Tuesday, December 18, 2012

WAC 49 (BHL phono preamp)

This is an original stripboard layout for the BHL phono preamp (if you are building this you should read up on construction details, and the schematic at  http://boozhoundlabs.blogspot.com/p/jfet-phono-preamp-kit.html).  Depending on the power supply used it's very quiet, I'll be trying a battery supply soon, hoping for even less noise and I'm curious how the sound will be affected.  I've never compared to other phono preamps on my current setup, which is an old Technics SL-Q200 turntable into my KRK V6 II monitors, but, frankly the sound quality that's happening is pretty amazing.  I can't describe it in audiophile terms but, I am hearing great transient response, a certain crispness and laid-backness at the same time, and great overall clarity.  I'm actually hearing little things I've never heard before, on albums I've listened to thousands of time, like The Wall.  It's a pretty snappy sound, and full but not overly full sounding.  I am very happy with my build.  I added 470 uF bypass capacitors in parallel to the 50 ohm resistors on Q1 of each side to get a little more gain.  It's loud enough now but I might add the same to Q2 in the future for even more output.

UPDATE:  I was getting an extreme motorboating kind of sound from one of my wall warts.  The other one puts out something like that but at a very low level--enough to be annoying when the record reaches the end.    Finding the right adapter might take some trial and error.  I switched to a bank of 20 AA batteries, which puts out about 32 VDC, and the noise is pretty low...lower, but there was a slight buzz still.  Swapping out the "POS" RCA cable I had between the turntable and the preamp with cables of higher quality got rid of most of the remaining objectionable noise.  A reminder to me that yes, cables still and always do matter.  Now the overall noise level is quite tolerable and pretty low, but, there is a very faint buzz in the right channel only.  The rest of the noise is a tiny hiss across both channels.  The next variable I'd be curious about is a higher quality turntable, regarding noise performance.


  1. Hello from France !
    Thanks a lot for the veroboard ;-)
    I'm building this one, with your vero ...
    I need some little parts (resistances + pola caps ...) but I've found the others (PIO caps, in Russia, and 2SK170 in Israel ! lol good adresses !!!)

    A question, what voltage is "ideal" for this one ?
    In this original blog article, author and kit saler says :
    "power supply options

    This circuit should be happy with any supply voltage between 12V and 24V, so feel free to experiment.

    I have sold many of these with a simple but high quality switch-mode AC adapter, but the one I used to sell has been discontinued. I have found that some switch mode AC adapters will produce a "motorboating" effect, but they are cheap so if you get this, try another one.

    AC adapters are cheap, easy, and usually quiet - but there are certainly better sounding options. One of the best fits for this circuit is to use ~24V worth of batteries in series. Batteries tend to sound really great, are the quietest option by a mile.

    The H-PS-1 power supply from Glass Ware (TubeCad Journal) would be really amazingly good I bet (though I haven't built one). The 18V version would be ideal."

    I will probably install 2 (or 3) 9V battery (6LR61), so 18v or 27v !
    27v are not dangerous ?
    What's your opinion please ?
    Is it important for the "gain" ? (= volume) of the preamp ?

    Thank you, greetings

    I'll say my results when it will be finished.


  2. Hi Sylvain, good luck with your build! Yes please post your results I'm very curious.

    The power supply voltage will not increase output volume, it will only affect the headroom of the circuit. What this means in practice is a subtle difference in sound quality. I found that a lower voltage supply, say 15V of AA batteries or a wall adapter, produces a slightly darker sound. 30V of batteries sounds just a little tighter or something, slightly more detailed, it's very hard to describe.

    I prefer running it at a higher voltage. I have been running mine at 30 V for the past several months. BHL said this was fine on their blog so I went for it. I generally like guitar pedals at higher voltage, as well, for the same reason I described.

