front panel pcbs). Then I have returned the varicom 'source 1&2' sma's back to the 'time' sma on the main panel by using a T-junction sma connector. Also in order to do this I had to take out the ribbon cables and do much of the connections via sma although there is a problem and bypass and using the pilot light 6v if you need that for your VU lamps so I used some dupont wires for those instead from the pin sockets.

As for switching in the 10Meg resistors I did a bit of my own botch job on some practice pcb boards. Firstly you need extra 6V to activate the varicom board on its front panel pcb as well as activating some relays to switch in your 10M resistors in the paths you have intercepted.

A lucky mistake I made was to have the varicom on switch go in two directions, one drops in the 10Meg at the attack and one doesn't, the latter makes the varicom do something quite interesting and distorty to the attack, which is kinda fun. When the switch is in the middle the varicom is off.

All in all this is a really versatile unit and very interesting. the Varicom is really fast and punchy on the attack. As I said I'll rock a video of this real soon and post it up here.

Oh by the way whilst I'm waiting for the Sowter 1377's I have bridged the 9375 with a 47k 5w resistor and changed R47 to 330R, it has given me 1.8v or thereabouts.

Here's a pic of the inside

Lee

EDIT: HERE'S A VIDEO LINK.....  https://youtu.be/H4nMj4J7rhE ,,,,,ENJOY!

 

[axl85]

Ok, an update-

Major breakthrough, I have the varicom working, its not pretty and its a long task to get it working I have to admit but I got there in the end.

FYI it sounds amazing so well worth persevering those who have bought this board, and whilst there may be discussion in the group about reverting to the original release time settings this works fine with the FC time constants and rocks. Will be making a video over the coming days and will post here.

Firstly, as promised - if you are using the Sowter transformer on the main board switch red and orange wires they are the wrong way round, fairly sure it's them

So - in order to get the varicom to take over control it is imperative to insert 10meg resistors into BOTH the attack (R80) and somewhere into the release path (I have inserted mine between the 'time' sma's from the main board to the front panel pcbs). Then I have returned the varicom 'source 1&2' sma's back to the 'time' sma on the main panel by using a T-junction sma connector. Also in order to do this I had to take out the ribbon cables and do much of the connections via sma although there is a problem and bypass and using the pilot light 6v if you need that for your VU lamps so I used some dupont wires for those instead from the pin sockets.

As for switching in the 10Meg resistors I did a bit of my own botch job on some practice pcb boards. Firstly you need extra 6V to activate the varicom board on its front panel pcb as well as activating some relays to switch in your 10M resistors in the paths you have intercepted.

A lucky mistake I made was to have the varicom on switch go in two directions, one drops in the 10Meg at the attack and one doesn't, the latter makes the varicom do something quite interesting and distorty to the attack, which is kinda fun. When the switch is in the middle the varicom is off.

All in all this is a really versatile unit and very interesting. the Varicom is really fast and punchy on the attack. As I said I'll rock a video of this real soon and post it up here.

Oh by the way whilst I'm waiting for the Sowter 1377's I have bridged the 9375 with a 47k 5w resistor and changed R47 to 330R, it has given me 1.8v or thereabouts.

Here's a pic of the inside

Lee

EDIT: HERE'S A VIDEO LINK.....  https://youtu.be/H4nMj4J7rhE ,,,,,ENJOY!

Wow your build looks awesome! Really impresed! Thanks a lot for uploading the video. looks and sounds like you have a great unit going!
I finished mine some month ago (without the varicom) and still have some minor issues... So i got some questions for you
At which transormer did you change the red and orange wires exactly? Is it the one at the varicom board or some of the other ones from the main board?
How exactly did you bridge the Plate choke? Did you just put a 47k resistor in parallel to the 9375?
What Power transformer do you use? I don't get 6.3v at the heater (about 5.7v) and turning the trimpot doesn't make a difference... So i thought it might be better to use a transformer with more headroom...?
Thank you a lot!!

 

[leeksoup]

Hey axl85

Here's what best info I can give ya...

1. two wires need switching if you use a Sowter on the Varicom board, I 'think' it's the red and orange but I'm not totally sure and going on memory so I could very well be wrong and haven't taken the board back out to be sure yet, all I remember is there were two wires that needed switching, I spoke with Walter over email who also had another solution so I would perhaps look at the pcb traces and work it out, there's definitely an issue with the Sowter colour coding on the pcb of the varicom.

