Vox Pathfinder Bass 10

My mate Steve and I both have pieces of paper that say "Batchelor of Electronic Engineering", but neither of us do that for a living. We both however want to be able to say that we can actually work on electronics. For example, a while back I fixed a broken amp. So when a broken Vox Pathfinder Bass 10 fell into my hands I felt compelled to fix it.

I have however come to realise that I will only go so far. If it's not a broken wire, popped fuse or simple power supply issue, then it's going to take too long and I neither have the patience or equipment to really dig in deep. This amp was no simple fix. It had a weird distortion coming through. Steve however, he loves a challenge. And since this is just a little analogue amp, I threw it his way and he persisted until he fixed it.

During the, I'm going to guess hundreds of hours he spent debugging it, he produced an electrical schematic. It needs to be on the internet, so here is a pdf of the electrical schematic and here is a jpg.

A short discourse...it presented with some high mid/high frequency distortion on top of the expected signal. You could set the bass volume and the amp volume to reduce it, and if you played softly it wasn't too bad, but it was always there.

On first inspection Steve discovered a hole in one of the speakers which I hadn't noticed and sent it back. Seemed fair enough, that could cause noise. The speakers in there were a fairly non standard 5", I decided that some cheap 4" speakers from AliExpress would do the job. Put them in, no, distortion still there. and they were pretty rubbish. Without thinkng too hard I grabbed some slightly less cheap 6" speakers, and put them in with some slight hassle (they were a bit big, but I made them fit). Still distorting. I had concluded it wasn't the speakers and sent it back to Steve. He was not convinced and bought some not-so-cheap correctly fitting 5" speakers...still distorting.

During let's call it "the speaker phase" Steve mapped out a frequency response curve of the 4" (YH-1008) and 6" (YH-600) speakers, and for reference the sub speaker from his home theatre system. Remembering that the low E on a bass is around 40Hz you can see that the two cheapy speakers aren't great around there and don't really flatten out frequency reponse wise until over 100Hz. The sub speaker starts flattening out at 50Hz which is better, but we discovered that for bass amp design you really need to think about how you are going to get those low frequencies pumping air.

But the speakers proved to be a red herring.

Steve's equipment was struggling to show the nature of the distortion, which is kinda frustrating "I can hear it, but I can't see it". Looking at a bass guitar signal as it goes through the circuit, we could see that there seemed to be a few pixels of high frequence noise superimposed on sections of the waveform. But neither of us would declare "that was it". Steve, being persistent, then went to town replacing components.

Signal vs Opamp 1a Maybe noisy?

Signal vs Opamp 1b Inverted, looks fine!

Signal vs Opamp 2 Inverted, maybe noisy?

Signal vs power Opamp 3 Inverted, DC offset, some noise?

An interesting part of this amp design is that the power side is an opamp! That is, an Operational Amplifier, which is more of a circuit in a chip than just a transister/FET/tube valve. Opamps are great, because they have a pretty flat frequency response across the full spectrum, super high gain, super high input impedence...I didn't imagine a power opamp would be the power house behind an amp! There are some low power opamps in the circuit too, which are there to handle the overdrive circuit, the treble, mid and bass EQ signal adjustments.

Steve's experience with electronics makes him suspect capacitors every time. Because capacitors fail. He popped every single one of the board, and tested them. None were a problem.

He discovered that although the signal opamps and the power opamps were obsolete, there were equivalent replacements which he also swapped out. It was not a function of the opamp.

At this stage we were both scratching our heads. There wasn't much left to swap out. Something that he had noticed along the way is that the transformer power supply was being pulled down pretty hard, getting close to the minimum operating voltage for the power opamp. While the supply was within spec, after looking at what the opamps can handle voltage wise, he decided to buy a higher voltage transformer with a few more VAs too. The one he selected could fit in, it was right at the upper limit of the opamp capabilities, se he swapped out two resistors to ease back a little on the voltage.

Oh, and he grumbled a lot about the board. How 240VAC was intertwined with signal voltages, how there were so many links on the board and just a generally poor layout of the board, and how difficult it was to pull apart and put back together - that it, like so many things these days, is not designed to be easily serviced. Are you listening Vox?

Well Steve was right. With a new transformer kicking in a bit more juice, the distortion went away. Fixed. My take on this is that the power supply selection is build down to a price, and most of the time, when things are running to specification, it will work. But without a little bit of over-engineering in place, the moment the transformer had dropped a few VAs, some higher frequency weird opamp distortion crept in. Getting those opamps back up to plenty of voltage headspace, problem solved. Vox - spend a bit more money on parts!

