Dual Mono vs. Stereo Amplifiers - A Technical Explaination

BG176 - Whether you are talking Tube Amp or Solid State, this video applies to both scenarios. We discuss the technical differences and why one maybe better than the other, or not...

[@jakep8484]

Inductors oppose changes in current and capacitors oppose changes in voltage.

[@jimmurray8713]

Mark, Being an audio nut, I generally agree with your conclusion that a well designed stereo amp has the potential to sound very good indeed. But I do have some quibbles with a few of your assertions. All dual mono systems that I am aware of have one preamp and two separate power amplifiers, so one volume control is not an advantage of a stereo. Also, while crosstalk includes any interference from one channel to another, it generally refers to bleeding of signal from one channel to the other. A dual mono setup precludes this, but it really should be not be an issue in a well designed stereo amp. It really comes down to the power supply. A dual mono setup fed from different phases of your power grid can have better specs than a stereo amp fed from one phase, but the difference is probably not audible to any normal human being. That said it all comes down to what you are listening to over what speakers. Chamber music through single ended triode through efficient speakers equals bliss. Krell amps driving Wilson speakers sound awesome. But if I had to settle on one amp for every thing I listen to it would be my MC 225.

[@millerellen2258]

Good Job Mark, as always, look forward to your amp build

[@djfrank59]

Power supply sag is very common under load. Sag can vary with transients at various frequencies. But those transients are for such a short duration, that it's not even an issue; at least to my ears. Guitar players tend to prefer a tube rectifier in their amps as opposed to a solid state bridge. That sag is part of their tone. I've seen some designs that use Mercury Vapor rectifiers (which have a very low voltage drop). You need to use chokes as well as filter caps when using MV's . But all in all, I tend to agree with your theory on making a good design VS. 2 mono blocks. Also, Bias must be spot on in both blocks which adds another issue. Very good video Mark. Keep 'em coming. I'm a working electronics tech, and I do catch little things that are useful.

[@swinde]

The Marantz Model 15 Power amplifier was actually a dual mono block that only shared a power cord. (the second amp was plugged into the AUX power outlet of the other amp). I was running this with a Dynaco PAT-4 preamplifier. The Model 15 was not too happy with 4 ohm speakers though, so I replaced it with a Model 250 M which used a common power supply.

[@1959Berre]

Crosstalk happens in all the stages before the power amplifier, including the source, let's say the record, in the first place. This applies especially to vinyl records.

[@whocares.20]

Tape media too can suffer from crosstalk :)

[@alexkatsaros6180]

I would like to build high fidelity tube amp as you have described in KT88 amp to use with my electric piano. As solid state amp fliers just do not have the tonal character that I want. What are your thoughts?

[@JoFreddieRevDr]

One volume control? a lot of Monoblock systems use a stereo controller/pre amp, feeding 2 Monoblock power amps, with all the "knobs" on the controller.

[@bwilson1649]

Another reason. My brother built a 12-watt Knight kit around 1962, then a year later built another. He then built a cabinet for them. Family poorly stored this for 45+ years. I replaced the electrolytics, a few leaking paper capacitors, and a few resistors that were easier to cut out of the way than to unsolder during the capacitor job. Replaced oxidized input jacks. Sadly, one transformer overheated. Now, I've added a fuse on the input power on both amps, but too late to save that one transformer. Looking for the replacement without much luck. Like to fix it for sentimental reasons. P.S. I even have the original manual and instruction sheets that came with it.

[@markteague8889]

Is there an advantage with mono blocks in the sense that they can be placed closer to the speaker with a shorter speaker wire. i.e. One can run the signal cable from the signal source to the amplifier; and then, use a short section of speaker wire for the higher power necessary to drive the speaker.

[@markteague8889]

Carver made a solid state amp that was composed of 2 mono blocks in a single chassis. I believe it was the TFM-75 unit. Required 2 power outlets for the 2 separate power sections. Kind of a monster at 750 W per channel.

[@boonedockjourneyman7979]

In my hands a set of mono blocks gets used with various "preamp" sources. The time and money in the monos is leveraged several times. For the same reason I build linear PSUs as separate "boxes." Versatility is one important reason to build several stages on separate chassis. Look at old Tektronix instruments (7000 & TM50x series for example) and imagine all the vast array of things you can do.

[@RobertKohut]

Nice!! Great points!!

[@MrMannakin]

I always thought that part of the aim of the mono-blocs was to locate them nearer the speakers to reduce the speaker cable length with a view to improving the damping of the speakers?

