Alex Rice Vs Metal Marshmallow DIY Phantom Piezo Preamp Comparison

[@ynschannel_]

This channel is gold, the only serious channel about piezo's. It would be great if you could compare comercial piezos like KNG SG-1, or use other kind of piezo, different quality...

[@dfiction]

yes comparing the acoustic response of different piezos would be a really, really interesting discussion. we could even nominate piezos from the audience for you to test, and you can run them all into the phantom powered metal marshmellow!

[@metalmarshmallowllc]

Actually this channel is just a vehicle for my nature photography!! Just kidding, thanks for the suggestions, these are already on my long list so maybe I'll bump them up a bit. Glad you enjoy my videos!

[@ProfessorHumblesDelusions]

This is probably the most honest and indisputable comparison video on the internet. The DIY phantom powered preamp kit looks like a fun project.

[@neslesman6708]

I am amazed and so glad to have found this.

[@wilbertopdedijk5741]

I brought the phantom kit!. am going to build it into my cajon. The issues you are describing are the exact issues I have had on my cajon.

[@funkbungus137]

man, I just found your channel, and I gotta say, this is so cool

[@stuartchapman5171]

Ive been following your stuff for a while, I make experimental elctronic soundscapes. Ive always been impressed. The ethical bit at the end reminds me if a retailer I worked for. The manager used to say, if a customers got a complaint, ask them to give negative feedback. We know what we do right, we need tj know what we do wrong, then we can improve what we do.

[@yenra]

Thank you for your work. I'm loving my Metal Marshmallow Pro!

I’ve built the blog orégano with the 2N3189 and some replacement jfet. I used 9v batteries in both. The first 2N3189 was not noisy at all and had a very nice bass response. The second BN something was crap.

[@dfiction]

this is amazing! i would be so curious also to compare your preamp to the "hi z" input on your interface.

[@sr3d-microphones]

I purchased two DIY kits for a stereo experiment- can’t wait for them to arrive!

[@metalmarshmallowllc]

Thanks for the order and happy recording, I hope you like them!!

[@sr3d-microphones]

@@metalmarshmallowllc if these work the way that I hope they work….. keep your fingers crossed for me 👍 I’ll be in touch with you soon once they arrive if they do!

[@gerainsan]

I am far from electrical engineering, but the videos on this channel are very interesting and understandable) I am also very close to sound design, so I can not wait for the ordered Metal Marshmallow Pro).

[@metalmarshmallowllc]

I carried that stupid robe all the way up there and in the end it just looks like I green screened it 😖

[@triboluminiscencia_]

Your videos need more robes, definitely!

[@hakank3841]

You are great person! I want to buy metal marshmallow DIY kits. Do you know can I use this preamp for geophone?

[@uxartmusicvideo-andphotogr2043]

Signal to noise ratio is most important for audio recording what manufacturers don't show. Do know signal to noise ratio we need to read enthusiasts test result charts. If we get lucky the product what we are interested are in test chart.

[@markg1051]

Nice job on your preamp Michael. Just had a quick look at the discrete JFET circuit you breadboarded, Not the lowest noise design. One obvious issue is the value of small coupling caps C2 and C3, also as there is no difference in DC voltage at the gates of the JFETS plus the piezo disk being practically open circuit at DC you can do without them. I'd be curious if you could repeat the measurement on the circuit after bypassing the C2 and C3 input coupling caps. I suspect that the noise floor should drop considerably.

[@metalmarshmallowllc]

Interesting thought, I might give that a try. My guess was that the noise was either due to the high value resistors feeding directly into the transistor bases, or the use of transistors optimized for high frequecy (maybe the other recommended transistors would be better?). Probably all of the components contribute. Even if the noise could be solved, I still don't think this preamp would be better than no preamp at all due to the low-frequency problem.

[@markg1051]

@@metalmarshmallowllc You are right about the majority of noise being from the high value resistors especially in the case of using low value coupling caps as they tend to go up in impedance at low frequencies making the bias resistors dominate. From past experience most of the piezo discs have a very high capacitance in nano or tens of nano farads which is the reason why the noise will reduce if the low couplers are bypassed. If you have an access to a capacitance meter measure the C-piezo, and work out/calculate the reactance of it at various low frequencies, this will give you an idea how or whether the 3 Meg resistors or the Xc of the piezo will dominate. I've worked a lot with the old Philips BF245A, B and C versions, these are all discontinued parts now unfortunately without any noise issues that showed up in your measurements. My thoughts are curiosity based, always wanting/needing to know the reasons for certain results. So I am not suggesting the use of one cct over another, the one with better performance is the winner. Let us know what you find if you end up repeating the test.

[@markg1051]

@@metalmarshmallowllc PS, if you want to see exactly where and how much the noise is generated remove the piezo and replace it with a short wire link, effectively shorting the inputs. Do this with the 220pF caps in. Then for comparison, move the shorting link between the two FET gates. Doing this should not alter the bias of the FETs as there should be no DC voltage difference between the two gates. Cheers.

