The Dynaco Tube Audio Forum

Would you like to react to this message? Create an account in a few clicks or log in to continue.
The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts.com products


+7
Bob Latino
vtshopdog
Tom
corndog71
sayntjack
gktamps
ttocs
11 posters

    M-125 Output Impedance Tricks?

    ttocs
    ttocs

    Posts : 18
    Join date : 2019-05-20
    Location : Northern Illinois

    M-125 Output Impedance Tricks? Empty M-125 Output Impedance Tricks?

    Post by ttocs Mon Aug 16, 2021 9:34 am

    Hi all! I don't think I've posted anything here before since building my M-125 amps more than two years ago, but could be wrong. I've enjoyed all the helpful info gleaned from this forum!

    This is something I've thought about from time to time since of owning these great amps but haven't really found any info which would directly answer my question.

    Is there any nifty way to lower the Output Impedance such that the amp would be just a little bit happier with low impedance speakers such as the Martin Logan Expression as still sound great? I've compared the frequency response to a Krell multi-channel amp and yes, the Krell has no issue with extending the flat response out to around 16KHz before slumping, but the M-125 slumps around 10KHz (if I remember correctly). I'd like to be able to extend the flat response out farther if that's possible.

    Measuring at various output levels the M-125 dutifully doesn't complain by showing any sag in the frequency response when pushed into higher volume, so for me, it's just to see if the frequency response could be extended a bit with these speakers. When connected to "normal" speakers the treble response goes past 20KHz, so the amps are working as they should, but the ML's are just a bit imposing on the amps. I think it says a lot that the Krell also has trouble well before 20KHz.

    Started with KT88 tubes, now am using KT120.
    I prefer and use the Weber WS1-T rectifier.
    I thoroughly enjoy the sound of these amps, I'd just like to see if I can enjoy even more thoroughly-er!

    Thanks in advance for any assistance!
    gktamps
    gktamps

    Posts : 33
    Join date : 2017-07-30
    Location : Santa Rosa, CA

    M-125 Output Impedance Tricks? Empty Re: M-125 Output Impedance Tricks?

    Post by gktamps Thu Aug 26, 2021 5:49 pm

    Yes, indeed there is. Although it doesn't lower the output impedance of the amps, it does essentially raise the impedance of the speakers.

    I used these with my custom built speaker cabs with Seas Prestige drivers, because nominal impedance was 4 Ohms, dipping down to almost 3 at times. There was a noticeable improvement in sound quality. My current speakers are 8 Ohm, so these are not being used at this time.

    https://anticables.com/store/%E2%80%9CNaked%E2%80%9D-ZERO-Autoformers-p14644819
    avatar
    sayntjack

    Posts : 5
    Join date : 2020-11-26

    M-125 Output Impedance Tricks? Empty Re: M-125 Output Impedance Tricks

    Post by sayntjack Thu Aug 26, 2021 7:34 pm

    It sounds like your M-125 is not quite kicking butt to the level you want.  I'm wondering which VTA driver board you're using as I have a thought on why.  This year I completed a rebuild of a pair of Mk IIIs for a friend using the M125 V19 driver board.  The amps sounded nice but simply did not have the energy / dynamics of other MkIII rebuilds I've done in the past using other driver boards or my own design.  I've been scratching my head over this for quite a while and am coming to the conclusion that the driver board simply does not have enough gain to allow adequate global negative feedback for the KT88s to drive the loads with optimum dynamics.  I'm following this up with Roy but as yet haven't got into the gritty details of same.
    ttocs
    ttocs

    Posts : 18
    Join date : 2019-05-20
    Location : Northern Illinois

    M-125 Output Impedance Tricks? Empty Re: M-125 Output Impedance Tricks?

    Post by ttocs Fri Aug 27, 2021 8:39 am

    gktamps wrote:Yes, indeed there is. Although it doesn't lower the output impedance of the amps, it does essentially raise the impedance of the speakers.

