RFZ KV80/1 pinout? (includes revised design)

[MusicWorks]

Hi everyone!!

I am preparing a rack for these old German preamp modules by RFZ, model KV80/1 originally inside Mixer MP4084, I am having trouble following the old schematic, could someone help me out?:

This is the connector pinout:

You can check the full diagram for this preamp here http://www.lightandfilm.com/KV80.jpg

Please note it has TWO inputs (one balanced and one unbalanced) and THREE OUTPUTS (A1 goes connected to the second stage, A2 is the main LINE OUT and A3 is the prelisten line, or preamp direct out). As far as PSU requirements, it has two voltage lines +24V for the modules and +100V for the microphone power.


Tell me if this is correct (pin columns, from left to right)

PIN1 - Input 1 (grd)
PIN2 - Input 1 (+)
PIN3 - Input 1 (-)

PIN4 - Input 2 (grd)
PIN5 - Input 2 (+)

PIN6 - Light Signal Go/Return

PIN7 - GRD for A1, A3 and E3

PIN8 - A3, the lower pin I can't figure out

PiN9 - +100V

PIN10 - ?

PIN11 - A1 to E3 jumper (preamp stage to amp stage connection)

PIN12 - +24V

PIN13 - ?

PIN14 - LINE OUTPUT (A2)

PIN15 - To safety ground (0V)


I believe upper and lower pins are co-related, but I can't figure out certain pins. The one under A3 for instance and PIN columns 10 and 13. Any help would be much appreciated!!!

I will be posting pics of this project as soon as I get my order from Mouser with all the required PSU and connectors.


Come back soon for more pics!

 

[MusicWorks]

By the way, you can find more info about this preamp here:

http://vintageaudiogearbox.com/goods/preamps/RFZ/KV800.html



Regards

 

[zebra50]

Thanks for this. I have a couple of these and got them running as mic preamps by looking and experimenting. I just used the mic in and one of the preamp outputs. They sounded quite nice. At a glance your pin numbers look sensible.

I just used a +24V supply. I certainly did not need to use a 100V supply at all. As you say, it is likely to be for an old format microphone power.

It is nice to see that schematic, but the link to  http://vintageaudiogearbox.com/goods/preamps/RFZ/KV800.html seems dead.

Did you manage to find the right connectors for the back?

Stewart

 

[MusicWorks]

Interesting. How would you describe the tone of these preamps? It's certainly hard to come by someone who has even heard of them!

Still can't figure out certain pins...or the wiring for A3 (Prelisten - Prefader Direct Out). It seems to be connected in between A1 (Output to 2nd Stage) and E3 (Input to 2nd Stage).

Does this mean the pre-listen insert is an independent output, or being routed in between the second stage connector as the diagram suggests...means prelisten is through the main line out (A2)?

Regarding the connector, I had the luck of getting 3 original connectors from the man who sold me these modules in Germany. One connector for each module. Having them hard soldered wouldn't have been a problem but I prefer having all with connectors...just in case I need to take some module out to recap or something like that. Can you recall which preamp output you used in your rack? It only could've been A1 in PIN 11 or A3 in PIN 7. Thanks, any info is much appreciated

Have heard wonders of this preamp design!!!

Charles

 

[zebra50]

Hi Charles,

To be honest I only used it a few times, probably about 6 years ago, so my memory of it's exact tone is hazy. I remember liking the sound though, and there was plenty of clean gain.

The modules are still on my bench, and last year I had a front panel made up with the intention of racking them properly. Maybe this year I will finish them and get them plumbed into the studio! You have me inspired to dig the project out.

>Can you recall which preamp output you used in your rack?

I don't recall but I could probably find out. I would have connected a generator to one of the inputs and then looked at the pins on the scope to see what came out! Is one pre fader and one post? I have a vague memory of that, and if so I went post-fader.

Cheers!

Stewart

 

[MusicWorks]

Stewart: You should totally get them out and bring them back to life!!

For a little more inspiration, this is my revised CAD design right out of the oven(!) :

The aim of this design is to isolate high voltage lines (PSU) from low voltage audio signals, and have a clean and direct signal path throughout the rack. Both power supply voltage lines are fused, for protection of the circuit and PSU units.

This is the revised CAD drawing with final specs (connectors, etc).

Tell me what you think!