    One thing to note is batteries sound quite a bit different from an AC supply. Running an AC adapter gives a strong firm sound with good bass impact. Running a battery supply gives a slightly "softer" sound. Batteries are much, much quieter than the laptop AC adapters I've run with it, which is their main advantage. A deck of 10 or 20 AA batteries will last several months of a few hours a day use, pretty amazing really. So you're not buying batteries all the time. I really want to build a linear regulated power supply for this thing though, as a final solution. I can probably post that veroboard plan when I get around to that project. Batteries are just fine for now, though.

    Please look at my most recent post blog from this month regarding bypass capacitors on the JFETs. I would really recommend adding these capacitors to one or both gain stages for a little extra volume. I don't feel that the stock BHL plan, as drawn on the veroboard layout, provides enough gain for my liking. I really think this amp needs a little more gain, at least with my turntable. I like it to be as loud as my CD player so I don't have to mess with my stereo preamp for volume differences. This is something you can experiment with. Slapping on a few caps for some extra volume is pretty simple on the veroboard, since there are plenty of holes to use. Make sure they are high enough voltage for your circuit.

    Good luck again! Really curious how yours turns out.


  3. I didn't mention it on my graphic but you want your RCA jacks to be isolated from the chassis also, use the plastic washers. Test them with a multimeter to make sure they are not grounded. The grounds are all coming together at one point and you run a single wire "chassis ground" to a single point on the chassis, I used the turntable grounding post as my ground point, another RCA jack for convenience in my case. If your turntable has a ground wire you connect it here. My build is very, very quiet with this grounding scheme.

    Also a silly 2.0 build note, you can use a little jumper wire instead of having power supply wires on both sides. You can just jumper the sides together kind of how the ground is done like this already, and use a single power supply wire, it's a little cleaner build like that I guess.

  4. Hello Dan !!!
    I finalize my order for the missing parts ...
    I had read your new article about pyramid caps ...
    I can't replace these ones right now (don't find exactly and quickly these ref.), perhaps after !!!
    But I'm interresting in your add of "bypass caps".

    Could you "explain" me this paragraph please ? :

    "The other difference this time around is I used 100 uF bypass caps on all four JFETs, in parallel with the 50 ohm resistors. The output is nice and high and easily matches a CD or MP3 of the same material in volume."

    Where are the caps on the vero (and resistances ??? or not ?) ?

    the RCA I will choose will be isolated, don't worry.
    I take also consideration for the "chassis ground" to, thank you for the tip.

    For the power supply, I'll try 2x9V and 3x9V batteries !
    Depending of the results and experimentstions, I will build a super good wall adapter power supply, like this one :
    PSU n°1
    or better : (best regulation, and best 50Hz buzz treatments) :
    PSU n°2

    Thanks for the goodies !!! I will be back soon !

    PS : my system (for your information) :

    Amp : Unison research Simply 2
    Speakers : Back Loaded Horn DIY with Fostex Fe206EN (sound really GOOOOD !!!!!) direct drive (no filter !)
    With the "Humblehomemadehifi" hifi plan :
    Solo 206 archive on HumbleHomeMadeHifi website
    Turntable : an old Sanyo TP625 with a Ortofon OM5e cartridge
    CD : Pioneer PD-S707 (really good player ;-) )
    Modulation cables : DIY with Sommercable Albedo wire (great !)
    Here is mine :
    my sytem

    And for the "solo" nirvana, a clone of Grado RA1 + Alessandro MS-1 Headphone (very cool !!!)

    Bye, best regards !