    I used these with my custom built speaker cabs with Seas Prestige drivers, because nominal impedance was 4 Ohms, dipping down to almost 3 at times. There was a noticeable improvement in sound quality. My current speakers are 8 Ohm, so these are not being used at this time.

    https://anticables.com/store/%E2%80%9CNaked%E2%80%9D-ZERO-Autoformers-p14644819

    Thanks.
    I looked at these a couple years ago, but am still unsure how these interact with electrostatic speakers, if at all. Still considering them, however, as a speaker-side helper.
    ttocs
    ttocs

    Posts : 18
    Join date : 2019-05-20
    Location : Northern Illinois

    M-125 Output Impedance Tricks? Empty Re: M-125 Output Impedance Tricks?

    Post by ttocs Fri Aug 27, 2021 8:58 am

    sayntjack wrote:It sounds like your M-125 is not quite kicking butt to the level you want.  I'm wondering which VTA driver board you're using as I have a thought on why.  This year I completed a rebuild of a pair of Mk IIIs for a friend using the M125 V19 driver board.  The amps sounded nice but simply did not have the energy / dynamics of other MkIII rebuilds I've done in the past using other driver boards or my own design.  I've been scratching my head over this for quite a while and am coming to the conclusion that the driver board simply does not have enough gain to allow adequate global negative feedback for the KT88s to drive the loads with optimum dynamics.  I'm following this up with Roy but as yet haven't got into the gritty details of same.
    Thanks.
    Well actually, the sound is wonderful! I'd just like to capture more upper freqs.

    I've been reading more about driver tubes and such, but haven't as yet delved into the mix. I should really start with this considering I've got other tubes I could try. Is it possible that driver tubes can "tailor" the frequency response for more treble vs bass?

    I don't need more punch, and frankly don't want that which is why I use Triode Mode.
    corndog71
    corndog71

    Posts : 798
    Join date : 2013-03-19
    Location : It can get windy here

    M-125 Output Impedance Tricks? Empty Re: M-125 Output Impedance Tricks?

    Post by corndog71 Fri Aug 27, 2021 2:11 pm

    When was the last time you had your ears checked? I ask this seriously because earlier this year I saw my doctor for a check up and he cleaned a bunch of ear wax out of my ears and that improved my perception of higher frequencies not to mentioned an imbalance.

    Another option is to try different coupling caps on your amp. My current favorite is Miflex copper caps.

    You might also consider room treatments. Diffusers can help open up the sound of your speakers.
    avatar
    Tom

    Posts : 208
    Join date : 2011-04-04

    M-125 Output Impedance Tricks? Empty Re: M-125 Output Impedance Tricks?

    Post by Tom Fri Aug 27, 2021 2:39 pm

    I get my hearing checked at work:

    Doc says, "Hmmm, you have some high frequency loss, not too unusual for someone your age."
    Me, "Gosh, is that going to be a problem."
    "Nope" he says, "those are the frequencies used by wives and children..."

    Very Happy

    ixe13, jimmeq and ttocs like this post

    avatar
    sayntjack

    Posts : 5
    Join date : 2020-11-26

    M-125 Output Impedance Tricks? Empty Re: M-125 Output Impedance Tricks

    Post by sayntjack Fri Aug 27, 2021 3:03 pm

    Hi ttocs.  Driver tubes:  I have not found that changing the driver tubes effects high frequency, only soundstage size and depth, bass and dynamics.  (I have the VTA M125 V19 driver board which uses two 12AU7s.)  In the phase splitter position I've found that a 12BH7 is superior in delivering a more dynamic and involving sound.  It doesn't seem to matter what brand.  Swapping the amplifier position 12AU7 with different brands and vintages I have found affects the bass and overall dynamics.
    One component that can have a significant effect on sound are the coupling capacitors.  These range in price from a couple of dollars to 100+.  For clean extended highs and good dynamics I have found the MIT Multicap PPFXS to be very good.  Like tubes, capacitors need settling in time to reach their characteristic sound.  This can range from 10 or so hours to 200+ for some Teflon capacitors.
    Given that you have ample punch and I don't I wonder if you could post the version of your driver board and any mods that you've made to it.  It should be printed right on the top of the board, eg. M-125 v19.
    avatar
    sayntjack

