RED!: Orange 86 MicPre finished (pics)

Flundran said:

Where did you find those rubber mounts visible on the red PCB's? Looks neat.

Click to expand...

-The Rubber mounts come with the PCBs

Damn, wish I could've built mine, but couldn't foot the bill.  That's some tempting DIY right there.  Nice one, Holger and Charlie both.  Fresh squeezed!

That is a totally funky build!  Great front panel, cool meter- it really shows the effort into it.  There are all sorts of personal touches.  Please replace any gaffers tape inside with gentle tie-wrapping very soon.  With the heat inside, that tape-glue will off-gas and get really schmutzige.  It is best to have NO glue products in any equipment, tube, or otherwise.  The guys in my shop don't like cleaning the dusty residue 30 years later :wrinkly-winky:
I really dig the personalization!
Mike

sodderboy, thanks for the hint regarding the tape, I will remove it. Usually I take my builds to the studio, do some testing and after a couple of weeks I'll finish the devices, do some rewiring, fix stuff here and there. So the final build will look different.

very, very nice holger! i like your style a lot.
cheers, alex

Nice work on the new preamp !!!

No disrespect to change topics , but since the V72 is mentioned here.......

Many comparisons sited with V72 and R47, are the comparisons based
on the stock V72 or the Abbey Roads EMI Modded V72 (higher gain like a V77) ?

I'm assuming stock V72, myself.

there is quite a difference between the two types of V72's ( moded and non-modded).
Overall , the V72 is a darker colored preamp from my experience and highs are not pronounced.

also, the V72 has a adjustable pf trimmer cap in parallel with another 40-50 pf cap , never heard
anyone discuss this as far as settings go. would like to hear about this since I have never come
across any documentation on its preferred setting. I'm guessing a Neg feedback adjustment on the Anode/Cath of
EF804s tubes -highlighted in yellow box in diagram below.

electrochronic, I think what looks to be a trimmer cap is really set with a fixed cap at the factory.  And that 10 pF range will not make much of a difference.

No , actually there is a trimmer cap in the V72, verified with a real unit , its not just fixed cap value. This trimmer is in
parallel with a fixed cap. So I'm thinking there is some kind of calibration or circuit tuning
in this location. Few folks ever really mention its purpose.

electrochronic said:

Many comparisons sited with V72 and R47, are the comparisons based
on the stock V72 or the Abbey Roads EMI Modded V72 (higher gain like a V77) ?

Click to expand...

I was talking more about my recollection of what Geoff Emerick had to say about the Siemens V72S'eses used in the REDD 37 console versus the REDD 47 preamps used in the REDD 51 consoles. The V72S was the studio version made by Siemens for EMI that conformed to Abbey Road's 200ohm operation standard and therefore had 6 extra dB of gain outside the console versus a standard V72.  One may take my recollection for what it's worth.  Also, for what it's worth, many Abbey Road engineers have stated that for several reasons the V72 was definitely a better practical design than the REDD 47.  It also cost much more than the REDD.  That said, which one sounds "better" is certainly subjective.

electrochronic said:

No , actually there is a trimmer cap in the V72, verified with a real unit , its not just fixed cap value. This trimmer is in
parallel with a fixed cap. So I'm thinking there is some kind of calibration or circuit tuning
in this location. Few folks ever really mention its purpose.

Click to expand...

most interesting...

electrochronic said:

No , actually there is a trimmer cap in the V72, verified with a real unit , its not just fixed cap value. This trimmer is in
parallel with a fixed cap. So I'm thinking there is some kind of calibration or circuit tuning
in this location. Few folks ever really mention its purpose.

Click to expand...

It a high frequency filter for the (rather complex) negative feedback path. It's probably originally there so they could better match frequency response with varying output transformers. Feel free to use it for the same purpose. It's similar to the variable pF range feedback trimmer in LA2A.

And on the virtues of V72 vs. redd... Redd a "low cost" preamp compared to V72. There's no plate choke (replaced with a resistor). Those things have always been difficult to make and are expensive.

Kingston said:

It a high frequency filter for the (rather complex) negative feedback path. It's probably originally there so they could better match frequency response with varying output transformers. Feel free to use it for the same purpose. It's similar to the variable pF range feedback trimmer in LA2A.

Click to expand...

Very good to know.  Thanks Kingston!

guavatone said:

Flundran said:

Where did you find those rubber mounts visible on the red PCB's? Looks neat.

Click to expand...

-The Rubber mounts come with the PCBs

Click to expand...

I didn't get any mounts with my PCBs, but I bet rubber grommets will work.
Best,
Bruno2000

bruno2000 said:

guavatone said:

Flundran said:

Where did you find those rubber mounts visible on the red PCB's? Looks neat.

Click to expand...

-The Rubber mounts come with the PCBs

Click to expand...

I didn't get any mounts with my PCBs, but I bet rubber grommets will work.
Best,
Bruno2000

Click to expand...

Yes rubber grommets from hardware store or mcmaster.com

After some rewiring according to German VDE standards I've gained some 15 dB better THD-N.

Before:



After:

The V72 trimmer cap and resistor on NFB to roll off high frequencies so it doesn't oscillate.

Anywhere from 30K to 100K cutoff would suffice, so it is not all that important.  At least in my
findings with the REDD.47 ckt.

Holger, what does that red line mean?  Are you getting distortion?
Is that your noise floor?

did you try to see if the transformers are ringing?  

Also.  I noticed your Preamp PCB grounds go to the JLM PCB.  I got better results running the Preamp PCB
grounds to the star ground which looks to be the rear panel of your enclosure.

Another think to be careful of is crosstalk issues.  I found I needed shielded IP and OP lines to help as well as
shields between channel PCBs.  Paying close attention to wire dressing of IP and OP lines will help too.
I think crosstalk is due to the high current output of V2.

guavatone said:

Holger, what does that red line mean?  Are you getting distortion?
Is that your noise floor?

Click to expand...

The red and yellow line is THD+N for left and right channels. Before the improvements the channels were a bit different.
After the improvements the channels have the same THD+N behavior.

guavatone said:

did you try to see if the transformers are ringing?  

Click to expand...

I didn't notice any ringing.

guavatone said:

Also.  I noticed your Preamp PCB grounds go to the JLM PCB.  I got better results running the Preamp PCB
grounds to the star ground which looks to be the rear panel of your enclosure.

Click to expand...

The fun thing is that I did it that way before the improvements.

I didn't measure crosstalk but I'm sure that crosstalk is below anything I can hear or notice  .

Charlie, I'll answer yor PM.

i love your Pre