Board Before

Board Modified

Good work Steve! We both learnt something! Oh, and one other very cool thing I learnt - inside the unit were two LEDs back to back. "Why are there LEDs inside the unit, that will never be seen?" After staring at the circuit for a while, working from our electronics first principles knowledge Steve and I realised that as the "drive" level is turned up, the LED foward volt drop, probably around 2V, will start to kick in, which will begin to clip the waveform. As we know, if you raise the amplitude of a signal but then start to clip the peaks, you get both an additional loudness increase, and all those extra harmonics as it clips which brings more complexity to the sound. After reading up about it on the internet, aparently LEDs have quite a sonically pleasing soft-clipping sound rather than the much harder clipping found in other diodes!

What's happening October 2024

I've continued to do a lot of mixing. It's easy to load an SD card into the deck at my local church and record all 32 tracks, and then you have 4 songs to experiment with. I have a mate from work who has been doing that sort of thing for years, and trained, so it's great to pass mixes to him for a critique. It is a universe into itself the world of mixing, I've got at least my toe in it now. The more I do, the more I practise, the better and faster I am getting at it. I'm not aiming for perfection, I'm aiming to be competant at it - so when it actually counts I might be able to mix a song with some skills.

From a fingerstyle guitar point of view, you may think "What's the point JAW?" I have noticed it is making me think more about production. What does a song need? How can I fit the bassline in? Percussive strums to make a strong beat? The melody IS SO IMPORTANT! There is no doubt that mixing a multi-instrumentalist song will improve your overall musicianship - and it helps improve your ear. So would many other musical pursuits - like learning more theory! What is the best bang for buck? I don't know. But I do know that I'm enjoying the world of mixing and I'm more likely to do something that is fun than something that may be more beneficial, but I don't currently have any interest in.

Meanwhile I need to do a stocktake on fingerstyle arrangements that I really should record. Before I forget I can play them :-)

• Don't Dream it's Over - Crowded House
• It Feels Like We Only Go Backwards - Tame Impala
• Come on Eileen - Dexys Midnight Runners
• White Room - Cream
• I Want to Break Free - Queen
• Horse With No Name - America
• Rain - Dragon

There's few others that I have put effort into but I'm not sure if I will continue to pursue them...

• Got What You Need - Eskimo Joe
• Live it Up - Mental as Anything
• Pumped Up Kicks - Foster the People
• Toccata - Bach (Sky Version)
• 19-2000 - Gorillaz
• Fly Like an Eagle - Steve Miller Band

Mmm. Fly like an Eagle.

Mmm.

<Some Time Later>

I'd forgotten how groovy that song is! I noodled further with my previous efforts from a few years back, started developing a cool bassline. I needed to refer to the chords (ultimate guitar) and a quick check of melody (musescore). I had a rough for the verse and the chorus pretty quick just from memory. I then re-listened to the song again :-) So much cool electronics in it. But I can't really emulate that. The bassline rocks, but the studio recording relies on the synth and the electronics to carry the, um, chord extensions progression? You can hear the chorus and verses moving through some chord extensions, but it's not in the bass. The bass is just hanging onto an A, popping up from a G on a beat, but it's hanging on the chord of Am. I couldn't come up with a chord progression and hang onto the A without it sounding a bit boring. But I can make the bassline emulate the chord extensions.  Maybe the first verse could be just on the A?  So much I could do!

And so groovy! I hooked up my practise electric guitar, dialed in a tiny bit of distortion and recorded a quick rough so I'd remember what I was playing with, have a listen!

Fly Like an Eagle rough thoughts:

Yamaha G65-A

Another vintage Yamaha found its way to me, I was pleased that it was not a C40. Don't get me wrong, a Yamaha C40 is an adequate classical guitar, often not bad at all. But often not good. This G65-A (serial 31109517 - 0426423 so probably 1983) is in good condition, doesn't look like it has been played much. I whipped the few remaining strings off it and checked the fret level and neck angle, all was okay. Well, neck angles always seem out once a classical guitar is 20 years old, but we make do.

I ran a block with sandpaper across the frets and it did not take very long before it was touching everywhere.  I barely needed to put my fret file on it. Note: my latest fret file is nice, the one with the wooden handle, but the profile is too deep and was barely touching the frets. I am going to have to splurge on a decent fret file.

There were no sharp fret ends!  I think it is because the manufacturers tapped in frets already cut to size with pre-finished ends...and they are slightly too narrow!  It feel like that's not great because you lose a bit of fretboard at the edge. I want every bit of my fretboard to count. I reckon it is better to put the frets in and then sand them flush to the fretboard edge.

