Splitting off from one of the two outputs

0 Members and 1 Guest are viewing this topic. Read 711 times.

SCM

Splitting off from one of the two outputs
« on: 20 Apr 2018, 11:33 pm »
I have only two outputs, one goes to a tube amp the other goes to a subwoofer amp.

I want to add another amp to power the low bass section of my bi-amp-able speakers and leave the tube amp for the mids and top.

What do I need to consider when shopping for an amp to do the job ?
« Last Edit: 21 Apr 2018, 02:30 pm by SCM »

SCM

Re: Splitting off from one of the two outputs
« Reply #1 on: 21 Apr 2018, 02:33 pm »
What do I need as far as impedance`s and all that ?
I have the Tortuga set at the 99K setting right now.

tortugaranger

  • Facilitator
  • Posts: 1291
  • Handcrafted high performance audio gear
    • Tortuga Audio
Re: Splitting off from one of the two outputs
« Reply #2 on: 23 Apr 2018, 01:42 pm »
What do I need as far as impedance`s and all that ?
I have the Tortuga set at the 99K setting right now.


Numerous Tortuga users drive both main and sub amps from the dual outputs. When you connect a second amp to a resistive passive preamp the impedance of the 2 amps present as 2 impedances in parallel. So let's say each amp has a 50k input impedance. The resulting effective input impedance becomes 50*50/(50+50)= 25k. These are now also in parallel with the preamp. With the pre set at 99k, you get an effective impedance (as seen by the source) of 99*25/(99+25) = ~ 20k. As long as the output impedance of your source is 1k or less you should be ok. Lower is better of course. And the final determinant is always how robust is the output stage of your source regardless of its output impedance. A robust output stage (strong ability to deliver ample current regardless of signal voltage or frequency) will be less impacted by a lower impedance load.

SCM

Re: Splitting off from one of the two outputs
« Reply #3 on: 23 Apr 2018, 08:45 pm »
 Thanks for the reply Morten that should help me.

I`ll be running at least 3 amps off the Tortuga and 4 if I decide to run a set of mono blocks.

Is the 4 amp setup feasible ?

I don`t think my source has much of a power supply at all. It`s a tubed Herron VTPH 1-MC phono stage, the VTPH2 has a toroidal  transformer but  mine has a very small finned whatever in there.

tortugaranger

  • Facilitator
  • Posts: 1291
  • Handcrafted high performance audio gear
    • Tortuga Audio
Re: Splitting off from one of the two outputs
« Reply #4 on: 23 Apr 2018, 10:46 pm »
Thanks for the reply Morten that should help me.

I`ll be running at least 3 amps off the Tortuga and 4 if I decide to run a set of mono blocks.

Is the 4 amp setup feasible ?

I don`t think my source has much of a power supply at all. It`s a tubed Herron VTPH 1-MC phono stage, the VTPH2 has a toroidal  transformer but  mine has a very small finned whatever in there.


Running 2 amps (main & sub) is pushing it but quite doable. I would be concerned with 3 or 4 since the combined parallel impedance will drop quite low. Adding a buffer would mitigate this.

SCM

Re: Splitting off from one of the two outputs
« Reply #5 on: 24 Apr 2018, 10:25 pm »
Ok..but wouldn`t the sound quality take a hit adding something like that ??

The idea of the signal being as clean as possible is what brought me to Tortuga in the first place.
 

tortugaranger

  • Facilitator
  • Posts: 1291
  • Handcrafted high performance audio gear
    • Tortuga Audio
Re: Splitting off from one of the two outputs
« Reply #6 on: 25 Apr 2018, 02:26 pm »
Ok..but wouldn`t the sound quality take a hit adding something like that ??

The idea of the signal being as clean as possible is what brought me to Tortuga in the first place.

Driving 3-4 amps off of a resistive passive preamp will, by virtue of the physics of mutiple parallel reistances, drop the effective impedance (as seen by your source) to the point where it's likely you will end up taking a hit on sound quality because that low of an impedance will over-burden the ability of your source(s) to deliver power and maintain sound quality. This isn't unique to our passive preamps and would apply to any resistive type passive preamp/attenuator including stepped attenuators or a pot-in-a-box.

Adding a buffer will mitigate this problem but yes a buffer will introduce its own characteristics which may or may not be to your liking depending on the nature of the specific buffer. Our tube preamp buffer does add a touch of tube euphonics to the sound but to my ears that's a net plus and not a sound quality hit.

