NCD and important discovery about the Ampeg Micro VR

ICBM

After having had the Micro VR head http://www.thefretboard.co.uk/discussion/85492/nbad for just over a year, and been looking for a second hand matching cab for it without any success, I spotted a B-stock one in the Boxing Day sales and decided just to buy it and be done with it.

So now I have a complete miniature SVT . The whole thing weighs less than half what the head alone of a full-size SVT does.



A few months ago I acquired a pair of Celestion neodymium B10-200Xs which I was planning to put in the cab - the stock speakers give an 8-ohm cab which restricts the amp to 150W, so I thought that if I changed it to a 4-ohm one I would get the full 200W and lighten the cab by a few pounds at the same time - since I don't plan on ever using two cabs with it, it seemed sensible to get the most out of the amp. So after a very brief test just to make sure the original speakers were working OK (since I planned to sell them, or use them for repair jobs), I took them out, fitted the Celestions and expected to hear a big improvement.

Wrong.

Firstly I thought that there was almost no noticeable increase in volume, and if anything I wasn't sure the cab sounded quite as good. Much worse, when it was pushed hard the amp's limiter made an audible clicking noise as it came in and out, which was extremely annoying and unmusical-sounding. Turning it off and allowing the amp to clip naturally was no better - still horrible-sounding. On a hunch I guessed it was that it didn't like running at 4 ohms...

So I decided to put the original speakers back - which I convinced myself was worthwhile since at least it gave me the opportunity to solder the speaker wiring as I prefer, rather than using the original crimp connectors. And I was right - the cab definitely sounds better, is no quieter, and best of all the amp now does not clip with the limiter on and sounds fine when it does so without - which actually means I can play it louder if I want, since I don't have to hold back for fear of nasty clicking noises.

So this is important - it means that although the amp is rated for driving a 4-ohm load, it really isn't suitable for it. It's an 8-ohm amp - bear this in mind if you're thinking of getting one.

Which also means that it's a very good thing that I didn't do what I originally thought when I first got the head, which was to buy a 4-ohm Barefaced cab, at about £700!

Winny_Pooh

Interesting, you playing it with a 4 string? Home use?

ICBM

Winny_Pooh said:

Interesting, you playing it with a 4 string? Home use?

Yes, 4-string - is there any other kind of bass?

Home use - although I may still have to do something about the fan noise, for quiet evenings - recording, and maybe even small gigs if it's loud enough... it probably will be if it's also going through the PA. The slight disappointment is that it may not be quite enough for backline-only band practice. But I can live with that since I can never really be bothered taking my own amp anyway, even one this light.

Bridgehouse

Hmm. There was a lot of chat on talkbass a while ago about these heads driving two of the cabs for 4 ohms and doing exactly as you describe. 

Lots of to'ing and fro'ing with Ampeg and the conclusion was that the limiter/clipping was very sensitive to any setup that was slightly under 4 ohms - apparently the original cabs together end up at 3.7 ohms or so. The drivers in them are quite pokey and need quite some oomph and being closed back as well it seems to encourage the limiter to kick in. 

I wonder if you can match up a pair of speakers to get exactly 4 ohms and see if that doesn't clip?

ICBM

Bridgehouse said:

Hmm. There was a lot of chat on talkbass a while ago about these heads driving two of the cabs for 4 ohms and doing exactly as you describe. 

Lots of to'ing and fro'ing with Ampeg and the conclusion was that the limiter/clipping was very sensitive to any setup that was slightly under 4 ohms - apparently the original cabs together end up at 3.7 ohms or so. The drivers in them are quite pokey and need quite some oomph and being closed back as well it seems to encourage the limiter to kick in. 

I wonder if you can match up a pair of speakers to get exactly 4 ohms and see if that doesn't clip?

Well, it is interesting that I didn't notice the problem when I ran the head through the 4-ohm Black Widow in my old Peavey T-Max combo at the rehearsal studio... but it was very heavily limiting and not sounding very punchy, and I assumed that the clipping noise might just have been obscured by the drummer .

In any case, it sounds like it's a bad idea to plan on using it at 4 ohms. I forgot to mention that I also managed to make the whole thing shut down after a few minutes when I tried it at 4 ohms with the limiter turned off, which at least proves that the thermal protection works!

