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.

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.

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 diyaudioprojects.com 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

DIY Audio Note M77 Clone

I have just converted my 12B4 tube pre-amp to this Audio Note M77 Clone. The 12B4 / 12B4A circuit was my reference bettering all other tube pre-amps I have owned in the past but this just betters it in so many ways. The circuit was linked from another overseas forum over at DiyAudio. Someone had opened up a real Kondo M77, took photos and traced the circuit plus measuring all voltages sketching this onto lined paper. I have re-drawn the circuit in X-Circuit and the supply I used. The M77 is built to such as high standard using quite special parts, with an equal special price that most of us could never afford or justify. Dave H as usual built this first in a few variations / tube types.

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