Bi-Amping mismatch amp

Hy everybody.
I will like to bi-amp my Cornscala speaker (8 ohm) and keep the existing passive crossover that I put expensive stuff in.

The two amp that I want to use is a
-ST-120 for the mid and hi (60w)
-Marantz 2325 (120w) for the bass.

My problem, the gain. The pre amp at desirable volume, (50Hz sound track) output 0.125V. which is about the 1/4 on a
Now, the output of the ST-120 is 2.10V
The Marantz show 3.76V

So 2 questions.
1- Can I use a potentiometer on the interconnect between the preamp and the Marantz?
What is a good value to start? 10K 50K ?

2-in-line attenuator or interconnect attenuator are sold by Decibel (dB)
How can I match this ?

Thank's
Denis

I'm doing something rather similar involving a Marantz SS front end feeding VTA tube gear and then using the combo to biamp my Tannoys, with really satisfying results. No attenuation or otherwise applied. So first I would simply try as is, you may be pleasently surprised.

I did and it's way to bassie.

I run the tubes to low taps and set to triode. Do you have this option available with your ST-120?

Yes i do,
I did some research this morning and find some on-line calculators.

A gain calculator give me 24.5dB for the ST-120 and 29.56dB for the Marantz.

I have to attenuate 5dB.

And RCA Phono Lead Attenuator calculator give me this.

in --------4.8k-------------- out
                           |
                         10k
                           |
G ---------------------------- G

For -5dB. I will give this a try.

Thank's LaGrace.

I always thought that bi-amping meant using an active crossover.  There are so many reasons to do this, not the least is that you can level match by turning a dial.  The quickest and cheapest solution would be something like this thing from Rolls.

What would be a much better solution would be the DDRC-24 with a measurement microphone from minidsp.  You can measure your system, in your room, and then create a digital filter to adjust the system response for your room.

I recently tried something like this.
I have Cornwall IV speakers.
For the mid/highI used a pair of nice 300B mono blocks. (Class A, 8 wpc)
For the bass I used an NAD C298 which has an adjustable gain control. (Class D, about 200 wpc)

At first I thought it sounded great but after several weeks I noticed some things just didn't sound right. This was usually on recording I was very familiar with (listening to them for over 40 years). No matter how I adjusted the gain on the NAD some recording sounded improperly mixed.
For example, on Guitars In The Sky by the Records, there is a nice backwards guitar lick on the chorus. I could never get that to sound right, no matter how it was adjusted.

I came to the conclusion that in this case the internet was right and the correct (only) way to do this is with an external crossover bypassing the one in the speaker.

For me it was soooo much easier just to go back to driving the Cornwalls with the 300Bs and swapping over to the NAD when I wanted a different listening experience.

rustybutt wrote:I always thought that bi-amping meant using an active crossover.  There are so many reasons to do this, not the least is that you can level match by turning a dial.  The quickest and cheapest solution would be something like this thing from Rolls.

....

Biamping can be active, passive, or hybrid combination of both....biamping simply means splitting the amplifier duties between two amplifiers.  In addition, there's also vertical and horizontal configurations to choose between, depending on whether the amps are identical or not.  Typically two identical amps are used for vertical biamping (one amp on each side).  With that said, there are pros and cons to each approach.  

You've highlighted a benefit of using an active crossover for the ability to vary the output level.  In the OPs case, it's a solid option to bypass the passive woofer crossover, and use an active low pass in it's place.  Fairly simple, and doesn't have to be expensive.  You can even add a 12V wall wart and use an inexpensive automotive active crossover for such an application, and get really good results.

Vertical vs Hortizontal Biamping:



My hybrid biamp setup: