1

MP566 Tube microphone preamplifier / Re: MP566 not working

« on: April 04, 2024, 07:38:18 AM »

Seems like a good idea.
Where can I send it?

2

MP566 Tube microphone preamplifier / Re: MP566 not working

« on: April 02, 2024, 04:45:05 PM »

New testing sessions, new results:

U4 Pin 4 with U4 inserted: -14,91V
U4 Pin 4 with U4 removed: -15,05V

Between U4 Pin 4 and V- > 0V

Voltage on V+ 14,99V
Voltage on V- 14,91V

But meanwhile C23 is not looking healthy anymore:

3

MP566 Tube microphone preamplifier / Re: MP566 not working

« on: March 25, 2024, 03:58:06 PM »

I removed U4 and measured again:

1 > -14,9V
2 > 13,9V
3 > -15,04V
4 > -15,05V
5 > -5,393V
6 > 13,7V
7 > 13,7V
8 > 0V

4

MP566 Tube microphone preamplifier / Re: MP566 not working

« on: March 23, 2024, 03:31:15 PM »

I have bought a new U6 and a fourth (!!!) U4

(It is getting pretty expensive by now)

The values have changed significantly on Pin 4 and 8. Everything else remains the same.
The tube does not glow.

1 > -14,5V
2 > 12,15V
3 > 11,68V
4 > 2,86V
5 > 6,02V
6 > 12,22
7 > 12,21
8 > 5,66

Will it ever work?

5

MP566 Tube microphone preamplifier / Re: MP566 not working

« on: March 06, 2024, 01:09:50 PM »

I doubt it. I just replaced U4 two days ago.
It's the 3rd one now.

6

MP566 Tube microphone preamplifier / Re: MP566 not working

« on: March 05, 2024, 04:21:02 PM »

I removed U7 --> -14,51V on U4 Pin 1

I removed U6* --> 0,0V on U4 Pin 1

I removed the tube --> 5 MOhms (and falling) between 0V and TP8

*removing U6 was not possible without destroying it.

7

MP566 Tube microphone preamplifier / Re: MP566 not working

« on: March 03, 2024, 01:19:54 PM »

I bought a new 0372

The values have changed a bit, but pin 1 is still negative.
The tube is still not glowing:

1: -14,50 V
2: 12,80 V
3: 12,02 V
4: -15,01 V
5: -5,722 V
6: 12,40 V
7: 12,40 V
8: 2,922 V

8

MP566 Tube microphone preamplifier / Re: MP566 not working

« on: February 18, 2024, 11:38:19 AM »

1 -14,49 V
2  12,78 V
3  12,00 V (1 times sparks, when touching the pin )
4 -15,01 V
5 -5,677 V
6  12,53 V
7  12,55 V
8  2,850 V

9

MP566 Tube microphone preamplifier / Re: MP566 not working

« on: February 12, 2024, 03:38:48 PM »

I confirm:
black Probe on 0V + red probe on U4 pin 1 = -14,49V (negative)

DC voltage measured against pin 8 of U4:
2,851V (slowly rising by +0,001V)

10

MP566 Tube microphone preamplifier / Re: MP566 not working

« on: February 11, 2024, 01:28:36 PM »

black Probe on 0V + red probe on U4 pin 1 = -14,49V
red probe on 0V + black Probe on U4 pin 1 = 14,5 V

U6 - orientation ok, solder joint ok
U7 - orientation ok, solder joint ok
R51 = 7,6 Ohms, solder joint ok
C26 = 10uF - 63V, solder joint ok
C28 = 100uF - 25V, solder joint ok

I resoldered all the joints.
The tube is still not glowing.

11

MP566 Tube microphone preamplifier / Re: MP566 not working

« on: February 05, 2024, 04:17:04 PM »

No the tube does not glow at all.

12

MP566 Tube microphone preamplifier / Re: MP566 not working

« on: January 28, 2024, 11:41:11 AM »

I finally got the time, to resolder and do the tests again.

The signal is now coming through louder
- Pot IN and Pot OUT turned to max
- input level on my apollo is turned to max (65dB)
- Signal is louder but only in position mid gain (solid level up to 0dB)
- but Signal is very very noisy.

Test 4 (low voltage check) -> -15V

Test 5 (signal check)

Code: [Select]

    |          Line In         |/|           DI In          |
    |   Lo   |   Mid  |   Hi   |/|   Lo   |   Mid  |   Hi   |
----|--------|--------|--------|/|--------|--------|--------|
TP1 | 0,271V | 3,043V | 3,043V |/| 0,496V | 0,496V | 0,496V |
TP3 | 0,000V | 0,006V | 0,000V |/| 0,000V | 0,000V | 0,000V |
TP4 | 0,001V | 0,019V | 0,001V |/| 0,002V | 0,002V | 0,000V |
What else should I try?

13

MP566 Tube microphone preamplifier / Re: MP566 not working

« on: January 09, 2024, 04:10:13 PM »

I checked all the connections. Solder joints look okay to me, only T1 looks a bit strange.

I remember having trouble soldering the 90° connectors of the tube PCB (A) to the Main PCB. The solder just didnt stick correctly.

Please find attached pictures of the joints.

Should I resolder?


RLY1


T1


P1


Tube socket


PCB Connector


P2

14

MP566 Tube microphone preamplifier / Re: MP566 not working

« on: January 08, 2024, 03:36:09 PM »

Thank you for clarifying.
I remeasured: black probe to oV - red probe to TP1, TP3, TP4.

