Dynaco Mk lll Mono Blocks Phase reversed in one amp..

[DominicL]

EDIT. I made one helluva stupid mistake! The wires were indeed reversed! Actually, I reversed the colors of the wire connectors vs the wire codes on the pigtails I made. DOH! I am truely sorry and thank you all for your help. Now, I crawl back in my hole in embarrasment!!

See the picture I just added of my very senior moment! Blue to blue stripe. Yellow to blue stripe. Moral of this wasted bandwith i created:

Check the simple things first!!!


I had these amps in my system for a year now and the only way to get them to image properly was to reverse the + and - speaker wires on ONE amp. The speaker wire polarity or speaker polarity are NOT the problem because because three other solid state stereo amps image fine when wired correctly. They were worked on at some point and look to be orphans brought together from different origins. The inputs seem to be wired the same as shown in the pictures below. Any idea what the problem could be? Could a quick fix be to reverse the input on the one amp that does not match with the solid state comparison amp? Thanks in advance

 

[dcgillespie]

The pics didn't make it. If both amps are complete stock, then having one reverse polarity over the other is pretty much an impossibility without other more serious symptoms being present.

On the other hand, if they have different driver boards installed from the original -- and particularly so between them -- (i.e. one has one board, one has another), then that could definitely cause a problem.

Reversed speaker polarity in one channel shows up primarily as a hole in the middle, with greatly attenuated bass frequencies.

Good luck with it!

Dave

 

[DominicL]

Yeah, no pictures. Senior moment! Not sure if you can tell from these. I'll snap pics from above.

What ever the problem, the image, particularly the voice, would not center unless I reversed the speaker wires on one amp. Let me take some better pictures. I am a little groggy from allergies today!

 

[cademan]

Can't really tell anything by those pics but just make sure the output transformers wires are connected to the speaker terminal strip with the same colors. I can't seem to see the black wire in pic #2.

 

[DominicL]

This one is the problem child. I put the other MK lll on one channel and a HK citation solid state amp on the ohter channel and it imaged perfectly with + to + and - to - on both sides Let me know what other pics to snap. I will look at the wiring on the speaker terminals, but I think they both had the black on the neg side.

And a bi old THANK YOU!

 

[DominicL]

First two pictures are of the out of phase amplifier speaker terminals from the inside. The second two are of the good amp that matches and images with a known good (I think! per my testing) opposite channel

 

[cademan]

Just something to check is the plate wiring on pins #3. I have a stereo Stromberg-Carlason tube amplifier where my NFB was tweaked because someone else had messed with it before I got ahold of it.

My speakers were out of phase even though both speakers were wired correctly to both positives coming off of the speaker terminals. Dave G's recommendation would be the best thing to check out with the preamp driver boards.

 

[DominicL]

Thanks. I will check that. That's exactly what my amp is doing!

 

[dcgillespie]

Dom -- Unless you know for a fact whether the SS HK amplifier inverts polarity or not, then you don't really know anything yet. All you know is that one of the amps works well with the HK, and one doesn't, but without knowing what the HK does to polarity, then you don't know which Dynaco is good, and which isn't at this point. For the record, a properly operating Dynaco MK III does NOT invert signal polarity.

Dave

 

[Pio1980]

Dom -- Unless you know for a fact whether the SS HK amplifier inverts polarity or not, then you don't really know anything yet. All you know is that one of the amps works well with the HK, and one doesn't, but without knowing what the HK does to polarity, then you don't know which Dynaco is good, and which isn't at this point. For the record, a properly operating Dynaco MK III does NOT invert signal polarity.

Dave

It's pretty much impossible other than if the speaker terminal board is totally wired reversed, the FB loop would cause the amp to go full-on unstable oscillation otherwise.

Sent from my SM-N900V using Tapatalk

 

[battradio]

Are both the output transformers original and have the same part number on them , and can we see photos of them .

http://www.the-planet.org/dynaco/Misc/Transformers.pdf

 

[gadget73]

No chance you have a scope and a signal generator is there? That would tell the story real quick.

 

[dcgillespie]

Dom -- As I originally suggested in post #2, the idea of one of your (basically) stock Dynaco's changing polarity -- without ANY other (and more serious) symptoms present -- is pretty much impossible. As Pio1980 further expounded on, those more serious symptoms would include the unit turning into a high powered oscillator due to reversal of the NFB connections.

Let me also again state that a stereo system operating with one speaker system out of phase with the other will OVERWHELMINGLY display a sonic "hole" in the middle of the speakers, with the bass frequencies all but sucked out and gone. If you are familiar with the sound of your system in this regard, this effect -- if present -- is unmistakable, and immediately noticeable.

But you have not indicated this symptom at all, instead, focusing on sound stage issues surrounding the centering of (particularly) the human voice. Therefore, I would suggest that you don't have a phase problem at all, but that one of the amplifiers is either displaying less sensitivity than the other (causing the sound to shift between the speakers), or has frequency response issues, causing sonic information to smear between the channels -- or both. Your reversing the speaker leads to one amp can cause some stereo information in the mid-band frequencies to be unnaturally accentuated -- possibly appearing to correct the issue, but this remedy will definitely cause other problems in the process.

I would therefore attack your problem with the idea that one of your amplifiers has less sensitivity/frequency response than the other amplifier does. This scenario makes much more sense than the idea of reversed polarity, based on the information you have supplied.

Since it appears that both amplifiers have been rebuilt, I would start by verifying that the amplifiers are wired identically to each other, and have the exact same components in the exact same positions between them.

