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Old 13th February 2013, 08:23 PM   #21
mouzer is offline mouzer  United Kingdom
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I'm completely new to the concept of bi-amping, so I was considering getting a couple of T-amps to play with (something like the Topping TP30); I have a couple of questions:

1. Do you need something like a B1 preamp sitting between the source and the two tripath amps to act as a unified volume-control?

2. If using a separate preamp (as per Q1) is it advisable to bypass/remove the volume control (or the entire integrated preamp) in the T-amps? Is that even possible?

This would be using split passive-crossovers in my speakers, not active crossovers.
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Old 9th March 2013, 07:13 PM   #22
xrk971 is offline xrk971  United States
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I tried bi-amping an OB by using the line output rca from my cd player for one set of drivers (sub woofers) and the variable headphone outs with 1/4 in to twin rca adapter as my full range input. In my case, I was using the amps as separate sub amps and separate full range amps. I used the fact that the sub woofers were 4th order bandpass which limits their output freq response and drove everything crossoverless. The headphone output allowed easy level adjustment for my amp which dis not have volume control. It worked well.
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Old 26th March 2013, 05:55 PM   #23
Davet is offline Davet  United States
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Default Bi-Amp Quandry

I had been running my system in a (passive) bi-amp mode for some time using a Tripath 2020 for the subs and a 2024 for the mids and highs. I was using y-cables to split the signal out of my pre-amp to provide a signal to each of the amps. I had a problem with the 2024 and I had to take it out of the system for a while until I made the repair. I was enjoying the single 2020 amp.

When I re-installed the second amp using the Y-cable, I noticed noticed there was a considerable drop in the overall volume level. I considered there may have been an impedence mismatch so I bypassed the pre-amp using the Y-cable from the CD player source. I got the same result - low volume. I anticipated I would have greater clarity and a little more volume, but it seems the reduction in volume is so great I can't discern any difference in clarity.

I have a second pre-amp which I could use to drive each amp. However, I would still need to use the Y-cable to split the signal.

I also have an active crossover I could use, but I would have to reset the crossover points for my current speaker system.

Currently, I have the variable resistors for each amp. I think they are 50K units, but they are turned all the way up. Do I need to adjust the resistance for each amp?

Am I missing something? Is this overall drop in volume to be expected?

Please, help!
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Old 28th March 2013, 12:22 PM   #24
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Interesting subject! I also plan on doing that on my own system, using a minidsp module for crossover.

I am a crosstalk hater, so I even want to use tri or quad mono, if possible. I do understand the necessity to keep both coupling capacitors, however could only one be modded?

Davet, I think a secondary preamp will make things better, as Y cables halves the tension, that is probably causing it. Since you already got one, try using your reserve, splinting right after the source.

Also, good job on that coupling cap thread a while go!
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Old 28th March 2013, 02:00 PM   #25
xrk971 is offline xrk971  United States
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Davet,
I think the problem with using a Y-splitter is that you are dividing the power of the source between two amps. Assuming each amp's input is (say) 50 kOhm then you are running 2 x 50 kOhm loads in parallel or equivalent to driving a 25 kOhm load and voltage appearing at inputs to amps drops by -3 dB. What you need is a unity gain preamp with two buffered signal outputs (you can build this with a good quad op-amp chip like the LME49740 http://www.ti.com/lit/ds/symlink/lme49740.pdf). You can also leave as is and increase gain on each power amp by +3 dB (but that adds noise floor to amp). Use the "Pan-Pot" circuit in Fig 36 and this gives you ability to balance gain between the two splits.

Last edited by xrk971; 28th March 2013 at 02:30 PM.
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Old 29th March 2013, 12:46 AM   #26
Davet is offline Davet  United States
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I will try the second pre-amp, first. Depending on how the pre-amp goes I may try the active crossover as well. The active crossover just requires a lot of work; its not just plug and play. I will report back how these setups go.

The LME49740 pan-pot circuit appeals to me. I have some quad op-amps and resistors on hand. So, breadboarding a pan-pot proof of concept can be accomplished rather quickly.

Ultimately, I had wanted to do a tri-amp, but one step at a time.

Thank you, xrk971 and ramp3 for your ideas, and for the compliment regarding the coupling cap thread.
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