Posted 13th February 2015 at 05:16 PM bywlowes Updated 4th March 2015 at 11:54 PM bywlowes(Tube amplifier tuning - manginin resistors)
As with other projects, I like to start with the disclaimer that this entry is just a scrap book of my personal journey with a build. No fresh engineering here, so those seeking engineering insights can save the read.
That said, I now have a week of burn in on my new music server, and for me its a delight. It is a collage of ideas developed by diyaudio members and by Lukas Fikus, aka Lampizator.
I still need to do some debugging, and create an aluminum top plate. There will be holes in the plate allowing the Tubes, RCA outlets and power cord to rise vertically out of the box. I have a home built AVC volume control in matching American Walnut which sits on top. The interconnects are a short path to the AVC and then to OLT mono blocks. Attached are some pics from the top and bottom sides as my layout is a 2 story affair.
My approach is heavily influenced by Lukas of Lampizator fame. I have enjoyed his tube output amp...
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.
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.
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...
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:
Vifa TC 3520 woofer:
Vestra PW-250-2154 woofer with it's crossover, microphone located 10 cm from the driver:
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:
It is pretty flat, and the bass is very nice now....
Posted 7th February 2015 at 07:47 AM byrjm Updated 14th February 2015 at 10:13 AM byrjm
I recently obtained a pair of AKG K702 headphones to complement my long-standing reference Sennheiser HD 600s. I figured since I'm building headphone amplifiers it would be a good idea to have a reference grade low impedance model as well as the high impedance HD 600s to use for evaluation.
At the same volume position I quickly discovered the HD 600s play slightly louder than the K702s. The datasheet values predict the K702s should be about 3 dB louder, so it seems the sensitivity is off by as much as 6 dB.
K702: 62 ohms, 105 SPL/V ... 93 dB/mW from datasheet, 87~89 dB/mW (99~101 SPL/V) in practice.
HD 600: 300 ohms, 97 dB/mW ... 102 SPL/V.
The K702 requires as much as ten times more power to drive than the HD 600s. The voltage sensitivity is about 3 dB lower than...
Posted 31st January 2015 at 01:28 PM byrjm Updated 27th February 2015 at 05:40 AM byrjm(update schematic to final)
A couple of years ago I built a standard op amp + diamond buffer headphone amplifier, called the Sapphire.
It's a fairly common circuit, from eBay on up its not hard to find similar designs. The Sapphire is distinguished by its full dual mono design, Zener voltage regulators (Z-regs), and by keeping the buffer circuit outside of the op amp feedback loop.
Regarding the feedback loop, there are two schools of thought:
1. Put the buffer inside the feedback loop, so the op amp does active error correction on the output signal, and the buffer provides the high speed currents required to make that correction.
2. Put the buffer outside the feedback loop to isolate the load from the op amp. The load currents are provided by the buffer, but the output signal relies entirely on the low output impedance of the buffer for accuracy.
The explanation is too long to bother with here, but I am strongly in favor of using a buffer...
Posted 27th January 2015 at 03:07 AM bygooglyone Updated 26th January 2015 at 09:02 AM bygooglyone
I recently picked up a pair of, I guess, 1970's Richard Allan three way speakers. The line-up are RA drivers with which I am not familiar. Bass, LP10B, midrange LP5B and tweeters - long dead and replaced with mismatched dome tweeters.
Richard Allan was reasonably popular in Australia in the 70's and 80's, and did some pretty good gear. I was interested to see how these went, but did need to do something about the tweeters.
On pulling the drivers out, I noted a few things:
- The LP10B is a 10 inch bextrene cone woofer, using a 1.5" voicecoil rather than the HP10B's 2" coil. It is also very much an "acoustic suspension" driver - read on.
- The LP5B is very much like a 5" version of the KEF B110 - as used in the LS3A. I read somewhere that Richard Allan made a version of the LS3A under license, but that might be an "internet fact".
- The crossover was made by KRIX, a local speaker manufacturer...
Posted 16th January 2015 at 12:55 AM byabraxalito Updated 13th February 2015 at 04:23 AM byabraxalito
Thanks to Matthieu (Malefoda) for the heads up on this. It looks distinctly like a DAC inspired by the DAC-AH - note not only the 8 DAC chips but also the PCB layout closely follows that design's. The price on Taobao is about half the AH (368rmb) so I shall be ordering up one or more to have a play. Matthieu found it on another website with prices in USD, here - http://www.cart100.com/Product/42124644877/.
Note there are two options here (blue, black) - the cheaper one is a kit of parts I believe, the more expensive ($84) the finished unit. Going on the translation of the Taobao page, the kit does not include the transformers, mains switch or the case.
Update : here's the summary of the mods so far, for details go to Malefoda's thread linked in the comments.
1) Re-route the output ground so the opamp filtering caps aren't subject to injected CM noise from the destination component (amp or pre).
2) Reduce the supply voltage to the output opamps...