What's the Best Way to Reduce Gain in a Preamp

[rcollege]

Hi all,

This forum is so helpful...Thank you all!

Here's another question I hope will help me and others.

I have too much gain in a preamp. I'm using 6J5gt's or 6C5gt's in a simple SE circuit.

What is the best way to reduce gain?

I am using a 50k linear pot along with 7.5k resistor after the pot.
I am using a load resistance of 12.5k

Lower load resistor value?
Use cathode resistor and bypass cap?
Higher pot value?
Increase input resistance?
Find lower Mu Tubes? Triode connected pentodes? I have EL34's, 6V6's and 6DJ6's.

Any comments are welcome.
Thanks

 

[funk1980]

There are tons of ways to lower the gain, but a schematic would help to determine which would best suite you preamp.

 

[KatieandDad]

Do you actually need any amplification at all ?

 

[tomchr]

Without a schematic, it's nearly impossible to give advice for your specific circuit. I'm guessing the better options will be to use a tube with a lower mu or use an un-bypassed cathode resistor. But without a schematic, we're shooting in the dark here...

Messing with the volume pot will have little to no effect.

~Tom

 

[Andyroid]

If you just want to throw away some gain without affecting tone then I suggest splitting a plate load resistor in two, making a voltage divider. Done early in the amp it may give 'more headroom' but worse s/n ratio. Without a schematic...

 

[rcollege]

Thank you all,

I completely understand about the need to see the schematic.
I quickly drew it up.

Thanks again

 

[Ketje]

Wrong way 😱
Try it like this 🙂
Mona

 

[aardvarkash10]

you need to define what the source voltage is, and what the required drive to the amp is. Without that, everyone is giving well-intentioned best guesses.

I suspect that a simple cathode follower is what you need. But without the info above, I'm guessing too.

 

[jerluwoo]

Ketje has it right on the volume pot being wrong. I notice you are basically trying to use it at the generic operating point from the datasheets, plate voltage 90V, grid 0V, 10mA plate current. What they don't mention is that this is with a B+ voltage in excess of 300V, so the load resistor can be a sizable value. If you want to add distortion for that "tube" sound, this setup is fine.

 

[stocktrader200]

place a 150k in series with a 15k to ground. Take the output across the 15k

 

[rcollege]

Thank you all... and thank you for the corrections.
Jerluwoo...are you saying that the schematic you drew will add distortion?

I am trying to avoid having feedback from the cathode resistor...and avoid the need for a bypass Capacitor.
Also...will a higher B+ and load resistor allow for less distortion?

The impedance of the SS amp I'm currently using is 30k... the input for the ST-35 power amp this will be driving is 500k.

 

[rcollege]

I replaced the 6J5 with a triode connected 1Q5 ( DH Tetrode) just for fun.
I used the same dc power supply but dropped the voltage to 1.3v with 1n4007 diodes.
I did this just to try them out.

They have a definite edge over the 6C5 and 6J5's.
Now if I can just get the 1Q5's to stop ringing! It sounds like a haunted house with them.
They put out a clean, natural sound though!

 

[aardvarkash10]

so if you are using this pre to drive a ST-35, you don't need gain (assuming you are using a CD or similar as a source)

In fact, all you need is a selector and a volume control. But if you feel the need to include a tube, build a cathode follower.

 

[teemuk]

..if you feel the need to include a tube, build a cathode follower.

Or just wire the filaments of the tube only. Red LEDs positioned to look like even brighter glowing filaments can further enhance the tube LOOK. 🙄

 

[rcollege]

Blue Ray 200mV output

so if you are using this pre to drive a ST-35, you don't need gain (assuming you are using a CD or similar as a source)

In fact, all you need is a selector and a volume control. But if you feel the need to include a tube, build a cathode follower.

My sources are the following
- Pioneer Blue Ray player that puts out 200mV rms.


- Turntable that I will DIY a phono preamp with equalization...so I can choose the desired gain.

So a little gain - 5x will allow the ST-35 to reach the full 17.5W.... If I ever need it.

 

[WBCHUM]

Hi I would request adv also

Hi I also wish to reduce the gain of my DIY preamp. I attached schematic & will appreciate any instruction. I m not very knowledgeable in audio electronics so easy instruction would be appreciated.

 

[JMFahey]

Suggest you open a new thread, this one has been dead for 7 years.

 

[rayma]

Hi I also wish to reduce the gain of my DIY preamp.

Not easy, what is your reason? Do you need more than unity gain?

 

[WBCHUM]

it's because it's too loud, I m using a 100K volume, just 2 steps from the beginning already v loud . is the 100K volume not well match. Thanks for help adv.

 

[TonyTecson]

Hi I also wish to reduce the gain of my DIY preamp. I attached schematic & will appreciate any instruction. I m not very knowledgeable in audio electronics so easy instruction would be appreciated.

one quick way, reduce the 22k feedback resistor to say 10k...

another way is to replace that 22k to a series combination of 2.2k and 20k pot so you can adjust the gain to suit your taste..