Developing a 'Headphone Auditioner'

[ozboomer]

Hi again, everyone..

Having been to a couple of 'group sessions' in the last few weeks, I've come-up with something of an interesting idea...

The problem with the sessions I attended was the general cacophony that ensued during the sessions. There were maybe a dozen people, one of which was up the front, explaining some theory and demoing some ideas as a backing track was running. At the same time, most everyone else was noodling around, trying to get a handle on what was being explained. Whilst I understand it's a skill to be learnt, to be able to hear your own guitar amongst a stack of other people playing, I can't do it now (and haven't been able to do it for some years), so I finally bit the bullet on something I can do to deal with the issue.

The idea is this: another magic electronic gadget (of course). A block diagram to show what I mean:-

( The "alternate path" is to suggest that you might like to use a design that provides some boost/buffering between the guitar and the floor amp; recent experiments have shown that this boosting/buffering can make a significant improvement in your sound... but I'm not sure this "sophistication" is necessary in a learning environment... meh... )

So, this means that I could wear some lightweight headphones (with/out one ear 'open'), so I can (attempt to) hear what the fellow up the front is doing and yet, I will still be able to hear what I'm playing in the other ear. If I could get everyone to do something similar (which I doubt is going to be possible), the room would only contain the (amplified) sounds of the instructor, his playing and the sound of the backing track; much clearer for everyone to hear. If someone wants to do something for everyone to hear, they can switch from their headphone output to their amp output, so the example can be clearly heard by everyone, just the same.

So, to this end, the idea for a "Headphone Auditioner" comes to mind. A mock-up picture of the device:-

In essence, you would set-up the guitar and "floor amp" so that the sound is Ok for when playing 'open'. You'd also have the facility to switch to an internal amp/buffer that would have a small amount of gain that can be controlled by the "Level" knob, so you don't blow your ears apart. There would also be a switch to select between the two outputs.

Now, what to do about that boost/buffer/amp...!

As I'm wanting to get this thing done quickly and without much swearing and cussing on my part(!), I'd like to build something quickly and without too much "finesse"; after all, these sessions are more of a learning exercise than a performance exercise. As such, there is (no) little need for a high-quality sound, so the specs of the amp stage don't have to be too great.

Therefore, I've narrowed things down to a few possibilities (in something of a preferred order, I think):-

• Using a JFET booster approach (~ 8 parts) (see JohnH's posting - "Gain Stage"); I've done a couple of these now, so I'm familiar with how to get them working.
  
  
• Simplest LM386 amp (~ 5 parts) (see someone's project, which points to the schematic); a very simple design, with low parts count... and the link shows some photos of a constructed project.
  
  
• Another LM386 design (~ 7 parts) (see Little Gem amp); a standardized and well-used design.
  
  
• Higher-Spec design (~ 15 parts) (see Headwize Headphone Amp); probably overkill for this sort of project... but I quite like the engraved plate idea for the enclosure labels.
  

So, what do you think? I think the idea is a goody (from MY perspective, anyway), even if no-one else adopts it, as I could hear my playing clearly and stil be involved in the group. ..and for ease/speed of construction (and perhaps, a reasonable sound), which of the amp designs d'you think would be most applicable?

Fanx! a heap for your thoughts, folks...


John

[cynical1]

I think it's a pretty good idea. If you have a board at these sessions you could also patch your device into that. With noise canceling headphones you can adjust the mix into your headphone box and block out the din from the others in the room and still get the mix at a level you could tolerate.

Paul Gilbert does something similar to this:



Put a separate input into the box to allow you to run a backing track, or click track, into the phones, send your signal to the amp and be able to mic the amp to grab your guitar tone for recording.

Just thinking out loud...no pun intended...

Happy Trails

Cynical One

[ozboomer]

Well, here's an interesting development...(!)

I was moseying through YouTube last night and I was looking/listening to the various postings about LM386 amps and other small models... and I remembered something about our newey grabbing a Micro Crush in mid-2008.