SCM

Re: Splitting off from one of the two outputs
« Reply #7 on: 26 Apr 2018, 08:51 pm »
Thanks....Here`s what I`ve come up with so far for my components that I`m using right now.

The Herron phono stage (source) has an output impedance of 500 ohms.

The Rogue Atlas Magnum, according to Stereophiles measurements has "...well above 200k input impedance"

My subwoofer amp has 12k input impedance
Lastly..the amp I`m looking at to add to the system for bi-amping has 10k input impedance.

So, could the pretty high input impedance of the Rogue help save the day ??

poseidonsvoice

  • Full Member
  • Posts: 3395
  • Science is not a democracy - Earl Geddes
    • 2 channel/7 channel setup
Re: Splitting off from one of the two outputs
« Reply #8 on: 26 Apr 2018, 09:49 pm »
Thanks....Here`s what I`ve come up with so far for my components that I`m using right now.

The Herron phono stage (source) has an output impedance of 500 ohms.

The Rogue Atlas Magnum, according to Stereophiles measurements has "...well above 200k input impedance"

My subwoofer amp has 12k input impedance
Lastly..the amp I`m looking at to add to the system for bi-amping has 10k input impedance.

So, could the pretty high input impedance of the Rogue help save the day ??

Assuming those impedances are constant with frequency (and most of the time, they are not), the total resistance when resistances are placed in parallel can be described as:

1/Req = 1/R(1) + 1/R(2) + 1/R(3) + .....1/R(n); therefore Req = (R1 X R2 X Rn)/(R1 + R2+ Rn)

and in conclusion if you have the issue of a 200K input impedance combining with a 10K and 12K, all in parallel, the overall effective impedance is:

5309 ohms.

I would add a buffer if I were you... :wink:

Best,
Anand.

tortugaranger

  • Facilitator
  • Posts: 1291
  • Handcrafted high performance audio gear
    • Tortuga Audio
Re: Splitting off from one of the two outputs
« Reply #9 on: 26 Apr 2018, 10:43 pm »
I would add a buffer if I were you... ;)

Without a buffer you'd have an impedance bridging ratio of 5300/500 or roughly 10:1 which is on the raggedly edge of maybe ok with a passive preamp. It would ultimately depend on how robust the output stage is of your Herron phono stage and that is not something you can discern from specs. You'd have to try it and see if the results are acceptable but be prepared to introduce a buffer if the sonics are flabby and lacking in dynamics.

Sub amps seem to all be very low impedance with 10k being typical. You might consider an alternative amp for biamping that has say 47k impedance which would bump up the effective impedance to almost 8K with a bridging ratio of 16:1 given your phono stage. More better.  Or perhaps put a buffer between the passive and the sub. Assumming the buffer has an impedance of say 47k same as the biamp amp, you then get an overall impedance of 21k with a bridging ratio of 42:1 which would put you in fine cotton indeed.  :thumb:

SCM

Re: Splitting off from one of the two outputs
« Reply #10 on: 27 Apr 2018, 02:46 am »

I`d much rather do that I guess, but then, I need to find a different amp to power the bass section of my speakers to be able achieve this correct ?? :(

tortugaranger

  • Facilitator
  • Posts: 1291
  • Handcrafted high performance audio gear
    • Tortuga Audio
Re: Splitting off from one of the two outputs
« Reply #11 on: 27 Apr 2018, 01:27 pm »
I`d much rather do that I guess, but then, I need to find a different amp to power the bass section of my speakers to be able achieve this correct ?? :(

As I understand it you are looking to configure something like this...

Biamp/High - Atlas Magnum - 200k
Biamp/Low -  ** TBD ** - ??k
Sub - 10k

If so, then yes, look for a Biamp/Low with impedance of say 47k or higher.

Same could be accomplished by finding a higher impedance Sub amp but I suspect that will be harder to find based on the specs of most sub plate amps that I'm aware of which all tend to have low impedance. Unfortunately the lowest impedance device drives the bus on this subject. Finding a sub with a higher impedance would help a lot.

SCM

Re: Splitting off from one of the two outputs
« Reply #12 on: 27 Apr 2018, 01:59 pm »
Yes that`s exactly how I want to go about it.

My subwoofer amp is a stand alone box it`s a Dayton Audio SA1000 which is actually a rebadged Snell originally designed by Bob Carver or so I`ve gathered.

