Saturday, October 29, 2011

Preamplifiers

I finished two of my new projects with preamplifiers. One of them contains independent preamplifier schematics, another one is an audio mixer with modular system where the preamplifier-modules have to be connected to the mainboard.

The simplest preamplifier with very high gain contains only 1 dual opamp. The sound quality depend on the amplifier circuit. Recommended to try the PCB with TL072, NE5532, or LT1124. Maybe the maximum gain will lower with better quality circuits, but the noise and the sound quality will better with NExxxx or LTxxxx dual operational amplifiers. The board of this schematic contains potentiometers for gain and volume adjustment, and 6,3 mm stereo jack input. Stereo circuit, like all others except microphone preamp. The board contains all required potentiometers, jack input, and two switches for stereo/mono and true-bypass. The switches have to be soldered to the small PCB with 12 pins "L" connector. This switch-board have to be connected to the preamplifier's PCB if required, if not, just wire the required pins of the connector on the preamp-board to ignore these switches. This very simple schematic have very big gain, but for microphone is not enough, for guitars too much. The sound of circuit with TL072 dual opamp is good for mixed music, but not for instruments like guitar or guitar effect. This is the reason why I recommended for home music listening. The "P1" connector on board is option for LED output to indicate if something connected to the jack-input.

Schematic:


PCB:


The second version of above schematic with two single operational amplifier instead of one dual:

This PCB is bigger, but very good solution for single operational amplifiers. The ultra low noise single OpAmps are not cheaper, but easier to find than dual. LF356, OPAxxx, LT1028, LT1115 (instead of dual LT1124) are the alternatives for better solutions than the cheapest TL071. The board contains one "power filter" circuit to reduce the noise of power supply.

Finally I have version no.3 for the Opamp solutions. The stereo circuit contains 2 single Opamps instead of one dual like above, but two power filter circuits included, one-one for both operation amplifiers. This solution is better for ultra low noise circuits like LT1028 or LT11115.


The small circuit contains switches:

This circuit contains 3 switches, but SW1 and SW2 are same. Only the place of these parts are different. If required only one switch, use SW3 only.

The PCB of switches:

This really small board required for all preamplifiers, except Dual-jFET preamplifier. If the switches are not required, just wire the correct pins of the P1 connector on the amplifier's board.

The dual-jFET preamplifier.

This is my favorite schematic for guitars or guitar-effects. The circuit contains one dual jFET for stereo input. No noise, good dynamics, warm sound. No symmetrical power required, therefore the power filter is smaller and simpler. The gain and volume potentiometers, and the stereo jack input connected to the PCB. The maximum gain is lower than the Opamp preamplifier's, but enough for guitars, guitar effects, and keyboards, or another instruments, except microphones.

See the schematic:


PCB:

This PCB have no bypass and stereo/mono switches. Maybe later will be included. The originally planned part 2N3958 Dual jFET is not available now, but any low frequency dual N-channel jFET compatible with this solution. Here is the table to find another dual jFET.

The next schematic is a microphone preamplifier with very cheap and good quality operational amplifier INA217. This is the recommended application schematic of this integrated instrument preamplifier. The PCB contains two mono potentiometers for gain and volume, and one 6,3mm jack input for unbalanced inputs like guitars. The switch-module contains only one switch to select between unbalanced/balanced inputs. The unbalanced input is the 6,3 jack, the balanced have 3 pins connector, and external XLR input required. For 48V phantom power required an independent external switch to the case if you want to use condenser microphones.

Very cheap and good quality circuit. No noise, no feedback, very high gain, good dynamics. Compared to cheap Phonix mixer, this circuit was much better with Sennheiser and Behringer dynamic vocal microphones. The 48V input for phantom power included to the PCB but power supply required for this feature. Unbalanced to balanced converter circuit included after jack input to the board. This is cheap and simple converter, but with the recommendation of Jensen. Later will be changed this converter to better one. The PCB contains 3 integrated circuits, but one power filter circuit included.

The PCB:


The PCBs of these preamplifier circuits drilled with same positions on the bottom. With these holes possible to fix to the case of mixer or preamplifiers. Later, all of these preamplifiers modified to module of audio mixer. The inputs, outputs, and powers wired to the pins of connectors.

Finally here is the recommended +-15V power supply:


PCB:


The PDF about preamplifier projects.

