Archive for Recording

Microphone Preamplifier Part 2

facebooktwittergoogle_plusredditpinterestlinkedinmailby feather

Hello Project Ryu fans,

About a month ago i reversed engineered a mic preamp module from an old console. If you don’t remember please refer to the article here. After i rebuilt the modules with newer components i decided to build a nice 2 channel preamp with them.

Below you can see the circuit for the unit. M1 and M2 are the modules presented in part 1.

Dual Channel Mic Preamp

As you can see it splits a 12V rail into +/-5V duble rails. I did this because i wanted to make it more mobile so i can power it from a big battery.

Below you can see my example of chassis.

 

Dual Channel Mic Preamp

Dual Channel Mic Preamp

Dual Channel Mic Preamp

Dual Channel Mic Preamp

This preamp doesn’t have a phantom power although you could easily add a +12V phantom power. In this regard it is best suited for dynamic microphones.

Thank you for visiting.

Guitarists, prepare for a live session

facebooktwittergoogle_plusredditpinterestlinkedinmailby feather

Hello,

This post is for beginner guitarists.

Ever happened to you that you unplug the cable from the guitar? It must have! Either you stepped on the cable or you moved around too much. Here is a cheap and quick way how to take care of this problem.

Leave a loop of 10-20 cm between the clip and the jack. Adjust this length until you are comfortable and its not bothering you. When you are finished unplug the jack first then remove the clip. Keep cables in their own space and its best to hang them in long loops. Don’t wind them around your hand.

Do this every time. Don’t get lazy and leave the cable in just because you will play again tomorrow!

Thanks for visiting.

Guitar Cable Trick

Microphone Preamplifier Part 1: Restoration

facebooktwittergoogle_plusredditpinterestlinkedinmailby feather

Some years ago, i got my hands on an old and obscure mono mixing console. It was labeled just as PM5200. It wasnt of much use to me so i tore it down and salvaged parts for my own projects.

The other day i was looking through my things and found the mic preamp modules from that console and i thought this would be a great weekend project. I remember i used one of the modules for a guitar recording rig. Battery powered and with a transformer input it worked very well with Shure SM57.

The circuit uses only solid state discrete components and uses capacitor coupling. It allows for 3 gain settings and a nice line in/mic feature.

Original Mic Preamp Module

Original Mic Pre PCB

I do like the shield. 1mm thick steel.

You can see the original module with the busted gain setting. First i had to do is to reverse engineer and draw a schematic. It wasn’t very difficult, old PCB single sided, resistors all 500mW clear marked. You can see the schematic below:

PM5200 MIC PRE Original Schematic

 

With +/-15V the circuit draws about 10mA so its running pretty hot.

T101 along with D101, D102, R109, R110 for a constant current source. T102 and T103 form a long tail pair. You can attack it with balanced/unbalanced signal. You can use an input for more feedback or if you use the inputs together you can get a nice line in input with about 10x gain. T104 and T105 forms the main voltage amplification stage.

Next i took down all the components. Nothing was worth keeping.

MIC PRE PCB

MIC PRE PCB2

 

I changed the NPN transistors to 2SC2240 from Toshiba. I really like these transistors in audio applications. PNP transistors i used BC559C, low noise and i have alot of these.

Also i replaced R119 with a multiturn pot of 5k in value. I hope i can get rid of the last coupling capacitor. We will see. One thing that surprised me was the lack of any power rail decoupling on board. I added 2 100n MKT caps.

Modified Mic PReamp

Modified Mic PReamp PCB

 

After that i recorded frequency response which you can see below. It is pretty linear with just 1dB dropping at high frequency.

PM5200 Mic pre frequency response

 

In next part i will explore some improvements and just put it in a box, add controls and make it ready to be used.

Thank you for visiting.

 

Balanced Line Attenuator バランスラインアッテネータ

facebooktwittergoogle_plusredditpinterestlinkedinmailby feather

Hello,

In a home recording environment equipment often doesn’t come in a large variety because of either limited budget or limited space… or both. I am presenting here an balanced attenuator which comes in between fixed gain preamp and recording device/soundcard.

The purpose of this device is to adjust the level and monitor it to prevent saturation of the next stage in the recording chain. It uses a L-pad followed by a balanced buffer stage. The attenuation steps are 0dB, -3dB, -6dB, -9dB and -12dB.

The meter section uses a microcontroller with a 10 bit ADC. It monitors both polarities of the signal and detects the peak within a frame of 1000 samples. ADCs samples the signal every 12us.

