Dave, I learned a few things from reading this thread. Thank you for your diligence and completeness in the explanations.
What is "power supply modulation," and how does one know it is present when looking at a scope trace?
The Mighty Bogen MO-200A
- Thread starter dcgillespie
- Start date
Dave, I learned a few things from reading this thread. Thank you for your diligence and completeness in the explanations.
What is "power supply modulation," and how does one know it is present when looking at a scope trace?
Pio1980
AK Member
Put the o'scope inputs on the power rails at various points and drive the thing into a proper load up to rated power and look for drooping and any sign of signal impression.
Pio1980
AK Member
I think they also went into the last and largest Dynaco tube amps.
ricohman
Adventure Rider
Very informative thread. I think I need to read it a few times to soak it up and understand it all.
As an owner of Dynaco MK VI's driving Klipsch and Altec 19's, I am kind of like the guys you decribed! My big amps sound great but the efficiency of the Altecs is probably disguising the shortcomings of these amps!
As an owner of Dynaco MK VI's driving Klipsch and Altec 19's, I am kind of like the guys you decribed! My big amps sound great but the efficiency of the Altecs is probably disguising the shortcomings of these amps!
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This comes down to the heart of what the hobby is all about. We can read all sorts of fantastic specs and measure all we want but, in the end, it is the musicality that traverses our ears and satisfies our brain that really counts. The specs might be perfect but we are imperfect and widely disparate analog beings and so a singular definitive set of specs cannot satisfy every combination of different human senses. If it did, there would probably only be one equipment manufacturer and one product choice because we would all agree on what was the best and sounded the best. Vive la difference!
An engineer might be only satisfied by test results for their "technical" audio satisfaction - or might not if they are also sensitive to subjective results. To buy something on the basis of specs alone makes no sense to me unless that product performance also necessarily satisfies ones need. I have heard many systems with great specs that sound like sterile fatiguing electronics equipment and not like items that generate emotionally satisfying musical content. How many here like console amps when they know that they, by design, have a limited compromise performance vs. the premier HiFi products.
If the specs guarantee satisfaction then one tends to buy & use such a product (e.g. that a parachute will open 100% and will operate correctly and effectively for the load over the intended altitude and distance to termination, with proper control of terminal velocity to provide minimum impact and maximum, or at least adequate, safety). However, for audio, my advice would be that, where practical (not in the case of parachutes and such!) try to test drive the product and add that to the choice menu.
Seemingly what you heard from Micah's design was gratifying to you, such that you were motivated to find one for your self. I find it best to enjoy the hobby and cherish the musical enjoyment it provides rather than get stuck with numbers and comparisons.
Dave's findings provide us with qualified measurements that can be used to aide in the decision of whether to use and how to use this design. This is very helpful technical information. It is not a measure of what enjoyment this piece of equipment could bring (although it might point towards or provide expectation guidance) but, rather, it frames the performance parameters so that a designer can work from a firm basis of data to achieve desired technical results.
Yes, 8417s were used by only a few as noted above. Other users:
- Fisher SA-1000
- Quicksilver Audio
- Wawasee Black Cat Mobile Tube Amp
- Harman Kardon Commander
and several others that do not immediately come to mind.
nj pheonix
Lunatic Member
A quick question ,
I know its only mono but have you tried to listen to it as it is. I was just curious how it sounded to your ears (totally unscientific)?
I know its only mono but have you tried to listen to it as it is. I was just curious how it sounded to your ears (totally unscientific)?
Tink -- I couldn't have said it better myself. Ultimate enjoyment of the music presentation is the principle end goal of this hobby -- but is a goal that is different for each of us. In that regard then, specs mean little once that goal is achieved -- unless you are the Jones' who only care about how many people are trying to keep up with you.
Specs do serve a purpose though, and particularly so with the search. After all, a unit that is represented to be one thing, but is in fact quite another, can cost big dollars as a mistake in the end -- unless you trust others golder ears, or trust that the piece you fell in love with will sound the same on your equipment at your place.
Ultimately then, they are an aid in our search, but like everything else in this world, need to be kept in perspective -- and perspective on this unit is ultimately what this thread was all about!
kward -- In addition to Pio's comments, power supply modulation can also often be seen in the output signal of units with marginal B+ filtering to the output stage. As maximum power output is approached (onset of clipping), the area just under the peaks of the sine wave will begin to fill in with noise, indicating the power supply is showing strain. It was at this point that the Bogen registered 242 watts of power output. When the level was backed down just enough to eliminate the fill in, power was then found to be 215 watts.
NJ -- No, I haven't listened to it just yet. Frankly, the unit is a bit noisy (hum wise) for me on my Cornwalls. However, I am working on a plan for this unit. If I go forward with it, I will of course listen to the original design before doing anything first, and then address the noise issue going forward.
Dave
Specs do serve a purpose though, and particularly so with the search. After all, a unit that is represented to be one thing, but is in fact quite another, can cost big dollars as a mistake in the end -- unless you trust others golder ears, or trust that the piece you fell in love with will sound the same on your equipment at your place.
Ultimately then, they are an aid in our search, but like everything else in this world, need to be kept in perspective -- and perspective on this unit is ultimately what this thread was all about!
kward -- In addition to Pio's comments, power supply modulation can also often be seen in the output signal of units with marginal B+ filtering to the output stage. As maximum power output is approached (onset of clipping), the area just under the peaks of the sine wave will begin to fill in with noise, indicating the power supply is showing strain. It was at this point that the Bogen registered 242 watts of power output. When the level was backed down just enough to eliminate the fill in, power was then found to be 215 watts.