After polishing all the frets and giving the fretboard a heavy oiling, I decided to replace the nut. The existing one was pretty awful.  I had already bought a bag of standard classical bone nuts a while back, and they are a perfect fit.  Well, other than sanding the bottom down a few millimetres to get the nut height right.

The saddle was not the worst saddle I've ever seen, but, yikes, comes close! A cheap plastic one, and so thin! I've never seen a saddle so thin, I was tempted to open up the saddle slot a bit more to fit a bone saddle in, but, nah. A little too much effort for this calibre of guitar.

Restrung it up, it sounded okay.  Marginally better than your average C40. It has the usual G string resonance nastiness when you dig in, so many classical guitars have that.  I reckon that is your first test with a classical guitar. Pluck the G string hard, does it have a tedious resonance that grinds your ears - and does it sound a bit out of balance with the other strings? Otherwise this guitar has a good bass, the mids are bolder than I was expecting, and the trebles are adequate. It is not the worst vintage Yamaha I have played.

It is a cheap model, that's for sure, marginally up from my G-55A. For starters it does actually have a solid wood (rosewood?) fretboard, and a solid bookmatched soundboard (cedar?).  The rest of the body is all veneer, so quite cheap, and no attempts to bookmatch the back or sides. Although the back is interestingly pretty though, I mean veneer is still wood, just a really thin sheet of wood, I'm guessing this is an example of rotary peeled veneer. At least the veneer is not on a backing of MDF, it looks to be on some sort of (probably) laminated cheaper wood.

As found

Fret tool not quite right sadly

New nut installed, compared with old

Interesting veneer back

So overall it came up okay, sounds okay, and it is pretty, so ready to go back to its owner.

Here is my standard test song, raw from the microphone.

Yamaha G65-A:

My Reaper Mixing Notes

This article is a work in progress and will be constantly updated, for me, as I learn new skills!

I use the Digital Audio Workstation (DAW) called "Reaper" for mixing and I quite often get a multi-track recording from a Behringer X32/Midas M32 deck (they are virtually the same thing). This post is a dumping ground for all the things I have learnt from the process so that I have a coherent centralised place to keep them and maybe they will also be useful to you.

Remember some golden rules: use your ears, not your eyes, and keep it simple.

Raw files

Acquiring

While the X32 has a USB port it will only record a deck-mixed stereo signal to it. However if you have the SD card module added, you can record all 32 channels raw. Format any SD card to FAT32 and pop it in. While the manual talks about 32GB as the limit, I have been using 128GB cards no problem which can record a 5 hour session. Class 4 SD cards are fine for bandwidth.

It records everything into a WAV file, split into 4GB chunks. Drag these directly into a Reaper track, sequentially, and you will now have a single track, multiple items, all with the 32 channels. Run the Rodilab script that will explode the WAV into separate tracks. Next run my "prep" script which will get rid of the unused tracks, add colour, group, pan, all based on rules - change the script according to the rules you need.

Consolidating

tba

Rough Mix

Faders(volume)

Set all faders to an appropriate level before applying any effects to get a rough mix. You should only add effects to fix problems. With that said, if you already know a heap of problems that happen every time, and you have already solved them before, then add those effects in.

Pan

Not really an effect as such, but definitely think about where you want each track to be situated from left to right. It's a good idea to get tracks off centre, even just by 10%, to create 3D space, unless you specifically want your track to be straight down the middle.

Phase

*Usually not necessary* Maybe some of your mics have a different latency, and maybe the latency will cause phase cancellation or distortion. but if you want the tightest of the tight, then zoom right in on your master track and see how all the tracks are overlapping, specifically on punchy transients. Particularly useful on the drums, if you notice some tracks are offset to each other, you can move tracks in time slightly to line up the signals.

Effects

Delay

My favourite use is a slap back delay but with different timse in the left/right channels, with alow wet level so it is barely noticeable. This will turn a mono signal into a wide stereo signal and is great to place the track into a different 3D space to the rest of the tracks. Use "ReaDelay", set length to say time=80ms (musical=0), pan full left, then add a new tap, set to time=120ms pan full right. Adjust the wet for a good feel. Adjust the times to get the space you like.

