Can ya hear me - pumpin on yer stereo?

[peskywinnets]

So anyway, I'm dabbling with low impedance pickups - I wanted to AB one against a trad mag pickup. (ie feed them into two separate Cubase channels then solo one immediately after the other while listening on high quality headphones)

After AB'ing em ....they're obviously very different - a bit weird actually - the high impedance humbucker sounds somewhat nasal when put up against a wide bandwidth low impedance pickup, yet the same traditional (decent) mag humbucker sounds just fine in isolation! (some aural illusions going on there methinks).

IMHO the traditional humbucker kicks the low impedance's pickup's ass through a very high gain amp sim (some shocking noise with the low impedance pickup into a high gain sim ...and all this with a balanced preamp, well chosen components....but the Low Z pickup sounds fantastic into a clean channel). I'm figuring that's why EMG have a medium/high Z pickup into an active preamp - a far better SN ratio for metalheads (cos when you start off with a signal that only about 50mV peak to peak you have to apply a whole lot of gain just to get it up to a useable level...no matter how well your balanced preamp performs, it takes the noise floor right on up with it too...and through a high gain amp sim, well it sounds like a festival of white noise - btw I don't want to use a step up transformer)

Anyway, after AB'ing I thought I'd have a dabble with 'stereo pickups' (one pickup into Cubase & panned hard left - the other panned hard right)

Whilst there's not much in the way of a what you could call a wide stereo affect - the different frequency response (& no doubt phase response) of the low Z vs High Z pickups, does lend a little bit of 'width'...but some real aural fun (I said aural - ok?) to be had putting one of the pickups on auto pan, with the other just set off to one side of the stereo mix ....both with slight (& different reverbs) it gave me a nice warm glowing feeling which promped me to make my wife a cup of tea (which has never been known)

Worth a try when you get a mo. (no, not making my wife a cup of tea....the stereo pickups)

[imaradiostar]

Have you tried stepping the low z pickup up with a transformer?

good song, by the way.

jamie

[peskywinnets]

Have you tried stepping the low z pickup up with a transformer?

jamie

Hi jamie, as I mentioned above, I don't want to go the txfmr route...

1. I don't have one.
2. even the small ones are a little bulky for the intended space (& the inline cables ones are too expensive)
3. I suspect the whole sonic appeal of a low impedance pickup will be somewhat negated by a step up transformer.

[Mike Sulzer]

Hi jamie, as I mentioned above, I don't want to go the txfmr route...

Then you are going to have lots of hiss from the first tube stage. The only way around this is to build a solid state preamp with a very low voltage noise such as are used on moving coil phono cartridges. The transformer is a lot easier.

[peskywinnets]

Then you are going to have lots of hiss from the first tube stage. The only way around this is to build a solid state preamp with a very low voltage noise such as are used on moving coil phono cartridges. The transformer is a lot easier.

I should just say, that the noise floor for the pickup preamplifier I've knocked up is almost non existent under normal circumstances - I'm using a balanced bifilar pickup into a twin differential amp type arrangement (using the -ve pins on each diff amp, then summing in the next stage, which I believe should yield less voltage noise)...it's only when pushing the signal through a very high gain marshall amp sim (eg such as Revalver) that the background white noise floor is excessive.

I suspect even moving coil phono cartrige preamps would sound hissy when pushed through such a high gain amp sim!

[imaradiostar]

RadioShack Audio Output Transformer - RadioShack UK

Use it backwards, mount it at the amp end of things or even mount it in a stompbox.

Sorry man, just trying to help!

jamie

[peskywinnets]

RadioShack Audio Output Transformer - RadioShack UK

Use it backwards, mount it at the amp end of things or even mount it in a stompbox.

Sorry man, just trying to help!

jamie

I feel like an old lady who's had her arm grabbed & taken across the road....but the Post Office (where I was going to get my pension) is on the other side where I originally was!

Seriously, thanks for the input, it's this but that troubles me...

Frequency response.................300 - 10,000Hz +/-3dB

the whole appeal of a low impedance piclkup is the 0Hz-> '1 SillyHertz' bandwidth (note to all the pedants - joke ....right?), so slapping one in is gonna spoil my "Hehehe, let's annoy this sleeping dog with a harmonicly wild squealie"

[imaradiostar]

The listed frequency response is at a marginal level of output. It'll be much flatter than that at the levels you'll be using it. They're commonly used for home made ribbon mics. All I can say is they're cheap, readily available and regarded as the simplest way to compensate for the impedance mismatch you're experiencing.

Of course, listening to my suggestion may prevent you from discovering something that's a better solution!

jamie

[Steve Conner]

I should just say, that the noise floor for the pickup preamplifier I've knocked up is almost non existent under normal circumstances ...it's only when pushing the signal through a very high gain marshall amp sim (eg such as Revalver) that the background white noise floor is excessive.

Well, I think being pushed through a high gain amp is "normal circumstances" for a guitar pickup.

[peskywinnets]

Well, I think being pushed through a high gain amp is "normal circumstances" for a guitar pickup.

I concur...but I'm talking 'stupid gain' sims (knob set on 11) ....mag pickup = still quiet, active pickup= lotta hiss.

I'll maybe post some sound samples soon to illustrate what I mean. It's entirely conceivable that it's just my setup (I have some qualms about the grounding wrt my RME fireface)...or even the preamp I've knocked together....I'll have a bit more dabble (also I'm still breadboard,so there's no shielding going on which might account for a chunky percentage of the noise....this is hiss not hum). I'll try running to my soundcard balanced...from pickup all the way to the soundcard input (I'm summing the differential signals into a single ended feed into my soundcard's Hi Z input).