As I posted, all preamplifiers converted to module of audio mixer with 12 pins connectors. With these connectors the preaplifiers can be connected to the mainboards of mixer. All of the power filter circuits connected as module to the new PCB of preamp-modules. The mixer-mainboard contains only mixing circuits and 2 stereo line outputs:


Gallery about preamplifiers:



Picasa gallery about modular mixer:



PCB sales of this project
Module name Size
(mm)
Area
(cm2)
PDF SCH PCB image Tested Price (US$)
Des. Sim.1 Full2 Sim.1 Full2 Man3
Microphone preamp V:2
130x105
137 Yes Yes
Yes
Yes
-
No 20 30 Ask
1 dual opamp preamp
95x104
99 Yes
Yes Yes
Yes
-
No 15 24 Ask
2 single opamp preamp
89x110 98 Yes
Yes
Yes
Yes
-
No 15 24 Ask
HQ 2 single opamp
105x112
118 Yes
Yes Yes
-
-
No
18 27 Ask
jFET guitar preamp
70x108 76 Yes Yes
Yes Yes
-
No 12 20 Ask
Switch module
18x34 6 Yes Yes
Yes Yes
-
No 3 11 Ask
Simple Power supply
121x57
69
Yes
Yes
Yes Yes
-
No 11 20 Ask
Power supply with 48V phantom
168x89 150 Yes Yes
Yes -
-
No 22 32 Ask
How to order? Please read the rules carefully!

UREI546 parametric EQ like URS VST EQ bundle plugin

See again the project of parametric UREI EQ project. I posted I really like URS VST audio plugins. I wanted UREI cloned circuit, to make EQ like URS VST. Unfortunately this is impossible, because the required values of parts not available, but I think the differences are not too important because the parameters are adjustable, and maybe with some tricks (parallel connections for example) possible to create something like this. Therefore I choose two parametric EQ plugin from URS bundle, and trying to simulate the values with UREI EQ circuits. I think logarithmic potentiometers required for this simulation.

Look at my new values for 4 bands equalizer:
Lower values in URS VST plugin: 30 Hz, 75 Hz, 800 Hz, 2,5 kHz


Upper values on VST plugin: 400 Hz, 1 kHz, 12,5 kHz, 20 kHz:


The another VST plugin have 5 bands. I have only 4 and 6 bands of EQ PCB, but within 6 bands UREI have to be insert 5 EQ modules only. With this example, from the 5 bands 3 bands are similar. These 3 bands can be adjusted to different settings. Logarithmic potentiometers required again. No standard values of potentiometers like in the tables, but something with similar values will be useful.

Low values: 31 Hz, 75 Hz 3x, 2 kHz.


Upper values: 400 Hz, 12,5 kHz 3x, 20 kHz.


The table with capacitors and adjustable resistors:


I hope it's useful tip.

See also:

Thursday, October 27, 2011

6 and 10 bands for UREI 546 parametric equalizer

It is true, I cannot found really correct math expression to modify the band-frequency of UREI 546 EQ circuit, but I think I have a very useful Excel sheet. I think the not 100% exact expression is not a big problem, because the frequency parameter is adjustable. I have a plan UREI 546 with 6 bands, but I counted out values of potentiometers and capacitors for 10 bands. For 10 bands EQ I will design mainboard later.

The first table for original 4 bands, 6 bands, and 10 bands:


The result is the value of P1 stereo potentiometers for frequency adjustment, and the capacitor of filter C(a) = C(b). If somebody have better expression please send me a message.

Another table just for variations:


See also:



PCB sales of this project
Module name Size
(mm)
Area
(cm2)
PDF SCH PCB image Tested Price (US$)
Des./3D Sim.1 Full2 Sim.1 Full2 Man3
Parametric EQ module
56x61
34
Yes
Yes
Yes
-
-
-
7 14 Yes
2 Potmeter module
31x62
19 Yes
Yes
Yes -
- -
5 12 Yes
3 Potmeter module 41x83 34 Yes Yes Yes - -
-
6 14 Yes
Power filter module V:1
51x22
11
Yes Yes
Yes
- -
-
3 11 Yes
UREI545 clone mainboard V:2
217x143 310
Yes Yes
Yes
- -
-
43 53 Yes
UREI545 clone mainboard V:1 217x198 430
Yes
Yes Yes
-
-
-
59 70 Yes
6 band UREI546 mainboard 173x143
247
Yes Yes Yes -
- - 35 44 Yes
Power supply
121x57
69 Yes Yes
Yes -
- -
11 20 Yes
How to order? Please read the rules carefully!