    Posts : 5
    Join date : 2020-11-26

    M-125 Output Impedance Tricks? Empty Re: M-125 Output Impedance Tricks

    Post by sayntjack Fri Aug 27, 2021 3:35 pm

    Hi ttocs. You say that the lack of high frequency occurs on your Martin Logan Expressions. I looked into the ML specs - they have a built-in high power class D amp so you would only be driving the high frequency section. According to the specs, this load is 4 ohms at 91 dB efficiency and needs only a 20 Watt amp. So, there should be no problem with your M-125s. When you say that the high frequency is rolled off is this from listening, measurement with a mic in front of the speakers or measurement at the input terminals of the speaker? Does it sound like the highs are rolled off? There are complications to making electrical measurements on the amp output due to the complexities of the impedance characteristics of the amps and speakers and how they interact.
    ttocs
    ttocs

    Posts : 18
    Join date : 2019-05-20
    Location : Northern Illinois

    M-125 Output Impedance Tricks? Empty Re: M-125 Output Impedance Tricks?

    Post by ttocs Fri Aug 27, 2021 4:37 pm

    corndog71 wrote:When was the last time you had your ears checked?  I ask this seriously because earlier this year I saw my doctor for a check up and he cleaned a bunch of ear wax out of my ears and that improved my perception of higher frequencies not to mentioned an imbalance.

    Another option is to try different coupling caps on your amp.  My current favorite is Miflex copper caps.

    You might also consider room treatments.  Diffusers can help open up the sound of your speakers.

    Whaaaat? ?

    Ears are clear. Hearing normal for my age. But, it's something everyone needs to consider as time marches on.

    I'm trying to keep some distance between me and a lot of mods on the amps as much as possible because I consider what I want to be pretty minimal. I mean, I "could" just turn up the treble a bit, but I'm really just looking for some schooling on things I'm not as familiar with, and good suggestions like caps, Zero's, etc, are all "doable", as George Costanza famously said to his new secretary. I just need some learnin'.
    ttocs
    ttocs

    Posts : 18
    Join date : 2019-05-20
    Location : Northern Illinois

    M-125 Output Impedance Tricks? Empty Re: M-125 Output Impedance Tricks?

    Post by ttocs Fri Aug 27, 2021 4:50 pm

    sayntjack wrote:Hi ttocs.  Driver tubes:  I have not found that changing the driver tubes effects high frequency, only soundstage size and depth, bass and dynamics.  (I have the VTA M125 V19 driver board which uses two 12AU7s.)  In the phase splitter position I've found that a 12BH7 is superior in delivering a more dynamic and involving sound.  It doesn't seem to matter what brand.  Swapping the amplifier position 12AU7 with different brands and vintages I have found affects the bass and overall dynamics.
    One component that can have a significant effect on sound are the coupling capacitors.  These range in price from a couple of dollars to 100+.  For clean extended highs and good dynamics I have found the MIT Multicap PPFXS to be very good.  Like tubes, capacitors need settling in time to reach their characteristic sound.  This can range from 10 or so hours to 200+ for some Teflon capacitors.
    Given that you have ample punch and I don't I wonder if you could post the version of your driver board and any mods that you've made to it.  It should be printed right on the top of the board, eg. M-125 v19.

    The Driver Board is V-16.
    The Driver Tubes are both GE 5963.

    The powered woofers I think you've discovered in the next post.

    As I posted above, I'll look into reading more about caps and see where that leads. I'm in no hurry BTW, I take things slow when things are good.
    ttocs
    ttocs

    Posts : 18
    Join date : 2019-05-20
    Location : Northern Illinois

    M-125 Output Impedance Tricks? Empty Re: M-125 Output Impedance Tricks?