Compression

Tame a signal where the dynamics are bigger than you want them to be, squeezes the levels together. Use on almost anything. Set the ratio higher to have less effect, but 4:1 is a good starting point. Move the threshold up - if you aren't exceeding the threshold anywhere, you aren't going into compression, there is no point having it. Set the attack fast if you need to the compressor to respond quickly, set the release slow if you want the compressor to not come off so quickly, sounds more natural. ReaComp is a good go to, don't forget to tick "Auto make-up". Chosing one of the stock presets for your application is a great starting point.

The JS 1175 is an emulated Urei 1176 fast compressor worth looking at, ReaXComp get even more fancy by having multiple frequency bands of compression.

Limiter

When compression isn't enough...use a limiter to prevent clipping on agressive transients. Great on drums and in mastering to Make It Loud without clipping.

EQ

Boost and reduce frequency ranges, surely everyone knows what EQ does. A good way to work out what frequencies you want more or less of is to make a fairly narrow band boost, drag it extremely high, then sweep across the frequency ranges listening for what you like and don't like, and set it accordingly. Some good rules of thumb:

• 20-70 : Rumble/Subbass : Only really dums and bass need this.
• 70-300 : Boomy/Warmth/Muddiness/Fullness : Sometimes there are resonances here, notch them out.
• 300-1.2k : Boxy/Nasal : often worth reducing on some tracks to create space for other tracks.
• 1.2k-5k : Honky/Harsh : can add clarity. Look to remove vocal esses (sibilance) in here.
• 5k-11k : Sparkle/Presence
• 11k+ : Air

Use ReaEQ for basic multiband. ReaFIR set to Dynamic EQ mode can be great to tame harshness in vocals or solo instruments: Set mode to Compressor, set the Compression Ratio fairly low, say 1.5:1 and then set up a profile where the compressor is starting to do stuff on the peaks of the frequency spectrum

Reverberation

Ubiquitous and overused but quite essential. Because we aren't always recording in a warm room or a cathedral, but those sounds are nice, so apply artificial versions of them. Don't overdo it! Argh! Reverb does not make up for a bad recording! A little bit of reverb underneath a vocal or a solo instrument can be quite nice, my favourite as recommended by Kenny Gioia is ReaVerb: set to file, use the "Fat Plate" impulse file from the Lexicon 480L last seen at http://www.housecallfm.com/download.php?f=BGLex480.zip somewhere around -30dB.

A simpler reverb that can be quite effective is ReaVerbate: set the room size to massive - even say 95, and use very sparingly to make a vocal ring. Use side chained or automate the wet mix or manually add it in a separate track.

Gate

If something sits on background noise most of the time and then bursts into life, then gate it - ie, it will be silent unless the gate is exceeded. It will sound unnatural solo'd, but in a mix it will be fine. Drums are good to gate, sometimes even the vocals. Use ReaGate and set the attack/hold/release to something that suites your track, and most importantly set the threshold.

Tuning

Sometimes it's okay to tune up a few vocals here or there, but you can't fix a bad recording. The best way to fix a few vocal notes is to do it manually only with ReaTune: on the Correction tab change the attack time to around 100ms, then on the Manual Correction tab tick "Manual Correction" and then draw blue lines to fix missed pitches. Put your blue line slightly after the point at which the pitch is hit, to make it sound smoother, and finish the line a bit early. Put ReaTune first in your effects chains.

Saturation

This is a quirky little effect, basically distorts the signal based on the way old analogue equipment like tape machines or tube amplifiers would distort when driven hard. Adds harmonics which are "richer, warmer" ie pleasing. I found the free plugin "GSat+" does a good job, load it up and at the top menu press the right arrow to say "Medium" or "Warm", wind the input up until it is going onto saturation for at least part of the range.

Instruments

Drums

The setup I spend a lot of time with has 7 mics. I will always make a track that is a folder (bus) for all the drum tracks and I add a limiter to that to "clean up" those times when the drummer has hit 3 drums full tilt at the same time.

• Gate all drums except the overheads. Set the gate so that only the "fundamental" drum sound comes through, so usually the fastest attack possible and only a hold/release for as long as required, hopefully not before the next hit.
• Put on a limiter rather than a compressor. Drums have a massive impulse on the initial hit which doesn't suit any compressor. Whereas the limiter, with a brickwall ceiling, can bring up the tail but clip the initial impulse without making it sound awful.
• EQ to the drum in question. The full mix will contain everything, let the overheads glue it together. Let each individual mic have an EQ that captures the essence of that drum:
• Kick drum - keep low frequencies only.
• Tom drum2 - keep low frequencies and some mid.
• Snare drum - keep mid frequencies and some highs.
• Overheads - remove the low frequencies and most of the mids, keep only highs. The overhead mics glue the drum kit together through the middle - the low end is dealt with in their own tracks.
• On the snare drum add the free VST "snare buzz". It is fantastic to bring out that snare sound.