Wednesday, October 26, 2011

Math expression for UREI546 parametric EQ design

While I found math expression easy for gyrator EQ project, I cannot found mathematical help to customize UREI 545 and 546 EQ circuits. For the EQ module I found nothing, the biggest problem that all parameters can be adjusted by resistors. Therefore I made expression with excel, to count out frequencies to make more than 4 band parametric EQ. The expression is not the best, but working well with several C(a) and C(b) values where C(a) = C(b). If somebody design more than 4 channel UREI 546 EQ, the potentiometes of Q adjustment must be changed too. For example, if the Q adjustment is 10kOhm for 4 bands, for 8 bands must be half (5 or 4,7 kOhm). I hope it's enough and useful for customized parametric EQ design.

Look at the expressions for UREI 546 band-frequencies:

C(a) = C(b), the adjustable resistors for frequency 55kOhm stereo, the permanent resistors are 4,7 kOhm like in the schematic. You have to change the value of C(a) and C(b) capacitors. In the last expression you can get the fpot, which is the frequency depend on the value of potentiometer. The variable Rpot can be set between 0 and 55000 like in the "real life". The result getting in Hz.

The module contains EQ circuit, most be placed to the mainboard PCB:


See also:

Tuesday, October 25, 2011

Parametric EQ Project - Modular UREI545 and 546

Before my previously posted gyrator EQ projekt I designed UREI clone projekt. I would like equalizer like the best VST software effects like URS EQ bundle:

The most of VST equalizers are parametric, have low noise, high dynamics, very good quality. Maybe with real analog circuits cannot get same result, but we have to build and try. This is my second EQ project of three, the previous one is with gyrators, the last one will permanent Q RANE copy device.

I choose to reproduction of UREI 545 and 546 analog circuits because the users, primary musicians like it, and I want to use for vocal and guitar amplification. The original construction is very old and vintage circuit, the output of UREI EQ shipped with transformer. I changed this output transformer to jFET buffer, I hope this idea will not getting bad result.

The original UREI 545 EQ:

...and the schematic...

This project have modular system like my previous and future projects. The smaller curcuits have to be builded to the large "mainboard" like the cards in the PC computers.

Gallery about the modular design (schematic, PCB):


In this UREI clone project I did not made circuit what is useful alone like the 5 band EQ on gyrator project. This URE EQ is too difficult to make all at one PCB. This is the reason why only modules designed.

The equalizer module:

This is the EQ, must be fit and solder to the one of the mainboards. For the UREI 545 clone I have 4 band mainboard, but for 546 I made 4 and 6 band mainboards. For completion, power filer and power supply required, and I have two PCB for adjustable potentiometers. One of them contains three potentiometers for frequency, Q, and cut/boost adjustment. The second contains 1 or 2 potentiometers only for hi-pass or low pass filters and adjust the output gain.

PCB for three adjustable resistors (Q, Fr, Cut/Boost):


PCB for one or two adjustable resistors for output gain and high pass/low pass filters:


Module called "power filter" for less noise:

For this one module I have three PCBs. One is portrait, on is landscape, and the last is wider than portrait and thinner than landscape version. This module not required but suggested, I you decide you don't need, then just wire the pin 12 to pin 7, and pin 8 to pin 11 on the module plug.

the most important part of the project is the "mainboard". Look the first the 4 and 6 band circuits and PCBs for UREI 546 clone:


The modules - EQs, potentiometers, power filers - must be soldered to the plugs of mainboard:


And i have six band mainboard. Here is a link to see the PCB.

The first version of UREI project is 545 clone:

In this schematic need modules, but the most important, the EQ circuits built to this PCB. For this one, only power filter and adjustable resistor modules required.

The PCB:

This mainboard have only 4 band version, but one of them have three selectable frequency. This part called "multiband".

These EQ circuits are all mono, because to adjust some parameters we need stereo potentiometers for one mono channel only. Lot of adjustable resistors needed. All adjustable band need 3 potentiometers, and one-one for the low pass filter, high pass filter, and the output gain. For 4 channel EQ required 15 potentiometers, for 6 channel need 21.

