I'm a new member. I've been following the forum for about a year - great place with great quality of information and discussion.
I've been studying harmonica online for a year with David Barrett at bluesharmonica.com. Currently I'm working on LOA-7.
I don't gig or play amplified, but I do record study songs for a course. I'm using very cheap and basic equipment: Pyle-Pro PDMIC78 microphone connected to impedance transformer. It then connects to Joyo American sound and to the microphone input of my laptop.
This is the impedance transformer It has High/Low switch. In the High position microphone is much louder. Low position is very quiet.
When recording in the High setting I noticed in Audacity that even though the signal is louder I'm loosing a lot of signal "below zero". There is a bit more distortion as signal below zero is just cut-off. In the Low setting signal is very quiet but I'm getting full waveform with a bit cleaner sound.
Take a look at this screenshot from Audacity. Top is High setting, bottom is Low setting on similar phrase. I normalized both so the volume is comparable.
I don't understand what you mean by 'below zero'. Are you sure it's not just overloading and cutting off the waveforms above a certain level (i.e. 0dB)? ---------- Andrew. -----------------------------------------
Last Edited by Andrew on Nov 12, 2017 12:10 PM
The SM57 is 150ohm low-z balanced. The Pyle-Pro PDMIC78 is medium impedance 600ohm unbalanced. Though it has an XLR plug it is not wired for a regular XLR balanced cable, but comes with an XLR to 1/4" unbalanced cable. There are two cartridge outputs, with one being considered hot and the other bridging to ground. If you use a regular XLR cable to your IMT, you will lose signal, so that is not your answer. You can use it as is without the IMT or try to rewire it. Here is a video on rewiring your mic to be balanced:
I don't know if this mic would be worth rewiring for your purposes as a harp mic to an amp.
If you have use for an unbalanced mic, it might be worth the work. It might work with the IMT after rewiring to balanced.
[edit corrected "IMP" to "IMT"] ----------
Doug S.
Last Edited by dougharps on Nov 13, 2017 9:40 AM
That's odd. Something in the chain is (partially) rectifying the signal, as you say. I'd suspect the mic input on your laptop, maybe it can't handle the bigger output of the Hi-Z signal. My experience is that the built-in audio on laptops is often bad in a number of ways.
The output from the Joyo can be very large (much larger than a Hi-Z mic on its own) so it may be that you've simply got it turned up too much (gain and volume controls).
If you have an amp, try plugging into that and if you don't hear the same distortion then that would indicate it was the laptop input. If so, you could try getting a cheap USB audio adaptor - just one of those from ebay for a few £ should do it.
As an aside, the tube enthusiasts like asymmetric distortion as it is supposed to give a nice sound - one of the much-loved aspects of tubes. So you may have stumbled across a sound you like! Probably sounds horrible though.
Last Edited by MindTheGap on Nov 13, 2017 3:16 AM
Yeah, well, clipping/rectification. It's due to overload. Because the Z transformer is a voltage transformer. The question is what's overloading. Is the pedal a mic pedal (it's overloading) or a guitar pedal (something else is overloading). ---------- Andrew. -----------------------------------------
Unusual looking clipping though - normally you'd expect it to be symmetrical. I doubt it's the pedal, but you never know. A half-dead battery might do odd things like that I suppose.
Did either of you watch the video and see how the mic is wired OOTB? It is wired unbalanced with one element wire tied to the XLR ground pin from one hot pin. The cable that comes with the mic is XLR to 1/4", and it works with this wiring by sending an unbalanced medium impedance signal using the XLR to 1/4" cable.
If you run a regular XLR balanced cable from this mic to a matching transformer without first rewiring the mic to be balanced, the transformer will not receive two out of phase signals from the mic to convert to unbalanced, and you will lose signal. At least that is what I believe after seeing the wiring. The transformer needs a balanced input to work properly.
----------
Doug S.
Last Edited by dougharps on Nov 13, 2017 6:08 AM
Sorry, I only just looked at the picture. The negative clipping is just a phase thing, so I wouldn't puzzle myself over that.