  5. Please read the Boozehound Labs page, here is a quote,

    but my answer is to put a 100 uF cap in parallel with all four 50 ohm resistors on the board. the (+) leg of the cap goes to the Source of each jfet, and the (-) leg goes to ground. This is the same as the 50 ohm resistor, ie, "parallel." If you're using a high voltage supply make sure these caps are rated high enough. 220 uF would probably also work for even more gain but I'm using 100 uF caps. You can experiment, here. There should be a little room on the veroboard but you might have to "squeeze it in" a little depending on the size of the caps you use. I find this modification to be necessary, providing a nice output level with my turntable. Stock was too quiet, for me.

    please read (from the BHL website):
    "options for getting more gain

    I have had several kit builders ask about the options for getting more gain out of the BHL Phono. There are LOTS of options. Gain is determined (approximately) by the ratio of the Drain Resistor (R4 and R11) to the Source Resistor (R3 and R12). R4 if off limits though, because it sets the output impedance of that stage, and changing it would effect the RIAA equalization (which can always be recalculated). For a modest increase in gain, you can reduce the size of R3/R12 or increase the size of R11. Start by roughly doubling/halving them. If you want more gain, you can remove the Source resistors completely, or bypass them with a large (typically electrolytic) capacitor. If you want to get a bit more exotic, you can replace the drain resistor with current sources, or perhaps a current limiting diode (which is simply a preset current source).

    Another option to consider is the addition of a stepup transformer in front of the stage, which can improve the impedance matching with many low output cartridges as well. Conveniently, low output cartridges tend to prefer lower impedance loads, so if you need more gain definitely look into stepup transformers since you might be able to get more gain with the added benefit of better impedance matching."

  6. I'm going to build some of those RA-1 clones too, cool. I am using AKG K702 headphones and I love them. I'd also like to build an AMB Labs CK III 2, I just love the component choices they made, it's got me really curious.

    I've got a Pioneer CD as well, Elite, DV-46 AV it's actually a DVD player but it sounds great with CD and has a digital output as well that I use with my DAC, an Emotiva DC-1 that I'm very attached to.

  7. To complete the geekery I've got some Polk RTi A3 speakers coming along with an Audio Technica LP1240 turntable which I'll be starting out with an AT95E cartridge.

    I'm using a cheap old trusty Pioneer receiver, but an amp will be my next upgrade.

  8. Just another idea I had. I think another possible improvement to the original design would be some large filter caps on the V+ line. I think this could possibly make it quieter with cheap DC power supplies. I might give this a try... I'll report any findings

  9. I added 660 uF of filtering caps, tested with a very noisy power supply before and after. The noise was reduced, subjectively, but only slightly. This was a heinously loud and noisy power supply, though.

    In positive news, I used an old 18.5 Volt DELL computer power supply, and it is very, very quiet. There's a very small 60 cycle hum but it's only detectable with the record needle lifted, and the speakers cranked way up. It's very quiet. I had to solder a new connector on it so it would fit my Boss sized jack. The model number is HA65NS1-00 in case you want to look one up on eBay. They are going for about $15 make sure to only buy original Dell brand, not workalike generics. You'll have to solder some kind of tip on the cord that works with your phono amp's power jack. I can say that this is the quietest power supply I've tested out of about 4 or 5.

  10. Hello !

    Thanks for your several posts !!!
    I will read (and try to understand lol) all of them :-)

    I think I will build a "stock" BHL preamp, plug it in my system and test with different voltage (from 18 to 27 V)
    I will make changes only if the gain is very low ...
    (except Pyramid caps, I probably will test these one day !!! if I will found them)

    AMB labs 's projects looks very cool !!! I had seen the M3 before building my grado clone, but prices were to high for me ...

    Be careful with the RA-1 clone !
    this headphones amp isn't able to drive high impedance headphones ... AKG K702 seems to be good (62 Ohms => good)

    but when I bought my Alessandro (nearly a grado SR80 / 125), I prefered to test a Sennheiser HD-600 or 650 but the 300Ohms impedance were to high to be drived by the RA-1 ...

    I don't regret the Alesssandro ! It is perfect for the music I like !!!!
    for rock / blues-rock / guitars it'e really goooooood !!!

    Thanks for the tip "DELL PSU" !!

    My order for small parts is OK,

    I tell you when I begin to build my BHL Phono preamp