Dyna/VTA 70 as Single Channel Monoblocks in a Horizontal Bi-amping Configuration

My Dyna 70 with the VTA mods went into service in 2020, and have been really happy with them.  I started with the first amp as a traditional stereo amp while I built the 2nd one.  Then used both amps in a vertical bi-amp configuration, along with an active subwoofer.  Spectacular soundstage, great clarity, and overall a really nice situation.  However...nothing is perfect....

My speakers have an 8" Focal kevlar woofer in a transmission line, and a 5" Focal kevlar midbass driver mated to a Seas tweeter.  They were originally in a much smaller space, and have always had nice natural sounding bass.  The move to a considerably larger room left the 8" woofers sounding a bit smaller in that space. Adding an active subwoofer helped give more deep bass, but didn't help the mid and upper bass. Turning the variable low-pass crossover of the sub to a higher frequency just made it sound muddy in the vocals and midbass, so I tend to keep it set right at 50hz and let it augment whatever bass I had.

The speakers have a separate input for each driver, which is conducive to bi-wiring, bi-amping, or tri-amping.  In an effort to boost the output of the 8" Focal woofers in the T-line of the main speakers, I just recently added an integrated Kenwood amp plus an active low pass crossover to drive just the 8" woofers, and bypassed the stock passive low pass filter, running them from 80hz down.  Then hooked up the powered sub at ~ 50hz down from the integrated amp as well.  This essentially makes it a horizontal bi-amp configuration with mono blocks up top (monoblocks are inherently a vertical bi-amp configuration). So "hybrid" bi-amping if you will.

This setup gives a separate volume knob for both the woofer and the sub from 80hz down, plus variable gain control of sub at 50hz, plus the option of contouring the bass output at ~ 100 hz with the bass knob of the Kenwood... all fed by the master volume of my Lazarus tube preamp.  I'm loving all the options and flexibility it gives me to dial in the low bass, mid bass, and upper bass without muddying up male vocals.  It also changed the load that the Dyna/VTA 70s to 8 ohms, and they sound cleaner from the lower mids on up, which was unexpected, but always welcome.  

Adding a solid state integrated amp to the bass is a great way to add bi-amping to a system if your speakers have dual (or triple) inputs.  Your results will vary depending on your speakers, crossover frequencies, system, etc. The addition of the old Kenwood and an automotive active crossover (with a 12v wall wart) has been one of the best $100 improvements I've done in 40 years of messing with this stuff.  But, never being one to leave things alone, I tried some Tung Sol 7581A output tubes while I was at it, and have been really enjoying those. Last, and probably least, was the addition of some solid copper input jacks for the mids and tweeters. All in all...it's time to sit back and enjoy the fruits of my labor for a while.

Nice looking system! Sound should also be very nice. One comment to make regarding V,ertical vs. Horizontal bi-amping as I went through the same configuration challenges. Be aware that vertical bi-amping is much more stress on the amps in that both channels are being required to produce the same information at the same levels all the time. This could be taxing on the power supply. I Horizontal bi-amping the two channels of each amp would be working in the normal mode of reproducing the right and left channel in each of the amps... so unless the source is mono the two channels would not be producing the same information at the same levels all the time (thus the benefits of stereo) and the stress on the power supply would be less as the power level requirements of each channel would be constantly changing. A small difference to be sure, but the difference and advantage may slightly outweigh the slight amount of improved channel separation provided by the Vertical configuration.

Hope this makes sense to you. Either way, it should sound excellent!

Enjoy the music!

I have a question about biasing a tube amp - such as the Dynaco. Given that the bias will fluctuate with an audio signal going through it due to changes in incoming voltage and changes in the perceived load presented by the speakers, I have two questions:

1. Is it better to bias while connected to speakers or by placing a suitable resistor across the speaker posts of the amp?

2. What size / value (ohms / watts) should that resistor be?

Thanks in advance.

Do not bias the amplifier with an input signal present, turn the preamplifier volume control off.
Bias with speakers or load resistors connected. The wattage of your load resistors should be 35 watts or higher. But you can use lower wattage resistors if you know there are no issues with the amplifier. Issues that would cause an output when there is no input.

Nice looking cabinet.

Was wondering... How do you like the Topping E-30? Pros and Cons?

By the way in regards to your bass response and subs.... I can offer some suggestions. First of all get two subs if you have the room for them. Second try a GOOD 31 or 33 band dual channel equalizer with a source of matching test tones (warble tones preferrable). You can down load test tones in flac format and burn them to a CD. I use a pair of Technics SH-8065 eq's with an SH-8000 tone generator and calibrated mic and meter (these show up on ebay from time to time.

The reason your hi-brow audiophiles poo-poo eq's is that they have never heard one set up right. They are also the same people that never use tone controls because they think their rooms and electronics have as flat a response at the anachoic chambers where their speakers were tested... yeah right. So they have NEVER heard their system with the potential it could have.

Once properly setup, it is like someone took a veil off the front of your speakers and you just had your ears surgically cleaned. The audio difference is nothing short of AMAZING! More detail and definition whi..ch leads to better staging and depth. Try it you will like it. It will simply sound better. Also check out an AudioSource Richter Scale if you can find one...It will do wonders for your subs and smoothing out the bass response - has all the features you need to dial in your subs. Remenber, you should NOT be able to tell that you have separate subs running...until you turn them off. If you hear the subs, they are not properly setup.

As an alternative to the Technics eq's I have a couple of friends that are using the Rockville REQ231 (this will draw some negative feedback). It may take you one or two tries to get a perfect one but when you do, they work great and have a very nice feel to the sliders. Don't bother with the other controls or the subwoofer output. They come with DIN balanced connectors but you can get adapters or it is very simple to rewire and replace the balanced jacks with unbalanced RCA's. Just Google it, they are available at multiple sources for $135.00. Best bang for the buck you will ever spend! Like I said, they are not the same as the Technics but just buy it from someone that has a good return policy cause it might take two or three tries to get a really quiet one. It's worth the effort.

Hope this helps you out.

Enjoy the music.

Sorry for the delay...just got back from vacation.

The Topping made an audible difference right from the start. I wasn't sure I'd hear a difference between the stock Denon DAC, but I'd consider it a nice $130 upgrade to the CD side of things in this system. The remote with volume is a great addition to an old school system, and doesn't seem to detract SQ. In fairness, I haven't played with any other outboard DACs, but I consider my system to be fairly well resolved, and the Topping sounds pretty good in it. Perhaps someday I'll get the chance to try a better unit, but I really have no complaints for the money spent. I've had no issues.

I do have two subs, but only hook up the 2nd one when my interior decorator visits her sisters for a few days! Two is definitely better than one when dialed in, but we do what we gotta do!

Between the addition of the Kenwood integrated's volume and bass control features, the active crossover's gain and frequency options, and the sub's low pass and gain features, I have quite a few options to tailor the bass. Since posting the system diagram, I've lowered the active crossover to 80hz. Soon, I'll bypass the passive inductor completely. Someday I might look into DSP or other options, but considering the lost cost and the result, I'm currently pretty happy. (My son actually has a Rockville preamp that's not too shabby, so I'm not one to judge without hands-on experience).