Info on Haufe AKM 3000 transformer/opamp thingy..

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radiance

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Jun 4, 2004
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I bought this board on ebay. It has 6 haufe AKM 3000 transformers on it. After desoldering two off them I popped one open only to discover it has a NE5532 op amp in it.
The transformer part

akmsmall.jpg


Does anybody know something about these? are they any good?

Also, does the name Protec rings a bell? it's supposed to be a German broadcast equipment company but I can't find anything about them...
 
I have some of those opamp/transformers also...

This is just a buffer followed by a transformer. Maybe it drives the transformer in a PP configuration for lower distortion, etc..., I don´t know. So, You have a very high input impedance, and low output impedance, balanced... I haven´t use it yet, but think it might sound good. Use it after any preamp that can´t drive 600ohms output, or a discreet opamp that has a weak (high impedance) output to make it stringer, so that you can drive any gear you plug it in...

I guess those are also perfect for distribution amps, and line spliters, as they were used originally.

About the other "protec" transformer, try contacting PIKATRON and let them know the part number. I´m they can help you with this one :wink:
 
Thanks for your answer Rafafred.
I might use these transformers as output stage (maybe also input) on Steffen's solid state pultec which I'm about to make.
Protec is not only from the tranny, it's the manufacturer of the board from which I took the two Haufe transformers. I'll bet that transformer is made by either Pikatron or Haufe, and that they put their own company name on it. It looks exact like a Haufe rk 531 transformer, it only meassures differently.
 
RÜP is a PIKATRON part number. Contact him, asking for info. They have helped me before, sending schematics and specs for some models I have...


The Haufe transformer/opamp things looks perfect for this pultec SS EQ. The neve amp used for make up can´t drive low impedances, so that´s where the buffer inside the AKM´s take place...
 
Ok, I contacted Pikatron. we'll see what they have to say about the tranny's. I also contacted Haufe regarding the AKM 3000's but they did not respond yet (it was a week ago or so).

I'm glad to hear that I can use these transformers. I'm buying to much junk from Ebay lately without actually knowing if I can use it or not.
So I can use them as output stage right, but can I also use them as input stage?
 
Yes, you probably can use those as input stage, but why would you want to waste a nice german output transformer for unbalanced input??? Doesn´t seems the way to go for me. Also, if you get the active electronics part out, it´s probably too low of an impedance to use as input...

Use it how it was intended. As high quality output buffers/balancing units. It´s very usefull this way.

You could easily put together a three of four transistor gain satage driving the 5532. The first stage of a neve is just one of many options you have.
 
I started working on Steffen's Solid state pultec and came across some problems.
I want to use the Haufe AKM3000 trannies in place of the output buffer in Steffen's design.
In order to test everything I left the EQ part out of it for now so it looks like this:

Pultecschemoedit1.jpg


I tested everything apart from eachother and it all works but when connected like in the picture I get a distorted sound.
I suspect that the input impedance off the AKM3000 (= 3K ) is too low for the Neve BA 283 circuit but I'm not sure.
Can somebody tell me if there is a way to make this work or that I should forget about those AKM3000's and stick to steffen's design?

I tried some things and it functions almost OK when I connected a 100R resistor between point A and B and a cap from A to ground.
I could not get much volume this way but the distortion was almost gone but still unaceptable.
 
Protec is a german manufacturer refurbishing semi conductors (amongst other things)
http://www.servetec.com/iframes/frame_protec_site2.html
Lots of OEM work, cleaning, sticking new metal onto things etc...
 
What I do not understand is why you get lower levels with the 100 ohm in place. Are low level signals distorted as well? Did you check for oscillation? How are the Neve and Haufe connected? 2 m cable or 10 mm PCB track?

Samuel
 
Well, I could not turn the volume up much before the signal started to distort (with tyhe 100R in place that is) and I had to feed it a very low level as well.
Low levels are not distorted (maybe a little but I could not hear it) but at those levels it's useless in the pasive EQ I'm building. The Neve and the Hayfe are connected by a 10 cm wire (for easy testing different resistors) but I also had them connected by a very short (1mm) wire jumper. It did distort on both cases...

How do I check for oscilation?

Also, the Haufe works fine when connected straight to the input buffer opamp...
 
[quote author="Samuel Groner"]
How do I check for oscilation?

Best is with a 'scope - if you don't have one at hand, a good sign is distorted output, that's why I say.

Did you check the Neve out loaded with a plain 3k?

Samuel[/quote]

I don't know exactly what that means, just a 3K between point A & B?

When I power up with no input signal I get this chopped up low frequentie sound that seems to disapear after I feed some signal. What can I do against oscilation?

I'm sorry for all these questions but I'm into DIY for almost a year now and thinks like the SSL clone or the 1176 clone are also difficult, but this is way over my head.
 
I don't know exactly what that means, just a 3K between point A & B?

No. Remove the Haufe thing and solder a 3k resistor from the output of the neve board to ground. This way the neve output will see a similar load as with the Haufe connected, so we can see whether it is a matter of loading or something else.

Samuel
 
Now what do I meassure or listen to?

Listen to the output of the neve whether you get the same distortion as with the Haufe connected.

Some other things to test:
* Connect the Haufe again (3k removed), but listen to the output of the neve directly. If this reveals no distortion, the Haufe seems culpable, otherwise there's a good chance the Neve is the one to blame.
* Feed a sin wave through everything and record it into a DAW. Check the waveform for the form of distortion (i.e. clipping).

Hope that helps!

Im not sure yet whether you have some oscillation, but the answer on what to do against it is nontrivial. First make sure where the problem is!

Samuel
 
This is what I got:

Output Neve is fine with either a 3K resistor to ground, with the Haufe tranny connected or with nothing connected(I listened to the Neve output, not the Haufe output)

When I put the signal straight from the input buffer opamp into the Haufe I also get no distortion.

Like I said before, everything works fine apart from eachother but when connected like in the picture I get distortion.

When I disconnect the Neve circuit and only listen to the Haufe output I get this weird tremolo effect at power up. It disapeare's when I short the input from the Haufe to ground.
It seems that the haufe need's something connected to the input or it will act weird....
 
Did some more test's and it seems that the Neve part of my project is to blame for the problems.
What I did was measure DC at the output off the ba283 when powering up (haufe not connected). What I got was 7V DC which got to 0 V in about half a minute.
When powering down it swings to -3V DC in about 15 seconds or so.
I don't know weither this is normal for a BA283 but the Haufe trannies don't seem to like this.

When I power up with the BA283 output shorted to ground (and with Haufe connected ) and then remove the connection to ground, everything seems to work fine.
 

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