Broadcast lineamp from the 60´s.

[moamps]

@honkytonk
Your question gives the impression that you are not a very experienced DIYer. So I would warn you that if you are going to try a preamp be very careful because the two terminals and the fuse holder are uninsulated places that can be at the potential of the mains (230V or so) and quite dangerous if you touch them. I have always hated those designs where the audio inputs, outputs and the mains input are placed on one connector.
As for the design itself, I would try to increase the gain by connecting the primaries of the input transformer in parallel what Gyraf already proposed and reducing the value of resistor R6. In the end, I would rearrange everything and place it in 1 or 2 HE chassis according to today's safety measures.

 

[abbey road d enfer]

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.

I use dynamic mics on drums mainly, toms and kick, and condensers on overheads. Gain is usually between 25-35dB. I use condensers on snare, with even less gain.
The only ribbon mic I use is active, so again I don't need much gain.
The only time I need more gain is when I use the SM7 on vocals, which I tend to do only with shouters. Actually, the main reason why I use the SM7 is when the singer is a little intimidated by the AT4060 or the TLM49. Kind of midway between a big static and an SM58.
And I never use dynamics on acoustic instruments. TBH, I don't understand why you would do that...?

 

[honkytonk]

@honkytonk
Your question gives the impression that you are not a very experienced DIYer. So I would warn you that if you are going to try a preamp be very careful because the two terminals and the fuse holder are uninsulated places that can be at the potential of the mains (230V or so) and quite dangerous if you touch them. I have always hated those designs where the audio inputs, outputs and the mains input are placed on one connector.
As for the design itself, I would try to increase the gain by connecting the primaries of the input transformer in parallel what Gyraf already proposed and reducing the value of resistor R6. In the end, I would rearrange everything and place it in 1 or 2 HE chassis according to today's safety measures.

Yes correct, I am no real DIYer though I have some limited experience. And hopefully I will find and hand over this unit to someone with experience and knowledge. And thanks to inputs from all of you DIY guys, this unit may one day be passing on great recordings.

 

[Whoops]

And I never use dynamics on acoustic instruments. TBH, I don't understand why you would do that...?

Because someone might want that sound and fortunately we all don't think the same way, and everyone does things differently to achieve great results.
I love how the Sen MD421 or MD441 sound on Acoustic guitar, sometimes it's just the sound that fits a rock song without all the high end of a condenser mic and with a nice mid-range focus.
Also Ribbon mics are dynamic mics also and it's not rare that I need 60/70 dBs of gain with those.

But as I told before I wouldn't mind in leaving that amplifier at 42dBs of Gain and only use it with louder sources or louder mics.

 

[Matt Syson]

The amplifier circuit itself is a very basic 2 transistor 'gain' stage with a class b output, as was pretty common in the 1970's. The transistors used don't have a particularly high gain so not leaving much to help reduce distortion if you try to 'push' it to give more gain. It is a design that will distort (colour) more the higher amplitude you use. The distortion measurements quoted being a 'reasonable 0.1% at +6dbu output to 0.5% at +24dbu output.
Note that the frequency rsponse is shown for a 30Hz to 15KHz bandwidth (necessary for FM radio). It has no obvious filtering so will naturally 'roll off' outside the quoted limits so may or may not be 'flat' up to much higher frequencies. It may be that by experimenting with the output loading (differing load terminating resistances some useful degree of 'tone control' might be seen.
It was designed to be terminated (feed) 600 Ohms so if it sees greater than 600 Ohms (10K is quite typical of line inputs) you may get sonme interesting 'frequency 'peaks' (treble boost).