Balanced line attenuator schematics バランスラインアッテネータ

 

In the schematics above J7 will be used later on future revisions to indicate symmetry in the balanced signal.

J3 will connect the attenuation selector.

There are certain modifications i did the initial schematic tho. R7, R8 must be of greater value. At least 100k. With 100k you will get a -0.8dB signal at 0 dB setting.

The circuit is pretty straightforward, you can use any quad opamp chip for U3 as long at it operates from a 9V single supply. I do recommend a FET input opamp if R7 and R8 >= 100k as they tend to have lower noise than bipolar with high input impedance.

U2 i used a LM324 as it allows operation at 5V single supply. U2:C is used to bias the ADC inputs at 2.5V.

I will explain how to rectify the signal with a PIC in a future project but you will find the hex file for this one at the end of this article.

Here are the PCB drawings:

バランスラインアッテネータ Balanced Line Attenuator

pcb top layer

バランスラインアッテネータ Balanced Line Attenuator

pcb bottom layer

Balanced Line Attenuator バランスラインアッテネータ

pcb top silk

 

Warning: NONE of the PCB images are mirrored!

Here is how the PCBs turned out:

Balanced Line Attenuator バランスラインアッテネータ

Balanced Line Attenuator バランスラインアッテネータ

Balanced Line Attenuator バランスラインアッテネータ

Balanced Line Attenuator バランスラインアッテネータ

I used a rotary switch to select the attenuation levels. For 0dB you can just omit R15. Use POT2 to calibrate 0dB on your meter. I usually set it to 0dBV.

Balanced Line Attenuator バランスラインアッテネータ

Balanced Line Attenuator バランスラインアッテネータ

 

After building the first unit i made some measurements. I used 5% tolerance resistors so i wanted to see if the attenuation levels are correct. Here are the results:

Balanced Line Attenuator バランスラインアッテネータ

 

-6dB and -12dB settings are about 1dB off and it seems -3dB setting is also a bit off. For -12dB i soldered a 47k resistor in parallel with the 6k8 one and for -6dB i soldered one 100k resistor in parallel with the 22k. For -3dB i soldered a 470k resistor in parallel with the 47k one. Results were much better:

Balanced Line Attenuator バランスラインアッテネータ

 

I will be making kits available for this device with PCBs and programmed microcontroller as well as fully built units. Please subscribe to receive more details about this offer in the next newsletter.

Below you can find the hex file:

PrjRyu Balanced Attenuator

Thank you for visiting

 

Monitoring Amplifier モニターアンプ P4: VU Meter Driver

facebooktwittergoogle_plusredditpinterestlinkedinmailby feather

Hello, こんにちは,

In this part I will continue with the VU-meter driver for needle instruments. The circuit is very simple just a half-wave rectifier with adjustable gain and a comparator for clip indicator.

POT3 should be chosen to match your meter’s sensitivity but i think 100k will do for most. Components are not critical so it should be fairly easy to build.

Whats important to note is that the voltage at the inverting input of the LM339 comparator will set the clipping threshold, so you can use a voltage divider there to set it to what you want.

You will need to adjust POT3 to your preferred 0dB point, I usually use the dBV scale.

vu meter schematic

Monitoring Amplifier Vu meter circuit アンプVUメーター回路を監視する

Monitoring Amplifier Vu meter circuit アンプVUメーター回路を監視する

 

Monitoring Amplifier Vu meter circuit アンプVUメーター回路を監視する

 

Slowly but steady the whole unit is coming along. In next part i will do the source selection and front end.

Parts List:

Quantity: References Value
3 R1, R3, R5 10k
1 R2 1k
1 R4 680-1k
1 C1 10u
1 C2 3.3u
1 U1 TL072
1 U2 LMV339MT
1 D1 1N4148
1 D2 LED
1 J1 CONN-SIL3
1 POT1 10k
1 POT2 4.7k
1 POT3 100k-470k

Thank you for visiting

TRS to XLR Interconnect Cable

facebooktwittergoogle_plusredditpinterestlinkedinmailby feather

Hello,

If you have been around audio enough you know that accessories, while many times ignored, can become really costly. Interconnect cables are easy to built and you can apply simple techniques to make them much better than the more expensive commercial alternatives.

In this article i will make a TRS – XLR balanced line interconnect. The connection follows the rules described below:

TRS      TO        XLR

Tip                   Hot

Ring                Cold

Sleeve            Gnd

In choosing the cable i recommend to look for braided shield and cloth layer. These features will help get a reliable cable.