2. yes I put a 47k 5w in parallel with the 9375, and then 330R in R47 slot instead of the 500R, as I said this is temporary until I get a 1377 anyway, although it is functioning fine, and when I do get them I can open it back up and check out the Sowter wiring on the varicom for you

3. Yes you need a power transformer with more headroom, especially once you employ the varicom as you will have additional heater draw for that too. If the trimpot doesn't have any effect almost certainly you are not getting enough. Mine drops a little when the varicom is on but by 0.3v or something, but works fine, I have Hammond 370EX. The varicom board is powered from the 370EX too, using the left plate choke terminal on the power pcb  to the varicom pcb and then a dropping resistor to get the required high voltage (again I can find that out for you when I take it apart to do the 1377's)

Happy to answer any more questions if I can help in any way

Lee

 

[leeksoup]

I just found my notes!
Swap RED and GREEN of the Sowter on the varicom board, sorry about that! Lee

 

[Sc]

Hi Lee and axl85
The swap red/green should work fine - I'll include a pic of the possible connections. Primary and secondary are reversed as well on the board, but I really don't know about possible influence of this on a 1:1 transformer with CT.
When you shunt the 9375 with a 47k Resistor you have a DC-Resistance of about 13k - this is not far from the 1377 (measured). But you might loose some of the "compressorlike" dynamics of a platechoke. Important to have 1.8V DC max. on the cathode resistor there - otherwise one halve wave goes into cutoff at low levels already.
I'm working on integrating varicom and original time constants - let you know, when finished (could take a while .....).

Walter

 

[L091c]

Hi Lee,

very very impressive build, I'm about to start mine and was looking if there was a nicer panel than Drips or design one myself but you really nailed it!

Kind regards, Joshua

 

[axl85]

Hi Lee and Walter,
thank you guys again for the help!
I'm waiting for the 370EX Transformer now and will open the unit to check some voltages. If i remember right i didn't get the required 1.8v at the cathode... But i'll have to check.
The output level of my unit seems to be a bit low and i remember having trouble with the limiter calibration (i did switch the reley pins at the pcb). somehow if i put the theshold at about 12 o'clock i don't have enough headroom for makeup the gain reduction...
Could this be caused by the wrong Plate choke?

 

[Sc]

Hi Lee and Walter,
thank you guys again for the help!
I'm waiting for the 370EX Transformer now and will open the unit to check some voltages. If i remember right i didn't get the required 1.8v at the cathode... But i'll have to check.
The output level of my unit seems to be a bit low and i remember having trouble with the limiter calibration (i did switch the reley pins at the pcb). somehow if i put the theshold at about 12 o'clock i don't have enough headroom for makeup the gain reduction...
Could this be caused by the wrong Plate choke?

Hi Axl85
I'm not sure about the influence of the choke on headroom - but with heavily underpowered heaters you sure have less gain. But there's another issue - R60 (10k) next to the output transformer parallels the input of the transformer. In the original schematic ist says Abgl = Abgleich and this means, they corrected this value individually right after fabrication during final test. Since almost every modern transformer has far a lower DCR than the old one's (but the same impedance - same issue with the plate choke) this value 10k is not correct. We tried it with 60k and also without R60 - in both cases much more headroom and no negative influence on frequency response - so we just flipped R60. But having correct heater tension is certainly also crucial for the overall working and calibration. During limiter calibration the threshold has to stay fix on the last found position of compressor calibration. It's a good idea to mark this position.
Good luck and have fun - it will work out with these mod's ....               
Walter

 

[axl85]

Hi Axl85
I'm not sure about the influence of the choke on headroom - but with heavily underpowered heaters you sure have less gain. But there's another issue - R60 (10k) next to the output transformer parallels the input of the transformer. In the original schematic ist says Abgl = Abgleich and this means, they corrected this value individually right after fabrication during final test. Since almost every modern transformer has far a lower DCR than the old one's (but the same impedance - same issue with the plate choke) this value 10k is not correct. We tried it with 60k and also without R40 - in both cases much more headroom and no negative influence on frequency response - so we just flipped R40. But having correct heater tension is certainly also crucial for the overall working and calibration. During limiter calibration the threshold has to stay fix on the last found position of compressor calibration. It's a good idea to mark this position.
Good luck and have fun - it will work out with these mod's ....               
Walter

Hi Walter,
thanks for the reply!
Yes, i already skiped R40 and got i bit more head room but it still doesn't sound right to my. guess/hope it's the heater voltage whatever... i'll check the new TX next days and report the progress.

Thanks a lot!