I hope this helps!

Dave

 

[ConradH]

If you don't have test equipment, an interesting thing to try is putting your speakers side by side. Feed the amps a mono signal and play with balance. If the phase is opposite, and the signals are balanced, most of the sound will cancel out, especially the low end. The effect is dramatic. You can also use the balance control to null it and show where the control is really centered.

If the phase is correct, there will be no obvious null. I found this a useful technique for finding various response and balance problems by purposely putting one channel out of phase and seeing how good a null I could get, and over what frequency range.

 

[DominicL]

No chance you have a scope and a signal generator is there? That would tell the story real quick.

I do but im a total noob with this. Just got the Scope, signal generator, distortion analyzer, varaic and some other smalls like a millvolt ac meter,and signal tracer. Right now all pieces look the same to me!! Just kidding, but not by much! I am in the process of getting it all set up to tinker! Problem is, at 56, i feel like i have a learning disability!


Maybe my terminology is incorrect??

What I do know is, while listening with the speakers hooked up + to +, - to - ,the voice is all over the room, sounds like an acid trip from the 60's, unless i reverse the speaker polarity on one mono block or the other. When one amp's speaker polarity is reversed, they sound fine..voice is centered, sound stage is correct and the acid trip stops. Thank goodness!!


I will take all this information in and be back! ! I did notice that the multi can capacitor on one amp is oriented different than on the other. I will trace the wires.

EDIT Could the oreintation of the resistor across the can capacitor in the extreme lower right side (bottom shown in picture) have anything to do with the mismatch I have? Let me explain. The resistor on the can cap is oriented across the box and circle terminals on the fist picture on the left. On the one on the right, the original Dynao cap has the resistor oriented across the semi circle and the triangle. Pics don't show the "shape" markings on the right picture since they are stamped into the metal soldering tabs. That would be an easy fix! Fingers crossed!!

 

[DominicL]

If you don't have test equipment, an interesting thing to try is putting your speakers side by side. Feed the amps a mono signal and play with balance. If the phase is opposite, and the signals are balanced, most of the sound will cancel out, especially the low end. The effect is dramatic. You can also use the balance control to null it and show where the control is really centered.

If the phase is correct, there will be no obvious null. I found this a useful technique for finding various response and balance problems by purposely putting one channel out of phase and seeing how good a null I could get, and over what frequency range.

This i can do but not moving the Maggies..I have a pre amp that can mix to mono..i will try this now! Thanks

 

[DominicL]

Dom -- As I originally suggested in post #2, the idea of one of your (basically) stock Dynaco's changing polarity -- without ANY other (and more serious) symptoms present -- is pretty much impossible. As Pio1980 further expounded on, those more serious symptoms would include the unit turning into a high powered oscillator due to reversal of the NFB connections.

Let me also again state that a stereo system operating with one speaker system out of phase with the other will OVERWHELMINGLY display a sonic "hole" in the middle of the speakers, with the bass frequencies all but sucked out and gone. If you are familiar with the sound of your system in this regard, this effect -- if present -- is unmistakable, and immediately noticeable.

But you have not indicated this symptom at all, instead, focusing on sound stage issues surrounding the centering of (particularly) the human voice. Therefore, I would suggest that you don't have a phase problem at all, but that one of the amplifiers is either displaying less sensitivity than the other (causing the sound to shift between the speakers), or has frequency response issues, causing sonic information to smear between the channels -- or both. Your reversing the speaker leads to one amp can cause some stereo information in the mid-band frequencies to be unnaturally accentuated -- possibly appearing to correct the issue, but this remedy will definitely cause other problems in the process.

I would therefore attack your problem with the idea that one of your amplifiers has less sensitivity/frequency response than the other amplifier does. This scenario makes much more sense than the idea of reversed polarity, based on the information you have supplied.

Since it appears that both amplifiers have been rebuilt, I would start by verifying that the amplifiers are wired identically to each other, and have the exact same components in the exact same positions between them.

I hope this helps!

Dave

Most definitely will help, Dave. I think I may have my terminology wrong! Please see my other replies before this. Specifically, post #15. There is one resistor thats wired across the large alum can capacitor terminals square and circle on one amp, and on the other across semi-circle and triangle markings of the cap. You will have to take my word because the shapes are stamped into the terminals on one capacitor and can not be seen in the pictures. Not sure if this will cause anything like I am hearing? However, the "image" can NOT be dialed in via the balance knob on my pre amp. Just in case that means anything.

Thank you all for your help with this! Someday i too will be able to make some informed decisions on these amplifiers! Right now, I am more informed on the mechanics of turntables!! Pretty handy on them if I could say so my self!! Electronics, not so much as is obvious!!

 

[DominicL]

I am a total friggen idiot! I apologize folks!

I am so embarrassed here now. The wind up is that when I made my pigtail cables for this amplifier, I reversed the connector colors vs the wires codes! THANKS SO MUCH FOR THE HELP. Guess I'll be hearing about this for a while! DOH!! [/B]

 

[ConradH]

Hey, that's pretty darn good! The alternative was some kind of hole in the space time continuum because reversing phase in those amps just isn't easily accomplished.

 

[dcgillespie]

Congrats on finding the issue!

As is so often the case when a really perplexing problem exists: Something you think is true, is in fact not. You started off the thread saying that the speakers and the cables had been verified as correct, but in fact, that is exactly where the problem was. This is not a dig at you, but merely to show -- once again -- how true this so often is. However, it now begs another question: How could it image correctly on the SS HK amp if the cables were the problem??

Dave