But it isn't square-edged - it seems to be controlled; but some kind of deliberate compression would compress both the positive and the negative.
So I suppose it's accidental compression, due to an overload being unforeseen by the designers. But I was never a good Audacity user - who knows what features it has.
Certain amplification circuitry (type B???? push-pull????) has one set of components to amplify the positive signal and a separate set to amplify the negative signal, then they combine afterwards. If there is that kind of a set-up, then perhaps they are not as balanced as they should be (but even then, one side would be compressing rather than topping)? But that's old-fashioned transistor stuff - I'd have thought they'd use one integrated circuit nowadays. Otoh, IC's only have virtual transistor circuitry inside, and different batches of the same IC have different specs, so it may just be this ICs way of performing under an over-heavy load.
---------- Andrew. -----------------------------------------
Last Edited by Andrew on Nov 13, 2017 6:36 AM
"Negative clipping is just a phase thing" What means this?
Yes, it's an odd thing, I agree the picture seems to show a heavy compression of one side with some hard clipping too. I don't think any class B or AB amp (the push-pull types) ought to be that far out of balance!
My money is still on the dodgy laptop input or a dud battery. Maybe it's something totally different. I'll be interested to hear the answer.
Last Edited by MindTheGap on Nov 13, 2017 6:28 AM
@doug. Please don't tell people to rewire their mics.
If you earth one end of a balanced coil, it simply becomes an unbalanced coil, that's all. You don't lose half the signal. And the oscilloscope picture shows that half the signal is not being lost, it's being compressed. That's caused by active circuitry, not passive circuitry. ---------- Andrew. -----------------------------------------
@mindthegap "'Negative clipping is just a phase thing' What means this?"
It means if you reversed two wires somewhere, it might become positive clipping, so don't worry about it. ---------- Andrew. -----------------------------------------
Last Edited by Andrew on Nov 13, 2017 6:37 AM
@Mindthegap: Imagine what medical self-help forums are like! ---------- Andrew. -----------------------------------------
Last Edited by Andrew on Nov 13, 2017 7:13 AM
@Kajboj Please don't rewire anything based on my posts above.
@Andrew My post was not to advocate a rewiring of the mic, it was to point out that unless it was rewired it was not a balanced signal going into the transformer, even if an XLR cable was used. One half of the element's output (the opposite phased half of the signal)would be grounded if a regular XLR cable connected it to the audio transformer this way.
If you state that running this mic's wiring through a balanced cable into the matching transformer would not affect the level of the signal out of the transformer, fine. I will take your word on this.
The only point of posting the video was to illustrate that this mic is not wired for a balanced cable.
I will now shut the hell up and let you experts resolve the issue. ----------
I did some more tests and it looks like it's something about Joyo Amierican Sound pedal.
Audacity screenshot I posted was recorded through Joyo with pedal in the BYPASS mode (when it's not supposed to affect the signal). When pedal is ON I got normal full signal.
As MindTheGap mentioned half-dead battery I also checked with new battery - it has no impact - same clipping occurs in BYPASS mode.
I also have cheap Behringer delay pedal. When I take out Joyo and put Behringer (in BYPASS mode) in the path signal looks correct - no clipping.
Looks like it's just something weird happening in the Joyo pedal.
As for wiring of the Pyle microphone I'm not sure if it's balanced or not. There were some posts mentioning that Pyle changed their wiring lately and now they are balanced. I opened it up and wiring looks like this:
Pin 1 is connected to the bolt that touches the microphone casing.
Pins 2 and 3 are connected to the element. I'm not sure which one is hot as wires are twisted and both are red and very thin and flimsy.
Ok. I have one of those pedals and I think it's fine in 'bypass' so it may just be a fault then.
Re the wiring, I've got one of those mics and as I remember it was wired like you say - I'd call it 'floating'. Andrew is correct that pinning one of the terminals to ground doesn't lose half the signal, just means that one wire is at 0V and the other is at signal voltage.
