Rens Heijnis                                      custom-built audio equipment

Monitor amplifiers
Duncan Cowell from Sound mastering ltd.
They have a beautiful, neutral, natural sound that we want to listen to forever.

Active powered microphones after retrofitting (+60v)
Below you can read the opinion on active powered microphones of some recording engineers:

Neumann U89, Gonzalo Noque
They're sounding fabulous!
The improvement is magical, and you've turned a first class mic into a world-class one.

TLM49, David Spearritt
The modification that Rens has implemented has improved the TLM49 significantly.
The upper midrange brashness or exaggeration is gone, the top is sweeter, and the bass appears
to have a slightly greater output and more balanced with the rest of the spectrum. Very impressed. 

B&K 4006
1) I was never really satisfied with how they sounded but after the retrofit:
They captured the group very well and the sound is excellent. They are less strident now.
The piercing treble sound is gone---much smoother.

2) A smooth clarity and openness that was not present before with these mics was immediately evident.
I am very pleased so far!

DPA 4041
The conductor here is very happy with the 4041 sound - and me too. Huge difference.
I have even pointed them down, towards the strings which was a crime before your modification.

Schoeps
1)Retrofitted Schoeps acting like there is blanket removed from the capsule.
Very well defined, no boomy mid lows.
 
AEA A440 ribbon microphone
Immediately when I and my girlfriend heard the first sounds comming out of the AEA,
we were very surprised by the sound. Almost shocked, how round and solid it sounded.
This was not the sound we remembered before the modification! We are certainly very happy with it !!
 

Battery powered pre-amplifiers
Below you can read the opinion on the battery powered pre-amplifiers of some recording engineers:

I like the sound. It is very pure and lovely to listen to. Your preamplifier is making a really nice
difference here, It sounds fantastic. 

It has got the superb sound that made me impressed.

I am very impressed by your system. The words that come in my mind:
Very natural, quiet, round, more body, warm, intimate, you are directly involved.

It sounds a lot less electronic.

The sound is beyond anything I could have hoped for.

Headphone amplifier, Gonzalo Noqué
I´ve finally spent some time with the headphone amplifier, it is amazing!
I´m amazed by the level of detail it brings, and specially regarding the "spatial" feeling.
 

Modify microphones
Before modification of Flea microphones: I like the body and the depth of their sound
but they are definitely too harsh and acid...
After modification: they are softer, less harsh and give me a lot of satisfaction on the orchestra.