Just to clarify, do you get enough volume using your EPI speakers driven by the Magnavox amp when using the CD player as a source?
More Fun With Magnavox: The 9300 Series
- Thread starter dcgillespie
- Start date
Just to clarify, do you get enough volume using your EPI speakers driven by the Magnavox amp when using the CD player as a source?
Chip2020
Active Member
Definitely agree with you, gadget,
It's a matter of taste. Any high-efficiency set of speakers (>92db) that suites both his ear and his wallet would be his best option.
ArchieType
Active Member
Yes.
ArchieType
Active Member
I had a pair of KG 3.2s for about fifteen years, bought new. Excellent for the price.
Then you don’t need new speakers, you just need a way to boost the output from your phone. This can be a preamp as others have mentioned, or a phone docking station that has a digital out into a DAC.
While both of these solutions *could* cost many thousands of dollars, they don’t have to. You
can spend under $100 to accomplish the same thing.
agree, if its loud enough with the CD player, you just need some gain. Phones tend to have garbage output level. I've had exactly one amp that didn't need more gain, but it was just an insanely sensitive amplifier. It was actually too sensitive to be useful with anything else, but it was brilliant fed straight off my ipod.
Chip2020
Active Member
I know what you're trying to say here 6DZ7, but I don't subscribe to the, "if they sound good, they are good" philosophy. Those EPI 200C speakers take between 15 and 125 watts RMS to drive. At full blast, the Magnavox 9300 series amp would not only fall short of the threshold voltage required to move the cones properly but would likely be past its optimum performance curve (increased distortion).
With these speakers connected to the 9300 and a CD player providing a relatively high line-level input, one may hear some sound at a decent volume, but is it good? The answer to this question is very subjective. Listening to a speaker and evaluating its quality when the audio input source is a CD player (CDA audio files are basically just 128Kb MP3 files) is already a ridiculous place to start evaluating a good speaker like an EPI 200C. But it gets worse from here. The 1" tweeter may sound pretty good, but the anemic RMS voltage from the 9300 would barely even move the cone of the 12" passive radiator. This leaves the 8" woofer to handle the midrange and lower frequencies all by itself (like an old paper cone television speaker), which will sound flat and make the crossover circuit moot. So ultimately, the sound you are hearing will have a non-proportional high end, with a dynamically weak (lack of definition) midrange and bass that barely exists.
Will this sound terrible? Believe it or not, unless you compare it to another set of good speakers with higher efficiency, or by using an amplifier with a higher output, you may think it, "sounds good", but bench testing would show otherwise.
This is why a large majority of Millenials who stream MP3s on their iPhones into a pair of earbuds, think that they're music aficionados. It's not until they hear a high-quality music source (records, tapes, flacs, etc.) fed into a good amplifier (hopefully a tube type) and ultimately a great set of speakers, do they realize what they've been missing. Without a comparison, claiming that, "it sounds good" may not be good enough.
I always augment my subjective opinion about the quality of what I'm hearing with some objective test results (especially as I get older). Oscilloscopes, frequency and distortion analyzers, power meters, and a host of other electronic test equipment are used regularly in my lab to help make accurate comparisons between what just "sounds good" and what sounds (and is) great.
kentuckycat
Active Member
Looking forward to this thread getting back to the Magnavox 9300 amplifier.
ArchieType
Active Member
Sorry for the inadvertent hijack I started. I really didn't mean for it to go off the rails.
But given that the thread is 74 pages long, and the 9300 mods have been exhaustively covered, I don't think much damage has been done.
However, I do believe that the issue raised - that of insufficient power for driving vintage speakers with the buffered amp as designed is germaine to the discussion, and someome, beside myself might benefit from the insight provided by the detour.
kentuckycat
Active Member
Fair enough. When I decided to get into old Magnavox pulls, the first one for me was the 8600 “flea amp”. You can count the watts on one hand. So I knew I would need a pair of efficient speakers and I wanted big enough ones to provide some bass. My list was short, JBLs or Klipsch. I found a pair of Klipsch quartets for less than $500 and I was on my way. Playing the music from my phone to my amp with RCA cables was good but not great so I pulled the pins on my Pioneer receiver, plugged my phone into aux jacks and the Pioneer into the flea amp. Big difference. Now I was getting somewhere. The biggest audible difference for me was adding a Schiit DAC to the mix because Bluetooth takes so much out and iPhones have a 10 cent DAC in them. I don’t know too much about your current speakers, but I do tend to agree with Chip2020, efficiency is huge when the driving amp doesn’t have a lot of power. My 9300 tied to my ~ 98dB eff speakers can get up and go. Something to think about. Question; you said your sx-950 was not working. Is it possible that the preamp portion is working? You could pull the preamp pins and find out.