Now, all my memory was saying to me was that 'newey grabbed one', so I guessed everything must be good-ho with it... Still, I didn't think anything of it further.. until this morning.

I was heading to the electronics shop to grab some bits to do some preliminary checking with an LM386 design... when I passed one of the local music shops. I hadn't been in there for a while, so I thought I'd drop in for a looksee...

In short, they had a Micro Crush there.. and it was sitting there for $48. Now, my logic went something like.. I'm going to spend $25 on bits to just 'check' how an LM386 amp might work... and although I had an old (gutted) combo amp with a speaker I was going to use with the LM386 design (the speaker wouldn't do much with just an MP3 player plugged into it, so I guessed I would need some 'real' amp to drive that speaker), I thought that by the time I fiddle around, I'll have spent $48 or more... So I decided I'd grab this lil' amp for the current application. Here's the unit I bought:-

Front View:

Rear View:

Panel:

The interesting thing, tho... was that this was the last one they had in the shop - they had 4 on Tuesday and I grabbed the last one today (Saturday). They had been walking out the door for a while recently... and the bonus (for me) was that the silly things were on sale, so I only had to pay $36. So, I was pretty happy with that... and you may note that the name on the unit is something about "P.X" rather than "CR3", so I'm not really sure what that means, if anything...

Y'see, as we've so often said before, I think there's a bit of 'horses for courses' going on here. Whilst newey and most here are... shall we say... 'seasoned tone pursuers' ...and they approach the sound of this unit with that background, to me, this lil' amp is good as gold. Agreed, the distortion is pretty awful.. but I don't play with that much at all. ...and for me playing about, I reckon this unit will suit me very well. I reckon it sounds reasonable at the lower volumes (less than 7 or so)... and the slight overdrive of the amp that happens at those higher volumes is actually just good enough to provide the extra sustain.

Anyway, I'd still say it'd probably be worthwhile to have a listen to the Micro Crush if you're looking for a lil' low-level amp -- it might just be enough for what you want.

As for my current project, it now means my switching and so on can be more-or-less passive and will be outside of this lil' box, simplifying the requirements a good deal. Wheee!

For your consideration, folks


John

Edit: Typos

[newey]

Oz-

Yeah, I've been real happy with my Microcrush- I bought one when they first came out a couple of years ago and paid about $55 USD for mine.

I have found that, while the 9V batteries will last quite a while, it's best to keep a fresh one in there. As the battery loses power, the sound quality degrades since you end up going higher n the vol to get the same output- and end up leaving the "clean zone" and getting into the distortion at lower and lower levels.

They did change the model designations a while back to match the changes in the rest of the Crush line. But it's the same unit. They also now have a stereo unit which looks to be nothing more than 2 of these in one cabinet.

As oz notes, the distortion is basically useless. I use mine for travelling, and usually take my Pocket Pod along for effects if desired. I also sometimes use it with my Dano "Slap-back Echo" pedal which sounds pretty good through this unit, gives a a bit more "fullness" .

I have also been keeping my eyes open for a better 4" speaker that would swap in to the unit, but so far no luck.

[ozboomer]

A simple question, this... but just wonderin' if it would really make any difference...

With the addition of the Micro Crush amp, the arrangement for the "auditioner" (more as a concept, now) is simplified down to a switchbox arrangment, viz:-

...although, I am still experimenting with little amps; I managed to breadboard up a modified Ruby amp last night (minus the JFET front-end buffer) and it works a treat -- I just have to 'tune' some of the capacitors to get the frequency response I like...

but I digress...

Have a look at this quick diagram:-

Fig. a shows a simple arrangement of just switching the relevant 'hot' input to the 'hot' output. Fig. b shows the same but using a full DPDT switch, so we can also switch the grounds.

The question is: Is there any point to using the extra complexity of the DPDT over a SPDT? Y'see, as this is basically a passive gadget and I'm just wondering how things will go with switching "non-zero volume" connections and whether I'll get a *Thump!* as I switch between the inputs. Perhaps I need to drop in a 47uF cap across the output+ground to 'dampen' the *Thump!*... but won't that alter the output frequency response...?