    Post by ttocs Fri Aug 27, 2021 5:05 pm

    sayntjack wrote:Hi ttocs.  You say that the lack of high frequency occurs on your Martin Logan Expressions.  I looked into the ML specs - they have a built-in high power class D amp so you would only be driving the high frequency section.  According to the specs, this load is 4 ohms at 91 dB efficiency and needs only a 20 Watt amp.  So, there should be no problem with your M-125s.  When you say that the high frequency is rolled off is this from listening,  measurement with a mic in front of the speakers or measurement at the input terminals of the speaker?  Does it sound like the highs are rolled off?  There are complications to making electrical measurements on the amp output due to the complexities of the impedance characteristics of the amps and speakers and how they interact.  

    This "quoted" impedance is optimistic. The stat panels go as low as 0.7Ω. I found a comparison I did a year ago between the M-125 with KT88 power tubes and a multi-channel Krell S-1500 amp. It shows the nose dive being above 8000Hz. I'm ok with a little bit, 4dB-ish, but would appreciate less drop-off above 10000Hz.

    But yes, the wattage needed isn't as critical being that only the stat panel needs the external amp. So below 300Hz I'm golden. The speaker has dual self-powered woofers that I turned down to their minimum, and I added dual subwoofers to each Expression to take over the frequencies below 100Hz, so everything providing bass is basically loafing and dynamics below 300Hz are as good as I could ever hope for.

    The highs don't really sound rolled off, but they aren't as sparkling as when the Krell is used, but the Krell cannot be described as "Real" like the M-125's provide. My friends say "it's like I can reach out and touch the musicians".

    This is what REW measured at the MLP. FYI this was before adding the subs as extra woofers. Green=Krell, Yellow=M-125.
    M-125 Output Impedance Tricks? Krellv10
    vtshopdog
    vtshopdog

    Posts : 142
    Join date : 2015-07-11
    Location : UT, USA

    M-125 Output Impedance Tricks? Empty Coupling Caps - Separate thread started

    Post by vtshopdog Sat Aug 28, 2021 4:24 pm

    I noticed a couple comments regarding coupling cap substitutions here.  
    To avoid hijacking this thread starting a new one on this specific topic, please contribute if you have experience.

    Thanks
    Bob Latino
    Bob Latino
    Admin

    Posts : 3074
    Join date : 2008-11-26
    Location : Massachusetts

    M-125 Output Impedance Tricks? Empty Re: M-125 Output Impedance Tricks?

    Post by Bob Latino Sun Aug 29, 2021 8:13 am

    ttocs wrote:

    This "quoted" impedance is optimistic. The stat panels go as low as 0.7Ω.

    The highs don't really sound rolled off, but they aren't as sparkling as when the Krell is used, but the Krell cannot be described as "Real" like the M-125's provide. My friends say "it's like I can reach out and touch the musicians".

    1. You can't expect a tube amp that is expecting a 4 ohm load to be happy when it is fed a .7 ohm load ? A .7 ohm impedance on the M-125's will alter the frequency response. NOTE > There is very little music information above 10K and if you are over 40 you can't really hear much above 10 KHz anyhow. See hearing chart below. According to the chart a 40 year old male's hearing is down about 10 dB at 8 KHz.

    2. Re > "the Krell cannot be described as "Real" like the M-125's provide. My friends say "it's like I can reach out and touch the musicians". Is this not the more important aspect of the music ?

    Bob


    M-125 Output Impedance Tricks? Agerelatedhearing

    DavidR and ttocs like this post

    ttocs
    ttocs

    Posts : 18
    Join date : 2019-05-20
    Location : Northern Illinois

    M-125 Output Impedance Tricks? Empty Re: M-125 Output Impedance Tricks?

    Post by ttocs Sun Aug 29, 2021 9:59 am

    Bob Latino wrote:

    2. Re > "the Krell cannot be described as "Real" like the M-125's provide. My friends say "it's like I can reach out and touch the musicians".

    Is this not the more important aspect of the music ?

    Bob


    Yes it is! Which is why I love your amps so much!

