Laney VC30-210 problem - thoughts? [problem has come back!]

Voxman

Hi guys - just switched on my VC30 and there's a load of horrible hissing and 'motorboating' sound - still getting volume on both channels, and all controls work, no untypical distortion where it shouldn't be, so I don't think its valves - possibly might need new caps?  I'll probably need to get this to my amp tech guy but before I do, any thoughts?

steamabacus

Have you tried 'jumpering' the fx loop send/return - it seems they can cause problems on the VC series (I'm assuming the VC30 has the fixed 50/50 parallel loop?). I have a VC15 which exhibited something similar a while back - it was in a pretty complicated routing setup so I was never quite sure what was causing it (it would come and go). I went through the usual valve changes, etc without success but since I've left the fx loop permanently jumpered with a short patch lead I've had no problems.

Voxman

steamabacus said:

Have you tried 'jumpering' the fx loop send/return - it seems they can cause problems on the VC series (I'm assuming the VC30 has the fixed 50/50 parallel loop?). I have a VC15 which exhibited something similar a while back - it was in a pretty complicated routing setup so I was never quite sure what was causing it (it would come and go). I went through the usual valve changes, etc without success but since I've left the fx loop permanently jumpered with a short patch lead I've had no problems.

Interesting, and thank you because your reply prompted me to clean the FX loop jack sockets, and voila no more hissing!  But the motorboating is still there even with the FX loop jumped, and although it doesn't increase with volume on either channel it's clearly indicating something isn't quite right!   

ICBM

If the noise is not affected by the controls it sounds like it's from the power amp. First remove the phase inverter valve (the preamp valve next to the power valves) and see if it stops. If it doesn't, remove one power valve at a time until you've checked all four. It's safe to run with only three power valves for a short time, although they will run hot because it's a common-cathode-bias amp.

Voxman

ICBM said:

If the noise is not affected by the controls it sounds like it's from the power amp. First remove the phase inverter valve (the preamp valve next to the power valves) and see if it stops. If it doesn't, remove one power valve at a time until you've checked all four. It's safe to run with only three power valves for a short time, although they will run hot because it's a common-cathode-bias amp.

Thanks ICBM - I'll check that over the weekend.  So, do you think its possibly just a valve issue then?

ICBM

Maybe, but it's the easiest thing to check anyway so you might as well. It could be a power valve - they can be prone to rumbling/motorboating type noises - but it's best to eliminate the phase inverter first.

If pulling the PI stops the noise it doesn't guarantee it's the valve though - it could be something in the PI circuit, or it could even still be a power valve since it could be feeding back via the NFB loop, which removing the PI will break. So if pulling the PI *does* stop it, you then need to try another valve there - if you don't have any spare, use the V1 or V2 valve temporarily.

Voxman

Thanks ICBM - I'll let you know how I get on. 

jpfamps

The term "motorboating" is used to describe low frequency oscillation due to poor power supply decoupling, ie a duff filter cap. I've replaced a few on Laney combos, but not from memory seen one "motorboating".

Voxman

Voxman said:

ICBM said:

If the noise is not affected by the controls it sounds like it's from the power amp. First remove the phase inverter valve (the preamp valve next to the power valves) and see if it stops. If it doesn't, remove one power valve at a time until you've checked all four. It's safe to run with only three power valves for a short time, although they will run hot because it's a common-cathode-bias amp.

Thanks ICBM - I'll check that over the weekend.  So, do you think its possibly just a valve issue then?

ICBM - You are a steally-eyed missile man sir, and were spot on - thank you!  It was the phase invertor valve!  I had a spare 12AX7 chinese ruby that I put in, and my VC30 is healthy again.  Does the phase invertor valve need to be anything special - I also have a TAD 12AX7 - would that be better? 

ICBM

Voxman said:

Does the phase invertor valve need to be anything special - I also have a TAD 12AX7 - would that be better? 

You can try it, but it's one of the less critical positions so it probably won't make any difference.

Voxman

ICBM said:

Voxman said:

Does the phase invertor valve need to be anything special - I also have a TAD 12AX7 - would that be better? 

You can try it, but it's one of the less critical positions so it probably won't make any difference.

Thanks, I might experiment - so, in terms of numbering, is the phase invertor 'V1' and the other pre-amps V2-V4 in order (nearest to furthest from the power valves)? If I wanted to put in a 12AX7 that gave a bit more distortion/gain on the gain channel, which position would give the best results - would that be V2 (nearest to power valves opposite side to the phase invertor)?  

ICBM

Other way round - V1 is nearest the input/furthest from the power valves. (In almost all amps - there are a very few exceptions.) V2 is the valve for the drive channel, yes. My schematic only shows three preamp valves so your amp must be the revised version, but I'm pretty sure that's still the case.

Voxman

ICBM said:

Other way round - V1 is nearest the input/furthest from the power valves. (In almost all amps - there are a very few exceptions.) V2 is the valve for the drive channel, yes. My schematic only shows three preamp valves so your amp must be the revised version, but I'm pretty sure that's still the case.

Nope, you're quite right ICBM, my bad - three pre-amps and four power valves.  What tube would you recommend in V2 for a bit more gain?

blobb

I just swapped out my TAD's for JJ's (VC30 112). More drive, slightly brighter. G12H made a big difference too, what speakers are you running?

Voxman

blobb said:

I just swapped out my TAD's for JJ's (VC30 112). More drive, slightly brighter. G12H made a big difference too, what speakers are you running?

Hi Blobb, I'm very happy with the speakers.  These are 2 x Jensen C10Q16's which are excellent and give a wonderful vintage vibe thats a little brighter and snappier than 12" speakers. I also have the matching GS112VE  1x12 extn cab fitted with a Celestion Seventy Eighty.  When combined with the Jensen's it adds a bit more bottom end and fullness that gives me the best of both worlds.  

I have a spare Chinese Ruby 12AX7 but I was seeking tube recommendations for more crunch in V2.

ICBM

You can't get more gain with a valve substitution in V2 - it's already a 12AX7 and the standard Chinese ones have as much as any really. An RFT is the only one I can think of which has both good gain and a more 'harmonic' sort of sound.

You could possibly mod the amp, if you're into that… possibly by reducing the value of R11, which you can do by paralleling another resistor onto it, you don't have to remove it. Whether that would cause other problems, I don't know.

Or just get a Tube Screamer .

Voxman

Thanks ICBM.  I was thinking more harmonic ie a little bit nearer 'Marshallesque'. I'll look into RTF valves.  Not looking to do any mods, and yes I could use my tubescreamer clone - in fact the VC30 takes pedals beautifully and sounds great with TS and Guvn'r II.  But sometimes I just like to play my VC30  'straight' - it has a lovely glassy clean and I just wanted to get the natural gain and harmonics up just a tad on the drive channel.   

midlifecrisis

i have the vc30 212 version, i hardly ever use the gain channel, just use the clean and a tubescreamer ( these days a zoom g3 tube screamer patch or guvnor)  have tried other amps but i keep going back to the laney.

Voxman

Bugger - my VC30 was perfect after I changed the phase invertor tube.  Hadn't used the amp for a couple of weeks, switched on - and that 'motorboating' sound is back.  

I'll try changing the phase inverter again and checking the other tubes but I'm now concerned it may be something more than just tubes.