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12/21/14

Patchbay Neutrik NYS-SPP-L1

Patchbays can help minimize headaches when hooking up your studio. One unfortunate thing about patchbays is that there isn't any industry standard for defining how each connection is described.

PATCHBAY 101 - PART 1

trenton blizzard patchbay neutrik nys-spp-L1
In this post I will be demonstrating the basic connections of the Neutrik NYS-SPP-L1. The NYS-SPP-L1 is a relatively inexpensive 19" rack-mount patchbay that requires 1/4" TRS (Tip-Ring-Sleeve) plugs.

 WHAT IS A PATCHBAY?

A patchbay is a box that is made of jacks and switches. Depending upon how the "Panel Jacks" are internally connected determines how the signals will be routed when you insert your plugs.

WHAT ARE THE DIFFERENT CONNECTIONS?

There are many terms to describe the internal connections of patchbays. Each manufacturer interprets these terms a bit differently. So, it pays to ask a few questions before you buy one. The most common connection term is "NORMAL". Normal describes how the front panel jacks interrupt the rear panel connections when a plug is inserted.

"NORMALLED"

Full-Normal - Both front jacks interrupt the rear connection
Half-Normal - Only one front jack interrupts the rear connection (but you don't which one until told)
Half-Normal (Top) - The "top" front jack interrupts the rear connection
Half-Normal (Bottom) = NYS-SPP-L1 = The "bottom" front jack interrupts the rear connection

trenton blizzard NYS-SPP-L1 half normal

Neutrik identifies the "Half-Normalled" jack with grey plastic. See the first image for connection reference.

REAR PANEL CONNECTIONS

The rear panel connections are historically used for routing signals from the output of your mixer to the input of your tape deck or DAW these days. These rear panel connections are maintained until you insert a plug into the front of the panel (for "normalled" configuration).

MIXER OUTPUT SIGNAL


trenton blizzard NYS-SPP-L1 rear input signal

This oscilloscope image "represents" a signal that could be coming out of your mixer and into the "top-rear" jack on the patchbay. This signal is automatically connected, through front jack switches, to the "bottom-rear" jack as will be seen in the next image.

MIXER OUTPUT ROUTED TO YOUR DAW INPUT


trenton blizzard NYS-SPP-L1 rear panel connection

The pink trace represents the signal coming out of the rear-bottom jack. This is the same signal as the top-rear jack. Keep an eye on the pink trace as I insert plugs into the front panel jacks.

MIXER OUTPUT ROUTED TO "FRONT-TOP" JACK

trenton blizzard NYS-SPP-L1 mixer output routing to front plug

The green trace represents the output signal available at the "top-front" jack. Because the NYS-SPP-L1 is "half-normal (bottom)", the top-front jack does not interrupt the rear signal connections.

MIXER OUTPUT SIGNAL "INTERRUPTED"

trenton blizzard NYS-SPP-L1 mixer output interrupted

Notice that the "pink" signal is gone. Because the NYS-SPP-L1 is "Half-Normal (Bottom)", only the bottom front plug interrupts the connection on the rear jacks.

Note: The mixer output signal is still present at the front-top jack. So, to complete the connection we need to route the signal from the "front-top" jack into the "front-bottom" jack.

MIXER OUTPUT ROUTED THROUGH THE PATCHBAY

Assuming we plugged the "top-front" cable into the input of your compressor and the output of the compressor back into the front-bottom jack, this is how you would "route" the output of your mixer through a compressor, before you go into your DAW.

Patchbays can be very handy.
In a future post I will demonstrate the "SPLIT" patchbay configuration.

Thanks for reading,
Trenton

12/4/14

Vacuum Tube Preamp Stage

Calculating the "AC gain" of a 12AX7 common cathode stage is a fairly straight forward process. Follow along as I go through hand calculations, SPICE simulation and real world testing.

12AX7 GAIN STAGE SET-UP

The signal generator is on the left, the high voltage power supply is in the center, and the oscilloscope is on the right. The circuit was built on an electronics breadboard using a 12AX7 vacuum tube breadboard adapter.


THE CIRCUIT

This is the common cathode 12AX7 gain stage we will be building. It is a common design found in some popular amplifiers. The plate resistor is 100k ohms and the cathode resistor is 1k ohms. The predicted SPICE simulation is show as well.


This stage is "inverting" which means the output will be 180 degrees out-of-phase with the input at mid-band frequencies. The SPICE simulation plot shows the out-of-phase signals. SPICE predicts the output will be about 3.6 Vpk for a 100 mVpk input signal. This is a gain of 36 V/V.

HAND CALCULATIONS

You should always begin your designs with hand calculations. It is a good way to check your understanding of the circuit you are trying to build.


The equation in the top left is what you will use to calculate the gain of an "unbypassed" common cathode gain stage. If your cathode resistor is bypassed with a capacitor, you can remove the Rk(u+1) from the calculation and get much higher stage gain. Note: I have omitted the "minus" sign that indicates "phase inversion".

