GAIN Mic Pre / Makeup Amp Kit

[JOETONE]

I little messy on this test unit from larger parts I had in stock, but I checked every connection, I must one missing something.

Thanks for the help, I get one right, I can do the other 5...

[JOETONE]

RLOAD is 600Ω, what the EQ wants to see.

[Joe Malone]

I would ohm test the tracks back to the 470uF to one end of RGain and the other end of RGain to GAIN terminal. Encase a pad has been broken off a track.

As the soldering is a bit messy to see I would clean the pcb with alcohol and a toothbrush as well.

[JOETONE]

Ok! So I bought multiple GAIN PCB, so I did up another from scratch and works correctly.
Thanks for your help with my 1st DIY.

***One question regarding connecting power to (2) units.

Series or parallel from your: 48v 25w 520mA Switch Mode Power Supply. ??

Thanks!

Joe

[Joe Malone]

Ok! So I bought multiple GAIN PCB, so I did up another from scratch and works correctly.
Thanks for your help with my 1st DIY.

***One question regarding connecting power to (2) units.

Series or parallel from your: 48v 25w 520mA Switch Mode Power Supply. ??

Thanks!

Joe

You can only run multiple gains on 48v smps in parallel

[JOETONE]

Hi Joe,

I'm planning on feeding (2) GAIN kits from (2) Jensen JT-16-A for MIC pre input.
https://www.jensen-transformers.com/wp- ... -16-a1.pdf

Can you tell me what to fit for CZ,RZ,RLoad,CLoad?

Thanks,

Joe

[Joe Malone]

Hi Joe,

I'm planning on feeding (2) GAIN kits from (2) Jensen JT-16-A for MIC pre input.
https://www.jensen-transformers.com/wp- ... -16-a1.pdf

Can you tell me what to fit for CZ,RZ,RLoad,CLoad?

Thanks,

Joe

From the datasheet you linked to
Rload is 6k19 = 6.2k
Cload is not needed (leave blank)
RZobel is 4k53 =4.53k
CZobel is 620pF

[JOETONE]

Joe sorry to bother you again.

Jensen here in the US has no supply, backordered for long time on the JT-16-A.

Could you let me know same info, RLoad, RZobel, CZobel for this model recommended substitute.
https://www.jensen-transformers.com/wp- ... 15K-e1.pdf

Thanks,

Joe

[Joe Malone]

Joe sorry to bother you again.

Jensen here in the US has no supply, backordered for long time on the JT-16-A.

Could you let me know same info, RLoad, RZobel, CZobel for this model recommended substitute.
https://www.jensen-transformers.com/wp- ... 15K-e1.pdf

Thanks,

Joe

JT-115k only needs Rload of 150k. No RZobel or CZobel or Cload are needed so are left blank.

[JOETONE]

THANK YOU - you have been incredibly helpful. Much appreciated.

[JOETONE]

Thanks for your help!

Finished up this rack of 2 Fairchild EQ's with your gain PCB's for make up gain, sound great., kinda like a LANG.

[Joe Malone]

Thanks for your help!

Finished up this rack of 2 Fairchild EQ's with your gain PCB's for make up gain, sound great., kinda like a LANG.

Cool neat build. Great to hear you got it all working

[MarkFRS]

Hi Joe,
i've been working on this one for a while (my 1st email to you was in Jan 24.) There has been a recent steep learning curve with regards to Miller effect, particularly around the gain control pot between the 2 valve stages. Coming to the output stage now where the Gain Mic Pre is buffering into the Line output transformer, I"m getting a variable rolloff of the high end around 4dB @ 30kHz, but his is impacted by the position of the output control that feeds the input to the Gain Mic Pre. With this control down low, the roll off is about 1.3dB @ 30kHz. I have Rload at 1M, but get similar results with it at 100k.
Is there a way to minimise this rolloff, and to keep it consistent throughout the range of the output pot?
Should I be running the Output control after the Gain Mic Pre board?
The rolloff starts at around 10kHz, so is quite gently, but I'm hoping to keep it fairly flat when the "tone controls" are centred, or bypassed.

Thanks for anything you could suggest.

[Joe Malone]

Hi Joe,
i've been working on this one for a while (my 1st email to you was in Jan 24.) There has been a recent steep learning curve with regards to Miller effect, particularly around the gain control pot between the 2 valve stages. Coming to the output stage now where the Gain Mic Pre is buffering into the Line output transformer, I"m getting a variable rolloff of the high end around 4dB @ 30kHz, but his is impacted by the position of the output control that feeds the input to the Gain Mic Pre. With this control down low, the roll off is about 1.3dB @ 30kHz. I have Rload at 1M, but get similar results with it at 100k.
Is there a way to minimise this rolloff, and to keep it consistent throughout the range of the output pot?
Should I be running the Output control after the Gain Mic Pre board?
The rolloff starts at around 10kHz, so is quite gently, but I'm hoping to keep it fairly flat when the "tone controls" are centred, or bypassed.

Thanks for anything you could suggest.

OK if the 48v supply 0v is linked to the 0v of the tube hv then you cannot bypass the cdc as shown in the schematic and you cannot wire the -in to 0v as it should be shorting out the 24v referencing for the opamps on the GAIN. You should have no Rzobel or CZobel or Cload as they will roll off the high freq. I would think the roll off is caused partly by the change from 1M to under 100k on the output tube as the output is turned up. As tubes are more resistive the high the output frequency under heavy load. Also the 99v internal input capacitance on the input transistor will load high freq partly as well.