PIO upgrade from polypropylene - worth the effort?

[McIrish]

I've got a couple Miktek CV4 mics that I have swapped the capsules on. They sound very good now. the original capsule was a pretty bad K67 type. The circuit has no hi-freq reduction so that capsule sounded horribly harsh. Anyway, the Beesneez K7 and the Flat 47 both sound great in this mic. But, like everyone, I'm always looking for ways to upgrade it even further. I was wondering if changing the output cap from the stock film to a PIO would be a sonic difference that could actually be heard. My guess is that the change would be very subtle. What say you?

 

[rock soderstrom]

I was wondering if changing the output cap from the stock film to a PIO would be a sonic difference that could actually be heard.

What is the stock capacitor? I would be interested in some gut shots.

I always find capacitor sound discussions fun! Opinions vary widely, to put it neutrally.

 

[Tubetec]

I remember way back using Dubilier Nitrogol 0,1uF as a coupling caps , they were metal cased , I bolted the things down to chassis ,
The incidental capacitance to ground made a big difference in this case , responce started to tail off around 8khz ,
Physical size might be another issue , generally PIO's are a good bit larger than an equivalent value poly foil .

 

[McIrish]

The capacitor in question is the larger one, C5.

 

[rock soderstrom]

This could be a Panasonic film capacitor.

There seems to be enough space to try other caps. More "original" would be a MP capacitor from Bosch/Siemens or other manufacturers.

 

[dmp]

Might be worse... can be pretty subjective.. but subtle compared to a capsule change. Space might be a challenge as some PIO are large. Looks like you would need ~200v?
I might consider a different film cap... like a Wima MKP or Mallory 150.
I found parts swaps like this were too subtle for me to care too much - bigger changes come from capsule, transformer, and tube bias scheme (cathode or fixed)

 

[Tubetec]

I doubt you'd have room in the above for what you see below ,

 

[rock soderstrom]

ERO MKT 1816 in the 160V version might also do, depending on the B+. They are relatively small in design.

 

[C12VR]

why? If anything you might see reduced bass response and increased distortion from an old capacitor leaking DC into the primary and saturating the core of the transformer. In that case the change wouldn't be subtle, but it probably wouldn't be good, either. The output cap is a critical component and should be of known quality. Most if not all PIO and paper caps are decades old by this point, meaning the paper has acidified/electrolyte turned, and if not still have a shorter lifespan, as opposed to a film cap which should last more or less indefinitely. Plus cheap, plus smaller. gud.

 

[bremusound]

Neumann uses Vishay MKP 1839 HQ caps in the M49V.

 

[Khron]

"Upgrade to PIO" - a bit of an oxymoron?

 

[McIrish]

Well... sometime "oxymoron" is pretty descriptive of me.
I agree, it's probably a dumb idea but I wanted to get confirmation on how dumb the idea was. Space is a bit of an issue as well.

 

[Tubetec]

I have all kinds of paper in oils , most of them are 70 years or more old , as long as they dont leak oil they tend to work ok . Some of them will have PCB based insulating oils inside , so wear gloves while cleaning up any mess thats leaked out .

Those green ERO MKT caps are nice , compact size and available in voltages suited to tube mics.

Trying various values might be more productive , the value you end up using is always a compromise , I found 1uf good for smaller string instruments like madolin , then again up close on voice you might 0.47uf helps curtail any proximity effect better .

 

[doqmemory]

I was wondering if changing the output cap from the stock film to a PIO would be a sonic difference that could actually be heard.

Since this seems to be similar to the "Bulldog" version of Oliver's alternate U47 design (from the now-defunct Compass Studios site), the biggest difference (other than capsule and transformer) would come from replacing the self bias with fixed bias, using the schematics on the AMI website. I am not sure if the power supply will provide a clean enough heater supply.

 

[terry setter]

Here's my experience with this. C5 will certainly make the most difference. The cap in your picture can probably be improved upon. I find Audience "Auricaps" can sound quite good. I like the sound of the higher voltage versions more than the lower voltage versions (450 or 600 vs. 250V). The green Russian cap that Tubtec showed you is magical in a U47 clone circuit (.47mF/250V). The Bosh MP that was mentioned is in the original U47 and can still be found, but they're quite costly now. Those are my three favorites, but I've been experimenting with SMR caps because they are the fastest discharging caps currently being made. Results, so far, for the SMRs are promising. Teflons sound good, but the voltage restrictions, insane cost, and very long burn-in times have kept me away from trying them as output caps.

C2 can also be heard, if you're really paying close attention. When doing a U47 clone, I ended up with a ceramic - yes, I said ceramic - cap there and felt that it moved the dial 1% closer to my target sound when compared with the HiFi poly cap that I had started with. Also, I tried paralleling C0G ceramic caps for a mic's output because they are said to have "no distortion". That was a DISMAL failure! So bad I couldn't believe it, but I don't know why because the result was so awful that I wasn't willing to put even one more second of my time into investigating them. However, I do like C0Gs and NP0s quite a bit for AC bypass and related applications (such as C2 in your diagram).

Just remember that in comparison to changing the capsule (about 85% of the mic's sound) or the transformer (about 10+ % of the mic's sound) , or the tube (about 5% of the mic's sound), changing the caps is only going to make very subtle differences - except if you parallel C0Gs on a mic's output, but I've already warned you off of that.

 

[living sounds]

Somewhat OT, but I found that in U87 clones a "cheap "electrolytic on the output (before the trafo), like the Jamicon one Neumann uses in their current verison of the mic, sounds subjectively better than a high quality polypropylene cap of the same capacitance.

 

[Purplenoise]

In my mics I try a lot of out caps and most do make a difference. A PIO or mp cap sounds different than a film cap and sometimes it’s not even subtle. I have no idea why that happens ( and yes capacitance measures the same in the swaps) but it definitely happens. I don’t have a preference though…sometimes even an electrolytic could sound better ( subjectively) in a circuit.

 

[karloff70]

I remember swapping a Wima poIyprop output for an NOS Siemens PIO in a G7 buiId ages ago and Iiking it a Iot. You can aIso pIay with size I suppose and make bigger and see what happens to girth. But it's pretty much throw the dice, and between different oIder caps, circuits, tastes and ideaIs you wiII find out what pIeases you most in that particuIar mic. If you go there. IoI

I do swap a Iot of caps in rack gear to tone tweak, and agree with previous peeps that ERO Mkt have made me smiIe aIot more than once.

 

[Ricardus]

A PIO or mp cap sounds different than a film cap and sometimes it’s not even subtle. I have no idea why that happens ( and yes capacitance measures the same in the swaps) but it definitely happens.

Confirmation bias?

 

[tomas.borgstrom]

More info on the topic in this thread

https://groupdiy.com/threads/all-things-c12-output-capacitor.81149/