Thanks for any thoughts, everyone..


John

[ozboomer]

Aug 10, 2011 22:06:06 GMT -5 cynical1 said:

Put a separate input into the box to allow you to run a backing track, or click track, into the phones, send your signal to the amp and be able to mic the amp to grab your guitar tone for recording.

Actually, I tried this a little bit over the weekend and it worked out to be quite a nice tone (to my ears). The tone control on the Micro Crush might be simple... but in conjunction with the 5-way and the Treble Cut and Bass Cut controls on the guitar, it gives a pretty nice range of simple sounds.

Just thinking out loud...no pun intended...

...and another good thought it was, too... Fanx!


John

[ashcatlt]

At 47uF I'm not completely sure you'll hear much of anything! That's a big fricken cap! I wouldn't worry too much about switching pops, unless it's from coupling caps at the input of the amps. That might be solved with a largish "pulldown" resistor.

I think switching the grounds is a good idea, though, to avoid ground loops. With the chassis of the amps connected together you have (potential for) a real ground loop, unlike the questionable variety of which Mr. Atchley speaks. You will want the input and one of the outputs isolated from the metal enclosure. You could try a ground lift switch, but I think this is easier.

[ozboomer]

Aug 21, 2011 18:38:09 GMT -5 ashcatlt said:

That might be solved with a largish "pulldown" resistor.

Dang. I 'cap'-ped when I should've 'res'-sed. So we're talking about, say, a 1.5M resistor, eh? I think I was cornfuzzled with the cap on a power supply line..

[...about the switched grounds...]

Hmm... Well, anything that helps lose 'real' (large current/voltage) ground loops would have to be AGoodThing^tm, I guess...

Ta...


John

[ozboomer]

 
During some further recent reading on this, I found this random comment about using pull-down/tie-down resistors:-

Keep in mind, incorrectly placed pulldown resistors will not only NOT PULL DOWN, but will lower the resistance to ground of the path potentially reducing signal strength causing "tone suck."

No really relevant follow-up comment to the posting was made... so I'm not sure what would be an "incorrectly placed" pulldown resistor... other than putting it in series with the output, which is the sort of thing sumgai (amongst others) has spoken about before. ...*shrug*...

[ashcatlt]

Out of context, it's kind of tough to guess what the poster was saying there, but we can guess. The pulldown resistor needs to be on the "switched end" of the AC coupling cap between the cap and the switch so that it can slowly leak any stored voltage off to ground rather than sit around waiting for the switch to flip and then letting loose with an instantaneous discharge which we hear as a pop. Pulldown on the wrong side of the cap, or the wrong side of the switch, and it can't work.

Since it is a resistance to ground - parallel to the input of whatever device follows - it must reduce the overall impedance seen by the source. This increases the load and can cause tone loss. 1M or 1.5M is usually a pretty safe number. If the input is itself around 1M then you end up around 500K which is a barely noticeable change with most guitars. If the input is much lower than that, the big pulldown has a negligible effect on the total impedance - you'd already be losing a bunch of treble anyway. If the thing is following some other active stage there won't be any noticeable tone loss.

[ozboomer]

 
*thinks*...

I guess I can get the gist of what's going on with the AC (de-)coupling thingy...

...but for this passive switchbox, I'm guessing as long as I have one of these large-value resistors somewhere, it should be Ok... probably between the output hot and its ground (both connected to the "commons" on the DPDT)...

Heh.. even simple things aren't always so 'simple' huh!?

[ozboomer]

A switchbox of some sort is now built... and it works pretty well... except for the fact it's been wired backwards(!)... but I'm not bustin' a gut about that.

It took me a while to work-out the final wiring, 'coz I was getting a *hum* when there was no input going to one of the amps... but I had a look at the schematic for one of the amps and found it actually used a switched jack, which gave me a clue that I needed to ground the non-used input to lose the hum.