    I hope it's obvious by the fact that after 2-1/2 years of usage I haven't as yet done any mods to the amps, that this drop off in frequency is not a high priority item. It's just something I wonder about and finally asked the question.
    AmpedUp
    AmpedUp

    Posts : 26
    Join date : 2019-10-26
    Location : Kansas City

    M-125 Output Impedance Tricks? Empty Re: M-125 Output Impedance Tricks?

    Post by AmpedUp Sun Aug 29, 2021 11:18 pm

    Hi ttocs,
    I have to respond here as we have almost the exact same audio system. I have the M125 pair with a Don Sachs preamp. Because my listening room is only 12x22" I went with the Impressions instead of the Expressions and I only need a single sub, Dynamo 1500 to fill my room up with sound. That feeling that you can touch the musician is where the electrostats shine. These and Planers are known for their superb clarity. They do lack dynamics of some other speakers, but the ML hybrids like ours are plenty good for me. Every instrument that I listen too sounds "in the room" with one exception - the snare drum. I do not get the high frequency snap that comes from a live drum set. I am not sure what you are trying to improve what you hear from your system, but there are amps that can deliver these higher frequencies but they cost way more than our VTA amps. And those amps require speakers much more expensive our our Martin Logans to deliver that exceptional of sound quality. I am proud of and love the sound and value of my VTA amps with the ML speakers. Yes they could always be better but the cost of just a little improvement would be in the hundreds of dollars and many hours if I start swapping internal components and in the tens of thousands if I start swapping amps and speakers.

    I love your question. I appreciate anyone that looks to improve their VTA equipment for just a little better sound quality and shares that knowledge. I see that you got different advice. All will make subtle differences to what you hear. 12BH7 vs 12au7 driver tubes, Weber SS vs GZ33 vs 5AR4 rectifiers, I also run K-120 power tubes. I could have mentioned the difference in sound with cables but that would have opened up a hornets nest of opinions. IMHO Corndog might have given you your best options here in another article with his opinion with different coupling caps. If you are willing to spend the $ for just a little extra quality in sound measurements, the Juniper and Mundorf caps will cost you significantly more than the K42Y caps that Bob supplied but are supposed to be of better quality. I followed Bob's advice and I'm 100% satisfied with mine. I do not know if these will improve your measurement tests, but just like tube rolling it can be fun experimenting.

    I mentioned my experience listening to a snare drum to point out that what you hear is more important than any measurement. In my case I do not know the measurements of my system, but I used room treatments and the PBK kit to balance my system and the music in my life is very good. I hope that yours is also... The $100 for the ML PBK kit is worth the time to setup as if flattened my bass curve to really dial in the best sound. I have 2 kits and will give you the second if you would like it.

    Mike...

    ttocs likes this post

    ttocs
    ttocs

    Posts : 18
    Join date : 2019-05-20
    Location : Northern Illinois

    M-125 Output Impedance Tricks? Empty Re: M-125 Output Impedance Tricks?

    Post by ttocs Mon Aug 30, 2021 12:48 am

    AmpedUp wrote:Hi ttocs,
    I have to respond here as we have almost the exact same audio system.  I have the M125 pair with a Don Sachs preamp.  Because my listening room is only 12x22" I went with the Impressions instead of the Expressions and I only need a single sub, Dynamo 1500 to fill my room up with sound.  That feeling that you can touch the musician is where the electrostats shine.  These and Planers are known for their superb clarity.  They do lack dynamics of some other speakers, but the ML hybrids like ours are plenty good for me.  Every instrument that I listen too sounds "in the room" with one exception - the snare drum.  I do not get the high frequency snap that comes from a live drum set.  I am not sure what you are trying to improve what you hear from your system, but there are amps that can deliver these higher frequencies but they cost way more than our VTA amps.  And those amps require speakers much more expensive our our Martin Logans to deliver that exceptional of sound quality.  I am proud of and love the sound and value of my VTA amps with the ML speakers.  Yes they could always be better but the cost of just a little improvement would be in the hundreds of dollars and many hours if I start swapping internal components and in the tens of thousands if I start swapping amps and speakers.

