The "Bordello Red" GSG build and questions

2nd harmonics for the masses

Re: The "Bordello Red" GSG build and questions

Postby AlexLTDLX » Tue Apr 29, 2014 11:14 am

I do think the couping capacitors in a design like the GSG would have a significant impact on the overall sound of the amp due to the simplicity of the design and the crappy effects of a capacitor on an audio signal; thus my focus on them. I've swapped rectifier tubes and heard basically no difference. I've also had two 6sl7gt's in here and aside from the obvious faults in the first tube and the difference in gain, heard very little, if any difference. When Matt finishes his GSG, we'll do a thorough comparison of the two amps, and try different output tubes, but I'm not expecting a whole lot of difference - we both have NOS tubes of different internal design - spearate plates vs connected plates. But anyway...

So then I swapped the coupling caps - and there's a BIG difference. And it's actually logical, if you think about it. The Mudorfs are not "normal" capacitors. They're two larger value caps in series in a single housing. The orange drops are more "normal" capacitors - just a single winding of 2 plates & 1 insulator. All the flowery, subjective terms used like, "sweet," "bright," "musical," "dark," etc, etc are quantifiable and can really be broken down to three groups (on my thinking):

1. Distortions (I include resonances in this group)
2. Frequency response (this includes harmonics, which are frequencies)
3. Dynamics - in this case, the limiting factors are impedance, resistances and inherent noise.

The Mundorfs likely have a little lower distortion than the Orange Drops (probably measurable by ESR), but the two caps in one housing roll off the upper mids, for whatever reason - be it impedance or whatever. I'd bet my house on that. That's what I was missing. I don't have nearly the experience rolling caps as I do other parts, but I do have some; my stash is modest - I've got some vitamin Q's, a bunch of ERO/West Germans, some GE's, Western Electrics (out of a phone switching machine), Mundorfs and a slew of unknowns. My observations tend towards generalizing capacitor "sound" by construction type and materials - paper insulated caps tend to be highly "colored" - meaning they exhibit distortions, non-linear curves re: frequency and other funkiness that comes from the variables inherent in paper, along with paper's propensity to greatly change dimensions (therefore capacitance and other quantifiable electrical measurements) depending on humidity and temperature. That's why I generally shy away from them and other organic materials like wax. I've never tried teflon caps. Paying $200 for a pair of coupling capacitors crosses my personal line of, "a fool and his money are soon parted." That, and I'm a cheap bastard. And I've learned that more expensive, especially in the hi-fi world, doesn't equal better. In fact, it rarely does. Interconnects are a prime example. I can build a set of interconnects for a few bucks that will sound better or as good as ANY interconnect on the planet (unless you're in an RFI-heavy environment. Then we've got to use shielded cables; when it gets really bad, go balanced.) The secret - not much of a secret, really - good insulation, good conduction and minimize electrical interaction between the two - capacitance and impedance.

Here's an example:
Image
50 cent nickel plated brass connectors, bakelite connector housings (I've found fancy-pants metal housings typically introduce audible capacitance - even WBTs and the like; so I use them only in noisy environments), teflon insulated, stranded silver-plated copper conducts. Simple, cheap and will outperform thousand dollar "rhodium" interconnects. If you don't have that wire, try a twisted pair cribbed from an ethernet cable - almost as good.

Anywho - the differences between the Mundorfs and Orange Drops are huge, at least in my system. The one interesting great unknown is the psychological factor - here's what I mean by that. This morning, I fired up the Bordello, and it sounded a bit harsh and "glary" again this morning. It's now just afternoon, and I swear it's starting to mellow out. Now, is that the caps "re-breaking in," or is that just my perception? Is that a Seatlle Poncho or a real poncho? Who can tell anymore?

20to20 mentioned I might have some "meaningful insight" based on my profession - I dunno about "meanigful," but I can tell you this - we never "break in" ANYTHING. We might break it, but never break in. We just use it, and figure out how far from metered reference the "whatever it is" is - I look at vectorscopes and various flavors of waveforms and audio guys look at levels and phase meters. But mostly we just watch and listen what we're doing. That might explain why I NEVER watch TV at home. One of my composers hates what he calls, "Star Trek" equipment. One of his observations: if a vocalist brings a $5,000 mic onto his studio, he knows he's going to have a hard day, because the vocalist will suck.

Here's another interesting tidbit, work-related, and touches on the sound/brain interface. Do you know how Nielson and Arbitron (they just merged, btw), track over-the-air commercials? They insert an audio tone. SMACK DAB IN THE MIDDLE of the audio spectrum. This tone contains all relevant tracking information about that commercial. But have you ever heard anyone actually notice it or say something? Nope. But it's there, and loud/prominent enough to be recorded and played by by a VCR and heard by a mic in the room. As Spock (maintaining the Star Trek motif) would say.... "Hmmmm... fascinating."