TRS - XLR Interconnect Audio Cable  TRS - XLRインターコネクトオーディオケーブル

TRS - XLR Interconnect Audio Cable  TRS - XLRインターコネクトオーディオケーブル

The picture above depicts how i like to prepare the cable for the TRS plug. You can see the braided shield which will connect to the sleeve of the TRS plug.

TRS - XLR Interconnect Audio Cable  TRS - XLRインターコネクトオーディオケーブル

TRS - XLR Interconnect Audio Cable  TRS - XLRインターコネクトオーディオケーブル

TRS - XLR Interconnect Audio Cable  TRS - XLRインターコネクトオーディオケーブル

TRS - XLR Interconnect Audio Cable  TRS - XLRインターコネクトオーディオケーブル

In the picture above you can see my favorite way of securing the plug by using the cloth to tie it around the sleeve terminal.

TRS - XLR Interconnect Audio Cable  TRS - XLRインターコネクトオーディオケーブル

TRS - XLR Interconnect Audio Cable  TRS - XLRインターコネクトオーディオケーブル

I always use heat tube to isolate the shield connection of the cable when using XLR plugs. The XLR terminals are even in height so the shield will have a few mm of bare wire. I want to avoid it to touch the plug chassis on its own so i isolate it.

To solder the cable to the plug it is a good practice to hold the plug vertically like in the picture above.

TRS - XLR Interconnect Audio Cable  TRS - XLRインターコネクトオーディオケーブル

And the finished cable.

 

Thanks for visiting.

Monitoring Amplifier モニターアンプ P3: Speaker Coupling Delay

facebooktwittergoogle_plusredditpinterestlinkedinmailby feather

Hello, こんにちは,

私の日本語があまり上手くありませんが許して下さい.

In this article i will present a simple delay circuit that will be used to couple the speakers to the amplifier after a certain settling time was allowed. The circuit also allows for to be controlled by an external 5V logic signal. This can be used to decouple the speakers in case a fault is detected.

これは、アンプがオンされたときにスピーカーを保護するためのDELAY回路であります。それが徐々にコンデンサを充電することによって機能します。コンデンサ電圧が一定値に達したときには、リレーを切り替えります。

The circuit schematic is presented in figure 1 and as you can see it uses just discrete components. It is a linear voltage ramp generator that commands a power transistor. The current charging capacitor C1 and the capacitor’s value are the parameters that set the ramp’s slope.

POT1は、時間遅延を調整します。

Speaker delay circuit schematic

Figure 1

In figure 1 Q3 forms a constant current source adjustable via POT1. R1, R2, D1, D2 set a voltage on the base of Q3 of about 5.4V and this means about 6V voltage drop over R6 and POT1 series connection. Assuming Ic3 = Ie3=Icharge,

Icharge = 6V/(R6+POT1)

Lets set POT1 at 90kohms for ease of calculation. This gives R6+POT1 = 100k.

Icharge = 60uA

Since Q3 is in saturation mode we can assume a voltage drop over C-E of about 0.5V so the voltage over the capacitor Vc1= 5.5V. The time for the capacitor to be charged to 5.5V is defined by the below equation:

T= (C1*Vc1)/Icharge = 0.91 second

上記の式は充電時間コンデンサを計算します。

Q2 buffers the voltage across C1 capacitor. It also provides a small delay until Vc1 reaches around 0.6V to bias Q2’s B-E junction. Q1 acts as a switch and when turned on via a 5V signal it absorbs most of the current from Q3 and capacitor will not be charged.

Q4 has the role to drive the relay. It is a small power transistor and it’s enabled via POT2. This variable transistor has the role to set the on/off steps based on the ramp voltage. If too low the relay will be on very fast and stay on if too high the relay will never activate.

Speaker delay circuit schematic

Figure 2

In figure 2 the time step is 200ms and we can see the ramp is about 1s long, very close to what we calculated. The blue trace is the Fault signal. When a 5V pulse is present the capacitor C1 is discharged very fast (pink trace) and speakers are decoupled (green trace). When the fault signal goes to logic low or ground the ramp generator shortly starts the process and enables the relay after about 1 second.

Speaker delay circuit schematic

Figure 3

 

Speaker delay circuit schematic

Figure 4

Figure 3 shows how the relay is activated faster if the POT2 is set too low in value and figure 4 shows a correct setting. The yellow trace represents power switched on.

Below you can see the circuit in the right side of the board.