    I love your question.  I appreciate anyone that looks to improve their VTA equipment for just a little better sound quality and shares that knowledge.  I see that you got different advice.  All will make subtle differences to what you hear.  12BH7 vs 12au7 driver tubes, Weber SS vs GZ33 vs 5AR4 rectifiers, I also run K-120 power tubes.  I could have mentioned the difference in sound with cables but that would have opened up a hornets nest of opinions.  IMHO Corndog might have given you your best options here in another article with his opinion with different coupling caps.  If you are willing to spend the $ for just a little extra quality in sound measurements, the Juniper and Mundorf caps will cost you significantly more than the K42Y caps that Bob supplied but are supposed to be of better quality.  I followed Bob's advice and I'm 100% satisfied with mine.  I do not know if these will improve your measurement tests, but just like tube rolling it can be fun experimenting.

    I mentioned my experience listening to a snare drum to point out that what you hear is more important than any measurement.  In my case I do not know the measurements of my system, but I used room treatments and the PBK kit to balance my system and the music in my life is very good.  I hope that yours is also...  The $100 for the ML PBK kit is worth the time to setup as if flattened my bass curve to really dial in the best sound.  I have 2 kits and will give you the second if you would like it.

    Mike...
    All good stuff Mike, thanks!
    I have the PBK, but thanks much for the gracious offer!

    The snare drum analogy is a very good one. It represents something everyone can relate to. While you can hear "most" of the sounds a snare can make, maybe some of the "sizzle" is not so well represented, so this is pretty much a perfect way to explain what might be missing.

    While I am on a information quest to discover what might be needed to tweak just a bit more upper freqs out of the woodwork, I'm definitely not looking to lose the magic these amps have that I enjoy so much. Bob is very much correct in his comment about "real" being an important aspect of audio systems. It took me a long time to realize this in my home, so for me, I'm very happy with how things are with the M-125's, and frankly, I can and do connect the solid state anytime for times I want a different experience, like when watching movies. In a trade-off between more treble and less realism, I'll keep what I have.

    Also, this is probably my last pair of main speakers, unless I downsize to Alta Alec speakers if I were in a smaller space.

    Thank you very much for your contribution, and thank you to all you others for yours as well. I'm looking into what has been suggested so far, and considering some other things also, like simply adding a high shelf filter to simply boost a little bit of treble, or go the other way and lower the freqs below 8kHz a touch. Lower the water vs raising the bridge.
    avatar
    audiobill

    Posts : 426
    Join date : 2014-03-13
    Location : Albany, NY

    M-125 Output Impedance Tricks? Empty Re: M-125 Output Impedance Tricks?

    Post by audiobill Mon Aug 30, 2021 3:45 pm

    ttocs -

    For most realistic listening experience, you actually want your measured in-room response to gently decline about 1db/octave from 1K out to 20k. Please research "Target curves".

    Best,

    Bill
    tubes4hifi
    tubes4hifi
    Admin

    Posts : 1699
    Join date : 2008-11-30

    M-125 Output Impedance Tricks? Empty Re: M-125 Output Impedance Tricks?

    Post by tubes4hifi Wed Sep 01, 2021 6:40 pm

    agree with amped up and corndog in the other post.
    Change to a 12BH7 phase splitter and replace the output caps with either Mundorf silver-oil (if you can afford) or with Mundorf EVO silver for a very reasonable price and quality increase.
    One cap no one mentioned is the AudioCap Theta, which is excellent and not too pricey.   The MIFLEX caps are WAY too big, I'd take the Mundorfs anyday even thought slightly more $$.
    Also, change R28 on the board from 10 ohms to 8.2 ohms to increase the current thru the driver.
    ttocs
    ttocs

    Posts : 18
    Join date : 2019-05-20
    Location : Northern Illinois

    M-125 Output Impedance Tricks? Empty Re: M-125 Output Impedance Tricks?

    Post by ttocs Thu Sep 02, 2021 11:30 am

    audiobill wrote:ttocs -

    For most realistic listening experience, you actually want your measured in-room response to gently decline about 1db/octave from 1K out to 20k.  Please research "Target curves".

