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Hello inmates, a lot of you know I spent a couple of years restoring and rebuilding an ultimate McShane Citation II
I am kicking around the idea of building another one (if I can find a suitable candidate) and running each as a mono block. Why? well I just can't get enough.. my speakers certainly don't crave the power, put I thought maybe I would stiffen them up a bit :) Plus how cool would it be to have my mono 121 pre's each running their own separate amp?
I have looked at the HK instructions on how to run the amp in mono, and to be honest I don't understand how this can work.. They say to split off the input with a "y" splitter, but wouldn't this degrade or decrease the input signal?
Then it says to combine the speaker outputs.. is this really increasing the output power? seems kind of simple but for some reason I don't understand how this works. Also does this keep the 4 - 16 ohm loads all the same? My speakers are 16 ohm so do I just stay combined on that 16 ohm tap?
I tried this in a quick experiment. using a "y" splitter for the input and then just running a jumper from the left speaker output terminal to the right terminal and then out to the speaker. I think this is essentially the same as what is shown in the diagram..I left it on the 16 ohm tap. The result seemed pretty weak and thin.
I assume I must be doing something wrong or there is a better way of doing this. Are there any other inmates out there running Citation II's as mono blocks? I am pretty sure Samra is doing this on one of his systems..
thanks for any advice..
J
Follow Ups:
Because my answer might depend on that, esp. if they are three ways.
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
Zu soul super fly, they are actually omens but upgraded to the soul superfly drivers..mk ii version..
J
assuming that like most tube amps you have some headroom.
Let's rate the Citation II at 18dbw (64 watts) to add to the 101db. That's adding just 4 watts which is reasonable, given that the McShane PSU upgrades have been done as well as the audio ones.And, with two speakers you get an extra 3db.
So you can get 122db un-clipped at 1 metre, possibly as much as 125db.
Which is almost? enough even for Mahler or Wagner at full bore.
So, I really can't see how you need the extra loudness.
I have heard several strapped PP stereo valve amps and they weren't as nice or detailed as the originals.
If it were me I would be asking Jim if there are any niceness / nuance upgrades to the Cit.II.
OR spend the money elsewhere, on the room, or your inputs or pre-amp.
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
Edits: 12/15/15 12/15/15
Tim you are right on all accounts, and this is just a project I was just thinking of, for something to do, My Cit II is beyond McShaned and I added some Samra hot rods to it:)
However, I did like the change in these speakers, which as you found have no cross over, it's just a wizzer cone with a hyper tweet, when I tried these with a 20 watt amp then switched to the 60 watt amp. I like how they stiffened up and the bass got tighter, I thought maybe more power would tighten them up more, which I like. I am not looking to drive music at ear splitting levels or cause an earthquake. I realize I have more power than the room can handle already. I listen to everything but mostly Jazz and Rock. Intention was to do more power to tighten the bass, but who knows it might not get any better than what it is.
I didn't like how it sounded on the one speaker when I put it in parallel, it sounded horrible.
Pretty much with the feedback though, this doesn't sound like a good idea and everyone seems to indicate there will be sound quality loss, so I just might put this to rest..
thanks for your input,
J
If I had the Zu Soul Superfly and two citation amps, I would look into a pair of Subwoofers driven by a Marchland tube electronic crossover. Alternatively, I would strap one amp and drive a Mono subwoofer. You will need to go big on the drive to be able to keep up with the "satellites". Having the same amp driving to subwoofer and the speakers, with the tube electronic crossover, would sound a lot more integrated that the usual sand amp sub.
Dave
Dave,
that's an interesting idea, I thought of that once, but you know it's really hard to find passive sub woofers at all, say anything of quality. It seems you'd be left with trying to build a pair which could be a complete shot in the dark on how they would sound..
I do agree with you that if you could have it run by the same core system, it would sound more integrated..
interesting idea..
The best way is to build an outboard Phase inverter circuit and run the 2 amps in true push pull. You can get more power that way. There was an article in glass audio several years ago about doing this om an ST-70. Can't remember how they connected the speakers though.
Hi,
If your speakers are 16 ohm you can not properly operate the Citation II as a mono amp. A 32 ohm output transformer would be required which the Citation, like most tube amps, does not have. I operate two Citation II's as mono amps driving a pair of 8 ohm JBL Sovereign S7R speakers and it works very well.
Yes,I think this is the culprit. The more I read, I think this is why it didn't sound right. I know my speakers need 16 OHM. I once tried them on the 8 ohm setting in stereo, and they sound terrible, and thin, very similar to how it sounded on my experiment.
It's good to consult, this is why I figured I would send out the idea before gearing up for a another project..
thanks!
I don't think it is a problem to run 16 ohm speakers on an 8 ohm tap. At least not with quality output transformers like the HK. Running more than double or less that half could be trouble. It depends on the amp. It will lower the power output of the amp, which may defeat the purpose of strapping.
Dave
Dave,
I think you are right, and I am not saying it doesn't work or would be harmful, as I tried it on one speaker, I just noticed it "doesn't sound well" dynamics are lost bass is flat, just doesn't sound good like I actually lost "umph" instead of increasing it....
Does anyone have any experience doing the phase inverter method? I heard of this before but also heard there is sound quality issues..
thanks for the comments everyone..
J
"Does anyone have any experience doing the phase inverter method? I heard of this before but also heard there is sound quality issues."
Bridging, which is driving the 2 channels of a stereoblock containing a common ground with out of phase signals and connecting the speaker cables to the "hot" terminals, can work where parallel connecting the channels fails. Plenty of reports of overheating and bad sound can be found, when paralleling has been tried. :> ( Bridging sums the voltage swings of the amp sections in the load. The method is particularly well suited to your situation, as you have 16 Ω speakers. As each section of a bridged amp "sees" only 1/2 of the load, 16 Ω speakers get connected to the 8 Ω speaker taps. :> ) Bridging is a problem when 4 Ω speakers are on hand, as 2 Ω taps don't exist.
If your preamp has a low O/P impedance, a pair of Sowter's model 8920 transformers will take care of the split phase requirement.
http://www.sowter.co.uk/specs/8920.htm
If your preamp's O/P impedance is unimpressive, you may have to build a buffer or an active electronic bridging adapter.
Eli D.
Our buddy Mikey Samra runs his "strapped" driving his big Martin Logans.
Meat; It's the right thing to do. Romans 14:2
To run a stereo tube amp as a Mono-block you are 'Strapping' the two channels to operate as one -
The instructions that you have are correct - the one aspect that you did not mention/was not put forth in the instructions is that this will render the output taps at half their labeled resistance - so the 16 Ohm taps become 8 Ohm taps - this is a function of running the two output sections in Parallel-
If you do not want to use the "Y" connector- take the shielded line from one of the input RCA jacks and connect it to the other - you only need one - and that will replace the need for the "Y" connector-
Happy Listening
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