I suspect anyone who is trying to use these as a full-on gigging rig is probably trying to push what is basically a practice amp too far, to be honest - it's a super cool little thing to have in the house or a studio, and it's probably just about usable for a low-volume band situation, but I wouldn't rely on it for proper professional use.

Bridgehouse

@ICBM - bass world received wisdom is the portaflex 350/500 does the same sound with more oomph for gigging - it even looks cool with the flip top cabs. 

If I were you and I wanted to do super portable Ampeg tones in a trad package I would do pf500 with two barefaced one tens. One for practise, two for gigging. 

Mind you, my advice isn't worth shit - I've just ordered a low watt b15 clone from MJW to run through my barefaced - lots of cash for not much output at all - which is completely against the current bass trend

fftc

Bridgehouse said:

Mind you, my advice isn't worth shit - I've just ordered a low watt b15 clone from MJW to run through my barefaced - lots of cash for not much output at all - which is completely against the current bass trend

I'd be interested to hear some more about this @Bridgehouse
You gonna do a thread (here or there, I don't mind. Just need a heads up as I don't get on as often as I used to)?

ICBM

Bridgehouse said:

@ICBM - bass world received wisdom is the portaflex 350/500 does the same sound with more oomph for gigging - it even looks cool with the flip top cabs.

I've just had some experience with one of those and I don't think I'll be going down that path - a customer who runs a practice studio has one (PF350). Firstly it blew the speakers in the matching cab (in theory it shouldn't be capable of that - it's a 400W cab at double the amp's minimum impedance) and secondly now the speakers have been replaced with something more robust, the whole cabinet rattles and farts at high volume. The seal between the lid and the box just isn't good enough to resist the internal pressure, even with the clamps locked down.

As a concept with the original low-powered valve amps - or the modern ones, presumably - it's great, but at modern bass amp power/air movement it doesn't work.

I do know someone selling an SVT Classic and a 4x10", but... no. It weighs more than my house.

JezWynd

I've just taken delivery of a PF115HE cab and PF20T head to make a modern flip top take on the B15. I've only had a few workouts on it, so these are early impressions. I was a bit wary that the 15" would give a less defined sound than I like but in use it sounds wonderful - very sharp and full sounding. The horn gives a touch more top end, more noticeable with guitar.  It's for home use only atm so the 20w head is plenty of volume. I'm having an occasional issue with what sounds like it might be RF interference, although touching the strings kills it which would indicate a ground issue. I'm going to investigate further before deciding if I keep the head but the cabinet definitely stays - it sounds just as good taking a feed from my little Laney cub. A 400w cab is a little overkill for home use, I'll never get to push it in this scenario, but at the volumes I'm using it sounds great.

JezWynd

The noise I referred to in my prev post that I put down to the PF-20T head instead seems to be caused by the horn of the cabinet. I'm pretty sure it's some kind of interference as it's occasional and doesn't impair the sound of the notes but coexists with it for a while before going away. Seems more frequent in the evening. Turning the horn off stopped the noise completely. I'm thinking perhaps the horn crossover circuit (?) could be prone to interference. It also occurs when using a different amp head and again, goes away when horn is disabled.

ICBM

It’s more likely to be noise from the amp that’s in the frequency range of the horn. The circuitry in the crossover can’t be sensitive enough to amplify noise to that extent. If it’s being picked up from an external source, more than one amp would do it.

If it’s more noticeable in the evening, look for something that’s mostly turned on then... like lighting.

JezWynd

ICBM said:

It’s more likely to be noise from the amp that’s in the frequency range of the horn. The circuitry in the crossover can’t be sensitive enough to amplify noise to that extent. If it’s being picked up from an external source, more than one amp would do it.

If it’s more noticeable in the evening, look for something that’s mostly turned on then... like lighting.

Yes, it's occuring with different amps. I've tried turning off various lights etc but it seems to have no effect. I'm in a central location so it might just be something I have to learn to live with (unless there are filters that might work?).

I originally got the CL head but it was not good. I was a bit shocked that Ampeg would badge something so poor. The VR head appealed but the fan put me off. The PF-20 has a really nice sound and matches the cab well. I might try relocating the cab in the house to see if there's a sweet spot.

Apologies for hijacking your thread.

ICBM

JezWynd said:

Apologies for hijacking your thread.

Not at all, it's all good info and it keeps the thread bumped .

I was shocked at how poor the Micro CL was too - I thought about buying the cab from one when I couldn't find a Micro VR cab but it isn't even close to as good.