    Best,

    Bill

    Thanks. I have.

    My only really tiny complaint with the M-125/Expression matchup is the sudden drop near the top. When I use solid state I hear some extra sparkle that I'd like to experience with the M-125. It's not a huge thing, and I realize that everything in audio is relative - more of this means less of that, but it would mean a lot to have it all. If that sudden dropoff could be tweaked to be over a longer stretch of frequencies it would be less noticeable to the ear that the sparkle freqs are "covered" by the more dominant frequencies just below. It's all relative.

    Even live music is rarely perfect. After all the decades of concert going I can only point to a few that were about as perfect as they could ever be, and one of those was last Sunday with King Crimson which rated tied for second on my mental list of all-time greatest sound at a live concert. The opening band, The Zappa Band, was about as bad as it gets with the kick drum being boosted +18dB over the next loudest frequencies. So that night was the worst followed by the best (anything in the top ten is "best").

    So in the end, I'm still enthralled with the M-125's, and I might delve into trying a couple things.
    ttocs
    ttocs

    Posts : 18
    Join date : 2019-05-20
    Location : Northern Illinois

    M-125 Output Impedance Tricks? Empty Re: M-125 Output Impedance Tricks?

    Post by ttocs Thu Sep 02, 2021 11:31 am

    tubes4hifi wrote:agree with amped up and corndog in the other post.
    Change to a 12BH7 phase splitter and replace the output caps with either Mundorf silver-oil . . . .
    Also, change R28 on the board from 10 ohms to 8.2 ohms to increase the current thru the driver.
    Thanks for these suggestions.

    So if these changes are made, what would be the expected result.
    gktamps
    gktamps

    Posts : 33
    Join date : 2017-07-30
    Location : Santa Rosa, CA

    M-125 Output Impedance Tricks? Empty Re: M-125 Output Impedance Tricks?

    Post by gktamps Mon Sep 13, 2021 11:22 am

    ttocs wrote:

    https://anticables.com/store/%E2%80%9CNaked%E2%80%9D-ZERO-Autoformers-p14644819

    Thanks.
    I looked at these a couple years ago, but am still unsure how these interact with electrostatic speakers, if at all. Still considering them, however, as a speaker-side helper.

    You could always get in touch with the company and ask; I did the same with my own specific questions. My own understanding is that they would interact properly with your electrostatic speakers, since these affect the ac domain of the interactive impedance your amps see with the speakers; IOW, this is not dependent on the differences between cone or stat impedance curves. In fact, I used these with my cone speakers because the impedance dipped low, but have never needed them with my Eminent Technology LFT-8b panel speakers, which have a nominal 8 Ohm impedance.

    You seem to have identified the high frequency rolloff to be the result of using your ML speakers. My approach would not be to modify the amplifiers, but resolve, modify, or replace the speakers causing the effect, if other speakers do not exhibit this undesired trait.

    However, if you want to see if minimal changes to the amplifiers will make them play better through your MLs, I agree with the driver tube change recommendations - those tubes do affect the sound in a noticeable way. I would not start changing capacitors, given the information you've provided.

    I use my M125s with KT120s with JAN5963 and EH gold pin 12BH7A tubes with my LFT-8bs. Efficiency is lower than your MLs, but impedance does not dip nearly as low as your MLs, and there is no high frequency rolloff compared to my cone speaker cabinets. I avoided MLs out of this concern, even though I also use a bunch of different solid state amps (I rotate through systems), all of which can handle the impedance challenges of the MLs.

    Yeah. I'm with Bob. Issue is the speaker impedance/frequency response. The autotransformers may be just what you need.

    ttocs likes this post

    ttocs
    ttocs

    Posts : 18
    Join date : 2019-05-20
    Location : Northern Illinois

    M-125 Output Impedance Tricks? Empty Re: M-125 Output Impedance Tricks?