Here's an extract from my cct....





EMG are renowned for their clarity - presumably they are quiet too? I've never heard/played an EMG ....has anyone any comments about EMGs through high gain amp sims?

[David Schwab]

the high impedance humbucker sounds somewhat nasal when put up against a wide bandwidth low impedance pickup...

High impedance pickups have more like a band pass response. EWe are used to that tone though, and for many things it works better, like with distortion. This is why Alembic guitars have low pass filters with variable resonance.

I'm figuring that's why EMG have a medium/high Z pickup into an active preamp - a far better SN ratio for metalheads

EMGs use regular high impedance coils, but they don't have them wired in series, and they are connected to the op amp. They were also never intended for metal heads, but they ended up using a lot of them. They are damn quiet pickups.

[Mike Sulzer]

I(also I'm still breadboard,so there's no shielding going on which might account for a chunky percentage of the noise....this is hiss not hum). I'll try running to my soundcard balanced...from pickup all the way to the soundcard input (I'm summing the differential signals into a single ended feed into my soundcard's Hi Z input).

Shielding does not reduce hiss, it reduces hum. Using a differential amp does not reduce hiss, it increases it: the noise in the two active devices adds in power, while each sees half of the total input voltage, and the two halfs add in voltage, giving you a 3db worse SNR. A differential amp is intended to reduce interference pickup when transferring a signal from one place to another, not reduce the hiss from the active devices or resistors.

Low noise preamps for low impedance (that is, low output voltage) transducers exist. There was a discussion of such preamps for moving coil phono cartridges here some time ago. You will not do better than they do, and your current approach is not good.

[Steve Conner]

Well it could be worse, could be another PAF clone.

Moving coil phono pre-amps are all well and good, but the ones that don't use a transformer get their low noise by using a lot of transistor junction area and running it at a high current. If you built one into your guitar, the 9v battery would last about half an hour!

It seems to me the smart compromise would be to put as much wire on the pickup as you can without limiting the frequency response below what you think is acceptable. Hopefully it would turn out enough that one of the mic pres on a chip would finish the job. And voilà a 21st century version of the Les Paul Recording, or Studio or whatever it was called, back when there were still things left to be invented.

I always wondered whether the response of a pickup could be broadened by running it into a charge amplifier. At work, I've used zero-field techniques to broaden the bandwidth of cheap transformers. I was moving the LF cutoff downwards, but maybe you can move the HF one up too.

[Mike Sulzer]

Well it could be worse, could be another PAF clone.

Moving coil phono pre-amps are all well and good, but the ones that don't use a transformer get their low noise by using a lot of transistor junction area and running it at a high current. If you built one into your guitar, the 9v battery would last about half an hour!

It seems to me the smart compromise would be to put as much wire on the pickup as you can without limiting the frequency response below what you think is acceptable. Hopefully it would turn out enough that one of the mic pres on a chip would finish the job. And voilà a 21st century version of the Les Paul Recording, or Studio or whatever it was called, back when there were still things left to be invented.

That is exactly the right approach! And you can have a lot more turns than you might think. First, there is no cable capacitance since you are using a preamp. Second, using fewer turns lowers both the inductance and the capacitance. So you might think of it as: how many turns do I have to take off a normal pickup to do this?

I would start with about 2,000, check the resonant frequency, and then load the pickup with a resistor that would damp this resonance a bit, even though it is above the audible, to help keep the response very flat within the audible.


*** If I did want to make a very low noise preamp for very low impedance inside a guitar, I would run the first stage on a very low voltage (less power even at high current) and couple this into the negative input of an op amp running off a higher voltage battery. This would keep the voltage swing at the output of this first stage to a very low level, but allow a normal voltage output from the op amp.

[peskywinnets]

Ok, I got to the bottom of this last night - the problem was 'RF pickup' contaminating the 3 x 1.5m pickup tail wires connecting the pickup to my breadboard (& here was i thinking a balanced wire arrangement would have cancelled any grunge picked up by those wires). When I shielded those wires with bog standard kitchen foil & grounded the foil - RF totally disappeared (I live about a mile from a major TV/Radio transmitter in London) ...along with a whole HEAP of background hiss. (which is a nice little anecdote re how you can sometimes overtheorize eh?!)

BTW the reason the mag pickup sounded so clean vs the low impedance pickup was actually down to a noise gate embedded within the particular Amp sim I was using (I wasn't aware the Amp sim had one in)...becuase the low impedance pickup was rx'ing up RF/hiss, the noise gate wasn't kicking in (must have been just above its threshold)....when I disabled the noise gate the mag pickup was also very hissy....which means it's down to the amp sim.

It's quiet now...but where in the UK to buy thin pure copper foil without adhesive or backing (similar to kitchen foil but copper) that I can encase the pickup with & then solder onto the foil? The pickup won't actually be seen so I don't care if it looks like a turkey about to go into the oven.

Edit: Actually, I've just had cheapskate idea (have you seen the price of copper lately?!) - use aluminium kitchen foil then crimp a copper eyelet onto it at a point where it's been doubled over a few times - solder onto that! I can hear keyboards of the world whirring into action - DON'T DO IT, WHAT ABOUT EDDY!