 ASSUMPTIONS

 The gain equation we are using is based on the following assumptions:
1. All tube parameters are held constant
2. The signals being amplified are small
3. We somehow know the value of internal AC plate resistance "rp"
4. We somehow know the value of the tubes amplification factor "u" mu

I will show you how to get the values for "rp", "u" and "gm" in a future post.
For now, let's assume u = 82 and rp = 40k ohms. We don't need "gm" for this exercise.

 BUILDING THE CIRCUIT

The circuit was built on a breadboard using the resistor values shown in the schematic. The resistors are simply connected to the appropriate tube section with the header pins that are identified on the PCB. Heater connections 4, 5, and 9 are the center three pins. These adapters are designed for dual triodes so the second tube section is connected to the three pins on the right.


REAL WORLD RESULTS

Simulation is one thing. But, reality is what really matters. According to my hand calculations the voltage gain should be about 36.7 volts per volt. That means if we put a 0.1 Vpk signal into this stage we should get an output signal around 3.67 Vpk.


 The blue trace in the image is the 0.1 Vpk input signal. The yellow trace is the output signal which measures right around 3.6 Vpk. Not bad! Notice that the signals are out-of-phase.

DC PLATE VOLTAGE

SPICE predicted the DC plate voltage would be around 151.43 VDC. The acutal Plate votlage measured was 150.5 VDC. Again, not bad at all.

 

DC CATHODE VOLTAGE

SPICE predicted the DC cathode voltage would be around 0.985 VDC. The actual cathode votlage measured was 1.112 VDC. Again, pretty close.


WHERE TO LEARN MORE

If you are really interested in tube audio design here are some books I recommend.

1. Radiotron Designer's handbook by RCA - Totally old and totally awesome.
2. Audio Cyclopedia - Expensive but worth it.
3. Beginner's Guide to Tube Audio Design - Not for "beginners" but a handy reference for equations



Thanks for reading,
Trenton

11/9/14

HIGH VOLTAGE TUBE POWER SUPPLIES

If you are interested in working with vacuum tube audio circuits it is very handy to have an adjustable high voltage power supply on your bench. Not only will you need high voltage for the plates, but you will also need 6.3V or 12.6V for your heaters.

Sometimes you may even want an adjustable negative bias for measuring tube characteristics. There are a couple of classic power supplies on the used market that fit those requirements. And they are both built with vacuum tubes!

HEATHKIT IP-17

 

Trenton Blizzard Heathkit IP-17 Vacuum Tube Power Supply

The Heathkit IP-17 is a good high voltage adjustable power supply. It has an adjustable output that ranges from 0 to +400 VDC. The IP-17's typically run about a $200 in decent shape. The users manual is typically still available and it includes the circuit schematic.

HEATHKIT IP-17 features:

1. 0 to +400V High voltage DC output
2. Negative adjustable DC output for grid bias or characteristic measurements
3. 6.3 VAC for heaters
4. 12.6 VAC for heaters
5. DC current meter to monitor high voltage supply current
6. DC volt meter to monitor either the high voltage or the negative bias supply



EICO 1030

Trenton Blizzard EICO 1030 Vacuum Tube Power Supply

Another great high voltage vacuum tube power supply for audio design is the EICO 1030. It is very similar in operation and design to the Heathkit IP-17. However, the 1030's incorporate a printed circuit board in the design. These tube power supplies tend to be a little less expensive than the Heathkit models.

EICO 1030 FEATURES:

Pretty much the same features as the Heathkit but with a different front panel layout.

1. 0 to +400V High voltage DC output
2. Negative adjustable DC output for grid bias
3. 6.3 VAC for heaters
4. 12.6 VAC for heaters
5. DC Current meter to monitor high voltage supply current
6. DC volt meter to monitor either the high voltage or the negative bias supply

HEATHKIT IN ACTION

My next post will be about building a 12AX7 gain stage using vacuum tube breadboard adapters.

Trenton Blizzard 12AX7 Gain Stage

So, if you are interested in building vacuum tube audio gear, I highly recommend looking into one of these supplies. They are a extremely useful pieces of equipment. The ability to find the perfect plate supply voltage for your tube mic-pre's makes them worth the investment.

As with any electrical circuit, always use proper safety precautions and never let anyone touch the energized circuit!

Thanks for reading,
Trenton


10/13/14

CONDENSER MICROPHONE KIT

Have you ever considered building your own condenser mic? If so, then a kit from Microphone-Parts.com just might be your ticket.

DIY FET MIC KIT

Their RA-23 kit includes everything you need to build a working condenser microphone. You supply solder and soldering iron as well as precision screw drivers for assembly.

Trenton-Blizzard-DIY-MIC-KIT-2014

EASY TO BUILD?

Although these mics are not extremely difficult to assemble, they are probably not the best choice as a "first kit". However, after you have a couple stomp-box builds under your belt you should be ready to take it on.