By the way, if any of you ever need a rack design, I am a professional designer. Just give me a holler.

 

[zebra50]

Well, this thread got me moving again - here's mine so far.

I had a bit of time today to wire up the power supply, and am just adding a phantom supply. Many of my preamps don't have it as I use mostly ribbons, tubes and dynamics. However, I occasionally find myself wishing for a bit more choice for my 48V mics.

Pete at Grand Master Audio made the panel for me last year. The rear of the case is recycled from an old EQ project. XLR inputs are on the front to work with my XLR patchbay from the live room.

Previously I had used A2 as the output, and used a couple of second hand Sowter trannies to balance the outputs, which worked well. I've mounted them at the back.

So, nearly done. I hope to get the audio wired this week when I've made a few decisions on the transformer wiring and phantom implementation. It would be nice to hear these again.

Stewart

 

[MusicWorks]

That is one cool front panel design!!!



I am so glad you took your KV80s out and started soldering!! As soon as I get the output transformers- last thing on my list- I will start soldering myself. Love the inputs on the front, it makes it a much more useable design...easy access to inputs is crucial. I might go along the same road...

About the +48V phantom, did you get a separate +48v phantom PSU? I am going to cut my panels this week and was wondering, what size did you make the modules openings in the front plate? I have calculated 280x29mm as the perfect size, hope it fits! Also, did you use standoffs to space the modules in the vertical axis? I was wondering how to mount 3 modules that are separated by some distance, so each module has it's own opening hole mount.

I really like your rack design, it's so nice


Keep up the good work! hehe

By the way, what kind of music do you do?

 

[zebra50]

Hi!

>About the +48V phantom,

I have used one of RuffRecords phantom boards that I had kicking around, although his design is so simple that you don't really need a board to do it. The 24V supply I wired on strip board - just a couple of caps, bridge rectifier and a 24V regulator.

> I have calculated 280x29mm as the perfect size

According to my notes, my holes were 290 x 29.2 mm! Actually you can see that they are a couple of mm too wide in the long direction. They fit flush with the surface and I have used small brass plates screwed behind to mount them - you can see the four mounting screws on the photo. I would imagine your 280 mm sits them on tom of the face plate.

>Also, did you use standoffs to space the modules in the vertical axis?

No, they are just held by the front screws. Seems OK so far.

>By the way, what kind of music do you do?

I spend half my time repairing ribbon mics, but when I do get to record, mostly I do local acts, pretty much anything that comes up really. The local talent pool is not really deep/wide enough to specialise, so my only rule is that it must be original material, and not covers.

Cheers!

 

[MusicWorks]

Hey!

>

I have used one of RuffRecords phantom boards

If you would like to use the modules 48V phantom, the data sheet describes the modules power requirements in the following way: "This Device is designed for 24V Power Supply, negative pole grounded. For the Microphone Power 48 V/12V  +100V is also needed".

Basically, after discussing this with some german techs, I found out the circuit requires +100V for phantom because it is wired to a Zener Diode circuit implemented in the circuit board (VD1, VD14 and VD13 in the schematic) that supplies Z-voltages from 15V + 12V + 22V (= 49v).

The module delivers both a +48V when using a phantom powered microphone and 12V for regular microphones (activated at the switch).

They fit flush with the surface and I have used small brass plates screwed behind to mount them

I was thinking about different options for mounting them, even when going for a 280mm width (where just the circuit board would slide in) the mounting holes would be uncovered by almost bled to the side. I was thinking of using some kind of small clip holder, U shaped to fit and hold both side together neatly. I only have to find such clip. Those screws must be difficult to find, can't imagine the thread you used...

By the way, if you want a copy of the PDF data sheet for the module, just pm me with your email. It is in german, but has useful information about the preamps and the diagram.

Cheers!

 

[zebra50]

Interesting! I can see the zeners in the schematic now that I look properly. When I first started this project I didn't have a schematic, and didn't realise it was geared to supply phantom. Well, with the transformer I had it was easier for me to make 48V than 100V!

To turn the 12V off, it looks like you will need an additional switch off the board - which I needed anyway for my +48V.

>Those screws must be difficult to find, can't imagine the thread you used...

M2.5  very easy!