Anyway, here's the schematic for this lil' switchbox:-

...and a couple of photos:-

The 1.5M resistor has done a good job on stopping any *thumps*... and I think this lil' gadget will work pretty well. The next lil' get-together will be in a couple of weeks, so we'll see how it goes in 'real' use then.


John

[ozboomer]

I've been trying to use this switchbox in another application recently and I'm getting some strange behaviour out of it.

The primary devices I'm trying to connect are:

• a Behringer UCA202 Audio Interface
  
• a Fender 15R amp
  
• one of my Squier Stratocaster guitars

The intention is to use the switchbox so that I can play the guitar through the amp OR the guitar signal will go to the UCA202 inputs and on into the computer for recording.

With reference to the above diagram, I'm making the following connections:-

• UCA202 input connected to 'Output A'
  
• amp input connected to 'Output B'
  
• guitar connected to 'Input'

This is what I currently observe:

• Select 'A': guitar signal gets to interface Ok
  
• Select 'B': guitar signal comes through amp Ok

...but in both cases, there is a loud hum coming from the amp. If the UCA202 is disconnected from the switchbox, no hum is heard, so I'm assuming the UCA202 is the source of the noise.

The question is why do I get the noise coming through the amp irrespective of how the switchbox switch is set?

An interesting alternative set-up that I tried:-

• MP3 player output connected to 'Output A'
  
• amp input connected to 'Output B'
  
• guitar connected to 'Input'

With these connections, I start the MP3 player running and I observe:-

• Select 'A': no sound from amp (no bleed-through sound from MP3 player)
  
• select 'B': guitar sound from amp

In this case, there is no bleed-through at any time.

Any clues with what's happening here!??!

Thanks.


John

[newey]

Just a guess here, I'm sure someone with a more definitive answer will be along. But I noticed that the inputs to the Behringer unit are line-level inputs, although they are unbalanced. Perhaps it's an input impedance problem.

The manual for the unit talks of connecting it between a mixer and a computer, says nothing about a direct instrument input. Again, just a guess . . .

[ashcatlt]

Sounds like a ground loop to me. Try plugging both devices into the same power strip. Should help, but if it doesn't you'll have to figure out a way to isolate the ground connection on one of the output jacks. That might require a transformer.

[4real]

Interesting project/idea...though I can see a few problems that need to be taken into account...still...

On the hum with computersand such, I ahd heaps of problems with this doing similar things with some powered monitors and separate power strips or the same would not help. What did was to use the laptop on batteries only removing the ground out of the 'loop' so to sepak...so that might be a test for you. In the end I had to get a Behringer passive HD400 hum destroyer. You could likely make your own mono version for your project with a small transformer and probably a good idea.

I also needed a DI box...the behringer Ultra-G is a great device that you might want to check out and a bargain and exceptional build quality and offeres a 'ground lift' as I was getting hum too from the amp and computer and interface and all that. I includes an option of 4x12 speaker emulation and can take a DI signal to a PA or recording just before the amps speaker if you choose and avoid micing the amp cab completely if needed.

...

There could be a few uses for such a design and wearing headphones seems to be a bit of a 'trend' these days...l was exposed to 'linkin park' in recent times from the GF...hmmm...



Of course diamond encrusted LP versions might help...and if you have a fro as this guy had, keeps everything in check...check 1, 2.

In fact I have been seeing a few acoustic players that are using phones to get a click track along with the sound coming from the mics to ensure the timing is tight...especially good for recording for instance...though you will likely get that direct from most interfaces...but for live practice, that might be a good option to mix in a click into the mix and slap it on the drummers head LOL.

...

One thing to consider is that if you nare monitoring the sound out of the orange crush or an LM386 or similar, you are not hearing the actual sound of your guitar. Be aware that the sound in your head may be a lot better to you than your band mates who are hearing something else...but the idea is not a bad one...very cool!