[@metalmarshmallowllc]

@@markg1051 So I did some tests and it looks like you are exactly correct on all counts. I first repeated all the noise measurements using a wire link in place of the piezo. This was a much easier way of doing it, and the data I got was a lot cleaner (no noise from the neighbor's AC unit). Aside from that the graphs are the same as what I show in the video and everything I said stands. I then removed C2 and C3 from the blog preamp by shorting out their terminals with a blob of solder. I repeated bot the noise-floor and white noise measurements. I have to say that I was shocked, but that completely solved both the noise issue and the poor bass response issue. As much as it pains me to say it, without the caps the performance on both counts is essentially the same as the Metal Marshmallow at +12 dB gain. So I guess I might change my recommendataion from "don't build this" to "If +12 dB works for your application, go ahead but for the love of all that is holy leave out C2 and C3". If I have a spare moment I might post the graphs to my blog. Thanks for your insight, I'm sure a lot of people, including me, will be elucidated by this discussion.

[@markg1051]

@@metalmarshmallowllc Glad to be of help Michael. Love your attitude, real scientific mind set! There is one other quirk with the original circuit design, if you redraw the schematic to include the two 6.8k phantom supply resistors located between the interface, internal 48V supply and pins 2 and 3 you get a full picture of the actual "complete" circuit which is really a standard differential amp gain stage. You then realize that the bias is derived from the Q1 and Q2 outputs, i.e. their drain terminals which is not just a steady DC voltage but in addition contains the amp AC output signal component. This configuration creates a negative voltage feedback which reduces the input impedance to well below the combined value expected from the 2:1 divider of two x 3Meg resistors. This is another reason for the degraded low frequency response with the 220pF couplers. As I don't have any means of doing the tests you did, I ran the circuit in my Altium simulator Circuit Maker 2000 to get an idea of noise and frequency response using some standard JFET models in the library, I ended up with pretty much the same response curves for both frequency response and the noise that you did. When I say 'same' I couldn't simulate the piezo element and its resonant peak in the frequency response. The main difference I got was in the value of gain due to different FET models available in my simulator, this ended up being just short of 30dB of gain. Anyway, thanks very much for actually redoing your measurements with suggested changes, really appreciate it. Take care.

[@maxwag9263]

Really cool bro😊

[@davenelson5124]

When I use piezo pickups I go into a DI with high impedance (1M ohm) because I understand the contact mic has a much higher output impedance than a normal mic. The performance seems good and definitely better than straight into a channel. Is your preamp doing exactly this or is there some other benefit?

[@gossalex]

Zach Poff is a legend.

[@jjcale2288]

The S/N ratio is zero if the signal is zero.

[@tomdemojo45]

❤

[@DJ999ULTRA]

nice👍

[@guitchess]

Thanks for the vid. However, any lay person with an intermediate knowledge of electronics would know this comparison is apples to oranges, let alone a EE phd. I'm not arguing that your results are invalid, only that your "proof" experiment was questionable at best. A perf board prototype compared to a professionally manufactured smd PCB complete with ground plains? Come on! I'm about to build one of the many circuits that I've found on the internet. So, I'm hoping you're completely incorrect. It will be built like your complete smd version. In the search for the perfect JFET, I have noticed a wide range in noise figures while searching for the "perfect" component. My comment isn't meant to rag on you. Merely, an antithetical position taken because of your suggestion that all the products using similar circuits to that which you built were inferior. With no apparent consideration of the fact that the same circuit with the same parts built by 5 people will yield 5 performance results. In short, you set off my BS detector. It's been right, and wrong. I guess that's my $.02.

[@metalmarshmallowllc]

I appreciate your skepticism; peer review is an important part of the process even here on youtube, and I'd love to hear back from you especially if you can demonstrate that my results are wrong -- I have definitely been wrong many times before and I learn and improve every time. I did originally prototype the Metal Marshmallow preamp on a solderless breadboard and the performance is the same as on the professionally produced PCB. Apologies because this got buried in my replies to a comment by @markg1051, but the noise and low frequency issues in the Alex Rice preamp don't arise in the lack of ground plane or the perf board or even in the JFETs. They arise in C2 and C3, which are actually not necessary anyway. So if you build it, just get rid of those, and then the performance is actually very good. Or if you buy a version of it, check that they are not there or remove them. The only downside is that the gain is fixed at +12dB, so you won't get optimal noise performance and can't adjust the sensitivity, but that may or may not be an issue depending on what you are trying to do with it. Have fun with your project, let me know if I can help, thanks for your $0.02, and happy recording.

[@Jononor]

It would be great to see a comparison of a SMD professional manufactured version of the "blog" preamp, a breadboarded "blog" preamp. How did your quest go?