Strymon Co-Founder and Engineer Gregg Stock goes deep on power supplies

Strymon Co-Founder and Engineer Gregg Stock goes deep on power supplies

Our friends over at Japanese music tech publication 'Effect Book' interviewed Gregg Stock from Strymon's engineering team to get to the bottom of what makes a great power supply. 

[Effect Book]
Thank you for speaking to us. Please tell us your name, your role in your company, and your current position.


[GS]
I’m Gregg Stock. I’m one of the founders and our first “Analog Guy”. Recently I’ve been getting more involved in the DSP and the technology of Iridium in particular.

[Effect Book]
Please tell us the brief story of the power supply development team, from initial forming of the team to releasing the products.

[GS]
Putting powerful DSP chips in a pedal puts a strain on existing power supply solutions for pedal boards. I had experience with putting switching power supplies in audio equipment at QSC, Alesis and Line 6. So I was familiar with the challenges that it presented. I did the proof of concept designs and then Josh Forbes did the work of finishing the design, doing all the compliance testing and getting it into production.

[Effect Book]
How did Strymon find a way to newly enter the power supply product category? What are your features and strong points? Why have switching power supplies become overwhelmingly more popular than analog supplies?


[GS]
Switching power supplies have taken over almost every area of the electronics industry. They are more efficient, and the mass scale of their usage has brought costs down to where they are an option for almost every situation. The challenge in an audio setting is making sure that the high frequency noise that switching supplies generate is properly filtered. This was something that we had a lot of experience with. All the pedals we have designed, from Damage Control to Strymon have had internal switching supplies, so we knew what to expect. A large part of the testing was making sure that there were no issues with our competitors’ pedals.

[Effect Book]
The product names “Ojai” and “Zuma” seem unique. What is the origin of these names?


[GS]
Zuma is a beautiful beach near our office, and we liked the idea of the power of the waves in the ocean. Ojai is a nearby city and the name means moon or satellite in the Native American Ventureño Chumash language.

[Effect Book]
Power supplies for pedals tend to have interconnecting problems, especially noise. Would you explain potential problems for supplying power to multiple pedals? 


[GS]
It’s very important that each output is electrically isolated. That makes sure that each pedal has a dedicated path for the current that it demands. Our power supplies have a transformer on each output and not just a secondary winding on one main transformer.

[Effect Book]
We now live in a high-tech society with high-frequency environmental noise from wireless products, mobile phones, and computers. Do these environmentally related noise sources have an effect on pedal power supplies?


[GS]
By design, our power supplies have a high degree of immunity to noise. The same design techniques that apply to keeping the noise inside the box make the design more resistant to outside sources of noise. The biggest problems are from old pedals that were designed with the idea that they were getting power from a noise-free 9V battery. Many of those old designs are very susceptible to external noise.

[Effect Book]
According to the technical information available on Strymon’s website, Strymon’s power supply products make use of internally-built custom-made transformers. How did Strymon develop the technologies and architectures of audio power supply and transformer design? What is the reason for the adoption of custom-built components?


[GS]
We provide the specifications to companies that do the physical manufacturing for us. Designing custom magnetics is part of our design process. The magnetic components are so critical to the design that you are unlikely to find exactly what you need as an off-the-shelf part.

[Effect Book]
SMPS is used as the first AC-DC converter on the external adapter of Ojai and internally for Zuma and Zuma R300. Does Strymon’s SMPS have a special noiseless mechanism that is superior to others? Also, PWM is explained as the advanced switching circuit control system on your website. Is PWM one of the high-frequency noise control mechanisms in the SMPS? Please describe SMPS and PWM technologies to readers in words they can understand.

[GS]
A switching power supply is often abbreviated Switch Mode Power Supply (SMPS). Pulse Width Modulation (PWM) is how a switching power supply keeps the output voltage constant when the input voltage and load currents change.

