Broadcast lineamp from the 60´s.

[honkytonk]

Hi
I wonder if it would be possible to make a preamp out of this lineamp. It was built for Norwegian broadcast by Seem company. The schematics for the line amp is dated 1964, and
I have some of these lineamp modules. Maybe gold or crap or something in the middle but not useable at all ...-)).
Post a couple of photoes here.

 

[Whoops]

Show us the schematics, with the circuit it would be revealing if it could be made into a Mic Preamp or not

 

[honkytonk]

schematics

 

[honkytonk]

Text is in Norwegian, can translate the important parts.

 

[Whoops]

Were you planning on doing a Mic Preamp or a Line preamp?

 

[honkytonk]

Mic preamp if possible ..

 

[abbey road d enfer]

Mic preamp if possible ..

You would probably need to replace the input xfmr (T2) with a step up type. Unless you want to specialize this preamp for hot mics, such as kock and snare, guitar amps and vocals with condenser mic, wher a typical gain would be about 25-35dB.
That would require changing R5, R7, R7 and C3.

 

[honkytonk]

Thanks for replay and info. I would be happy to get 35dB. I wonder if there is somebody on this forum who could look into a project like this module.

 

[gyraf]

the module gives you a maximum of +36dB gain as it is

You may want to wire the input transformer primaries in parallel to get gain optimized further (if not already done) - the wiring is taken out to the solder posts beside the input transformer close to the front plate

/Jakob E.

 

[abbey road d enfer]

Thanks for replay and info. I would be happy to get 35dB. I wonder if there is somebody on this forum who could look into a project like this module.

What do you mean by that?
If you want someone to do it for/with you, you can address the Jobs available section.
If you want to do it but need some guidance, you may address The Lab or stay here.
Now, after some reading of your document, I see that the gain can be set from 12 to 36dB, which is fine. An additional 6dB can be achieved by connecting the two half-primaries in parallels instead of series as standard.

[EDIT] Ah, gyraf beat me to it! I had to take a crash course in norsk. [/EDIT]

Actually I think you don't have much to do to use it as a mic pre.
You may have to replace some electrolytics, though. Typical symptoms of caps needing replacement are lack of bass (check C1 & C3) and hum (check C2).

 

[honkytonk]

Thanks for info, addressed in Jobs too. Ref. optimize for more gain, could this eventually change the sound of the unit?

 

[Matt Syson]

As said previously the gain is up to about 36dB but with some alterations (beyond parallel feeding the input transformer to improve the gain to about 42dB), you could get more (within reason) and at expense of more distortion by changing a resistor (and cap as well to compensate for lowered resistance).
The fact it already uses a 48 Volt supply could be very handy, by adding say a 470 Ohm resistor in series, and a largish cap before a pair of 6K8 'phantom power' resistors.

 

[abbey road d enfer]

Thanks for info, addressed in Jobs too. Ref. optimize for more gain, could this eventually change the sound of the unit?

Any mod will change the sound of the unit, but how much is down to the extent of the mods. Particularly, increasing gain will result in more distortion and BandWidth restriction. That will be mesurable, but maybe (probably) not audible.
Anyway, what is the sound of the unit?
It depends very much on what you connect to it.

 

[honkytonk]

Actually, I do not know how the sound of this unit, and nobody I have asked knows these units. What I know is that similar units build by Seem company sounds very good in the v72 landscape. But I guess this unit is not built like a v72, no tubes etc.

 

[Whoops]

Any mod will change the sound of the unit, but how much is down to the extent of the mods. Particularly, increasing gain will result in more distortion and BandWidth restriction. That will be mesurable, but maybe (probably) not audible.

How about having your mic booster circuit in front of it?
It's 20 dbs boost isn't it?

Just changing the input transformer connection it is able of 42dbs, then with the 20dbs boost it would be 62dbs that is plenty. If if the Mic boos circuit is 15dbs we are talking about 57db's total without changing the circuit and lowering the specs

 

[abbey road d enfer]

Actually, I do not know how the sound of this unit, and nobody I have asked knows these units. What I know is that similar units build by Seem company sounds very good in the v72 landscape. But I guess this unit is not built like a v72, no tubes etc.

Indeed Tore Seem has a very good reputation. I would think this unit to be pretty neutral.

 

[abbey road d enfer]

How about having your mic booster circuit in front of it?
It's 20 dbs boost isn't it?

Just changing the input transformer connection it is able of 42dbs, then with the 20dbs boost it would be 62dbs that is plenty. If if the Mic boos circuit is 15dbs we are talking about 57db's total without changing the circuit and lowering the specs

Thank you for your appreciation of my little creation, but I don't think it's a fair arrangement. The equivalent input noise of this unit is probably a good 6 dB better than my MicBooster, if only due to the free gain and optimum source impedance due to the transformer.
Anyway, I almost never use more than 40 dB gain and I doubt anyone in the context of a home studio needs more, provided the mic/mic pre combo is adequate.

 

[Disco Volante]

That does indeed look like a very well built machine. I'd replace the caps, power it up and see/hear what it does. Expect some noise from those old transistors..

 

[honkytonk]

Thanks again for all inputs, I really preciate it. Now I see a hope for this old module to come to life again. Agree about 40dB, the V72 at 34dB get used alot on all kinds of close up recordings.

 

[Whoops]

Anyway, I almost never use more than 40 dB gain and I doubt anyone in the context of a home studio needs more, provided the mic/mic pre combo is adequate.

I need more than 40dbs quite often, if I use a Shure SM7 for example or a Ribbon mic. Or any dynamic mic on an acoustic instrument besides drums.
only exceptions are when using condenser mics.
But like you said before depends on the op usage, you can leave this amp just for condenser mic usage.