VOX: BM1 Escort Transistor Practice / Busking Amp

I just bought this rather beat-up Vox BM1 Escort practice amp from the seventies, or maybe early eighties today.  I'm thinking seventies, as it doesn't have an IEC power connector, and the grill cloth is the red/brown colour. 

The back panel looks different to the one on Vox showroom and other photos that I've seen, so not sure what’s going on here - maybe it’s from a different production run or regional difference?  The rotary battery/power selector switch has been replaced with a standard toggle switch, and the volume pot doesn’t look original; apart from that, all working as it should.

My first thought on this one - it's a little monster.  Way louder than I thought it would be, and the driven sound is cool.  I really punished my ears testing this...  slightly regretting it now.  It seems to like running somewhere between half and three-quarters volume, with the tone in a similar position depending on the input used.  It's also pretty happy with the volume on full - it really fires off some attitude.  I think it would be interesting to record this little thing running hot.

Clean sounds? Can't say I spent much time in this area of the amp.

VOX BM1 ESCORT - SOLID STATE PRACTICE AMPLIFIER

• One channel, two inputs.   Normal and Brilliant

• Single tone and volume control

• Battery or mains power switch

• 5” Elac speaker (Elac were used in a lot of Vintage Vox amps, quite sought after)

• Powered by a single TB810S IC amplifier

• Output for extension cabinet

• Manufactured from the mid-seventies to early eighties

• The cabinet is approximately 33cm x 22cm x 13cm, and it probably only weighs a couple of kilos without a battery

• Battery is a PP9 - 9v, 5aH, 6cm x 5.5cm x 8cm

The batteries are large, expensive and are reported to not last long, which I believe is why Vox created this version with the option to run off mains power.  As a busking amp, you would want to make money petty fast, as you would need to make $20 just to break even with the cost of the battery.

 

VOX ESCORT SCHEMATIC

IC AMPLIFIER DATASHEET

I've seen the amp mentioned as being 3.5 watts, but I can't see this anywhere on the data sheet - looks like 2.5 watts when running at 9v.

JANSEN: TR25 Solid State Guitar Amp from NZ

This is a fairly obscure solid-state guitar amplifier from New Zealand - I don’t know exactly when it was made, but it does scream the 1970s.   I bought it a few years back and have been using it as my test amp in the workshop/garage.

I haven't been able to track down a schematic, so this morning I pulled it apart to see if there was anything obviously wrong - there was a bit of corrosion, and some insects have been using it as a home at some stage (not uncommon in Australia for an old amp).  I gave the board a clean, and there was also a broken stabilising spring in the reverb tank, which I repaired.

It's rated at 25w, and it's very loud.  Single 12" speaker of an unknown brand - not sure if it's original.  Controls for volume, bass, middle & treble, tremolo and reverb.  It does have a really nice tremolo and combined with the reverb it can do a pretty cool vintage-sounding clean tone. 

JANSEN TR25 SOLID-STATE GUITAR AMPLIFIER

Looks like they used quality parts back in the day, with a couple of massive 3,300uf capacitors across the power supply

Sanyo STK029 Power Amplifier 

One very dirty circuit board - gave it a good clean before putting it back together.

Small Accutronics 2 spring reverb

Broken suspension spring

VOX: Pathfinder 15R Transistor Guitar Amp

Like others, I had read the hype about the Vox Pathfinder 15R and thought, really?  I'd never paid any attention to them until I saw an article in Premier Guitar recently.  So when I saw a Vox Pathfinder 15R pop up on Facebook marketplace at a reasonable price, I thought it would be worth a shot.  

VOX PATHFINDER 15R - SOLID STATE GUITAR AMPLIFIER

Positives

• It’s really loud for 15 watts of solid state amp with a little 8" speaker - surprisingly loud in fact

• You can get a few decent sounds out of it tonally, which hasn’t always been the case for some Vox amps that I’ve played

• I don’t mind the reverb, which a few people complain about.  It is a bit weak, as I think it’s a small two-spring reverb, but it works for me

• For an 8" speaker, it sounds big.  This may have something to do with the size of the cabinet, as it's way bigger than needed for an 8” speaker.  Vox may have been lucky with the speaker construction too.  Normally at this price point no-one expects anything from the stock speaker  

• It feels decent.  It certainly doesn't have a premium feel, but it doesn't scream cheap amp either 

• Trem is a bonus

• The foot switch is handy (boost and trem only, not reverb)

• Looks like a traditional Vox - which I guess I didn't need to tell you

• Some people have bad things to say about the overdriven sound - I actually like it, but I can see how some might really hate it.   It's a bit raggedy and rough around the edges at times.   It's in no way a tight, polished modern distortion/overdrive sound - I'd say it has character.   The flip side of this as that most amps that do a good polished modern distortion can't do a rough around-the-edges sound at all.  After playing with it for a few days and trying different guitars, my assessment is that the overdriven sound is not great with low-powered single coils, but it worked well with everything else.   Results may vary, as they say.