NJ -- No, I haven't listened to it just yet. Frankly, the unit is a bit noisy (hum wise) for me on my Cornwalls. However, I am working on a plan for this unit. If I go forward with it, I will of course listen to the original design before doing anything first, and then address the noise issue going forward.
Dave
Personally if I owned efficient speakers like Khorns, or Altecs, the Bogen wouldn't even be on my radar, it just wouldn't make sense to me, as I think I could find a much better amp of known quality for that application.
On the other hand some speakers such as some of the ones I own are known to sound best on tubes, but they demand significantly more power than most tube amps provide. The DQ 10's and AR9's are a much less difficult speaker load than some of the Infinity's and considering that I was somewhat hopeful that the Bogen with its capacity could be able to be an alternative to other more expensive amps that are known to sound good. I wouldn't have any problems if one came my way to give one a try, but I don't think I would want to spend a bunch of money getting one up to spec only to find its short comings.
Besides it is best to not hype up something to much, that is unless you want the rest of the world to rush into a frenzy and drive the prices beyond affordable.
On the other hand some speakers such as some of the ones I own are known to sound best on tubes, but they demand significantly more power than most tube amps provide. The DQ 10's and AR9's are a much less difficult speaker load than some of the Infinity's and considering that I was somewhat hopeful that the Bogen with its capacity could be able to be an alternative to other more expensive amps that are known to sound good. I wouldn't have any problems if one came my way to give one a try, but I don't think I would want to spend a bunch of money getting one up to spec only to find its short comings.
Besides it is best to not hype up something to much, that is unless you want the rest of the world to rush into a frenzy and drive the prices beyond affordable.
If thats the piece of gear I think it is, thats actually a CB linear amp, not an audio amp.
ab0ez
AB0EZ
It is.
Sincere kudos to Dave for doing this work!
My faith in humanity is restored! Well, that comment is a little over the top. Like many of you I was hoping for a diamond in the rough. However, at the same time it bothered me that a well respected for profit commercial sound company would design and sell an amp rumored to be "the end all" for high fidelity sound reproduction. It bothered me they would over design and hence, have to charge more, while trying to capture competitive market share. For that, my faith is restored, that the engineers and accountants did in fact design, build, and market to the targeted customer requirements and nothing more.
The other thing I'll take away from this thread is the almost comical low quiescent current the output tubes draw at idle. In my opinion, that was a very clever way to insure long life, especially, as an earlier poster pointed out, that these amps were likely left turned on 24-7.
My faith in humanity is restored! Well, that comment is a little over the top. Like many of you I was hoping for a diamond in the rough. However, at the same time it bothered me that a well respected for profit commercial sound company would design and sell an amp rumored to be "the end all" for high fidelity sound reproduction. It bothered me they would over design and hence, have to charge more, while trying to capture competitive market share. For that, my faith is restored, that the engineers and accountants did in fact design, build, and market to the targeted customer requirements and nothing more.
The other thing I'll take away from this thread is the almost comical low quiescent current the output tubes draw at idle. In my opinion, that was a very clever way to insure long life, especially, as an earlier poster pointed out, that these amps were likely left turned on 24-7.
OK. And from experience with the lesser power model, "linear" is a very generous term. These are quite non-linear in nature and by design.
ab0ez
AB0EZ
Especially when they were usually overdriven into, let's just say, less than optimum antennas. Great for tearing up the neighbor's television reception in your block!
rpampt
Analogeous Vinylitis
Ahh diamond in the rough! I was hoping for such as well, but as was somewhat expected by Dave, the overall specs just don't prove that out. At least not in stock form. Hopfully I'm not out of line in speaking for Dave, but in our discussions he has mentioned that although the Bogen doesn't have perfect specs on paper, it could sound quite pleasing as a hifi amp to many people, me included. Others using this and other amps similar to it are very happy and rave at the performance. That's great. I may go the same route, But that does not change the fact that the specs aren't competitive with the Dynaco MK III's on paper, which was a goal.
Anytime anyone here on AK does some work on gear, their name can be attached to that work indefinately. Therefore, if going in, we know that a conversion would still leave the amp lacking in some areas (on paper at least), Dave is attaching his name to something that could be questionable, not in quality of work, but in tested performance. So I certainly understand why it's nice to have specs to back up the great sound that hopefully goes along with it.
Thus far, Dave has gone the direction that we both agreed on, and that was to test and see just what it was capable of in stock form. At the same time, putting the information out to our AK brothers and sisters and possibly either prove or disprove some estimations. At the same time come up with some possible solutions if the amp was truly found lacking. Now some decisions have to be made.
We are leaning forward towards some type of mods, but haven't completely decided which way to go. But I don't think we are to the end of the journey just yet.
Anytime anyone here on AK does some work on gear, their name can be attached to that work indefinately. Therefore, if going in, we know that a conversion would still leave the amp lacking in some areas (on paper at least), Dave is attaching his name to something that could be questionable, not in quality of work, but in tested performance. So I certainly understand why it's nice to have specs to back up the great sound that hopefully goes along with it.
Thus far, Dave has gone the direction that we both agreed on, and that was to test and see just what it was capable of in stock form. At the same time, putting the information out to our AK brothers and sisters and possibly either prove or disprove some estimations. At the same time come up with some possible solutions if the amp was truly found lacking. Now some decisions have to be made.
We are leaning forward towards some type of mods, but haven't completely decided which way to go. But I don't think we are to the end of the journey just yet.
s-petersen
Scott
I would be curious, if with with the proper feedback,if the amps could be made into a slightly lower power Hi Fi amp.