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• The BSTRD - Measurements

  skrodahl • 12/19/2016 at 08:20 • 0 comments

  We've already established that The BSTRD sounds pretty nice, but how does it measure?

  Keep in mind that my QA400 audio analyzer has a tendency to pick up 50 Hz mains when used with a computer connected to mains (it does better on a battery-only laptop), so this will skew the results a tiny bit.
  

  I'd say it's what you can expect from a tube construction, or better.

  The frequency range +0/-3 dB is 10 to 30.000 Hz. SNR is 83.5 dB (without A-weighting) and 93.2 dB (with A-weighting).

  This thing produces harmonics, with the second being prominent. 3rd harmonic and greater are near or below the noise floor. As a result, it shows THD measurements of 0.35-0.4%.

  The SNR/THD(+N) measurements have been done at 1 Vrms output. The numbers are will be even better at 2V output, which is the common output of modern equipment.

  Frequency range (10 Hz to 30 kHz):

  SNR/THD(+N), without A-weighting (1 Vrms output):

  SNR/THD(+N), with A-weighting (1 Vrms output):

• Testing the BSTRD Some More - Sweetness

  skrodahl • 12/06/2016 at 22:46 • 0 comments

  This is quite a little performer,

  The sound is crystal clear, there's no hum, hiss or noise of any kind, the stereo imaging is wide and precise to the point where I can close my eyes and point out the instruments and vocals in the space in front of me. And the sound is very rich and warm. 

  I swapped the 15V AC on the PSU for the filament heater to 9V AC, and the heat sink (while still warm) is cool enough that there won't be any need for extra cooling.

  Besides, who can resist that little glow peeking at you? All in all, this is full tube/valve Class A sweetness :)

• Testing the BSTRD - Success!

  skrodahl • 12/04/2016 at 22:52 • 0 comments

  Testing the BSTRD - Success... Not entirely true at first; I had used a 330 ohm resistor in the feedback loop instead of 330k. The result? No sound. At all. Not even noise. What a bummer...

  Well, replacing the resistors made all the difference. It was a real joy to see the 1 kHz sine show up on the scope, nice and clean.

  I hooked it up to a power amp and a single speaker (I tested one channel at a time), and all I can say is that this thing sounds sweeeeet. All the way from the meaty bass to the tingly treble. :)

  Note that the PSU needs two transformers, because of the 78V part using a voltage quadrupler. Two tube filaments drawing 300 mA each, is 600 mA in total. The regulator and the heat sink get really, really hot. I should probably find a way to get more cooling, it will most likely mean moving the regulator off the PSU board. UPDATE: The excessive heat was because I used way to high AC input on the 6.3V side. Replacing the 15VAC power with 9VAC made it all better.

  I measured the regulated outputs for AC, and my multimeter shows 0.00 mV on both the 78V and the 6.3V. I am quite happy with that result. :)

• Components, Bill of Materials

  skrodahl • 12/01/2016 at 08:48 • 3 comments

  Here's the bill of materials for both the BSTRD Tube Pre and the Power Supply.

  It contains part numbers from Mouser, and other sources where Mouser can't provide the parts. It's recommended that you buy more than the specified component quantities, especially for cheaper parts like resistors.

  These are just suggestions, there are a lot of cheaper, more expensive, better, worse and higher or lower quality components available. There are also a lot of other places to get components, like http://elfadistrelec.com, http://digikey.com, http://tme.eu to mention a few.

  Mouser Shopping Cart

  All components below except LED resistor, transformers, tube sockets and tubes have been placed in this Mouser shopping cart: https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=b93f29a67d

  The BOM and shopping cart were last updated 2019-04-03, ensuring that everything is in stock.

  Note that the 470uF/160V electrolytic capacitor has been replaced with a 200V version, and that the 100V ceramic capacitors have been replaced with 200V models.

  The BSTRD Tube Pre:

  Quantity	Component	Value	Mouser Part #, or other source
  2	Resistor, 0.6W	1k ohms	279-LR1F1K0
  2	Resistor, 0.6W	22k ohms	603-MF0207FTE52-22K
  2	Resistor, 1/4W	100k ohms	603-MFR-25FRF52100K
  2	Resistor, 1/4W	330k ohms	603-MFR-25FBF52-330K
  2	Resistor, 1/4W	1M ohms	603-MFR-25FRF521M
  2	Electrolytic capacitors, 25V (≤10mm width, 5mm pin spacing)	47 uF	647-UKZ1E470MPM
  2	Film capacitors (7.5mm pin spacing), ≥ 100V	1 uF	505-MKS41.0/100/10
  2	Ceramic capacitors	0.1 uF	80-C320C104K1R
  1	Stereo Potentiometer, logarithmic, 16 mm	100k ohms	652-PDB182-K430K104A
  2	Sockets, for tube	8 pins	Search for "octal socket pcb" on eBay, Amazon etc.
  2	Tubes, valves	6J5 or equivalent	Available from various sources, such as eBay and other online stores.
  3	Screw terminals	3 ports	651-1705469