The simplest explanation I have is that to power electronics from an AC wall plug, a transformer is required to provide electrical isolation and reduce the voltage to a level that is compatible with the electronics. The size and weight of the transformer depends on what the input frequency is. You can connect a transformer directly to the 50/60Hz wall outlet, and this is what happens in the older style designs. A switching power supply, converts the 50/60Hz wall voltage to DC and then chops up that DC to a high frequency AC voltage of 60,000Hz in our designs. Now the transformer can be dramatically smaller. Maybe not 1000 time smaller, but a significant amount. The other thing we can do is to change the pulse width of the AC waveform (PWM) that is used, and now the supply can operate anywhere in the world with the same transformer.

[Effect Book]
Generally, DC 12V is the standard primary voltage of power supplies for pedalboards. Why do Ojai and Zuma use 24V? What is the value of that?

[GS]
Zuma and Ojai use an EIAJ connector that is rated for 24V 3A. This can deliver 24*3 72W of power. If we were to use 12V, we could only deliver 12*3 or 36W with this connector. We also gain some advantages in the efficiency of the AC/DC converter by using a higher voltage.

[Effect Book]
I believe that flyback transformers and common-mode choke coils themselves generate a magnetic field that can be a source of noise to some extent. Is Ojai, which has a plastic body for the external adapter, fully shielded against inductive noise?

[GS]
The chassis of Ojai and Zuma are aluminum. The jacks are plastic, but since the majority of the chassis is metal, the shielding is very good. The shielding properties of aluminum at high frequencies is one of the advantages of a switching design. At 50/60Hz, it is very difficult to get enough shielding from a typical metal chassis – even using steel. This is why we outperform the old designs when it comes to proximity issues near wah pedals and such. The magnetic fields generated from a 50/60Hz transformer pass right through the chassis.

[Effect Book]
With common-mode choke coil, anti ripple noise condenser, optical isolator, and the second stage regulator (9V-18V), Strymon’s power-supplies are designed to be strongly protected against noise. Which of these are the most important factors and design considerations? Do all your power supplies have the same anti-noise mechanisms? Are there any differences between the flagship models and standard ones?

[GS]
All our designs use the same anti-noise mechanisms. I can’t say that one is more important than another – they all contribute their part. They are a team without a star player.

[Effect Book]
Some power supplies output 9.6V, which is nearly the same actual voltage output of new 9V batteries. Do Strymon’s power supplies output exactly 9V, or a little bit higher?

[GS]
We are actually a bit above 9V to more closely match a 9V battery.

[Effect Book]
As one of the ways to achieve high-quality “galvanic isolation” on output, polyimide-based CMOS digital isolation is highlighted recently in the audio industry. Have you tested any technology like this?

[GS]
We haven’t looked at that. The photo transistor isolation used in millions of supplies is good enough. I imagine that the CMOS isolation is focused on very high-speed signals. For a power supply application, the isolator is used to provide feedback of the error signal. The bandwidth of the error signal is in the audio frequency range. I don’t think there would be much advantage to a very wide bandwidth isolator.

[Effect Book]
The quality of DC cable is also an important factor for sounds. Is there anything special about Strymon’s included DC cables?


[GS]
We source good quality cables, but there is nothing exotic about them. For Strymon pedals, the internal switching supply makes the quality of cable irrelevant. They can adjust to a wide range of input voltages.

[Effect Book]
The last question is technical. 24 watts is the maximum power rating for the “PS-124” adapter which attaches to Ojai. Can this maximum 24 watts allow users to connect multiple power supplies up to its specified limitation (theoretical values)? Is Zuma capable of that too?


[GS]
Yes, you can daisy chain Ojai to get more outputs until you reach the 24W limit. I can’t remember exactly but after five or so Ojai, on one adapter there can be issues with the startup sequence. Zuma can provide 48W and Zuma R300 can provide 30W at the 24V EIAJ connector.

[Effect Book]
It looks to us like Strymon’s power supplies have an increased presence in the pedal market recently. Do you have any specific plans for new power supply products? Please talk about Strymon’s future prospects.


[GS]
We’ve always got plans for new products in all of our categories. The challenge is finding time to get to all the fun new stuff we want to do.

[Effect Book]
Thank you for talking to us.


High Resolution Images

We use cookies to ensure that we give you the best browsing experience possible. We'll assume that you are happy about that if you continue using this website or click 'read more' to see our Privacy Policy.