1073 PRE + 1081 EQ Project. Searching for solutions

HI GUYS!

I have a plan to do pcb diy project of mic/line preamp based on 1073 pre with… 1081 EQ!
1073 contain very nice sounding class-A make up stage, 1081 contain most flexible EQ from all 10**'s series. Why we could not splice them together? I'll try

Here some ideas that I want bring to life:
1) I want to take away HPF from EQ chain and insert it right in to amp chain.
My arguments:
1) In generally I use HPF from all EQ most of all.
As 1073 HPF contains passive structure(right?). it's possible to move HPF from eq between input amp stage and out amp stage. So it will be possible to use HPF without inclusion of whole EQ. It will lead you to cleaner sound.

2) I have an idea to do switchable HPF before EQ of after EQ.
My arguments:
So you could boost low end and then cut some of low end with HPF or vice versa.
How do you think, could this feature be really useful?)

Will attach some images in next replays.

Here is my question to you:
1) 1073 HPF contain inductances, capacitors and resistors, so it have passive structure (right?). And is this fact allows me to move in right in to amp section between input amp and out amp?

2) Is it right to say that 1081 HPF is a second (third) order RC-filter?

3) It will be nice to made all unit in class A. But I haven't researched the question about difference between B184/284 C/B amp (1073) and 336 amp (1081) yet. This amps used for the same goal,I guess - for gain make up after eq.
May be any one of you describe some principal difference between them? Could I just feat 284C amps in to 1081 EQ?

Here is an images of 1073 HPF and 1081 HPF&LPF

Here is a EQ amps of 1073 and 1081.

Nice combination...

I'd put the HPF before the eq, never after... you prefer to cut before boost, mostly with bass to have better headroom... if you boost first it can go clip and then attenuated to the original level... if you put the HPF first you'll never goto clip because of it and then boosting (unless boosting too much, but in this case take out the HPF instead off boost)

It's nice if you can use HPF after the pre or before the EQ if the other isn't used... but you'll need a buffer with it because load and drive Z would change the response of a passive filter.

Go on with this project!

JS

joaquins said:

Nice combination...

I'd put the HPF before the eq, never after... you prefer to cut before boost, mostly with bass to have better headroom... if you boost first it can go clip and then attenuated to the original level... if you put the HPF first you'll never goto clip because of it and then boosting (unless boosting too much, but in this case take out the HPF instead off boost)

Click to expand...

I thought about clipping factor if HPF after EQ and yes,  agree with the fact that it is a bad idea.

Here is my first test psb's of preamp section. It's fool layout copy of 1073.

Good stuff!  FWIW the 338 amp stage used in the EQ section of the 1081 is a class-A stage.  It is only the output stage of the 1081 (BA340) that is class-AB.  You could make the preamp from the two 183/283NV stages, have the EQ use 338 stages, and finish with the 183/283AM stage and keep it all class-A.

Or, you could just build a 1081 with all 338 stages and finish with a 183/283AM stage in place of the 340 stage from the original design. 

Oh, and the HPF/LPF on the 1081 uses a little amp block called a BA306, IIRC.  I believe it is class-A as well, but don't have the drawings around to take a look for sure.

Either approach would make a wonderful final product, I'd think.

JC

rascalseven said:

Good stuff!  FWIW the 338 amp stage used in the EQ section of the 1081 is a class-A stage.  It is only the output stage of the 1081 (BA340) that is class-AB.  You could make the preamp from the two 183/283NV stages, have the EQ use 338 stages, and finish with the 183/283AM stage and keep it all class-A.

Or, you could just build a 1081 with all 338 stages and finish with a 183/283AM stage in place of the 340 stage from the original design. 

Oh, and the HPF/LPF on the 1081 uses a little amp block called a BA306, IIRC.  I believe it is class-A as well, but don't have the drawings around to take a look for sure.

Either approach would make a wonderful final product, I'd think.

Click to expand...

Great information! Thanks!

I'm planning to do my 1073/1081 exactly as you describe!
One question that I still have not solve - could I use HPF from 1073. And there one moment more: 1081 use HPF before EQ, 1073 use HPF after EQ.

Here is a BA306 schematic:

And here is whole 1081 filter section - HPF and LPF with BA306.

So... my pre works!
That's really inspiring news for me and it sounds really not so bad!))

During assemblage I found a couple of mistakes in pcb design. One of this - mismatched 2N3055 polarity
As gain switch I found in my region NOS Soviet mil spec hermetic 4pole 12 step switches that works great.
On sound test used pcb with carnhill in/out trafos.

What about sound? I compared my pre with Neve V3 console preamps that I have in studio. And could really say that my pre sounds MUCH wider and deeper, especially on the lows!

On future couple weeks I'll done tests with using different components.
I bought a large batch of different 2N3055 transistors from different companies/different ages and 2N3055 modification models.
I want to try vintage BC107/109 transistors instead BC184C, just for interest. And I want to test difference between using polypropylene/stiroflex/silvermica caps.
After all tests I'll redesign mic ore pcb and will design EQ section pcb.

Just finish enclosing procedure for my preamp.
From this point start to make an experiments with components.

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