[ozboomer]

 
I was thinking along the 'ground loop' route myself, although I'm not sure I'd recognize it, really.. So, to see if some more experienced Nutz might recognize the sound, I've made a rough recording of 'the noise':-

The Noise (128kbps, 320k)

...and have arranged a picture of what it looks like (ya, I know.. -35dB is prolly not worth worrying about... but I HEAR it and it BUGS! me!):-

Some details from the audio track:-

• 00:00 - guitar at 'Input' is switched through to 'Output B' (amplifier); you can hear 'the noise' even though the switchbox is routing the guitar through to the amp.
  
  
• 00:03 - a note is struck on the guitar, the signal coming through the amp; 'the noise' can still be heard.
  
  
• 00:07 - the switchbox is switched - guitar at 'Input' is switched through to 'Output A' (UCA202 inputs); you hear 'the noise' and that's about all, even though I strike a note on the guitar.
  
  
• 00:14 - The switchbox is switched back; 'the noise' is still heard
  
  
• 00:18 - I strike another note on the guitar, which is heard Ok, as before.

Now, as it stands, the PC is connected on the same 'power strip' already, so I don't know I can do anything more in that regard.

An interesting thing, though.. If I plug the UCA202 into a USB port that isn't configured for it in Windows, although the power light is ON, there is no noise coming from the connection. Windows sees the USB device and makes it available (although it doesn't work)... but as soon as the Behringer driver software is installed, the noise comes through.

I don't have a laptop that I can run on batteries, so I can't test that idea of 'no 240V connections'... but I *did* try installing the interface on another couple of PCs and laptops and the noise problem was always there, so it's not really a function of noisy power supplies (maybe).

Another thought I had... I wonder if there's any point in trying to filter-out the noise, using a couple of capacitors?... Naaaah,... it's going to be too variable to include in the switchbox...

How about doing something with an electronic switch? Hmm.. we're getting too complicated again...

I'm not sure how a DI box will help, either... but that's more about my electrical ignorance than anything else...

*frustrated growl*

I'll keep trying to nut it out...

[ashcatlt]

Can't listen to your clip right now. Your newer description tends to point away from ground loop, but I'm not willing to give up.

Have you got a known good cable that you can mess up at least temporarily? You could try cutting the shield connection at one end of the cable. Make sure the loose wire doesn't short to anything - maybe just leave the barrel screwed loose so you can see the wires while testing. Plug this end into your box, the othe into the behringer and see if it helps, or makes things worse.

[ozboomer]

 
Bingo.

I started by replacing the power lead on the Frontman amp... and that didn't make any difference; neither did changing the amp to a different power point (on another power 'strip').

I then tried connecting my Micro Crush amp (powered by battery alone) to the switchbox as described above (to 'Output B'). The other connections were the same, being the UCA202 input to 'Output A' and the guitar connected to 'Input'. What do you know? -- no squeal. When switched so guitar > amp, I hear the guitar and no squeal bleed through from the UCA202. With the connections switched so guitar > UCA202, no squeal from the amp.

Now, the Micro Crush can also be powered via a wall wart. Connected that up and plugged it into the same power point (on THE power 'strip') where the Frontman was plugged-in (I did remove the battery from the Micro Crush, just to be sure). Power everything up... and no squeal. The sounds were the same as when the Micro Crush was running on battery alone.

So, methinks the Frontman is on the way out... Can these amps develop 'internal' ground loops when something is failing? What's the chances of that happening again with another 'inexpensive' amp? Who's to say there isn't already something 'not right' in a brand new amp anyway?

As a side issue, 'coz of the not-right volume control and ineffective tone stack on this Frontman (apparently known problems), I've been considering grabbing a Fender Mustang I or Mustang II or Roland Cube 20XL as a replacement/upgrade anyway... and I'm still not interested in going the tube/valve route, thank you

Other than that, I'm not sure which way to go now. I have a means to monitor my recordings/overdubs/etc using headphones and that works Ok... but I would prefer to do something with 'open air' monitoring... and using the Micro Crush is not really an option, as has been said before, whilst a fun lil' amp to use 'on the run', it's not too flash to use for monitoring, let alone for practice at home or with a few mates..

The research continues...