Cafe Walter Audio

02/24/2024

You all know that I do not ask you for money and I do not re-post things. But. This June, my very dear friends Martha Enson, Caela Bailey, Sari Breznau, and a few others are presenting a new, original musical called Venus and the Vixens, a retelling of the legend of Cupid and Psyche. (Martha wore the amazing champagne glass dress at V’s and my wedding in October, and Caela officiated.) The cast and band are incredible, and the heart and work that has gone into it is incredible. I have the honor to be the sound tech, and some of the composing work has happened at V’s & my cabin, which I feel super proud about.

A production like this takes a lot of love, a lot of work, and a lot of money. We are begging all our friends: can you help make this happen? We have a Kickstarter: http://bit.ly/VenusandtheVixensKicky

Disclaimer: I will be getting paid as a sound tech, because we’re trying to pay all of the cast and crew, but I have already donated way much more to the Kickstarter than I expect to get paid, because *this stuff matters. Art matters. Seattle’s theater and circus scene matters.*

Please, please, help make this happen. And come to the show: it will be fantastic.

An interactive rock musical, and joyous antidote to isolation and technology overload. This immersive theatrical experience has it all!

03/17/2023

A lot of people have had bad things happen to them in the storms hitting California. My friend Ronan Chris Murphy is one of these people. Fortunately he and his partner are uninjured (so, better off than many folks). But a 150’ redwood bisected their house/studio. While he was in it. The building is totalled and tens of thousands of dollars of studio gear is destroyed, and of course this is also his livelihood. Much of this - as those of you in the music biz will understand - will not be adequately covered by insurance.

Check out his video here. He’s trying to get some money to cover expenses. He’s got a GoFundMe but also is generously offering his 12-hour course on drum recording, normally $247, to anyone who pays anything. I watch his videos and have learned a lot.

If you would like to help raise funds by paying what you want for my Drum Recording Boot Camp course head on over to https://drumrecordingbootcamp.com A dear...

11/28/2021

A few days ago on the Tube Amplifier Diagnosis and Repair group on FB, where I hang out, I mentioned an oddball class A single-ended amp I was working on for a customer. One complaint was excessive 120Hz hum. The hum was constant even with the power tube grid grounded and the preamp tube removed.

Single ended amps do not have the built-in power supply ripple rejection that push-pull amps do. There is ripple on the B+ rail; with the power tube grid constant, the tube tries to keep its plate constant as well; thus that ripple is imposed upon the output transformer primary, and shows up at the output.

I thought about the problem and decided what I needed to do was siphon a bit of that B+ ripple off and inject it into the circuit somewhere where it would cancel out. But where? I couldn't inject it into the preamp tube, because then with master volume turned down the hum would be turned up. I couldn't inject it into the power tube's grid, because then it would be inverted on the plate and the hum at the output would be even worse.

The only other answer was the power tube cathode. But how? The cathode is bypassed to ground with a big capacitor, so it is by definition hard to inject an AC signal and have it do much. You need a lot of current, and that rules out using a resistor, because a resistor from B+ to cathode would be dropping hundreds of volts while also passing a lot of current - it would get very hot.
The answer is a capacitive divider, and just as I realized this, I was happy to discover this article: https://www.tubecad.com/april99/page2.html which came up with the same suggestion, two decades ago. Nothing is new under the sun!

In my case, the cathode bypass capacitor was 220uF. A 1.5uF capacitor from B+ to the output tube's cathode proved to completely null the hum, regardless of master volume position. The amp is dead quiet and tone is unaffected.

A handy trick to have up one's sleeve when working on single ended amplifiers. As much of my repair business consists of old and odd amplifiers, I'm sure I'll be using this again!

08/14/2021

This week I’m in Mexico City, having had the amazing honor of running sound on Wednesday for Degenerate Art Ensemble’s performance “Skeleton Flower” as part of the Festival Internacional de Danza Contemporánea de la Ciudad de Mexico (FIDCDMX).

Costume by Wyly Astley, photo by Bruce Tom.

05/19/2021

Can I brag a little? I’m feeling super proud of myself. This is the guts of a Strymon Flint, a popular but expensive reverb/tremolo pedal for guitar. Needless to say, schematics for things like this are not available; you can’t even trace the PCB by hand, because it’s a multi-layer board. But I figure, it’s basically a big DSP chip, a bunch of RAM, a few different switch-mode power converters, some control encoder buffering, an ADC, a DAC, and a bit of analog I/O, right? How hard can it be?

In hindsight it actually took longer than it should have... the TL072 that buffers the input was fried. The trick was, it wasn’t *totally* fried, it just had crazy high bias current, that was causing a protection diode to conduct enough to shunt the input signal. Enough signal was getting through to fool my troubleshooting.

The clue, that I initially discounted? There was a small DC voltage on the input.

05/05/2021

In rehearsal with Degenerate Art Ensemble. I am so excited to be back in a theater again!!

03/28/2021

So my customer brings me an amp with a loud fan. And I think “no problem, just get a PWM thermal fan controller and a PWM fan.” Well, there’s a bunch of PWM fan controllers on Amazon, but no specs and the instructions are written by someone who is not a native or fluent speaker of English, which is sadly the only language *I’m* fluent in. I buy one anyway. It does not work. But it comes with a temperature sensor... and I have an Arduino lying around....

03/06/2021

Death cap from a Gibson GA15RVT that somebody worked on. They replaced all the caps (including, undoubtedly, caps that were perfectly fine) - but the soldering is atrocious. See how on this one they just draped the capacitor lead over the terminal and added a little solder? They didn’t even trim the lead! Other solder joints weren’t even joined at all.

I love working on old amps. I hate working on old amps that were “fixed” by hackers like this - it’s much harder to undo the damage.

02/12/2021

Before & after of a Univox 1236 bass amp from the '60s. Almost all the oil-filled caps had high leakage current, so all the voltages were wrong; one preamp tube needed to be replaced; the electrolytic caps were failing (e.g. those 50uF actually measured around 25uF); some of the carbon comp resistors had badly drifted; and it needed a grounded cord.

This thing is now a BEAST! Sounds awesome. It's so quiet you can barely tell it's turned on. Produces 30 pretty clean watts before the onset of clipping, with an input sensitivity of 20mVrms. I don't usually covet my customers' amps, but this one... yum.

02/11/2021

Hey all you nice people! I’ve been posting lots and lots, but mostly just as myself (Walter Walter Harley) and mostly on FB groups like Tube Amp Repair and Solid State Of Mind.

Would you like me to post more here, or is it just more noise?

08/06/2020

Hi, folks. My DNS registry got hacked and my domain (both email and web) is pointing to a Russian server right now. Please do NOT vvisit my site or send email (or click on anything you get from “me”) until this is resolved. Should just take 2-3 days to fix.

05/08/2019

My first ever Reddit post! https://www.reddit.com/r/Nest/comments/bmcf0p/the_nest_hello_chime_connector_teardown/ . In which I eviscerate a small household automation device.

Posted in r/Nest by u/cafewalter • 1 point and 0 comments