• I've also heard people saying just leave the boost on all the time, or otherwise, it doesn't sound any good - not my experience, I like both options.   The boost is really quite a loud boost too.   Almost too loud in terms of balance between the options (especially on clean settings).  Not having the boost on provides more range at low levels with the gain and volume controls

Negatives

If I had to mention downsides, I could only think of three when it comes to my needs;

• The boost level is way higher than the regular level on clean settings - so much so it may be too different from being useful.  Care factor - we all build pedals right?  This is also much less of an issue if the amp is already overdriven.  The boost is appropriate when driven.  

• The overdrive can get a little dark compared to the clean tone, but given that there's no way to switch between the two, it's not a big deal.   Maybe being a one-channel amp is a downside, but it is an inexpensive amp...  how much can one expect for the price?  And to repeat myself, we all build overdrive pedals yeah?  So not a deal breaker for me.  

• Despite liking the reverb for what it is, it's obviously not an awesome reverb.  No surf sounds from the Pathfinder.  I use a Carl Martin Headroom spring reverb pedal with my other Vox, which doesn't have verb - the Headroom costs more than this amp, so maybe nor a fair comparison    

Occasionally you will hear its limitations, but whether you find that to be the charms of a small amp struggling or the sign of it not being a great amp is up to you.  These are cheap enough to buy two, for a dual rig.

SPECIFICATIONS - VOX PATHFINDER 15R

Dimensions:        396 x 400 x 193

Weight:                8kg

Output power:    15 watt RMS into 8 ohms

Speaker:            1 x Vox Bulldog (8", 8 ohm)

Inputs:                Input jack, foot switch

Outputs:            Extension speaker, headphones, line out

Controls:            Gain, Master volume, Treble, Bass, Tremolo speed, Tremolo depth, Reverb, Gain boost switch

Options:            VFS-2 dual foot switch for boost and tremolo (not reverb)

CONTROLS

EXTENSION CAB

The extension cab works a little differently from some larger amps - the stock speaker is bypassed when an extension cab is used.

note: you must use a cab of 8 ohms or more.  Lower than 8 can damage the amp.  16 is ok, but it will reduce the output level.  

LINE OUT

This output carries a specially filtered signal for direct connection to a soundboard or recording console. This gives you a good-sounding signal for recording or live work without having to mic up the amp.

HEADPHONE OUT

Guess what plugs into this?  Yes, headphones....  

VOX: UL Series Preamp

I quite like some of the guitar sounds from The Beatles Revolver album, and after looking at the Vox Supreme, I thought I might have a play with the UL series preamp.

I'm also waiting for the build docs to come out for the Aclam Dr Robert on pedalpcb as a comparison.  It's also a UL730-based pedal - I believe it's the normal channel, and they have also modelled the power amp section.  Keen to see how they have done that.

VIBRATO CHANNEL

Everything below relates to the vibrato channel on the amp, which also happens to be the channel with distortion/fuzz, which is what I'm interested in.

FUZZ / DISTORTION

Strangely there's no control to dial in the fuzz/distortion circuit on the amp itself - it was turned on by a foot switch, and you got what you got.  

The switch increases the gain of T1 & T2 (using T3 and T4 as switches), and at the same time, it ties the OA200 silicon diodes to ground or V+ to create fuzz/distortion.  I'm really not sure which way the diodes connect, as I don't know what's happening with the foot switch.  The schematic is not clear in this regard.  Either way, it all looks about the same regarding wave shapes and frequency response.  

Bypassing the distortion leaves you with a nice clean signal, not unlike the normal channel.

BOOST SWITCH

There's also a boost switch on the front control panel of the amp, but it doesn't appear to do a great deal at the output, maybe a bit of a top boost.

LAYOUT

For some reason, the mid-range control is immediately after the clipping section but before the volume control and gain recovery section (T5 & T6).  The volume control feeds the gain recovery section, with bass and treble controls at the end of the signal chain.  I'm sure they had their reasons at JMI.   This is not a master volume amp either - one volume control per channel, and that's it.

VOX UL SERIES PREAMP SCHEMATIC

VOX UL SERIES PREAMP LTSPICE

This is with a 200mv sine wave at 440Hz, with the distortion/fuzz switched on.  LTspice file is here if that's of any interest.  You may need to change transistors if you don't have the BCs in your library, but the rest should be fine.

Collector T2

Post diode clipping

Output - bass, mid and treble all set to 50%

Output - bass, mid, and treble all set to 50%   Diodes removed from the ground - which I don't believe is part of the normal switching, but I might have to give this a try.  Looks like a rather large square wave.  i.e. a solid fuzz...  

The tone controls are pretty interactive - bass / mid sweep

Mid / treble  sweep