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markmcmuz
Well-Known Member
Here is my second 9300 DG build. Next step will be a hardwood case. This one is dead silent and via my oscilloscope it's putting out 20 watts per. Is that possible? 26v peak to peak into 8 ohm dummy loads. Big step in my tube journey: had a problem with low output in one channel but instead of panicking and pleading for help I diagnosed it and found the NOS buffer tube only works on one half. Finding out also that "matched" tubes are not always "matched" very well.
Attachments
They are a pretty good sounding amp. I should put mine back in rotation just because its been a while and I don't think I've actually run it in my current setup. I'm sort of curious how it will do. If it holds up OK maybe I'll run it in the summer. Should put out a fair bit less heat than what I'm using now.
ArchieType
Active Member
Hey Gadget73,
For us slow kids in the back, could you do this magic again, but this time with notes and arrows, so we can maybe get the idea of how to perform the trick ourselves? I've managed to set plate dissipation, (and thus calculate output wattage) on a number of guitar amps I've built, but the formulae and such never quite stick to the old brainpan.
Too much brown liquor, or passing notes in class perhaps, yet I remain optimistic that someday this will click. And stick.
markmcmuz
Well-Known Member
I derived mine using an oscilloscope with a signal generator. Increase the input voltage till your sine wave starts to flatten at the top and bottom back it off till it looks ok check peak to peak voltage divide by the 2. something ( that extra something it to convert to rms-I forgot that and divided by just 2 hence the wrong number) square that and divide by ohms of dummy load 8 in my case.
so the 26 volts was his peak to peak measurement on the scope. To convert peak to peak volts to RMS, you divide it by 2.828.
That gives us 9.2 volts RMS
The formula for determining power when you have voltage and resistance is voltage squared divided by the load, so (9.2 * 9.2) / 8
or 84.64 / 8 which is 10.58 watts RMS
If you need to do voltage conversions, thats not hard either. Generally speaking you'll deal with peak volts, peak to peak volts, or RMS volts. A pic to explain what I mean here
On a scope, peak to peak is simply the voltage from the most negative point to the most positive point.
Peak voltage is from the zero line to the highest (or lowest) point. With a normal, symmetrical sine wave, this is 1/2 of the peak to peak voltage, so to convert p-p to p, simply divide by 2.
RMS is a little more complicated, but basically its a value that is equivalent to DC power. For a sine wave, this is peak volts / 1.414, or peak * 0.707. Comes out to the same thing.
Juggling that around a little, since peak volts is 1/2 peak to peak, and to convert peak to RMS we divide by 1.414, if you want to convert peak to peak to RMS you can simply divide it by 2.828. Or divide it by 2 and then by 1.414, both will give the same answer.
If we're talking other wave forms, the RMS conversions are different.
dogwan
Dogwan
Finally got around to putting the DCG-9302 into full rotation!
The Hafler speakers are 88db sensitive and 4Ω nominal. Although I think they are a little more efficient than those specs would indicate.
I'm running a cheap and cheerful Celestion S20 subwoofer (ported 8") off to the side, which has a line-level high pass 100hz crossover. So, I am running the pre to the sub, and then the sub feeds the amp via RCA's. Still dialing in the sub integration in. But so far it's sounding really good. I don't think the Sovtek output tubes are even anywhere close to broken in yet.
Compared to the PSE Studio IV amp I just pulled out (100wpc/8Ω... 195wpc/4Ω) you would hardly notice that it's < 15wpc! Comfortable listening levels that are just on the cusp of annoying my downstairs neighbors is still only at about 10:00 on the volume knob.
The Hafler speakers are 88db sensitive and 4Ω nominal. Although I think they are a little more efficient than those specs would indicate.
I'm running a cheap and cheerful Celestion S20 subwoofer (ported 8") off to the side, which has a line-level high pass 100hz crossover. So, I am running the pre to the sub, and then the sub feeds the amp via RCA's. Still dialing in the sub integration in. But so far it's sounding really good. I don't think the Sovtek output tubes are even anywhere close to broken in yet.
Compared to the PSE Studio IV amp I just pulled out (100wpc/8Ω... 195wpc/4Ω) you would hardly notice that it's < 15wpc! Comfortable listening levels that are just on the cusp of annoying my downstairs neighbors is still only at about 10:00 on the volume knob.
When you get a sub right it really makes a nice difference. Mine has an internal high pass but its too high and I don't use it. One of these days I need to map out the components and figure out what the crossover point is, and determine how to mess with it. I think it crosses around 180, I'd rather it be not over 100. Above that it starts getting directional and I can hear things coming from the sub instead of just getting some bottom end fill. Since its behind and to the right that really screws up stereo effect.
dogwan
Dogwan
I'm actually considering getting a MiniDSP just for situations like this. I've always been a purist and scoffed at any digital manipulation. But they seem to have come a long way and really come down in price. I used to have a Heathkit AD-1702 that I rebuilt and then never used. Ended up selling it. Kind of regret it. Would have been perfect here.