Gregg - Thanks, and yeah, these speakers definitely have some of my serious time poured into them. There's another way to look at these speakers - just Fostex 103's with a tweeter and sub added. I actually codified that journey on AudioKarma:

http://www.audiokarma.org/forums/showth ... p?t=345806

Clearly, I was funnier then. I hope this is only a temporary lull in my humor. They started out as Cerwin Vegas - then I ultimately replaced virtually everything except for the boxes. Here's how the crossovers started:

Image
The original crossover is on the right. At the top left is the Erse crossover I started with, and on the bottom left is how the Erse crossover went into the boxes *at first*.

And this is what they ended up like:
Image

That's what they've looked like since I "finished" them. That picture actually makes me laugh. But it works. See - I do spend some time "tweaking" the sound, :'(

It's probably good that I'm using those speakers as my reference point, because I just ordered a pair of Fostex Kanspeas with 103n's as desktop speakers to go with the Bordello.

And, because I've taken the photo, here's another "Bordello Red" beauty shot - notice how much taller the Sylvania 6sl7GT is compared to the GE tube (look back at an older photo):

Image
AlexLTDLX
 
Posts: 22
Joined: Sat Feb 08, 2014 10:02 pm

Re: The "Bordello Red" GSG build and questions

Postby AlexLTDLX » Mon May 05, 2014 8:51 am

A couple more observations and updates. I spent WAY too much time researching stuff about capacitors over the last week or so. Nothing makes me quite so sleepy as reading page after page of technical documentation about dielectric constants, absorption and dissipation. Just typing that last sentence makes me yawn. So here's the REALLY simplified view:

The higher the dielectric constant, the more capacitance can be crammed into the same size capacitor. Electrolytics have a high dielectric constant - around 8 or 9. Their dielectric (i.e. insulator) is either aluminum oxide or tantalum oxide. By comparison, air has a dielectric constant of 1. The reason why people complain about electrolytics in an audio application is that, along with a high dielectric constant, typically comes a high dielectric absorption. Have you ever run down a battery in a flashlight until it got very dim, switched it off, and then switched it back on after a little bit and the light was brighter than just before you switched it off the first time? That's a similar effect to dielectric absorption. When a capacitor is charged, the dielectric "absorbs" some of that electricity. When the capacitor is discharged, like the flashlight, the output goes pretty close to 0. Then, as the dielectric "relaxes" (whatever that means - I stopped caring at around this point), the charge INSIDE the dielectric works it's way to the plates of the capacitor, and the capacitor is "magically" charged again, without an outside electrical input.

So, in short - generally speaking, the lower the dielectric constant, the more "accurate" a capacitor is. This goes along with a capacitor's ESR (equivalent series resistance) and ESL (equivalent series impedance) to form the "sound" of a capacitor. Teflon has a dielectric constant of 2.0; polypropylene is around 2.2-2.3, polystyrene is around 2.4, paper/oil is around 3-3.5. Interestingly, when tested for bridge residual (i.e. noise), polypropylene capacitors are quieter than teflon - at least in the two tests I found.

So there you have it. Now, in the words of Gregg - "all that matters... is the sound to your ears," here's real world impressions:

Last week, the Kanspeas showed up:

Image

I've already admitted that I like these things; they're the mids in those giant speakers in the back, and I've grown fond of their very close cousins over years of listening to Fostex 6301b's in different studios - I actually now generally prefer them to just about anything else, price be damned. I can listen to them for hours without any fatigue, headaches or unwanted pregnancies. So I took the Bordello Red and the Kanspeas into the editing suite for a few days, and went to work.

The first thing I noticed was how much clearer and detailed they are over the professional, all-digital 5.1 surround system that's in the suite and was voiced SPECIFICALLY for clarity. It's not even close. We're not talking "subtle." The difference is HUGE. I could run the sub along with the Bordello/Kanspea combination. Let me tell you - unless you need "rock the house full of people" volume levels, the Kanspeas with a halfway decent subwoofer along with a GSG is a system that you won't beat for anything under 5 figures (at least). The sound is amazing. I actually ran the setup without the sub 90% of the time. At reasonable levels, it's not really needed.

Next observation: with professional gear, when somebody's cell phone receives data, you hear it in the mix. I'm not talking about the ringer (which is hopefully muted) or the vibrator (too easy to make a joke here, I'll take the high road). I mean the actual data makes a noise. It's not subtle. If I'm directing a talkshow and the guest has their cell in their pocket and it's set to silent, but the data's still active, when a text comes in, the ENTIRE control room will collectively sigh, "UUUUGGGGHHHHH" - not just the audio guy. It's a sound you can't miss. Anyway, I had my cell next to the Red and my cell was set to silent; I got a text and I heard that noise. First time I've ever heard it in an edit suite.

The red is also sensitive to the media raid getting pinged for data - it'll come through as little clicks in the speakers. That could probably be worked out pretty easily by re-routing cables. This was just a temporary setup, after all.

However, after several days (we have a documentary-style job in the suite that features interviews from mayors around the country shot in a hotel room at a convention, so it's lot's of talking with odd noises from the hallway), it would be tough to go back to the other digital setup. Not sure what I'm going to do yet.

And the Orange Drops are staying in. I have a hard time believing $200 teflon caps would be worth the cost.
AlexLTDLX
 
Posts: 22
Joined: Sat Feb 08, 2014 10:02 pm

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