Speaker delay circuit schematic スピーカ遅延回路図

 

Parts list does not contain the connectors in the schematic because the circuit most likely will be used as a part of something bigger:

Part Quantity
BC549 2
BC559 1
BD139 1
1N4001 3
R 12K 5% 0.25W 3
R 10K 5% 0.25W 2
C 10u 25V 1
POT 250K 1
POT 10K 1
RELAY DPDT 1

Thank you for visiting,

ご覧いただきありがとうございます。

Making Interconnect Cables – TRS Male Plug

http://www.youtube.com/watch?v=2UlzA7toUNI facebooktwittergoogle_plusredditpinterestlinkedinmailby feather

Hello,

Many times at many gigs, either due to tiredness or being in hurry, I unplugged the equipment by pulling the cable instead of pulling the plug. Needless to say many times the cable came out but not the plug. It’s been a while though since i don’t have this problem for i found a very simple solution. It might’ve been around but I’ve never seen it.

Today i had to make a new interconnect so i decided to document it. Please read the disclaimer and be warned as i will use sharp tools and a lighter, things that might get you hurt or damage things if you try it. So be advised this is just informative article and I’m not responsible for any of your actions.

Making Interconnect Cables, TRS Male Plug

Figure 0

Now that tools needed are represented in figure 1 plus a soldering iron. I will be using a 6.3mm TRS male connector on both ends of the cable. TRS stands for Tip Ring Sleeve and it is also known as Jack connector.

tools for cables

Figure 1

My way of connecting is pretty standard using a 2 wire shielded cable color coded white and red, i connect the white to tip and red to ring. It is important to choose a quality cable. I always look for 2 things. First the shield has to be braided (figure 2) and second between shield and the core it has to have a cloth layer (figure 3).

High Quality Audio Cable

Figure 2

High Quality Audio Cable

Figure 3

All metal TRS male plugs will have a plastic insulator inside to protect the body of the plug touching the tip or the ring. Most are transparent so it is easy to loose it, in case you do (it happens ^^ ) you can use thermoretractable tube to isolate the connections. I usually use both just to be sure but it also protects the connections better especially if the cables work outside.

TRS Jack Male Plug

Figure 4

I will begin by removing the PVC isolation about 50 mm (2 inches) and cutting the shield around the cable so that you have about 6 mm clear to the PVC layer, just like in figure 5. Insert the plug’s body and plastic isolation on the cable.

DIY Audio Interconnect TRS Jack Male Plug

Figure 5

Fix the cable on the plug with the shield in the sleeve’s grip. Now that the cloth around the sleeve and tie it very tightly. This is the trick that will keep the plug on when pulling the cables. After that cut the excess cloth and use a lighter to melt it so that it wont come loose. See figure 6.

DIY Audio Interconnect TRS Jack Male Plug

Figure 6

Cut the signal wires about 10mm from the point it meets the tip and ring connections. Remove the isolation. At this point i put a small thermoretractable tube (3-4 mm) on the signal cable. Insert the cable through the tip and ring connection and then wrap it around as far as it goes. It is of very high importance to make a good mechanical connection before soldering. Also the signal cables must not be stretched. Leave a small bent or loop.

DIY Audio Interconnect TRS Jack Male Plug

Figure 7

DIY Audio Interconnect TRS Jack Male Plug

Figure 8

Solder the joints and then cover it with the shrink tube and heat it with the lighter. Now solder the shield to the sleeve as well to make a firm connection. Attach the plastic isolation and screw in the plug’s body. Refer to pictures below.

DIY Audio Interconnect TRS Jack Male Plug

Figure 9

DIY Audio Interconnect TRS Jack Male Plug

Figure 10

DIY Audio Interconnect TRS Jack Male Plug

Figure 11

DIY Audio Interconnect TRS Jack Male Plug

Figure 12

This is it, it is simple and will ensure a very sturdy and long lasting cable. To show better what i mean to do with a cloth i recorded a video. Please take a look at the link below. Also the music is something i composed a while ago. Hope you enjoy it.

Thanks for visiting.

 

Monitoring Amplifier モニターアンプ P2: Tone Controls

facebooktwittergoogle_plusredditpinterestlinkedinmailby feather

Hello, こんにちは,

私の日本語があまり上手くありませんが許して下さい.

In a previous article I wrote about a monitoring amplifier i want to build. This weekend i could continue with this and i built the tone control circuitry. It is a Baxandall type but the values are a little atypical as i made this tone control tailored for my needs.