Last Edited by MindTheGap on Nov 13, 2017 2:30 PM
I am not an expert... Your description sounds as though your mic is wired balanced. I found this video that may apply to your mic and help you confirm it:
I agree with you that it sounds as though your Joyo American Sound may be the cause of your problem. Maybe yours has a problem with bypass. Andrew and MindTheGap can advise you on this far better than I. ----------
Doug S.
Last Edited by dougharps on Nov 13, 2017 2:34 PM
Interesting info, dougharps. In fact I don't know what the effect would be of grounding one of the signal-carrying pins, then connecting them to an a balanced (Lo-Z) XLR input as in a mixing desk. In might be in the balanced-audio spec, or maybe depends on the particular preamp model.
What I can say is I've used this mic in all configurations, and they all worked, with no distortion. As I say, mine is wired 'floating'. Different signal levels of course, but no distortion.
This mic doesn't seem to have a transformer built in, or if it does it must be inside the capsule. Other mics do, even Lo-Z ones. In that case it's possible that the transformer could have a centre-tap that is grounded. And then, grounding one of the signal wires as well could lose half the signal.
Last Edited by MindTheGap on Nov 14, 2017 12:27 AM
...for instance this wiring diagram on the Shure site for SM57 shows a floating type of scheme too - there's an audio transformer but no centre tap. So I think that pinning one of the signal wires to ground (as in the cheapo XLR-1/4" cable) and plugging into a pedal or guitar amp shouldn't lose half the signal. Other mics may be different.
But the proof of the pudding is in the eating, I should try it and see.
http://pubs.shure.com/guide/SM57/en-US?_ga=2.207134995.1809281054.1510647481-935889915.1505482616
Last Edited by MindTheGap on Nov 14, 2017 3:58 AM
The first video I found when I looked up the mic showed the wiring and stated there was no transformer in the mic. It explained about rewiring to balanced.
With that version of the mic with one element pin tied to the ground pin I figured the XLR to 1/4" would work fine, but I had concerns (apparently unfounded) about using an XLR to XLR cable to an IMT and potentially losing signal. I decided to leave the discussion to you and Andrew as resolution of the problem was outside my knowledge base.
When kajboj posted about reading info on recent changes in the mic wiring I searched based on that and found the second video. Apparently they now are wired balanced.
This change makes me interested in these bargain mics. Are you satisfied with yours? How do they compare to an SM57 as an instrument mic?
By testing each device in his signal chain kajboj seems to have isolated his signal problem as being in the bypass of the Joyo American pedal, a pedal many have recommended. Is this usually a true bypass pedal? Do you or Andrew have suggestions for kajboj addressing this problem?
I have nothing further to add, as problems like kajboj's need on-site investigation to a large extent, and he has implied that the pedal might be malfunctioning. If it's still under guarantee, I'd take it back to the shop. ---------- Andrew. -----------------------------------------
Last Edited by Andrew on Nov 14, 2017 7:07 AM
Doug - yes I see. I don't about the XLR-XLR-IMT setup with one of the signal pins grounded either. It wasn't clear what it would do. Now we have an experimental answer! It was definitely worth pointing out as an unconventional wiring and so something to look at, but perhaps after ruling out other things.
Although the mic is shipped with an XLR-1/4" cable, it is sold primarily as a conventional Lo-Z mic, so it's surprising that they did that grounded wiring. But I also guess they must have tried it direct into XLR sockets?
As for the mic itself, it's very good indeed. I know it's clearly supposed to be an SM57 replacement - but it's not a fake like you see on ebay. The sound it just fine, for harp and also for other 57-y applications. It's not as robust though. I have a couple that have lasted several years, although a friend has one and the grill came off - it's a different construction from the SM57. Also, if it really doesn't have an internal transformer in the module, then I don't know for certain but it could be vulnerable to the 48V phantom power accidentally being switch on. I don't know it that would fry it but it might.
As for the 'True Bypass' thing. I've given up trying to understand the marketing vs reality. In the old days, True Bypass meant an actual physical switch that switched out both poles of the effect signal circuit completely. But I'm not sure it's true any more. I believe the Lone Wolf pedals still do that. So I don't know about the Joyo - the evidence here suggests not.
So no solutions from here I'm afraid! Apart from try another one :(
