Noob needs help with z5600a II mic repair

[Adam Frandsen]

The resistors soldered together first band is red, giving 250KΩ, they are in parallel giving 125KΩ - the pic you posted of someone else’s mic has a 100KΩ resistor in that place - your board number matches that of the other mics - SE06000.
I wouldn’t trust that schematic either - there appear to be 3 R3 resistors - one 51MΩ on the 0 - 120V line to the back diaphragm of the capsule connects to C2, one 51MΩ on the feed line to the backplate joins R1 1GΩ and between C9 and C10, one 1MΩ connects to K2-1 and C8??? The 300KΩ is R5 connected to the anode of the first tube stage pin 1 of the tube - I’m not sure why there’s a drop to 100KΩ - maybe there are other changes on your board.
I don’t see any burn damage - if there is it’s likely from someone using a soldering iron too close - I wouldn’t worry about that - you need to worry if resistors become discoloured/brown or caps the same or electrolytics with swollen tops or leakage out of the base.

Bottom line is someone has done some work on this and not cleaned up. I suggest you contact SE and inquire as to what value R5 should be (I am assuming here that pair of parallel resistors are R5). It could be that the value in this was originally 125KΩ and they used two resistors in parallel to double the wattage as in the other picture the resistor looks like a 1 or 2 watt resistor. It would make sense if the replacement resistors are 1/2 watt and replacing a 1 watt.

Okay, I will contact sE - I read on another thread on the forum with the schematics that the person had contacted sE to get the original schematics, because he couldn’t read them, but had been sent the exact same pixelated ones… Either way, should I just desolder all of it, clean the PCB with some alcohol/water solution, order everything new from digikey and then redo everything?

 

[RoadrunnerOZ]

It doesn’t sound right, and no matter what tube type i put in 12ay7, 12at7, ecc83, 5751 it needs the exact same amount of gain to reach the same volume… it sounds distant, weak and unrefined. As I stated in one of my first posts, the 8th pin of the socket in the PSU has no wire attached, I understand that it doesn’t have to have that necessarily, but since so many things are wrong in the mic already, and the first thing I did was replace a blown capacitor in the PSU that caused a terrible hum, I have to question everything about it. I know the color of the wires don’t have to match, but the red wire that has 180v written on the pcb inside the mic, that must be the voltage for the plate in the tube, is coincidentally also the only wire color not present amongst the wires attached to the socket in the PSU… One user here read the schematic as having the pattern dial connected to pin 3 and pin 4 being a second ground(?), but in my PSU pin 4 goes to the pattern dial… Frustrating and confusing…

In the PSU schematic the pattern dial midpoint goes to pin 4 - this derives the 60V reference midpoint between 0V and 120V. In the mic schematic the 0-120V, which is derived from the pattern switch wiper which sweeps the resistor divider network, shows as pin 3. This has a resistor of fairly high value in the PSU between the rotary switch wiper and pin 3. I would not trust the pin numbering, although I think you’re reading it wrong here regarding pins 3 and 4, but use your meter to check connections. There’re only 5 coming in directly from the PSU to the mic PCB plus 2 coming from the output transformer secondary winding in the mic to the XLR out in the PSU.
1. There should be one to ground from supply to mic. This would be pin 7 of the cable
2. Then one to pins 4 and 5 of the tube - this is your tube filaments, pin 9 goes to ground to complete the heater circuit - both filaments in parallel - check this with the tube out. This will come from the output of the 6V 7806 regulator in the PSU. This would be pin 2 of the cable.
3. Then one to pin 6 of the tube which is HT from the PSU - this also connects to one side of R5. This would be pin 1 of the cable.
4. Then one to the centre-point pole of the pattern select switch comes into the top of C10 in the mic then through a couple of resistors to the backplate - this is reference midpoint 60V for the backplate (the big thick metal plate between the front and rear diaphragms ) of the capsule as the top of the switch has 120V and the bottom is grounded - front diaphragm is grounded, back diaphragm ranges from 0 to 120V - at midpoint of the rotary switch this is the same potential as the backplate at 60V and thus ceases to work, the front diaphragm at ground potential is 60V below the backplate so it functions - this central position of the switch is your cardioid position. When front and rear diaphragms are at the same potential (0V) then they are both working in phase, this is Omni. When front is at 0V (which it always is) and the rear is at 120V they both are - or + 60V away from the centre backplate but working in opposite polarity creating your figure 8 pattern. This would be pin 4 of the cable.
5. Then the feed from the wiper of the pattern switch via a high value resistor (unreadable from the schematic) in the PSU between the wiper and the cable socket. This would be pin 3 of the cable.
6. Then from the output transformer secondary in the mic Hot and Cold to the XLR in the PSU. These would be pins 5 (Cold) and 6 (Hot).

 

[RoadrunnerOZ]

Also another possibility - the capsule is on back to front - have you tried singing into the other side of the mic?

