Reducing Gain in the BeePre

[Gerry E.]

Hi:

I use high-sensitivity speakers, so I would like to reduce the gain in my BeePre/Paramount system.  As of now, the usable  range on my BeePre volume control, is only 1/4 turn.  After searching the BH forums, my first thought was to convert my Paramounts from the 5670 tube to a 6SN7 which has less gain.

For several reasons, that idea was rejected.  My next idea was to purchase a pair of Harrison Labs attenuators.  However, I have some concerns that they may degrade the sound a bit.  After talking this over with Boulos, who built my BeePre, he came up with another idea.

Convert the unused BeePre XLRs to RCA outputs and add a couple of resistors to the jacks to reduce the gain.  I believe the resistors would act as a voltage divider.  Is there any reason this couldn't/shouldn't be done?  If not, what would be the recommended values for the resistors to reduce the gain by say 12dB?  Of course we are open to any other ideas.  Thanks!

Gerry   

         

         

[Grainger49]

Either at the BeePre output or the input of the Paramounts.  Since the BeePre has a pretty low gain I would put the attenuators in the Paramounts.

[Paul Joppa]

It's always best to put the attenuator at the input of something, in this case the Paramount. I use the Harrison 12dB attenuator on my Paramounts (my speakers are 101dB) with no problems. I'm still using the Foreplay III at the moment.

For more detailed information, you can read my signals and noise notes, available from the "bottlehead/more...community" page.

[Paul Birkeland]

Here are some ideas:

#1 - go to the lowest impedance taps on your Paramounts to see if that's enough of a drop in gain.
#2 - change the balance pot to a 250K linear, change the 33K resistors between the pots to 75K, change the 100K logarithmic level control to a 25K pot. (PJ may want to chime in on this mod - it's his design).
#3 - install the BeeQuiet, there will be plenty of useable steps with the BeeQuiet installed.

-PB

[Doc B.]

Just put the BeeQuiet in.

[boulos]

I think one concern with installing the BeeQuiet is the loss of balance control.

If we go to a lower impedance tap (say one level; I'm not sure what it is right now), assuming it is currently matched with the speakers and not already at 4ohm, won't that double the load to 5-6K resulting in lower distortion?  If that's indeed the case, then it may be a good option to try first.

Boulos

[Paul Joppa]

If you change the ratios of component values then it will no longer be my design, and it will no longer work as I intended it to. Specifically, it won't maintain constant loudness as the balance is shifted.

To maintain as-designed operation with less gain, one could put a 100K L-pad in front of the 100K volume control without changing the rest of the circuit. To get a greater range without losing maximum gain, one could replace the 100K volume control with a 100K stepped volume control.

As I said though, my preference would be to put the L-pad in the Paramount input. If I weren't so busy with other products, I'd modify my own to put a level control at the input.

[Doc B.]

The balance control is in the BeePre because the stock pots don't track perfectly at low volume settings and the balance control can be used to compensate for that. Once you put in the BeeQuiet the potential issue of imbalance at low levels is gone.

[Paul Birkeland]

If we go to a lower impedance tap (say one level; I'm not sure what it is right now), assuming it is currently matched with the speakers and not already at 4ohm, won't that double the load to 5-6K resulting in lower distortion?  If that's indeed the case, then it may be a good option to try first.

Yes, you'll get less power, less distortion, and a bit more damping. 

I agree with Doc B. that the balance control was implemented in order to account for the tracking error at low levels of most common carbon potentiometers.

[boulos]

It sounds like the BeeQuiet will be a good upgrade.  I'll leave that decision up to Gerry

For the L-Pad, would 1.5K + 4.42K resistors work well? (These are available Vishay RN series 0.5W 1% tolerance resistors I could find).

Thanks!

[johnsonad]

Gerry, I still would recommend giving the 6SN7 a try at some point.  You can get the adapters off of EPay for $40 a pair from 6SN7 to 5670.  Nothing to change other than put the adapter on and drop in a 6SN7.  This is how I run mine every day. 

Thank being said, I'm a big fan of the Bee Quiet also.  Try both when you have the time!

[Paul Joppa]

I would keep the L-pad in the Paramount at a high impedance (100K or so) even with the great drive available from the BeePre - it will keep the distortion low.

[boulos]

Got it.  I'll look for ~100K + ~300K resistors.
Thanks Paul!

[Grainger49]

I was about to add a link to VoltSecond's page about attenuators.  The link is dead.

V-S is everything ok?

[Gerry E.]

Thanks Everyone!  I just ordered a BeeQuiet and 6SN7-to-5670 adapters.  Though I'm reluctant to give up the balance control, I know the BQ will sound and track better.

A special thanks to Boulos who is going to build and install the BeeQuiet for me and Aaron for confirming that the 6SN7 is a drop-in replacement for the 5670s in the Paramounts using the adapters.

Gerry