I had this setup in bi-amp mode with great results but I felt as though I didn`t need all the power based on my lowish listening levels so I sold the amp and kept my tube amp using it full range.

But now I want to go back and do it all again just to have the headroom on tap when/if needed.

I was using a Class D Audio 470C for the bi-amp duty (low end) and it worked nicely but I want something different this time around.
I think the 470C was 30K impedance.

I need an amp that has volume controls to help blend things together.

 

SCM

Re: Splitting off from one of the two outputs
« Reply #13 on: 30 Apr 2018, 12:16 pm »
I`m not at liberty to sink a bunch of money into a buffer  :|

Are there any buffers out there that are relatively cheap that have 2 inputs/outputs and will boost the impedances that the two amps will need to see ??

It`s obvious by now that I know next to nothing when it comes to this stuff  :oops:

SCM

Re: Splitting off from one of the two outputs
« Reply #14 on: 8 May 2018, 05:20 pm »
Total change up now. No bi-amping

I`ll be running the speakers full range with a much more powerful amp. So the super nice sounding Rogue will be sold  :o

The new amp is 300/450 watts per channel and has (according to specs 28K nominal input impedance).  I`ll still be using the subwoofer setup with its 10K impedance amp.

I`m hoping this sits well with my Tortuga...

tortugaranger

  • Facilitator
  • Posts: 1291
  • Handcrafted high performance audio gear
    • Tortuga Audio
Re: Splitting off from one of the two outputs
« Reply #15 on: 9 May 2018, 01:46 pm »
Total change up now. No bi-amping

I`ll be running the speakers full range with a much more powerful amp. So the super nice sounding Rogue will be sold  :o

The new amp is 300/450 watts per channel and has (according to specs 28K nominal input impedance).  I`ll still be using the subwoofer setup with its 10K impedance amp.

I`m hoping this sits well with my Tortuga...

The combined parallel impedance of your new amp/sub would be 28*10/(28+10) = 7.4k.   With the passive preamp set at say 50k, the effective impedance seen by your source would be 7.4*50/(7.4+50) = 6.45k. The resulting bridging impedance with your phono source would be 6450/500 = 12.9 which while on the low end may also be perfectly adequate depending on the robustness of your phono stage's output.

Note that we do plan on coming out with a solid state buffer fairly soon (July ? ). We're on the 4th round of prototyping and expect to have test boards in house in a couple of weeks. The solid state buffer will be much lower cost than  our tube buffer and will probably also be available as a true kit with all discrete through-hole components.

SCM

Re: Splitting off from one of the two outputs
« Reply #16 on: 9 May 2018, 05:12 pm »
My Tortuga is set at 99K impedance does that help some ? Also I found that my phono stage has 78,000 Uf of energy storage ? I have not a clue how that equates  :oops:

Thanks for you patience and help Morten  :thumb:

tortugaranger

  • Facilitator
  • Posts: 1291
  • Handcrafted high performance audio gear
    • Tortuga Audio
Re: Splitting off from one of the two outputs
« Reply #17 on: 9 May 2018, 08:06 pm »
My Tortuga is set at 99K impedance does that help some ? Also I found that my phono stage has 78,000 Uf of energy storage ? I have not a clue how that equates  :oops:

Thanks for you patience and help Morten  :thumb:

The thing with parallel impedance is the low impedance device sets the upper limit. Given the formula Z = Z1*Z2/(Z1+Z2), whichever Z is the lowest sets the max possible combined impedance. In your case you have 7.4k and the preamp set at 99k. Best you can do is around 6.9k in parallel. Only way to really raise this up substantially is raise up the 7.4k which in your case means get a sub with higher than 10k input impedance (not so easy to find) or put a buffer between the passive preamp and sub where the buffer has a higher impedance.

The 78k uF of capacitors in your phono stage is most likely the filtering on the DC power supply downstream of the AC->DC rectifier. It's a decent amount of filtering for a phono stage which needs a really good low noise PS. Doesn't really tell you much about the phono preamp's line out power capacity other than to generally indicate a good DC power supply.

SCM

Re: Splitting off from one of the two outputs
« Reply #18 on: 10 May 2018, 04:22 pm »
A YAQIN SD-CD3 tube buffer just popped up here on the 'Circle and I went ahead and bought it just to see how it works.
I can always sell it off if it doesn`t do the trick or if I like the up and coming SS Tortuga buffer better.

The Yaqin has 100K impedance.