 

[Adam Frandsen]

Bottom line is someone has done some work on this and not cleaned up. I suggest you contact SE and inquire as to what value R5 should be (I am assuming here that pair of parallel resistors are R5). It could be that the value in this was originally 125KΩ and they used two resistors in parallel to double the wattage as in the other picture the resistor looks like a 1 or 2 watt resistor. It would make sense if the replacement resistors are 1/2 watt and replacing a 1 watt.

I think it is a carbon resistor in the other mic, so 300k orange, black, yellow, gold

 

[Adam Frandsen]

In the PSU schematic the pattern dial midpoint goes to pin 4 - this derives the 60V reference midpoint between 0V and 120V. In the mic schematic the 0-120V, which is derived from the pattern switch wiper which sweeps the resistor divider network, shows as pin 3. This has a resistor of fairly high value in the PSU between the rotary switch wiper and pin 3. I would not trust the pin numbering, although I think you’re reading it wrong here regarding pins 3 and 4, but use your meter to check connections. There’re only 5 coming in directly from the PSU to the mic PCB plus 2 coming from the output transformer secondary winding in the mic to the XLR out in the PSU.
1. There should be one to ground from supply to mic. This would be pin 7 of the cable
2. Then one to pins 4 and 5 of the tube - this is your tube filaments, pin 9 goes to ground to complete the heater circuit - both filaments in parallel - check this with the tube out. This will come from the output of the 6V 7806 regulator in the PSU. This would be pin 2 of the cable.
3. Then one to pin 6 of the tube which is HT from the PSU - this also connects to one side of R5. This would be pin 1 of the cable.
4. Then one to the centre-point pole of the pattern select switch comes into the top of C10 in the mic then through a couple of resistors to the backplate - this is reference midpoint 60V for the backplate (the big thick metal plate between the front and rear diaphragms ) of the capsule as the top of the switch has 120V and the bottom is grounded - front diaphragm is grounded, back diaphragm ranges from 0 to 120V - at midpoint of the rotary switch this is the same potential as the backplate at 60V and thus ceases to work, the front diaphragm at ground potential is 60V below the backplate so it functions - this central position of the switch is your cardioid position. When front and rear diaphragms are at the same potential (0V) then they are both working in phase, this is Omni. When front is at 0V (which it always is) and the rear is at 120V they both are - or + 60V away from the centre backplate but working in opposite polarity creating your figure 8 pattern. This would be pin 4 of the cable.
5. Then the feed from the wiper of the pattern switch via a high value resistor (unreadable from the schematic) in the PSU between the wiper and the cable socket. This would be pin 3 of the cable.
6. Then from the output transformer secondary in the mic Hot and Cold to the XLR in the PSU. These would be pins 5 (Cold) and 6 (Hot).

Very helpful once again, thanks!

 

[RoadrunnerOZ]

I think it is a carbon resistor in the other mic, so 300k orange, black, yellow, gold

Yeah that could be orange - makes me wonder why 2 250KΩ in parallel in your mic - maybe they are 150KΩ and they didn’t know the diff between series and parallel. Says 1W in schematic BTW. I’d unsolder them and measure them - if together as they are in parallel they measure 75KΩ then they’re 150KΩ separated - you could then try putting them in series to see if that makes a difference.

 

[RoadrunnerOZ]

You need to get the mic working properly in its current state before contemplating recapping and replacing transformers and capsules - otherwise there will still be a problem. Once you unsolder those two resistors that are joined and get the right value in there it may work fine and you may like the mic as it is without expensive mods that could give you no idea of improvement if they’re working in a faulty environment. The fact that you are getting a thin sound and no real change in gain may mean that this anode resistor change of value is affecting the sound and how the tube should be working.

 

[Adam Frandsen]

You need to get the mic working properly in its current state before contemplating recapping and replacing transformers and capsules - otherwise there will still be a problem. Once you unsolder those two resistors that are joined and get the right value in there it may work fine and you may like the mic as it is without expensive mods that could give you no idea of improvement if they’re working in a faulty environment. The fact that you are getting a thin sound and no real change in gain may mean that this anode resistor change of value is affecting the sound and how the tube should be working.

Right

 

[Adam Frandsen]

Looks like a clueless individual with poor skills has made a mess. No evidence that any electrolytics were replaced. All that solder flux and crud on the board isn't good where the high impedance nodes are. I guess they were too lazy (or afraid) to disassemble and solder from the correct side.

You don't even have to disassemble, you can just pull the tube out on the other side and there is full access... *Facepalm*

 

[Nen'O]

Just a few pictures inside my mic - as you can see the soldering job from its last recapping is not very good and done from the wrong side(?) and there is burn damage to caps and resistors ... am I seeing this right?

Oh boy, That doesn’t look good at all.
At this point it might be even better to look for new pcb and use this mic as donor body. It might be even cheaper to do that than trying to restore stock pcb .
We need to check size, there must be something that will fit there .

 

[Adam Frandsen]

Oh boy, That doesn’t look good at all.
At this point it might be even better to look for new pcb and use this mic as donor body. It might be even cheaper to do that than trying to restore stock pcb .
We need to check size, there must be something that will fit there .