[@CDJF1]

My Optonica sm 4646 is dual monoblock in one chassis with a third transformer for the preamp= Delta powerd

[@tomdewey9907]

The great Nelson Pass did the dual power supply design in his amp designs back in the 1980s' (Threshold Stasis) and the fine Adcom amps later (single power transformer).

[@RobertKohut]

Keep in mind higher end stereo amplifiers can have independent power supplies and are a "dual mono" design. My vintage Bryston 4B is designed like that.

[@Lee-NN7X]

Thanks Mark..

[@friedmule5403]

You are mostly correct but you say that an advantage by stereo is a single volume control. I have never heard anyone using two pre amplifiers to the volume control. Normally do you use one pre and then dual mono power. :-)

[@desmondroche7805]

I love all your videos and am looking forward to the SE KT88 amp build. Would it be difficult to take the stereo schematic for the SE KT88 build and convert into a mono block amp without a lot of parts changes ? I ask not so much because I want to build a dual mono pair of amps, but because I’m considering building a single mono block amp for a dedicated monophonic lp only system. The truth is, I really want to build one of the amps you’ve presented in your videos, but can’t justify it to myself because I already have a single ended Bottlehead kit and don’t really need another stereo amp. I hope this isn’t a greedy request. I’m just curious.

[@RobertKohut]

Both a mono block and stereo amplifier setups use only one volume control, the pre-amps volume control. Typically amplifiers have no volume controls.

[@davekazoroski6548]

For the most part, dual monoblocks are in the realm of audio snobbery, and offer nothing but the"coolness factor" mentioned in the video.A properly designed common power supply has a sufficiently low output impedance to totally prevent one channel's signal mixing with the other channel.Actually, the biggest source of channel crosstalk is the recording studio. A power amplifier contributes little to nothing in the way of crosstalk.

[@dandonna852]

Mono blocks in home theater setting 5.1 or 7.1 or more

[@5Antvin]

I’ve seen amps with 1 power transformer claiming to be dual mono --

[@larryshaver3568]

I agree a STEREO amplifier is as good as two mono blocks possibly even better

[@whocares.20]

Well if you want to get real critical, they both share the same power supply, mono block and stereo, your AC wall supply :P And yes, one mono block will load, "swamp" that circuit a tad more, while the other is not, on a high output amp, while the stereo amp will suffer equally on both channels, driven buy a single internal power supply. So really, how critical do you really need to get? Enough to make it sound good :)

[@dragonflyfab8982]

Shorter speaker cables!

[@johnsweda2999]

That's not true to say a monoblock has better stereo separation that's not the case depends how the stereo amplifier is constructed and fed. it's down to the power supply dual rectifications each amplifier or if you have two separate power supplies for both amplifiers there's no reason why a all in one unit should be any worse than a monoblock construction. You could say a separate monoblock could be worse because of interference impedance and the amount of wire what you wouldn't get in a one unit system. That's why I think you should have the thermistor?? pass the rectification not beforehand so the power supply can always be charged ready to go when demands are put onit, plus I believe this helps in different voltages scenarios same thing. But what do I know!! I was thinking what about this preamplifier your designing what about designing it like a primaluna, DiaLogue? Highly rated in the industry as the test preamplifiers of choice, at $3,000 is not cheap by anybody standards and I think something like this could be designed a lot cheaper as a kid. around $1,000 or so. Have you had any experience with this manufacture american-based highly rated what's your opinion if any! Making sure that you have impedance jumper on the back or better designated resistor and values? so it's suitable for numerous types of power amplifiers valve and solid-state the last thing you want to have as a pre amplifier that is not a good match with a power amplifier. They have a good filtering system on the power supply what can easily be copied. What did you think of that volume attenuator I left comment on, I've been told they are the best you can get if you get your impedance correct.

[@markteague8889]

Every component you add to the signal path increases the probability that the signal will be distorted and suffer. From that point of view, a monoblock design may provide the “opportunity” to implement a circuit that molests the signal to a lesser extent than a comparable stereo circuit. Yes? No? Maybe?!? ;)

[@Detailverliebt]

I think you are right and wrong at the same time. Obviously when you double the size of your power supply there is a huge difference and everybody can hear it. That was a huge part in the French L'Audiophile philosophy with such ridiculous designs like "LeMonstre". On the other hand a double sized power supply costs double the money. Coz nobody would claim "Ah we're building monoblocks so we can use the crappiest power supply on the planet coz you know we have two of them ;-)" Ok so we are already comparing apples with oranges to a degree. Next thing is you build it stereo with completely separated power supply (who can stop you) but then you are dealing with 2 power transformers in one box kicking magnetically into all your components, what a pain. Now IMO you are better off when you spend the additional 100 bucks to get a 2nd case. I think monos make sense but you gain only a little for a lot more money.