Electric Piano

Since it is electric it's already perfect, leave it along. The only thing you might want to do is compress it if you want to squish the dynamics, or adjust the EQ to create some space for another instrument.

Acoustic Guitar

Generally this is already coming in from a pedal, so like the piano you might not need to touch it. However I rarely find an acoustic guitar that has a frequency response I like, so I usually add EQ to remove boominess and boxiness. It's also a good idea to remove everything from around 80Hz and below, acoustic guitars can't hit those frequencies.

Vocals

Ah, the most challenging instrument of all. Compress - if there are really peaky parts, use two compressors, one to scrub the peaks, the other to smooth it out without crushing it.

EQ - varies from person to person, but 120Hz for fullness, 240 for boxiness, 5k for presence, 8k for sibilance, 10k for air. Sweep the mid to find frequencies you like/dislike

Sax

I found that the sax is dynamically unbalanced even between notes. I compress it a lot. Either go for a little bit of reverb, or add some back slap delay if you don't want to muddy it with reverb. EQ this for sure.

Violin/strings

tba

Electric Guitar

tba

Fine tuning and Mastering

Envelopes

Right click on a track header, click Envelopes and then choose say Volume or Pan. Now you can drag the fader/pan around as the song progresses. I normally do the 4 click trapezoid to bring a section up or down. You are almost re-producing the song with this - you can say drop a solo instrument right down so it isn't competing with the vocals, and then crank it up during insturmental sections.

Edit

Don't be afraid to split tracks up! You can realign missed tempo notes, or copy sections from another take or verse to punch out bad sections. Overlap all cuts so they seamlessly transition. Normally you can drag around the cross-fades, but if the fade isn't showing, right click the track, select Item Properties, and then type in new values for the fade in and fade out.

Side Chaining

tba

Mastering

The JS 1175 Compressor is nice to glue it all together if it feels a bit unstuck. Use the ReaXcomp multiband compressor to make it pop. Some very minor EQ to tweak up anything that presents itself in the final mix (because you were too keen EQ'ing individual insturment). Top it all off with the JS Event Horizon Limiter/Clipper, set the ceiling to 0, and wind down the threshold a little bit to make it louder but don't go too far or it will start to distort.

Rendering

tba

Handy Functionality

SWS

tba

Channels

Generally, each track will only have 2 channels shown in the mixer. Even for mono, because FX will often create stereo. If however you have ended up with say 32 (and the track is really wide) you can fix it by clicking on the Route icon, set channels 2.

Scripting

What's happening July 2024

I continued to progress "Don't Dream it's Over" and very nearly recorded a Jawmunji Talks video. I still might, it's worth a discussion.

However this month my local church had an open night, and the kids and I wrote two tunes for it. So a bit of time spent working on that. We had actually written the tunes some time ago, which came down to me putting together chord progressions and writing lyrics...yes, I do them both at the same time...as in, I don't write lyrics and then set it to music - I don't write music and then create lyrics - they are informing each other as I go. I have a vague idea of melody, but once I have a chord progression and words, I give it to my youngest daughter and she immediately comes up with a melody far better than I could do. It must be a singer thing. And she'll normally tweak the words to fit better with her word flow. Finally, once we have that together, we play it a few time for my son, give him the chord structure, and he will improvise something over it on the sax.

I decided to play the double bass for this one, plucked, bluegrass style. I love the sound of the double bass - particularly when bowed, but I'm bad at bowing it so plucked it needed to be. My youngest played keys and sung on the first song, sung and played electric guitar on the second song.

We needed to have done a bit more practise, but the gig went off without a hitch. All three of us had more anxiety than we were expecting, which was weird, we have all played to audiences many times. I think it was because we normally play covers, there must be something about originals that heightens the anxiety. An increase vulnerability perhaps.

Anyway, good fun. My youngest daughter is a born performer, having her front our little trio with a low slung telecaster belting out some lyrics is in her element. My son can wail out soulful expressions on the sax, we were using a new sax pedal which introduced some nice tones. I love the big fat sound I can get from the double bass, we had it mic'd up so it was kickin'. It is still hard to play, and I am still sporting two blisters on my right first two fingers. I did carefully knife them open, splashed with a methylated spirits to keep the bugs away. A long time ago I decided that pricking open blood/fluid blisters is much faster recovery than letting them do their own thing.

All done, back to working on my fingerstyle arrangements!