    Post by ttocs Mon Sep 13, 2021 2:48 pm

    gktamps wrote:
    ttocs wrote:

    https://anticables.com/store/%E2%80%9CNaked%E2%80%9D-ZERO-Autoformers-p14644819

    Thanks.
    I looked at these a couple years ago, but am still unsure how these interact with electrostatic speakers, if at all. Still considering them, however, as a speaker-side helper.

    You could always get in touch with the company and ask; I did the same with my own specific questions. My own understanding is that they would interact properly with your electrostatic speakers, since these affect the ac domain of the interactive impedance your amps see with the speakers; IOW, this is not dependent on the differences between cone or stat impedance curves. In fact, I used these with my cone speakers because the impedance dipped low, but have never needed them with my Eminent Technology LFT-8b panel speakers, which have a nominal 8 Ohm impedance.

    You seem to have identified the high frequency rolloff to be the result of using your ML speakers. My approach would not be to modify the amplifiers, but resolve, modify, or replace the speakers causing the effect, if other speakers do not exhibit this undesired trait.

    However, if you want to see if minimal changes to the amplifiers will make them play better through your MLs, I agree with the driver tube change recommendations - those tubes do affect the sound in a noticeable way. I would not start changing capacitors, given the information you've provided.

    I use my M125s with KT120s with JAN5963 and EH gold pin 12BH7A tubes with my LFT-8bs. Efficiency is lower than your MLs, but impedance does not dip nearly as low as your MLs, and there is no high frequency rolloff compared to my cone speaker cabinets. I avoided MLs out of this concern, even though I also use a bunch of different solid state amps (I rotate through systems), all of which can handle the impedance challenges of the MLs.

    Yeah. I'm with Bob. Issue is the speaker impedance/frequency response. The autotransformers may be just what you need.

    Thank you very much for the detailed information! Much appreciated.

    I'll try some tubes first since this is the least invasive approach.

    And thanks again for the extra explanation about Zeros. Helps a lot.

    RE the ML speakers, they are staying. My "complaint" is not much of a complaint. The sound is so glorious the way things are. I only posed the original question as to whether there are ways to improve upon the slight mismatch just to see if there are things to consider, and as you've so eloquently proven, there are. Some of these helpful suggestions are easier to adopt mentally and try physically than others, so I'll start simple, tubes.

    Next, I'd have to try the Zeros. Or maybe do this first? As I'm writing this it occurs to me that this would be an easy way to really see the effect of changing impedance on a measured output curve.

    Anyway, I've been working on some setup house cleaning things. Neatening up the wiring and such. So starting next weekend will be when the tube amp impedance issue will be addressed. Thanks again!
    gktamps
    gktamps

    Posts : 33
    Join date : 2017-07-30
    Location : Santa Rosa, CA

    M-125 Output Impedance Tricks? Empty Re: M-125 Output Impedance Tricks?

    Post by gktamps Mon Sep 13, 2021 5:28 pm

    ttocs wrote:

    I'll try some tubes first since this is the least invasive approach.

    Next, I'd have to try the Zeros. Or maybe do this first?

    Least expensive would be tubes. The Zeros are somewhat pricey, even raw, which is how I bought them, and then installed into nice stout chassis boxes of my choosing.

    Sorry if I missed it, but what preamp are you using? Do you have tone controls? There is no shame in using them if you have them, and I say that as an owner of 10-11 preamps ranging from very good to excellent but not esoteric - with and without tone controls. No intention of starting a tone control discussion with the forum here, but there are good preamps with tone controls that don't kill the sound quality.
    ttocs
    ttocs

    Posts : 18
    Join date : 2019-05-20
    Location : Northern Illinois

    M-125 Output Impedance Tricks? Empty Re: M-125 Output Impedance Tricks?

    Post by ttocs Yesterday at 8:54 am

    I ordered 12BH7 tubes and resistors that'll arrive next week.

    Sponsored content

    M-125 Output Impedance Tricks? Empty Re: M-125 Output Impedance Tricks?

    Post by Sponsored content


      Current date/time is Thu Sep 16, 2021 9:28 pm