Code: [Select]

    | Line-in |  DI in
-----------------------
TP1 |  0,0V   | 0,496V
TP3 |  0,0V   | 0,0V
TP4 |  0,0V   | 0,0V
Same results for Gain Switch lo, mid and hi
Potentiometers did not affect the measurement

I got 0,496V on pin 8 and 10 of the extender - my multimeter showed 1,044kHz - so the input should be right.

15

MP566 Tube microphone preamplifier / Re: MP566 not working

« on: January 01, 2024, 03:05:31 PM »

I re-checked:

Audio-Check:
POT in & POT out set to 10
Apollo Twin set to 65 dB input (fully turned up) - Noise is at 46dB constant

Code: [Select]

Line-in:     |  High-Z in:
Lo:  -27 dB  |  Lo:  -18 dB
Mid:  -5 dB  |  Mid: -18 dB
Hi:  -25 dB  |  Hi:  -36 dB

Then I followed the signal. I sent the 1000Hz sine to the line-in, measuring 0,5V between 8 and 10 of the extender

Code: [Select]

    | black probe | red probe
------------------------------
TP1 |  0,142 V    |  0,207 V
TP3 |  0,137 V    |  0,217 V
TP4 |  0,164 V    |  0,227 V

16

MP566 Tube microphone preamplifier / Re: MP566 not working

« on: December 29, 2023, 01:31:28 PM »

Thank you - I replaced the tube, now audio is coming through. But very very quiet.

The sound is not distorted or anything, but very quiet.

Here is what I did:

I set the Input Level on my apollo twin to 3/4 (that is 52dB)
I set the MP566 Input to 10 and output to 10

With the Gain Switch to low: I receive 46dB of level
With the Gain Switch to mid I receive 20dB of level
With the Gain Switch to hi: I receive 36dB of level (yes, acutally quieter than with mid)

Still seems something to be wrong. What else could I do?

17

MP566 Tube microphone preamplifier / Re: MP566 not working

« on: December 15, 2023, 01:49:21 PM »

You are right. I was off by one pin.

I measured again with the tube disconnected: 127,5 Ohms.

Do I need a new tube?

18

MP566 Tube microphone preamplifier / Re: MP566 not working

« on: December 15, 2023, 09:14:14 AM »

I measure:

between TP8 and V- => 12,3 ohm - Sometimes wildly jumping up to 15 to 20 Ohms

between pin 4 and 5 of the Tube (bottom view): 16 ohms and rising

between pin 5 & 6 (bottom view): 12,2 Ohms

19

MP566 Tube microphone preamplifier / Re: MP566 not working

« on: December 14, 2023, 04:07:16 PM »

Thanks for your help.

I replaced both ICs - but nothing changed. It still does not work.

Test 1 (Short circuit test) -> 2,72 MOhms

Test 2 (High Voltage Test) -> 223,8V

Test 3 (Low Voltage Test) -> -0,04 and rising to 0

Test 4 (Signal Check) -> LED stays off all the time. I measure 0,003 VAC with in and out turned on to max.

What could it be?

20

MP566 Tube microphone preamplifier / Re: MP566 not working

« on: December 11, 2023, 02:46:03 PM »

Thank you. I switched the ICs and now it tests as follows:

Test 2 (High Voltage Test) -> 223,7V

Test 3 (Low Voltage Test) -> 0,0 V

Test 4 (Signal Check) -> LED stays off all the time. I measure 0,003 VAC with in and out turned on to max.

Where else can i look for problems?

21

MP566 Tube microphone preamplifier / Re: MP566 not working

« on: December 08, 2023, 07:25:45 PM »

Thank you. I checked the components you told me:

U4 - direction ok, solder joints ok

D14 - direction ok, solder joints ok

D15 - direction ok, solder joints ok

R47 - 330k - ORG-ORG- BLK- ORG-BRN measures at 105 kOhm

R48,49,50 - 47k - YEL-VIO-BLK-RED-BRN measure at 41kOhm

So there is one difference in R47... is that the problem?

22

MP566 Tube microphone preamplifier / Re: MP566 not working

« on: December 07, 2023, 10:54:40 AM »

Thank you for replying.

I was not able to follow the instructions to "follow the signal" - I am new to this DIY stuff and I simply don't know what to do with the instructions.

Since this is my first build, I might have done something wrong, although I took special care to insert all the components in the right direction.

This is what happenes:
- I turn on the power of my R6, the LED flashes red for about a secont or two then it goes out
- the device emitts a faint smell, so I think some components are heating, the tube is not getting warm and the tube does not light up

Here is, what the test-restults are:

Test 1 (Short circuit test) -> 2,72 MOhms (If I got the test right, since there is no GND test pin on my board)

Test 2 (High Voltage Test) -> 0,03V and decreasing over time to 0

Test 3 (Low Voltage Test) -> -0,02 and rising to 0

Test 4 (Signal Check) -> I read 1,63V between OV and TP4, the LED stays off even if I max out the Output potentiometer

If you know what that means; I would be greatful to get any advice how to find and fix the problem.

23

MP566 Tube microphone preamplifier / Re: MP566 not working

« on: December 06, 2023, 05:38:47 PM »

I have the very same problem as described above.

I also checked Topic: "In case your MP566 doesn't work as expected" - there are no "usual suspect" to be found on my build.

Neither the DI nor the Mic in let any signal through.

What should I do?