Help identifying output transformer

[MortenB]

Hi there.
First post here on this great board. I've already found tons of usefull info on this board so far, so thanks a lot for that!

I have this old Klark teknik DN-50 spring reverb that I like and use a lot. It has an option on the PCB for adding output transformers, and I've been wanting to try ít for quite some time - but I can't find the exact transformers anywhere.
They are called "6887/1" on the PCB.
I wrote klark teknik (music group) and they where helpfull (sent me the schematics) but did not have any info on which transformers where used. They suggested Lundahl and I wrote them too, but they told me that it wasn't  one of their models from the past.
Then I wrote and asked Nuvotem since I think they did some audio transformers for Klark in the past, but got no answer back from them.

So I hope one of you can help me out identifying this transformer. I've attached a pic of the pcb. Maybe the pin positioning on the pcb can give a clue?

 

[dmp]

First, you first need to know what the transformer winding needs to be - I would guess 1:1 (turns ratio)
Second, you need to know the pin sizing and layout, so put a ruler on the board to measure the dimensions and determine from the schematic which connections should be to what on the transformer.

Then you can look at transformer datasheets to see if something will fit. For instance, look at the datasheet for the Lundahl LL1540, which is a line transformer. The turns ratio, dimensions, and hook up are all specified.

For the manufacturer to not know the transformer is a big red flag, IMO.  It could be they drew in a transformer that doesn't exist or it was custom made for KT. It could be you would have to retrofit a transformer to the board with wire leads and secure the transformer with a zip tie or a couple additional drilled holes for mounting screws.

Once you know the specs of the transformer (i.e. 1:1 with 20-20kHz freq) then you could put a good line level audio transformer in from any of the high quality makers: Lundhal, Jensen, Cinemag, etc...
This is going to give you a true balanced out. It looks like it currently isn't a true balanced out.

Adding transformers may not give you any noticeable difference in performance unless you are experiencing interference problems.  In fact unbalanced out can sound great if you don't have interference or connectivity issues.

 

[JohnRoberts]

First, you first need to know what the transformer winding needs to be - I would guess 1:1 (turns ratio)
Second, you need to know the pin sizing and layout, so put a ruler on the board to measure the dimensions and determine from the schematic which connections should be to what on the transformer.

Then you can look at transformer datasheets to see if something will fit. For instance, look at the datasheet for the Lundahl LL1540, which is a line transformer. The turns ratio, dimensions, and hook up are all specified.

For the manufacturer to not know the transformer is a big red flag, IMO.  It could be they drew in a transformer that doesn't exist or it was custom made for KT. It could be you would have to retrofit a transformer to the board with wire leads and secure the transformer with a zip tie or a couple additional drilled holes for mounting screws.

That part number may be a house number for KT's internal use.  KT has changed ownership multiple times so that is the type of corporate knowledge that can be lost. It is unlikely to be a full custom transformer, more likely some major (UK) manufacturer's standard part.

Once you know the specs of the transformer (i.e. 1:1 with 20-20kHz freq) then you could put a good line level audio transformer in from any of the high quality makers: Lundhal, Jensen, Cinemag, etc...
This is going to give you a true balanced out. It looks like it currently isn't a true balanced out.

Adding transformers may not give you any noticeable difference in performance unless you are experiencing interference problems.  In fact unbalanced out can sound great if you don't have interference or connectivity issues.

If the transformer is good, you should not hear anything.

If you have a full schematic, specify an appropriate transformer and make it so...  or not.

JR

 

[MortenB]

Thanks a lot for all your good advice.
My main reason to try and add the output xformers is to try to get rid of EMI. Don't know how much difference it will make but it's worth a try I guess.

 

[PRR]

> try to get rid of EMI

Don't say "EMI". Don't say "noise".

Use better words. "Humm". "Power Buzz". "Hiss". "Mexican Radio". "Cellphone pings". They all have different causes and cures. Reducing hiss probably will not reduce Peruvian Polka in your signal.

 

[CJ]

attach the schematic and we can make a good guess,

does the pan feed the xfmr directly? if so, measure DCR of pan jack that drives xfmr,

 

[MortenB]

> try to get rid of EMI

Don't say "EMI". Don't say "noise".

Use better words. "Humm". "Power Buzz". "Hiss". "Mexican Radio". "Cellphone pings". They all have different causes and cures. Reducing hiss probably will not reduce Peruvian Polka in your signal.

Point taken.
What I get is buzz from another devise (a tc 1280 that I use for pre delay) when it's close to the spring reverb. From the 1280's power transformer I guess. I wonder if it is the springs themselves picking it up and if adding balancing transformers would even help getting rid of it?
For now I've placed the spring reverb 1,5 meter  away from any other powered devises and that helps a lot.

 

[MortenB]

attach the schematic and we can make a good guess,

does the pan feed the xfmr directly? if so, measure DCR of pan jack that drives xfmr,

Schematic attached.
I'm not familiar with the term "pan" I'm afraid and google is of no help. I'm still quite new to electronics and try to learn.

 

[CJ]

ok now measure the spring reverb tank (pan) input and output DC resistance

 

[PRR]

The reverb tank ("pan") and the "Recovery" circuit are super-sensitive to external crap (primarily buzz). A full metal box helps a lot. (Don't judge the problem when the chassis is open.) However sometimes you just have to keep reverb tanks AWAY from crap-sources.

 

[dmp]

Point taken.
What I get is buzz from another devise (a tc 1280 that I use for pre delay) when it's close to the spring reverb. From the 1280's power transformer I guess. I wonder if it is the springs themselves picking it up and if adding balancing transformers would even help getting rid of it?
For now I've placed the spring reverb 1,5 meter  away from any other powered devises and that helps a lot.

I doubt adding output transformers will make a difference. It sounds like the hum is being picked up in the circuit, probably at the reverb tank, and amplified to the output.

 

[Audio1Man]

Typical REVERBS are spring type. They have a drive coil and a pickup coil. The pickup coil is subject to STRAY AC ELECTRO & MAGNETIC FIELDS. As PRR said keep it away from all fields. Place the reverb in a FULL METAL JACKET, as this will reduce all of the fields.
Find a quiet place to store the tank. I use a cheap dynamic plastic microphone connected to a meter with 400Hz BW and search for low fields for many debugging problems as it easily finds “HUM & BUZZ” places.
Good hunting
Duke

 

[JohnRoberts]

+1 the noise is coming in the pickup coil, not the entire spring.

Back last century we had to put spring reverbs inside powered topbox mixers so the reverb had to share a common chassis with power amp and power transformer.

Sometimes distance is the easiest solution.

JR

 

[GrantB]

Hi MortenB,

I struggled with the same issues on my SA-20/DN50.  I found that mine also picked up hum/buzz from the internal power supply.  Replacing the power transformer with a new one helped some, but it still wasn't good enough for me (I often use very loud reverb with my synthesizers).

I spent a lot of time on this and in the end, I was only able to get acceptable results by adding an external power supply.  Fortunately the fine folks at Statik have provided us with convenient jumpers on the power rails.  I removed them and wired up a switch so that the unit can be operated from external or internal supply.  I have attached a photo of the modification.

 

[Odk1]

Hi, if it can helps, just some pictures of mine...
Best