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Maciej Czerwinski Maciej Czerwinski is offline

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  • About Maciej Czerwinski


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  • Last Activity: 10th February 2015 09:39 PM
  • Join Date: 17th February 2011


Latest Blog Entry

Posted 10th February 2015 at 09:22 PM by Maciej Czerwinski Comments 0
Posted in Uncategorized
I bought these speakers in 2000. I was unhappy with the way they reproduce low frequencies. I decided to add a subwoofer. I used the fact that the lower part of the housing of the speaker is empty and isolated from the upper part in which the speakers operate. I cut a hole in the side of the bottom part and installed a 25 cm driver.
Attachment 1551
It is Vestra PW-250-2154 woofer.
It has a 19 cm coated-paper membrane, foam external suspension, extruded metal sheet basket, ventilated 4.5 cm coil, the diameter of the magnet is 12 cm, 80 W, 4 ohms, the self-resonance (Fs) at 27 Hz.
Attachment 1552
I damped the interior of this newly created enclosure space with bitumen mat and felt glued to the walls and filled it with fleece. I cut out the rear wall from the top part of the enclosure. Inserted a reinforcing crossbars into the lower and upper housing. The upper part of the housing is entirely filled with a damping material (with fleece filled pillow, which...

Posted 10th February 2015 at 09:16 PM by Maciej Czerwinski Comments 0
Posted in Uncategorized
All measurements done with Panasonic WM-61A microphone with Eric Wallin preamplifier and E-MU0202. Single driver frequency response without any crossover. The microphone is located at a distance of 1 meter from the driver on its main axis.
Vifa 3075 dome tweeter:
Attachment 1560
Vifa TC 3520 woofer:
Attachment 1561
Vestra PW-250-2154 woofer with it's crossover, microphone located 10 cm from the driver:
Attachment 1562

The complete speaker after modification.
Measurements done at my usual listening spot, 2.5 m from the speaker, microphone positioned 50 cm closer, farther, higher and lower around the spot. Obtained frequency response curves are strongly smoothed, because changing the position of the microphone produces a large change in the jags of the curve, and I wanted to show invariant features of the speaker frequency response:
Attachment 1563
It is pretty flat, and the bass is very nice now.

Posted 6th January 2015 at 12:30 PM by Maciej Czerwinski Comments 0
Posted in Uncategorized
Finished, front:
Attachment 1468
Attachment 1469
what's inside:
Attachment 1470
This device is built around DIYINHK ES9018 DAC board, with USB to I2C CM6631 converter, also from DIYINHK. USB is the only signal input. Power amplifier uses two LM4780 chips, one per channel in mono-parallel configuration. Power supply for the amplifier is made out of two HP printer power supplies. DAC power supply is more complex, but also uses three, a little bit modified, 12V supplies, wall plug in type, general use ones. Volume regulation (attenuation to be exact) is entirely digital, provided by ES9018 dac chip. It is controlled by PIC16F84 microcontroller via I2C. There is also 3-digit attenuation level display and rotary encoder is used for setting the attenuation level. Details are described in next posts.

Posted 6th January 2015 at 12:30 PM by Maciej Czerwinski Comments 0
Posted in Uncategorized
On the DIYINHK DAC board we can find ES9018 chip and ADP151 1.2V linear regulator (VDD) factory soldered. You have to populate the rest of the board yourself. I have soldered:
- ceramic and electrolytic noise filtering bypass capacitors,
- various resistors, mostly in the I/V stage,
- I/V stage op-amps (4xAD797)
- output signal low-pass filter capacitors.
The board is designed for 6 op-amps with SE output. I wanted differential output, so I have done some modifications, following the ES9018 demo board datasheet.

The I/V stage and power amp schematics (one channel):
Attachment 1478
When the main power is switched off, the relay shorts the power amp inputs in order to avoid oscillations, generated by I/V stage during discharge of its power supply bypass capacitors, to pass to the power amp.

A/V stage section of the DAC board one channel, ES9018 chip side (top side in my case)....

Posted 6th January 2015 at 12:29 PM by Maciej Czerwinski Comments 0
Posted in Uncategorized
It works in parallel configuration in order to drive 4 ohm speakers easier. Such configuration has quite low input impedance, around 5kOhm, and low gain of 3.7. This, with the 3x20k input signal resistor divider, gives the maximum output power of only 1W for single sine.
The two pairs of 100k, multi-turn potentiometers set the symmetry of each amplifier. It has to be adjusted manually. In order to do it, you have to supply in-phase (single ended) signal to the input of each amplifier and turn the potentiometers until the signal at the output of each amplifier drops to zero (or rather goes below the noise floor). Unfortunately it also affects the voltage at the amplifier output. There is a lot of trial-and-error work needed to achieve zero signal and zero volts at the output. It is good to do it separately for each of the amplifier from the pair by unsoldering output 0.1 ohm resistors. Signal generator and frequency spectrum meter comes in handy for this...
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