That was another option that occurred to me too… but it kinda hurts that I spent money on this mic, sigh

 

[Nen'O]

That was another option that occurred to me too… but it kinda hurts that I spent money on this mic, sigh

DIY doesn’t necessarily means cheaper route to get good mic, but it’s fun route to take

Some folks like JJR shop as well as gototoolz offer some very interesting tube mics for bargain,


https://www.jrrshop.com/nos12
https://gototoolz.com/shop

 

[Khron]

That was another option that occurred to me too… but it kinda hurts that I spent money on this mic, sigh

Then again, the parts in that mic don't cost a fortune anyway. You could consider just removing all of them, cleaning out all the holes with a solder-sucker and/or solder-wick, and rebuilding the circuit with new parts. You have the schematic, arguably clearly enough labeled.

Sure, the "mod soldering" is far from great, but i really doubt the circuit board itself is utterly fubar'd. But that's just me...

 

[RoadrunnerOZ]

You could replace the parts by reading off the existing as a lot of the schematic is illegible.
That board needs cleaning, it’s a mess- I’d suggest using CRC CO contact cleaner which evaporates totally and leaves no residue - safe on plastics - used with a stiff artists paintbrush you can spray the brush and use it wet to dislodge all the flux and dirt and then flood the board to rinse everything off with the CO - the board will dry in about a minute - you can blow away the excess using a can of compressed air (used for cleaning dust off camera lenses - great for blowing down circuit boards while cleaning). You need to mask off the capsule - wrapped in soft cloth and cling wrap after that. Take out the tube for access and you’re away. Remove excess solder from the dodgy joints, reposition the components you remove neatly (you can use the photo of the inside of someone else’s mic you posted for guidance) and resolder. I’d use leaded solder, as lead free has a habit of developing dry joints and doesn’t tend to tin as well as the lead/tin solder. Using isopropyl alcohol is a bit risky as it leaves a lot of moisture behind and residue marks which can contain the dirt you’re trying to remove which may be conductive. There’s a 1GΩ resistor (R1) which needs to have very clean surrounding areas, as do the other high value resistors, as even the slightest conductivity on the board between the resistor legs will affect that resistance value.
These are photos of the boards in an AKG C12 I’ve worked on - it had problems with the Zener diodes in the divide network for the capsule and the centre voltage as a result was out as well as the top voltage on the high side of the pattern switch. This mic sounded bad in cardioid and worse in figure 8 - Omni was fine as both diaphragms were at ground potential.
The only product on the boards is the original cover lacquer and anti-vibration goop for caps.

 

[Adam Frandsen]

I measured the two resistors and they were 74.6kohm, so two 150kohm in parallel. I managed to get it desoldered well, and also bought some pcb cleaner spray with a brush attachment, it must be super toxic, because it cleaned it up completely. Now resistor R7 measures 9.1kohm, and I think it should be 8.1kohm according to the schematic…

should I just replace it with a 8.1kohm?

 

[Adam Frandsen]

R6, R9 and R10 are all the same type in my mic, but they measure R9 1.1kohm, R10 and R6 .268megaohm… R8 i cannot successfully measure, and I cannot see/find it on the schematic… neither can i measure r3 and r4. My meter goes up to 20 megaohm, if someone can read the schematic and write me the resistor values, it would be greatly appreciated!

 

[Adam Frandsen]

is it like this:

r3, r8 51 megaohm

r4 3.9 k?

r1 1gigaohm

r2 200m

r5 300k

r6 270k?

r7 8.1k?

r9 1megaohm?

r10 1megaohm?

 

[Khron]

R3, R8 - yes
R4 - looks like it, and makes sense, given the higher-than-usual B+
R1 - yes
R2 - yes
R5 - yes
R6 - yes (although i dare you to tell the difference by ear if you used either 270k or 300k for both R5 and R6, so you don't need to order two different values)
R7 - 9.1k is actually an E24 value; but it's not all that critical, since it's only handling some B+ filtering duties - even 10k should be just fine
R9 & R10 - yes

 

[Adam Frandsen]

R3, R8 - yes
R4 - looks like it, and makes sense, given the higher-than-usual B+
R1 - yes
R2 - yes
R5 - yes
R6 - yes (although i dare you to tell the difference by ear if you used either 270k or 300k for both R5 and R6, so you don't need to order two different values)
R7 - 9.1k is actually an E24 value; but it's not all that critical, since it's only handling some B+ filtering duties - even 10k should be just fine
R9 & R10 - yes

Awesome - so I just leave the 9.1k in there, I really don’t mind putting a 8.1k there. The local HiFi dealer had the Cardas Quad Eutectic, and it is very easy to use.

 

[Khron]

Given the uber-low resolution of that schematic, we can be quite certain it's supposed to be 9.1k; you probably can't even find 8.1k resistors anywhere; closest standard value is 8.16k (E192 series); 8.2k is an E6 value though.

The "debate" about this is purely academic though - as i mentioned, the exact value is NOT essential at all, in that position / role in the circuit.