Marik
Pro Microphone Design
OK,
As some of you know the deal was I offered to the first interested person to install a PK47 and do mods for free in exchange to being able to test the PK47, I was interested in and wanted to compare to my mint original PVC M7.
Although not identical, those capsules are quite similar and have in common a single backplate construction, which is very different from K67/87 type.
Today the mic has arrived, and although I did not have much chance to play with it, just wanted to post some first impressions, if somebody is interested.
The thing sure looks impressive--heavy PSU made of thick sheetmetal, good sized mic itself. 24 karat gold grill is sure not my favorite, but what's the heck.
I have a bad habit of opening things before I even tried them out, so that one was not an exception.
Since I got the mic with the tube already swapped, and original one was not marked it is hard to say which tube originally was intended to work with this circuit, without seeing its internal structure. The tube socket is fastened with a rubber ring, and another end is damped with another rubber thingie--nice solution, as it reduces tube microphonics.
Another surprise--the transformer was actually a U-core type--something not very often you see in Chinese tube mics. The core sure looks on a smallish side, but who knows? Before any measurements are done it is hard to say.
I did not see any cheapo ceramic caps stuff. The caps look like nice films. The electrolitic C6, which is in signal path, as well as shunting cathode resistor cap will definitely need to be replaced for better quality, but this is later.
The grid resistor is actually a very clever for a tube circuit 150M value, as opposed to generic 1G, most of the manufacturers through into that part without thinking.
The B+ is 166V so there is a lot of space of playing with voltages and anode resistor values.
Things I did not like. The most noticable--the tube is located "upside down", where the grid is connected to the capsule blocking capacitor through a pretty long piece of wire--not good for a number of reasons. We don't want to through into highZ part of the circuit anything that long, so even moisture in air would work as a conductor, increasing noise. Also, it introduces stray capacitance, which loads the capsule signal, as well as degrades sonic qualities.
The most obvious way of fixing it is to mechanically flip it... but not yet, as later there might be some other solutions.
Capsule bias sits @80V. There is nothing wrong with it... maybe, but looking at the transformer size something is telling me the signal is pretty healthy and we might hit the transformer little too hard.
The main thing--the heater sits @6.54V!!!
Bad, very bad, VERY VERY BAD!!! The rating is 6.3V, so we are killing our poor tube in a matter of months. This should be fixed the very first thing.
I had a listen to it for a few minutes. Unfortunately, at this point I cannot say much. For last month my ears are very much got used to a ribbon sound, so I need a couple days to get back on track and get re-adjusted.
In any case, the capsule should arrive next week, so the whole fun has not even started quite yet...
So stay tuned, Gentlemen
As some of you know the deal was I offered to the first interested person to install a PK47 and do mods for free in exchange to being able to test the PK47, I was interested in and wanted to compare to my mint original PVC M7.
Although not identical, those capsules are quite similar and have in common a single backplate construction, which is very different from K67/87 type.
Today the mic has arrived, and although I did not have much chance to play with it, just wanted to post some first impressions, if somebody is interested.
The thing sure looks impressive--heavy PSU made of thick sheetmetal, good sized mic itself. 24 karat gold grill is sure not my favorite, but what's the heck.
I have a bad habit of opening things before I even tried them out, so that one was not an exception.
Since I got the mic with the tube already swapped, and original one was not marked it is hard to say which tube originally was intended to work with this circuit, without seeing its internal structure. The tube socket is fastened with a rubber ring, and another end is damped with another rubber thingie--nice solution, as it reduces tube microphonics.
Another surprise--the transformer was actually a U-core type--something not very often you see in Chinese tube mics. The core sure looks on a smallish side, but who knows? Before any measurements are done it is hard to say.
I did not see any cheapo ceramic caps stuff. The caps look like nice films. The electrolitic C6, which is in signal path, as well as shunting cathode resistor cap will definitely need to be replaced for better quality, but this is later.
The grid resistor is actually a very clever for a tube circuit 150M value, as opposed to generic 1G, most of the manufacturers through into that part without thinking.
The B+ is 166V so there is a lot of space of playing with voltages and anode resistor values.
Things I did not like. The most noticable--the tube is located "upside down", where the grid is connected to the capsule blocking capacitor through a pretty long piece of wire--not good for a number of reasons. We don't want to through into highZ part of the circuit anything that long, so even moisture in air would work as a conductor, increasing noise. Also, it introduces stray capacitance, which loads the capsule signal, as well as degrades sonic qualities.
The most obvious way of fixing it is to mechanically flip it... but not yet, as later there might be some other solutions.
Capsule bias sits @80V. There is nothing wrong with it... maybe, but looking at the transformer size something is telling me the signal is pretty healthy and we might hit the transformer little too hard.
The main thing--the heater sits @6.54V!!!
Bad, very bad, VERY VERY BAD!!! The rating is 6.3V, so we are killing our poor tube in a matter of months. This should be fixed the very first thing.I had a listen to it for a few minutes. Unfortunately, at this point I cannot say much. For last month my ears are very much got used to a ribbon sound, so I need a couple days to get back on track and get re-adjusted.
In any case, the capsule should arrive next week, so the whole fun has not even started quite yet...
So stay tuned, Gentlemen
Last edited:
). To me, the old GE tube made a big improvement - more full and mellow sound. To find out that it's in grave danger 
. No bigie though for a DIYer.
.
. Why would we go tube, then? We could just as well go solid state. 
(I spend a lot of happy time in that "don't know what you don't know" corner of the chart 