  Alternative tubes that can be used with this preamp are:

  • L63
  • 6S2S (Russian tubes, also known by the Cyrillic 6C2C)
  • 7A4
  • CV1067
  • 12J5 (needs 12V filament heater)

  The BSTRD Power Supply:

  Quantity	Component	Value	Mouser Part #, or other source
  10	Diode	1N4004	821-1N4004
  1	Resistor, 2W	180 or 200 ohms	71-CPF2200R00FKE14
  1	Resistor, 1/4W	100 ohms	603-MFR-25FRF52100R
  1	Resistor, 1/4W	820 ohms	603-MFR-25FTE52-820R
  1	Resistor, 1/4W	3k3 ohms	603-MFR-25FRF52-3K3
  1	Resistor, 1/4W	6k2 ohms	603-MFR-25FRF52-6K2
  1	Resistor, 1/4W	Suitable for LED @6.3V	Calculate here
  4	Electrolytic capacitor, 100V (≤13mm width, 5mm pin spacing)	390 uF	661-EKZN101E391MK35S
  1	Electrolytic capacitor, 100V (≤13mm width, 5mm pin spacing)	47 uF	647-UHE2A470MPD
  1	Electrolytic capacitor, 200V (≤18mm width, 7.5mm pin spacing)	470 uF	647-UCY2D471MHD
  4	Electrolytic capacitor, 25V (≤13mm width, 5mm pin spacing)	3300 to 3900 uF	661-EKYB250E392MK40S
  1	Electrolytic capacitor, 16V (≤5mm with, 2.5mm pin spacing)	47 uF	UKZ1E470MPM1TD
  4	Ceramic capacitor	0.1 uF	80-C320C104K1R
  1	Voltage regulator, TO-220	TL783	595-TL783CKCSE3
  1	Voltage regulator, TO-220	LT1086 (or LM317)	512-LM317T
  2	Heat sink	SK104	567-637-20ABPE
  2	Heat sink mounting kit	TO-220	532-4880SG
  3	Screw terminal, 5 or 5.08 mm pin spacing	2 ports	651-1711725
  1	Screw terminal, 5 or 5.08 mm pin spacing	3 ports	651-1705469
  1	Transformer, ≥ 15VA	6 V AC (or up to 12V)	The print on the PCB says 9-12V. but 6-9V is better suited.
  1	Transformer, ≥ 10VA	18 V AC...

  Read more »

• Eagle Project Files

  skrodahl • 11/29/2016 at 17:11 • 0 comments

  Eagle Project Files for both the Tube Pre and PSU are now added to the files area:

  https://hackaday.io/project/16944-the-muffsy-bstrd-valve-preamp#menu-files
  

• Power Supply Built and Tested

  skrodahl • 11/29/2016 at 17:10 • 0 comments

  The Power Supply has now been built and tested (without load).

  There are two parts to the power supply:

  • +78V, 700 mA (using a full wave voltage quadrupler and an RC low pass filter)
  • +6.3V, 1.5A for filament heater

• Boards Received, Construction of Preamp Board

  skrodahl • 11/28/2016 at 20:58 • 0 comments

  There's been a little progress, now that the PCBs arrived today.

  The heat sinks fit nicely, and coupling two 2-port screw terminals together worked out nicely:

  Everything fits as it's supposed to, and I like having ceramic components on a PCB. I really think they look the part.

  The only thing left to do on the preamp board is fitting the tubes:

  There you have it, one preamp fully assembled. Next up is the power supply.

• BSTRD Update

  skrodahl • 11/23/2016 at 23:00 • 0 comments

  The BSTRD has been updated. Changes in layout, component values and footprints.

• Power Supply Updated

  skrodahl • 11/23/2016 at 22:55 • 0 comments

  Here's an update to the power supply. Same principle, different layout and correct component footprints/values.

• From Russia with Valves

  skrodahl • 11/03/2016 at 08:35 • 0 comments

  These puppies just showed up, all the way from Smolensk in Russia. They are 6S2S (C is the Cyrillic letter for S), which is one of the models that are compatible with 6J5. Others that will also work with the BSTRD are L63, VT-94 and 38565J.

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