この記事では、Baxandallのトーンコントロール回路図について書きます。私は、シミュレートし、測定結果を示します。ローレベルで音楽を聴くとき、このトーンコントロール回路は、低音レベルを調整することができます。また、それは大規模な2ウェイシステムでウーファーとコンプレッションドライバー間のSPL差を調整することができます。

I wanted controls that can help in a large format 2 way loudspeakers employing a crossover frequency around 1kHz. I need a shelving filter that can gradually bring up or down that range. Below is the schematic and the graph showing the maximum boost-cut levels.

Schematic of Tone Control Circuit

Schematic of Tone Control Circuit

Tone control range

Tone control range

The schematic represents 1 channel and it is not showing two 100n/63V polyester film capacitors used to decouple TL074 power rails.

List of Materials
# Component Quantity
1 TL074 1
2 C 100n/63V Polyester Film 2
3 R 10k 10
4 R 4k7 4
5 C 47n Polyester 4
6 C 10n Ceramic 4
7 C 150p Ceramic 2
8 Pot Dual 33k 1
9 Pot Dual 150k 1
10 Molex Connector 8 pin 2
11 6 pin header 1
12 Prototype Board 1

I didnt include the 3 pin Molex connector for input you will see in the pictures as i use it temporary to connect 2 RCA female plugs to it. Below you can see the picture of the circuit. It is a bit annoying soldering the SMD components on the prototype board but not a big problem. Since this is a high gain circuit grounding needs increased attention.

tone control circuit トーンコントロール回路図

tone control schematic トーンコントロール回路図

 

tl074 and caps TL074オペアンプ

SMD resistor

8 pin molex

Connection between boards will be made with a 6 wire shielded cable. This cable type is often used in home security installations like alarms systems and has each of the wires individually shielded.

シールドケーブル shielded cable

 

The shields are tied together and grounded to one side of the cable only as signal ground is carried on one or more of the six wires. Used thermoretractable tube to isolate the open shield cable end.

shielded cable molex connector シールドケーブルMolexコネクタ

 

Using the line input of the soundcard i could measure the response of the tone control circuit. As can be seen it is very close to the predicted response. At the bass boost you can see the line getting flatter towards the end because of saturation.

TL074とトーンコントロールオペアンプの周波数応答 Measured Tone Control Response

 

Here is a picture during tests:

Monitoring Amplifier LM3886 モニターアンプ

 

The bass control indeed it is just right, at low volume levels you can still get the deep bass without going through walls.

Thank you for visiting,

ご覧いただきありがとうございます。

Monitoring Amplifier モニターアンプ P1

DSC03860 facebooktwittergoogle_plusredditpinterestlinkedinmailby feather

Hello, こんにちは,

私の日本語があまり上手くありませんが許して下さい.

I like listening to loud music usually, i like to feel the impact of instruments close to live levels. Of course this is not always possible especially after work at late hours.

私は、大音量の音楽を聴くのが好きです,ライブのレベルでの楽器の影響が好きです。もちろん、これは、特に深夜の仕事の後に必ずしも可能ではない。

To overcome this I decided to build a monitoring amplifier this weekend. It will allow me to see the level of the source before coupling to the power amp and also to switch speakers off and just use headphones.

モニターアンプこの週末を構築することを決めた。ソースのレベルをチェックすることができます, そしてまた、オフスピーカーを切り替え、ヘッドフォンを使用しています。

It is also important to have a good tone control circuit to adjust loudness at low levels.

トーンコントロールは低レベルに音量を調整することができます。

A first block diagram is presented below. アンプのブロック図。

Monitor audio Amplifier

Looking through my things to select components for this project, I found the chassis from the preamplifier module of a soviet Reel to Reel deck Rostov 105. The chassis has all the controls i needed on the front panel including two nice needle VU-meters.

amp chasis

I took the chassis down and cleaned it and i verified all the pots and switches and cleaned them.

Audio Monitor Amplifier

For Power Amplifier i have a LM3886 stereo kit which will be extremely useful. I used this kit for a while and it has a decent sound being one of the best audio chips in my opinion. I attached this kit to a heatsink from a Yamaha A-500.

The kit also comes with a dual VCA chip for DC volume control, the M5283P. This is a very good solution to keep noise from potentiometer out of audio path.

モニターアンプM5283 dual VCA

モニターアンプM5283

I built a power supply for the amplifier section and mounted them on the chassis.

LM3886 Audio Amplifier

LM3886 power amplifier

LM3886 Audio Amplifier

LM3886 Audio Amplifier

Potentiometer controlling the VC input of the dual VCA chip.

 

LM3886 Audio Amplifier

In the next article i will discuss more about the VCA and build the tone control, metering circuits.

Thank you for visitng,

ご覧いただきありがとうございます。