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Pass Labs B1 Buffer Rebuild



Having sold the last B1 buffer I built I ended up building another. I had a spare pcb sitting around for a while and since it is such a good pre-amp, easy to build and the fact I had 90% of the parts already it was a situation of... might as well. It also meant I could use one of those nice aluminium cases from modshop in Italy to match my copland cd player and the lightspeed pre-amp case. Solid state builds such as this simple design do not have much to go wrong and testing is safe unlike tube gear. A big difference working on 18V here rather than 300V plus.


Matched Vs Unmatched

In the first build I used a quad matched set of FET's having read forums saying the pre sound better with a matched set. Anyhow seeing as I has some FET's already but not matched I ignored the usual chatter and just built it with what I had. I can honestly say that in my build it makes no obvious difference. Channels are still balanced and it has the same character B1 sound. Infact this time I had some better output caps.



Grado PS500



For the past year I have been using a pair of stax lambda pro electrostatic headphones with my Copland 288 cd player in one of my setups. I sold my Martin Logan speakers and wanted something as good but more suited to a small room, able to be used any time of day or night and as loud as I wanted with minimal external noise. Quality headphones are very hard to better with similar priced loudspeakers. They also provide a highly involving listening experience. Their diaphragms are much lighter than typical dynamic speakers and so have timing and pace unmatched bar the very best speakers. Electrostatic speakers do try to overcome this problem by the use of lightweight film which only weigh a few mg. Dynamic coil based systems have the weight of the coil and cone to move, including mechanical resistance from the 'spider' and surround.

Linn Valhalla Supply Repair


Some Info

I recently helped a friend to repair a Linn Valhalla power supply pcb. It would seem that these are prone to particular failures and a common one is low motor torque in which the motor buzzes or vibrates since it is too weak to drive the platter. This turned out to be R32 (560k) on the board. R33 had also deteriorated with the ceramic body breaking up. I have uploaded the circuit as a png and pdf file which some may find useful.

If you are having motor problems I would first replace these 2 resistors R32 and R33. Failing that then the next step is to replace the small orange caps around the logic chips if the motor does not turn at all.

If the unit will not power up then some early Valhalla units could blow the bridge rectifier so you will need to test this and the large power supply caps it feeds, assuming the fuse is ok. If the bridge has part blown then AC can reach the caps and damage them. If replacing any parts then consider using something slightly higher rated and higher quality as the standard parts are nothing special.


Lightspeed Attenuator Rebuild


Lightspeed Passive Pre-Amp

I have slowly been working on building another light-speed attenuator but in a much nicer case matching the chassis type used in the Nelson Pass F5 and F3 builds. This again is a scratch build rather than a kit. As usual I have built it with parts I already had to save cost but needed to buy the case from Italy and the 4 x Silonex NSL-32SR2 LED-LDR's from in the states.

The circuit is simple so I built it on proto-board with hard-wire links on the copper side with the shortest routing possible esp on the audio links. I used some left over silver wire I had on the links that carry audio signals and these are situated at the back of the unit very close to the RCA sockets. I also avoided fitting a selector switch so it is 1 pair RCA in and 1 pair RCA out for the most direct signal route. That way we don't lose the advantage of using the LDR's to eliminate the usual audio carrying volume pot and its contacts and spoil that by routing audio through a selector switch or relay.

F5 Power Amp Headphone Adapter


Power Amp Driven Headphones

I was wondering if it was possible to drive a pair of regular dynamic headphones from a power amp such as my Class A F5. Sometimes I have periods of time without a pair of speakers such as if I have sold them and looking for something new to replace them with. In the meantime it would be nice to use a pair of headphones which quite frankly are hard to beat with most speakers. It seems that you need to spend quite a few more in pennies on the speakers to match even a modest pair of cans and once you are in the realms of higher end headphones then most speakers don't come close to the same levels of enjoyment and immersion in the music.

I found a neat little project over at ESP. It is nothing more than a 6 resistors, 3 per side to give the correct voltage levels and impedance to the headphones. You could probably solder these resistors in-line with the headphone to speaker banana leads and heatshrink them but I used a small box, proto-board to hold the resistors and some nice nylon sleeving.

Pass Labs F5 New Power Supply


Upgraded Pass Labs F5 PSU

I decided to upgrade the standard build power supply in my Pass Labs F5 with some large screw terminal Aerovox caps from CPC. My original build used 4 x 22,000uF snap-in caps shared between both channels L+R on the PCB which is the recommended minimum. Some have used 2 of these PSU PCB boards, 1 per side which is the next step up. My late friend Dave Hewitt used 4 large caps in his F3 so I eventually followed and bought 4. This provided 47,000uF per cap so more than double the original capacitance and storage. I also by-passed each side of the supply lines with 10uF film caps.

The picture of the amp without the front fitted and test leads shows the original power supply PCB and snap-in caps. The new caps are about the size of a Red Bull can.


Sound and Aerovox Caps

Grado RA1 Headphone Amplifier Clone


Grado RA1 Headphone Amplifier Clone

Fancy making your own Grado RA1 amplifier clone. Well the circuit below is all you need. About £10 worth of electronic parts minus the case and regulated supply. Also very easy to make on veroboard or protoboard. The original circuit came from who I understand reverse engineered an original RA1. The design can be easily altered to use other better quality op-amps and more importantly E24 series preferred resistor and cap values.

The opamp used is the LM4562 or better still the OPA2134. You can use the cheaper original JR4556 but the OPA2134 should be easier to buy and is much higher quality than the JR4556.

Put it in a nice case with a power supply like Grado do and you have neat little headphone amp for little cost. Probably one of the simplest circuits to make based around an op-amp as it is a standard non inverting circuit.


Battery or Regulated Supply

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by Dr. Radut