Finally look at the power supply:


Examples for the C(a) C(b) and C(c) condenser values of 4 channel UREI 545 clone:

  • Low band: C(a) and C(b)= 100nF ; C(c) = 1uF - 30Hz-330Hz
  • ow-Mid band: C(a) and C(b)= 27nF ; C(c) = 100nF - 110Hz-1.2kHz
  • High-Mid band: C(a) and C(b)= 8nF ; C(c) = 100nF - 390Hz-4.2kHz
  • High band: C(a) and C(b)= 2.2nF ; C(c) = 100nF - 1.4kHz-15kHz
The 3 band section of UREI 545:
  • Low band: C(a) and C(b)= 100nF ; C(c) = 100nF - 24Hz-310Hz
  • Mid band: C(a) and C(b)= 13nF ; C(c) = 100nF - 190Hz-2.24kHz
  • High band: C(a) and C(b)= 2.5nF ; C(c) = 100nF - 960Hz-12.5kHz
The 4th band of 545 is the multiband section of EQ:
  • Multiband Low: C(a) and C(b)= 160nF ; C(c) = 100nF - 15Hz-200Hz
  • Multiband Mid: C(a) and C(b)= 16nF ; C(c) = 100nF - 150Hz-2kHz
  • Multiband High: C(a) and C(b)= 1.6nF ; C(c) = 100nF - 1.5kHz-20kHz
The values of required potentiometer modules:

UREI546 clone:
- Low cut and high cut: 55k stereo (P4)
- Bandwidth (Q): 10k mono (P2)
- Frequency: 55k stereo (P1)
- Boost/Cut: 10k mono (P4)

UREI545 clone:
- Low cut and high cut: 50k stereo (P4)
- Bandwidth (Q): 10k mono (P2)
- Frequency: 10k stereo (P1)
- Boost/Cut: 10k mono (P4)

For both:
Output gain: 5k mono (P4)

Upgrade:
Here is two tables for 6 band and 10 bands parametric EQ design.

Link to help to design custom bands for the parametric EQ:
I think its enough if you want simple but very good quality gyrator EQ circuits.

See also:

PCB sales of this project
Module name Size
(mm)
Area
(cm2)
PDF SCH PCB image Tested Price (US$)
Des./3D Sim.1 Full2 Sim.1 Full2 Man3
Parametric EQ module
56x61
34
Yes
Yes
Yes
-
-
-
7 14 Yes
2 Potmeter module
31x62
19 Yes
Yes
Yes -
- -
5 12 Yes
3 Potmeter module 41x83 34 Yes Yes Yes - -
-
6 14 Yes
Power filter module V:1
51x22
11
Yes Yes
Yes
- -
-
3 11 Yes
UREI545 clone mainboard V:2
217x143 310
Yes Yes
Yes
- -
-
43 53 Yes
UREI545 clone mainboard V:1 217x198 430
Yes
Yes Yes
-
-
-
59 70 Yes
6 band UREI546 mainboard 173x143
247
Yes Yes Yes -
- - 35 44 Yes
Power supply
121x57
69 Yes Yes
Yes -
- -
11 20 Yes
How to order? Please read the rules carefully!

Monday, October 24, 2011

Modular equalizer with gyrator filter

Posting again about my modular gyrator-EQ project. This project not tested yet, but I made 5 channel EQ with gyrators and 10 channel active filters EQ formerly. Look at older pictures:


EQ with gyrator filter is noiseless, simple, and cheap. Because the first version made for guitars or instruments, the adjustment was too fine for me, the "Q" of separated bands was not permanent, one of the EQ band adjusted another frequencies too. Therefore this method is better for home stereo hi-fi instead of instrument amplifications.

After my first gyrator EQ project I made 10 band active filter EQ by RANE. This EQ have permanent Q, the result is much better for instrument amplification. But 10 channel was too much for me, very hard to set the best sound, because I got too much possibilities. Otherwise the noise of this method is much higher than simplest EQ with gyrator filter, but for instruments was much better for me.

Now I have new (untested at this time) equalizer-projects, with 3 different versions. The first is the modular EQ with gyrator, maybe just for home hi-fi. The second is an UREI545 clone parametric EQ, the 3rd is the new modular RANE based permanent Q equalizer. Now I posting about the first type of EQ with noiseless gyrator filers. With current version, I have module with adjustable gyrator circuit only. I made two versions of PCB: the first mounted with one stereo adjustable resistor for home stereo systems, the second is mounted with two mono adjustable resistors for instrument amplification systems to separate left and right channels.

