That's her loosely hooked up and WOW! she's a cracker Alex! There was a bit of a problem on initial fire up as I'd fitted one of the 2200uF PSU caps the wrong way round so there was a loud crack followed by smoke Swapped it out and everything working 100% A OK...... fantastic!
First thing to go was the OPA2134, I'm presently burning her in with a couple of AD-843 on B-Dogs and boyo this thing sounds very good and will DEFFO be getting tarted up with some boutique parts
Yeh, you were right..... I just couldn't resist one of those purple LED's!
Thats coming on well Mike. So your using 2 single op-amps on a browndog? What happened to the torroid you had ordered?
Yes, 2 single channel opamps on a single to dual convertor. The toroid never materialized and Jaycar refunded me....... The encapsulated is fine, I've got 40 of them in a box so would be daft not using one wouldn't it? ;D
Now off to do the corned beef tin mod............ ;D
It's pretty early into the burn in (about 4 hours) but already this is a very fine sounding amp indeed, being refined and naturally balanced.... nothing is over emphasized.... it's actually not dissimilar to the tone of the JLH Chiarra running OPA627.
So far it's driving the HD-600 and K-701 perfectly, I have yet to try the Grados with it. I actually like the stock gain level as my preferred listening level dials in at about 1pm.... fantastic as this is the sweet spot with most of the ALPS RK27's I've measured.... full volco with shpongle is about as loud as I'd ever want to go anyway so I'll just leave the gain as is.
It may only be £8 for the amp kit and £5 for the PSU kit but, don't be fooled, this is no toy folks, it's a seriously good headphone amp and I'm sure I will have a LOT of fun with.
SandyK, you're not wrong.... it's a beauty and IMO the best VFM I have EVER come across in this game.... hell if the PCB was £8 by itself it would represent amazing VFM but to get ALL the components, a comprehensive easy to understand manual, a reel of solder blah blah as well............ bargain of the century as far as I am concerned. Factor in the amp actually sounds like it cost £500 and......... I better stop now before I salivate over my keyboard! After all she's only 5 hours into the burn in.
I've got around 45 different chips to try in her but, as is, am pretty impressed with the 843's on single to dual B-Dog..... I'll try the LM-4567 once she's stabilised.
Probably the fugliest looking enclosures on planet earth those Maplin things aren't they leo? They've got as much finesse as a house brick getting chucked through your window. This was intended to be a cheap project though and that was the cheapest (that would serve the purpose) I could find.
So, Alex, what mods have you done to your own Jaycar? From my brief look at the circuit it's going to be a matter of deducting rather than adding anything and basically getting the best out of your chosen opamp.
I really like the sound of the amp so will be tuning it up a bit.... I'd like a tad more depth and maybe a bit more clarity.... first to go will be the suntans and I'll try ELNA tonerex, Nichicon fine gold and the obligatory Panasonic FM and see which I prefer.
One criticism (if you have the cheek to critisise the bargain of the century) is the space on the PCB.... there isn't any if you're contemplating using the likes of polypropylene film caps, uber large electrolytics etc... quite a shame really as I've got a box of 500 x 100nF EVOX Rifa I'd like to make inroads into..... the pitch on the PCB for the 100nF caps is way too small to accept anything other than the el cheapos supplied with the kit.... a real shame as I'd really like to use polyprop here.
I'm not into funky angling but it's going to be the only way to go if I'm to get any quality components into the circuit..... even fitting the heatsinks onto the BD139/140 is a PITA as the 100nF film caps get in the way, by the way...... did you bother with the sinks on yours? I didn't..... the transistors don't take the skin off my fingers so no need for heatsinks IMO..... famous last words I'll be sitting here listening to something when "BINGO!" up she goes in a puff of smoke
Have you increased the quiescent current on yours Alex? From my lengthy affair with the WNA amps I found this beneficial with regards to bass slam and general GRUNT.... of course, heatsinks WILL be required if we up the QC
It would be great to spend a LOT of quality time with this amp but the way things are at the moment I'm either building pinkies, packing kits, working on amps, responding to e-mails, forgetting to respond to e-mails, pedalling back and forth to the post office...... etc. etc. it's like wading through a pile of shit every day and BOY don't the days get a lot shorter the older you get? A day seems more like an hour these days..... so much to do, so little time to do it.... when the crap piles up it gets harder and harder to shovel back down to ground level and even if you do manage to clear it another pile soon dumps down in front of you!
I couldn't put it better myself so I'll quote the mighty Floyd.........
Run rabbit run Dig that hole, forget the sun And when at last your work is done Don't sit down it's time to dig another one For long you live and high you fly But only if you ride the tide And balanced on the biggest wave You race towards an early grave
I agree the Maplins cases aren't the prettiest things but they serve the purpose and as you say, cheap! TBH I don't care if the case looks like a biscuit tin, I'm not picky at all regarding an amps looks long as it delivers the important bit
So, Alex, what mods have you done to your own Jaycar?
I haven't increased the bias, as I found that the quiscent current was close to the 15-20mA mentioned in the original article. This figure is calculated by measuring the voltage drop across the emitter resistor of Q2. The case was reused from a previous valve preamp project, mainly because all the metal work etc was done, and the toroidal transformer already there too. The transistors with the small fan type heatsinks are the JLH PCBs current limiters, which for this project are linked out under the PCB. This JLH PCB is a much earlier,less compact version. Using the JLH gives an awesome bottom end with my Sony Headphones, as well as improving detail, without harshness. Click on the photo for a larger picture. SandyK
CORRECTION. The ouput resistors shown in the attached schematic as 47 ohms, are 68 ohms For standalone Headphone Amplifier use, R3 and R6 may be changed to 2.0K. This gives slightly lower distortion.
dc The present case is too big. But it sits O.K. on top of the PC. I have asked one of my friends, who also uses a JLH board in his preamp, if he would use his Protel program to come up with a better PCB layout for the JLH board than the current (newer) version, so that we can get some made at RCS Radio. So far he hasn't got around to it. Pagan (Allan) has come up with a REALLY small JLH layout that works,but it isn't able to be used for PCB making by a PCB manufacturer. Several people have asked for PCBs , but it is very time consuming (and fiddly) to make more than the odd one for yourself. As Allan and Leo, can confirm, these JLH boards really do make worthwhile improvements to power supplies for DACs, amplifiers, etc. Alex