I finished my wiring today. The preamps are working but the gain switches have been a pain - the contacts are quite oxidised after all these years and it took me quite a while to get audio at all the settings. Loud pops when you switch settings so I would recommend pulling down the fader when switching. I also had to grease the fader track rod to make it move smoothly.

Anyway, they sound well now and have oodles of gain - more than you will ever need! The 64dB setting is insane, and you will run into clipping very quickly unless you are recording distant starlings in a silent wilderness.

I ran a quick frequency sweep with fuzzmeasure, with the HPF out (red) and in (green)...

Note that the mic power switch also acts as a filter (blue), due to C1!

Also... the little trimmers at the bottom of the faders are vital for matching the channels. Mine were about 10dB apart!

Time for some recording. And possibly some noise / distortion measurements.

 

[MusicWorks]

It looks simply amazing! Thanks for posting those frequency tests. The HPF filter looks pretty nice, and quite a "clean cut".  Bet it sounds even better!

>"To turn the 12V off, it looks like you will need an additional switch off the board - which I needed anyway for my +48V."

I hadn't thought about it before, but you are right. To use dynamic mics and be on the safe side I should add a switch. Probably the best idea is to locate it in the +100VDC line directly (?), this way the main AC switch turns on both power supplies at the same time -but only 24V is supplied to the modules until I turn the +48V switch on. This way I can also wait until the big power supply (100V) line is stable before supplying high voltage to the modules.

> "M2.5  very easy!"

Thanks for that!

> "The 64dB setting is insane, and you will run into clipping very quickly unless you are recording *distant starlings in a silent wilderness*"

(I laughed so hard I fell off the chair)

> "Note that the mic power switch also acts as a filter (blue), due to C1!"

Do you think this might be matched in the original design to correct whatever effect the "high voltage" +48V phantom power does to the signal? It also seems a pretty clear cut, probably to roll off some bass induced when using condenser microphones with this sort of design (?)

Anyhow, your rack is really nice! Basically drooled when I saw the picture.

As an update to my project, I found a list of companies that offer laser cutting services for metal in my area and already sent CAD drawings with final measures to one of them. Hope I can get them cut by next week! I am certainly eager to start work on this !


Would be really interesting to hear some of those sample recordings...Show me yours, and I will show you mine? : p

 

[zebra50]

>Do you think this might be matched in the original design to correct whatever effect the "high voltage" +48V phantom power does to the signal? It also seems a pretty clear cut, probably to roll off some bass induced when using condenser microphones with this sort of design (?)

I _think_ it is a consequence of having the 22uF cap there to filter the supply to the zener diodes, but then (in my case) not supplying a voltage to charge it. It would be interesting to know if you get the same thing with your approach.

I had a couple of other thoughts about your project. Have you finalised your power supply design yet? One way would be to get a 2 x 24V transformer, and use one side with a bridge rectifier for +24V DC. You could then use the other side with a voltage tripler to generate your 100V!

Have you tested your modules on the bench? Because the switches can be noisy, I think if I had three modules I would pick the best two for a stereo pair and leave the third for spares or sale. Just a thought.

I'm not sure where you are in the world. Pete at Grand Master Audio did my panel (see the white market), and I am sure he would be happy to do one for you. You can use my 'design' if you like. You will notice that a bit of the 'd' is missing as I left it outside the cutting area. But I kind of like it.

>Would be really interesting to hear some of those sample recordings...Show me yours, and I will show you mine? : p

I haven't recorded anything. I could post something up next time I get a band in to record.

Cheers!

Stewart

 

[MusicWorks]

Stewart,

Will continue with the reply of the technical information here, so it will remain in the forums.

> "I had a couple of other thoughts about your project. Have you finalised your power supply design yet? One way would be to get a 2 x 24V transformer, and use one side with a bridge rectifier for +24V DC. You could then use the other side with a voltage tripler to generate your 100V!"

Yes, I decided to go with industrial high quality filtered PSUs. For the +24V I got an Astec-Emerson LPS55. It's a small footprint, fully filtered (EMI) power supply that is also used in the medical field (LPS55M) and seemed quite nice (10x5cm).