Images:
Stereo gyrator module:
Link

Dual mono gyrator module, the channels (Left, Right) can be adjust separately:


One of the upper modules have to be insert to one of the mainboards.
For 10 bands:


For 5 bands:


To the upper mainboards required one of the gyrator module (stereo or double mono), and module called "power filter" for less noise, and certainly power supply. I have three versions of "power filer" PCB, portrait, landscape, and something between fat and thin :). Look at all pictures about modules.

In this project, very important to able to count out the values of capacitors and resistors. Look at examples, links, and expressions:

5 band EQ:
  • 100Hz - 330nF
  • 300Hz - 100nF
  • 1kHz - 33nF
  • 3kHz - 10nF
  • 10kHz - 3.3nF
The upper values are valid for all of the C(a) capacitors in this schematic:


For 10 band EQ:
  • All of the 50k adjustable resistors must be changed to 25k.
  • For capacitors and resistors look at the table below:
HzC3 and C1C4 and C2R3 and R1R4 and R2
316.8 uF100 nF470 Ohm100 kOhm
633.3 uF47 nF390 Ohm100 kOhm
1251.5 uF33 nF390 Ohm100 kOhm
250680 nF22 nF330 Ohm82 kOhm
500330 nF10 nF330 Ohm100 kOhm
1k150 nF4.7 nF330 Ohm100 kOhm
2k100 nF2.2 nF330 Ohm82 kOhm
4k56 nF1 nF390 Ohm82 kOhm
8k22 nF470 pF390 Ohm82 kOhm
16k10 nF220 pF390 Ohm100 kOhm

Here is the online gyrator calculator:
http://awasteofsalt.com/gyrator/

A little math:


Links for several method to get values of parts:
I think its enough if you want simple but very good quality gyrator EQ circuits.

See also:

PCB sales of this project
Module name Size
(mm)
Area
(cm2)
PDF SCH PCB image Tested Price (US$)
Des./3D Sim.1 Full2 Sim.1 Full2 Man3
Power filter V:1
51x22 11 Yes
Yes
Yes - - - 3 11 Yes
Power filter V:2 27x41 11 Yes Yes Yes
-
-
- 3 11 Yes
Power filter V:3 21x45
9 Yes Yes
Yes - - - 3 11 Yes
Power supply
212x57 69 Yes
Yes
Yes Yes - - 11 20 Yes
5 band gyrator EQ
132x122
161 Yes Yes Yes -
- - 23 33 Yes
Stereo gyrator EQ module
30x61 18 Yes
Yes Yes
- - - 4 12 Yes
Double mono gyrator EQ module
30x65
20
Yes Yes Yes - - - 5 12 Yes
5 band EQ mainboard
75x95 71
Yes
Yes Yes - - -
11 20 Yes
10 band EQ mainboard
152x63
96
Yes
Yes Yes - - - 15 24 Yes
How to order? Please read the rules carefully!

Saturday, October 22, 2011

Using autorouter for homemade PCB

I made a movie about the autorouter of my favorite electronic CAD software:



When I finished the schematic, I switching to PCB creation and using autorouter. Most of Altium users don't like autorouter, but I think after correct configuration will be really useful for large boards. The most important is the correct strategy and rule settings. Because I made PCB by myself, I need wider lines and high clearance which is the distance between lines on PCB. Finaly I made very high quality photo film of PCB image, and finalized the job with photo resist method.

Here is the movie how to finalize the PCB creation, and a picture gallery about the very good printed circuit board:



My previous movie about the PCB creation :)

The image gallery of the result:

The first...

This is my first message in english-version of Hungarian blog of me. I'm DIY amateur in Hungary who like technology and electronics. I like to plan and build simple but sometimes difficult electronics devices from the planning to final testing and building. in this page i will blog about my projects, methods, or other stuff about my DIY activity.

While the text-content will be largest, visit my previously created contents:

- My youtube videos. PCB and schematic creation, altium Designer autorouter, and very good quality of homemade PCB creation by photo resist method.

- My Picasa album. Pictures about my DIY projects.

- My another youtube playlist about my band. I used my DIY amplifiers and speakers.

The PDF documents about my projects with schematics and PCBs available on the right side of this blog.