Trenton-Blizzard-DIY-MIC-PCB-2014

There are two PCB (Printed Circuit Board) assemblies that need to be "assembled". This kit included their MP-V57 PCB kit. Capsule bias, or "sensitivity", is adjusted with the blue trimmer potentiometer.


Trenton-Blizzard-DIY-MIC-2014

CAPSULE CHOICE

You choose the capsule type when ordering. You can go from mild to wild if you like. I went with their most popular RK-47 capsule because I am going to be modifying this mic in the future.


IS IT WORTH IT?

If you are looking to gain some "build experience" with condenser microphones then I think it's worth it. It's a good kit, with good parts and the instructions are really good. It's a great microphone for the money. And, you get bragging rights because "You-Built-It-Yourself".


Thanks for reading,
Trenton

7/15/14

VACUUM TUBE BREAD BOARD ADAPTERS

Prototyping with vacuum tubes is always challenging. So, a while back I designed  a few simple adapters to make it easier to prototype tube circuits with standard electronics bread boards.

Make sure to use a high quality bread board with these and don't go too crazy with the voltage levels. Also, pay attention to the heater current because it can be a few amps with larger tubes!

BB-X7 TUBE ADAPTERS


BB-X7 tube adapters are specifically designed for 12ax7 tubes. All tube elements are marked on the PCB for easy identification. Of course, they work equally as well with 12AT7, 12AU7 and 12AY7 tubes. These things make it a breeze to prototype 12AX7 preamplifier designs. Of course, high voltage precautions should always be followed when using these little gems.

BB-84 TUBE ADAPTERS


BB-84 tube adapters were designed specifically for EL84 power pentode tubes. All tube elements are marked on the PCB for easy identification. Now those single ended and push-pull power stages are much easier to design. Once again, always follow proper high voltage precautions when in use.

BB-OCTAL TUBE ADAPTERS


BB-Octal vacuum tube adapters were designed for a 6SN7 preamplifier I was working on at the time.
They can, however, be used for power amplifier designs if you pay very close attention to how you hook up the heater current. Also, extreme care must be exercised when using high voltage power tubes.

BB-NOVAL TUBE ADAPTERS


I love the EF86 pentode tube. So, I designed the BB-Noval adapters for tubes that do not follow the 12AX7 pin-out. All of the vacuum tube pin numbers are identified on the PCB for easy hook-up. Now all of those class-A pentode preamplifier designs can come to life much faster. As always, good high voltage design practice should be followed during use.

UPDATE 6-15-2017

These are now available again on EBay at these links:

BBX7 - specifically for 12AX7 type tubes
BB84 - Specifically for EL84 Pentodes
BBNOVAL - For almost any 9 pin noval tube
BBOCTAL - For 8 pin tubes such as the 6SN7

They are cheaper if you get them directly from me.
Just contact me by commenting here or on my web page at trentonblizzard.com.


Thanks for reading,
Trenton

5/15/14

DIY RIBBON MIC TUTORIAL by Austin Microphones

Ribbon mics have got a "thing". They've got this texture "thing" that other mics just don't have.
Don't get me wrong, I love condenser mics too. But, they're built differently and don't respond like ribbons do.

With a condenser mic project already in the works, I've been looking around for what might be my next mic build project. As it turns out, there's a cool place called Austin Microphones that offers ribbon mic kits as well as DIY instructions for building your own ribbon mic from scratch. Yes, from "scratch". Too cool!



So, to see what's involved in the process I ordered their DIY Ribbon Mic Tutorial. It's available as a .pdf download for about $10.00 USD. The payment process was a breeze using PayPal. Also, with the purchase of the tutorial you get a password for their online DIY video content.

So, here's a sneak peak at what's included in Rev 4.1 (not necessarily complete or in order):
1. Body & Screen Fab - Shows simple setups to create the mic body and wind screen   
2. Corrugating the Ribbon - Part of the "art" of ribbon mic design - This will be fun
3. Ribbon "Motor" Assembly - Construction & assembly of the ribbon element and truss
4. Transformer Info - Build your mic with a quality output transformer (purchased separately)
5. Final Assembly - This is where it all comes together
6. Test Procedures - The magical moment of hearing it work! Or, figuring out why it doesn't!

Every time I read through the plans I say to myself "I really want to do this'. It's got me fired up about building ribbon mics. So, if you are into building mics or maybe considered building a ribbon mic before, be sure to at check out the DIY plans. I think you will enjoy the read!

Please note: All images used by permission and are property of Rickshaw Records.

Thanks for reading,
Trenton



1/15/14

PULP LOGIC P-VERB

I took a photo of a P-Verb the other night for my friend John Kennedy of Pulp Logic.  John is making a kit you can buy that allows you to adapt an old Alesis Picoverb into a Euro rack module. It's pretty cool and is available while supplies last at Erthenvar.com. Check it out if you get a chance!
Thanks for reading,
Trenton