And for the +100V I really had no idea what to get, its not a very common DC voltage for electronic appliances. Finally I located in Mouser a low-noise PSU transistor based, open frame mounted design, from International Power (made in USA - Mouser Ref. Number is #597-IHB120-0.2A)). Was one of the few, if not the sole, option. Mouser listed no Data Sheet, picture or brochure. I went for it, and it is very nice solid design. It has a huge transistor, a nice trafo and a small board with a couple of caps all mounted on a thick insulated aluminum plate. . It can be fine adjusted from +100V to +135V.

Both PSU are sufficiently small and enclosed to be able to mount inside my 3U rack, and occupy just one corner inside the housing (upper right if seen from above) next to the main AC switch (both independent AC lines that go to both PSU are properly fused (0.175A and 0.375A  respectively) in my design.

>Have you tested your modules on the bench?

I am an amateur, I have no bench xD No, seriously, I usually do the designing and planning of hardware, layout...not so much into soldering action -except maybe for cables, as in the studio I usually do the soldering myself-. Also have done work on Reel-to Reels and Multitrack machines....soldering to PCBs, so it should be no problem.

I also thought hard about the Stereo option. It would have saved me 1U in height, and probably some money on the PSUs. But in terms of preamps I usually need a mono pair just to mike up the acoustic guitar properly and have the third track for vocals. Never really used 4 preamps when recording by myself....most of the time 3 is the magic number

> I'm not sure where you are in the world

I live in the land where the terms "laser cutting metal" are perceived as science-fiction...(really...)

> Pete at Grand Master Audio did my panel

Will probably dream about Pete tonight xD

Thanks for offering me your design, it is certainly a neat one!! I made the mistake of getting a cheap but quite nice rack housing (1.2mm steel) and, separately, an amazing front panel (4mm aluminum anodized). Now I need to cut and match both, to make it work. And the "not so bad" housing....its pretty good for the price I paid...will come together with the "awesome" front panel neatly. Had to cut a bit on the housing to have all these great components inside...trying to balance it out hehe

> Sample recordings

I hadn't read your reply when I sent that email! Sorry for being repetitive!


Will post some pictures of my modules later this evening, high res! Come back later!

Carlos

 

[MusicWorks]

Here are the pics:

Enjoy!

 

[fluxta]

i know this post is years old but nice read. Very interested as I've got a 24 channel RFZ MP4084 console I brought back with me from Berlin to Australia (don't ask how much it cost ;-{.
I bought a lab power supply and ran a power cable to the big connector on the back after tracing the power wires and confirming 24 volts like the Telefunken designs of the time from a tip off from Oliver Archud who said the desk would sound great. and it does (rest Oliver's soul).

I used this desk for these album projects linked here at the bottom and loved it so much, I had to hang on to it. I've now got it here in Sydney as the main console in my studio I'm building...I LOVE IT

The KV preamps have heaps of gain and are fantastic with ribbon mics but are fussy with condenser mics? My audio technicas become quite noisy whereas my cheapie Rodes (NT1, K2) and Neumann U77 are silent and clean. Impedence issue?

I've also got a bunch of other very nice modern preamps but the bite, agression and character of the MP4084 preamps wins out most times...I've just used it for a drum sample library production where we used a Neve VR series console and the MP4084 and the samples done through the MP4084 were some of the best sounding takes.

Issues are the clicky gain pot which needs constant spraying and the binding faders that also need constant use or cleaning.
The three stage eq's in the desk are interesting as you can't have the high and mid eq's on at the same time. It's one or the other.
There are a pair of limiters with fast and slow settings which sound great squashing drums and the built-in monitor speaker is very handy and also sounds so great I often send sounds to that and mic it...guitars, mixes, reverbs etc...very fun

Recordings Using MP4084 KV preamps:

Trap Set
every sound went through the desk...

https://itunes.apple.com/us/artist/trap-set/id890208353

Aidan Bartley
https://itunes.apple.com/us/album/vaudeville/id283589718

Kat Frankie

https://play.spotify.com/album/4UzG0EnizK8QlxGle7hSK0?play=true&utm_source=open.spotify.com&utm_medium=open

 

[Otofonik]

Hi guys,

I've just purchased a pair of these KV80 preamps which were rehoused. They came with very little information and I was hoping you could tell me which of the three switches is for the phantom power, which is for the HPF filter and which is for mic/line level? And what is the button with the loudspeaker symbol for?

Many thanks!

 

[fluxta]

From left: filter, line or mic, phantom. The speaker switch is solo or listen