Amp repairs: Laney Session 40 Bassman

So: I’ve rambled a bit about some music that I like, now it’s probably time I dealt with the other intended aspect of this blog and talked about some of the paraphernalia used in the making of music. This post concerns my first and most long-suffering bass amplifier.

I first acquired a bass guitar at the age of 14, and stumbled across a very good price on a second-hand amp a couple of weeks later. The amp looked like it was older than me (and what little information I can find suggests it is), and I had no idea what tonal qualities I should have been looking for, but it was a bass amp, it was affordable, and that was all that mattered. In hindsight, I think I did rather well.

Doing a Google search these days for “Laney Session 40 Bassman” – for ’tis its name – yields a few results for second-hand sales, a little discussion on bass or guitar-related forums, and very little information. It’s a 40W combo with a single 12″ speaker, and mine has been used at rehearsals, gigs, for teaching, even used as a guitar amp for a brief period, and has borne it all with good grace. The only gripe – and it’s always been there – has been the strange squeaking or howling noise it sometimes makes when you play around with the parametric midrange control. Otherwise, it has soldiered on without complaint.

A few months ago, I found a slightly more concerning problem, which was a humming sound that, I established, wasn’t due to the ropey earthing on my bass guitar. Experimentation (well, unplugging the guitar) showed that the hum persisted, suggested there was a problem with the earthing on the amp.

The good news is that these amps are relatively easy to get into: a couple of screws at the top released the head, which slid out without too much resistance. Thus I realised that my diagnosis had been spot on:

The transformer's bid for freedom

So the earthing was indeed a problem, because the transformer had fallen off its mount, taking the earth from the power supply with it. Closer inspection showed that the transformer had been attached to the back of the chassis by two bolts (and two corresponding nuts) – which were nowhere to be found. I found a single bolt, sitting sheepishly in its hole on the loose transformer. Where the hell did two nuts and a bolt disappear to? Do amps just eat their innards if you don’t feed them enough?

It was time to take a closer look and make sure everything else was in order – perhaps I could find something which might explain the squealing mid-range control. Unfortunately, there was a limit to how far out I could pull the head, as it was still connected to the speaker. (I’ve noticed that some more modern Laney amps get around this problem by having a jack connection on the back of the head.) I unscrewed the back of the cabinet, freed the wires from the back of the speaker by judicious application of a hot soldering iron, and was able to pop the head out fully.

In the process, another bit fell off. I’m fairly sure said bit wasn’t supposed to fall off, seeing as it was a big, chunky capacitor. Don’t know about you, but I’ve always been of the opinion that big, chunky capacitors should probably be secured inside the amp as opposed to rolling around on the floor.

Errant capacitor

Worse still, the little bugger had left one of its legs in the PCB from whence it had fallen. Thank heavens for small mercies – at least this made it easier to identify which way round its terminals were supposed to go. But how to reattach it? Why, by popping the errant leg out of the PCB and stuffing it in the hole next to the remaining stump. Apply plenty of solder to make sure it sticks to the stump and no flowing electrons will be any the wiser.

Back to a more concerning problem – the transformer. With no bolts of a suitable size, I decided my best course of action was to tie it back onto the chassis. Now, I should probably admit that I’ve always been a dreadful hoarder – I have a tendency to look at just about anything and think
“That might come in handy at a later date.”
As such, I had the spiral binding from an old notebook that I’d long since dismantled into the recycling bin. Wrapped a few times through the bolt-holes and tightened on with a pair of pliers, the transformer was duly tied into place, and the earth wire soldered back into its original position.

Transformer reattached.

From the picture above, it may look like it was an easy job. Was it? Well, it is widely said that soldering is one of those jobs that requires three hands. In my experience, it’s true. It’s even more fun when, due to your room being in a bit of a state, the best thing you can find to balance your subject on is an old computer case.

So I found myself with the preamp balanced on top of the amp casing, and the amp itself balanced on the old computer case. The soldering iron was in my non-dominant hand as the dominant hand had to hold the pliers. And an extension cable to the soldering iron balanced in my lap. Oh, if health and safety could have seen me. It’s a wonder to this day that I still have all ten working fingers and no lasting injuries.

Unfortunately, there was still no sign of any obvious problem that could be causing the mid-range control to make strange noises. I decided to cross my fingers and hope that reattaching the transformer and capacitor would solve this problem as well, and set about reassembling the patient. Results? Well, when I closed my eyes and flipped the power switch at arm’s length, the amp came to life with no complaints. The hum was gone, and everything sounded perfectly fine when I connected a guitar. Unfortunately the mid-range control still squealed like a stuck pig, but everything else seemed to be in working order. Victory was, at least partially, mine.


6 thoughts on “Amp repairs: Laney Session 40 Bassman

  1. I am doing a repair on one of these amps. SAME ISSUE!!! I have the trans re-attached and soldered. I also have a burned resistor on the smaller board. Can you send me a pic of the resistors on the small board?

    • Hi again Jerry, really sorry about the lack of photo so far, but I don’t think I can get a good enough view of the boards without completely dismantling the amp again, which I’m reluctant to do! I’ll try again if I can get a view with better lighting.

  2. I’ve got one of these amps. Replaced a couple pots, but it still works. Just looking for a knob to replace a missing one (or a new set of six that will look OK!).

  3. Crow, I also have a Session 40: which I bought brand new in 1970-something! I have never had the problem you describe with the mid-knob, and to this day my Laney is my only amp., and goes gigging with me (I don’t play BIG gigs LOL!).
    I read your description of the repair through fingers over my eyes — with a mixture of amusement and horror. Personally, I would have bought a new cap. from Maplins or wherever instead of trying to bodge the existing one; but that’s your call. I also think that the ‘busted’ cap. is probably why your amp. still squeals.
    But much more shocking was you using the wire from a notebook binding to secure the TRANSFORMER?!! Don’t you have a B&Q or Homebase nearby to buy replacement bolts? I recently did some work on my (musical) partner’s Roland HP 2900G piano, and easily found a bolt to replace the one that was inexplicably missing from it, and which made the ‘lid’ much more secure.
    Seriously dude, IMO using WIRE to secure the tranny to the chassis could EASILY cause a short, a fire, or even electrocuting yourself when you plug in your bass at some point in the future >shudder< but as above, it's your funeral (hopefully not literally!).

    And to Dave: I also needed a knob or two recently for my Laney. A local 2nd-hand guitar shop turned out to have a 'little drawer' full of knobs they'd collected down the years and I managed to buy a couple that fitted and didn't look totally 'wrong.' Swapping around the knobs meant that the two silver-topped ones I bought look quite spiffy and 'intentional,' so that's my tip to you.

    • Hi Cad, thanks for stopping by. Firstly, thank you for narrowing it down 1970-something; I couldn’t even be sure whether it dated back to the ’70s or the ’80s!

      As for my dubious electronics workshop…well, you’d be quite justified in being horrified! The repair was carried out in my room in a pokey little flat in London. I probably could have – nay, should have – gone out looking for a Homebase or similar, but at the time I had no idea where the nearest one was, and figured a wire tie would do the job. As you rightly suspected, it didn’t! But the transformer has since been re-secured with a couple of old guitar strings and hasn’t made any threats to come loose for a couple of years now.

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