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Build help and troubleshooting => MP566 Tube microphone preamplifier => Topic started by: Kev4272 on February 25, 2021, 08:30:23 AM

Title: No Mic Input And Saturation on DI
Post by: Kev4272 on February 25, 2021, 08:30:23 AM

Hi! I just finished a MP566, but I don't have any Mic Input. The signal on the DI seems to work but there's a lot of saturation on it, its almost distortion. I checked the click on the gain switch and I have a click between the Low and the Mid but nothing for the High. I also have no click when I insert a jack in the DI. 

Thanks!

Title: Re: No Mic Input And Saturation on DI
Post by: JPK on February 25, 2021, 06:31:09 PM

The No Mic issue may come from a damaged 2N7000 (Q1). This component is sensitive to static electricity and is better handled without your shoes on (body grounded).
You can check this by creating a short between the 2 extreme pins of this component. It should activate the mic relay.

Quote

I have a click between the Low and the Mid but nothing for the High

This is normal, the high gain is directly controlled by the switch, without a relay.

Do you have a gain variation between the mid and high gain?
Check the DC voltage on TP4. it should be close to 0.

Title: Re: No Mic Input And Saturation on DI
Post by: Kev4272 on February 28, 2021, 04:37:18 AM

Quote from: JPK on February 25, 2021, 06:31:09 PM

You can check this by creating a short between the 2 extreme pins of this component.

By the two extreme pins of the component, do you mean the 0V and the V+ ?

Quote from: JPK on February 25, 2021, 06:31:09 PM

Do you have a gain variation between the mid and high gain?
Check the DC voltage on TP4. it should be close to 0.

I have a big difference of dB between the three of them. The Low gain is the loudest and the Hi Gain the least loud. But I don't really hear a lot of difference in terms of saturation between the three of them.

Do I have to put the black probe on the 0V and the red probe on the TP4? If yes, I am getting 0V

Title: Re: No Mic Input And Saturation on DI
Post by: JPK on March 01, 2021, 05:08:59 PM

Quote

By the two extreme pins of the component, do you mean the 0V and the V+ ?

NOOOO!

Q1 is a component with 3 pins in a row. I mean between the 2 pins which are not the center pin.

Quote

Do I have to put the black probe on the 0V and the red probe on the TP4? If yes, I am getting 0V

Correct. This is OK.

Title: Re: No Mic Input And Saturation on DI
Post by: Kev4272 on March 03, 2021, 07:30:13 AM

Quote from: JPK on March 01, 2021, 05:08:59 PM

Q1 is a component with 3 pins in a row. I mean between the 2 pins which are not the center pin.

Alright! So I did it, but I don't hear the mic relay clicking. Does that mean that the Q1 is damaged?

Title: Re: No Mic Input And Saturation on DI
Post by: JPK on March 03, 2021, 11:11:24 AM

No, it means the issue is in the relay or R26 or D2.
If R26 and D2 are OK, try replacing the relay. Send me an email here (https://www.soundskulptor.com/en/content/6-contact) for a replacement part.