Author Topic: Amp 182BA experimentation  (Read 8054 times)

AlexanderMartin

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Amp 182BA experimentation
« on: January 04, 2016, 11:18:03 AM »
I recall seeing a thread awhile ago talking about the lack of bass response from the Magnavox bi amped units, and I also share the sentiment that the bass response is quite poor from these amplifiers. I decided to do an experiment, so I hooked up my laptop to a JDS Labs ODAC which is simply a DAC that has a good 2.1v of maximum output coming from it, quite adequate for a power amplifier. I decided to bypass the tuner, and hook it right up to the amp. One of the big issues I have is how absolutely overbearing the horns are in contrast to the woofers. I find this fascinating, as the woofers have push pull 6V6's while the tweeters are single ended, but the difference it output is ridiculous. This is most likely why the put as many treble controls as they did, because without them the unit's treble is far too much. I EQ'd the frequencies right at around 2k and bumped it down to an appropriate level, and once that happens the bass becomes even however it doesn't get nearly as loud as many units I've seen. As much as you guys may disagree with this, I am going to experiment with the front end of the bass amps and see if I can find what exactly is knocking the output down so much to the point where it's less then half in comparison to the treble output. if I can find what it is, it's going to go away for good. I'm assuming they did this for the same reason there's a huge resistor on the output of a Magnavox Windsor, as a sort of insurance so they didn't blow the speakers.

Here is the front end of the bass channel, there's some things out of the ordinary but this stuff is weird. I think L1, C4, and R4 are part of the crossover for the speakers. The .022 obviously isn't helping the bass response, so we're gonna put in a .1 to get the proper frequency response in the unit. What is interesting me is the R5 100k that the signal passes on that comes right after the coupling cap, this seems quite unusual to me as to why they did that. Spo I'm gonna experiment and see what exactly these things are doing in the circuit.

Wish me luck on finding the source!


voxACthirtee

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Re: Amp 182BA experimentation
« Reply #1 on: January 04, 2016, 12:15:39 PM »
i've wanted to mess with this for a while now. I'm "self taught" in this and understand the basics, but thats more of an advanced filter than i'm familiar with. I'd love to tweak the crossover frequency and/or make it adjustable with a rotary switch.

To me it doesn't present itself as just a simple RL or LC filter, which is where it loses me.

Since the frequency of boost or cut in a circuit is effected by circuit impedance, i'd guess that in this circuit just changing it to a .1 might change more than just how much low passes.

I read a post on AK  where a guy wanted to use a 182 as an amp for an E-Wave(Simple 2 way with Horn) Speaker, but he went through the 182 and changed values to the simulate values in the E-Wave speaker crossover.
But the impedances in a passive speaker crossover driving speakers will be different than a circuit
driving a 12AX7 tube grid, no? The "E-Wave" concept is meant to crossover at about the same frequency as the Mag already crosses over. So there's that. I was going to contact him eventually to inquire, but have not yet.

I'm a Mac guy, so i can't use it, but if you have Windoze you can download Spice and simulate the circuit.
I'm very interested in knowing with some certainty what the original Mag crossover frequency is, and what can be done with it.(Changing the Cap or Resistor after the Inductor will raise or lower the filter Frequency)

AlexanderMartin

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Re: Amp 182BA experimentation
« Reply #2 on: January 04, 2016, 01:09:19 PM »
I was personally thinking of changing the crossover, supposedly these are crossed over at 1khz, which in my opinion is quite low especially for a compression driver IMO. I'd probably bump it up to 2khz, I know the woofers can easily do that. First things first of course, we can experiment with crossovers later. Glad to see I'm not the only one interested in this.

voxACthirtee

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Re: Amp 182BA experimentation
« Reply #3 on: January 04, 2016, 09:48:09 PM »
So i finally came up with a calculator i think actually works/fits.

For the low pass anyways-

http://sim.okawa-denshi.jp/en/RLClowkeisan.htm
(scroll down and use the bottom calculators)

When i punched in the BA182 i get a hair over 1Khz as the filter.
The Inductors are all .725Henries per the SAMS.
Changing the R4 changes the "Q" and changing the .033 Cap to ground changes the frequency. Going to a .0085 cap gives you about 2Khz.

That .022 cap would then just be a coupling cap and the 100k/100k is then just a simple voltage divider busting the signal down before the tube Grid.
(Equal leg voltage dividers drop signal voltage 50%)

i'll try to figure out the high pass tomorrow

AlexanderMartin

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Re: Amp 182BA experimentation
« Reply #4 on: January 05, 2016, 04:31:35 PM »
Fantastic work! Will apply that knowledge, this could be a good thread if I manage to actually get this rolling.

voxACthirtee

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Re: Amp 182BA experimentation
« Reply #5 on: January 06, 2016, 11:42:41 AM »
From the same site for the high pass-

http://sim.okawa-denshi.jp/en/RLChikeisan.htm

If you enter the values from the 182 it does come up with the same 1kz filter.
Thats entering the values for the inductor - .725H, C16 - .033 and R33 - 2.2k.
SO that math works. But the .068 that essentially bypasses the 2.2k resistor, i don't know what it does for sure.
My depth on filters is not great. Also, changing C16 - .033 to the same .0085(do they make an .0085?)
gets you to the same 2K ish point for a high pass, but it will
give you a peak at the crossover point that you can seemingly smooth out by changing R33 to a higher value.

Thing is, these circuits never seem to be as simple as punching values into the calculator,
so i'm not sure its that simple. I think the lowpass is ok, just not sure how C24/.068 effects this circuit.


I'm in the boat where i bought the guts of '60 Imperial w/182BA, from a guy who trashed the cab,
So i'm looking for an EMPTY Imperial(or GC) cab to populate, and my shop is in my barn, and technically not heated, so i'm not sure when i'll could get to this either, but knowing now where to start, might be motivation to fire up the kerosene heater....

AMP82-01-00

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Re: Amp 182BA experimentation
« Reply #6 on: January 07, 2016, 09:51:14 PM »
Problem is a amp 182ba has small output transformers for the bass channels compared to the later updated imperial 81 series amplifiers. I was never impressed with mine. It takes big transformers to give you bass that can rattle stuff on the walls.
David        "If it ain't interesting, its really just boring"

AlexanderMartin

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Re: Amp 182BA experimentation
« Reply #7 on: January 07, 2016, 11:22:55 PM »
Problem is a amp 182ba has small output transformers for the bass channels compared to the later updated imperial 81 series amplifiers. I was never impressed with mine. It takes big transformers to give you bass that can rattle stuff on the walls.
Not true, it all depends on the efficiency of the speaker drivers. Transformer size mainly indicates power handling and low frequency extension, not the actual amount of bass that's present.

AMP82-01-00

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Re: Amp 182BA experimentation
« Reply #8 on: January 08, 2016, 07:22:29 PM »
By the same logic you could change the trebel ch to a bass channel. those are tiny transformers that won't deliver much low end regardless of speaker efficiency.

Then you hit the wall with how much bass a thin cone high efficiency driver can deliver.

So yes you can improve bass with proper speakers vs improper ones.

It's like making a 4 cylinder engine move a 8000 lb truck it may do it ok with exelent gearing but a v8 it will push it much easier.
David        "If it ain't interesting, its really just boring"

voxACthirtee

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Re: Amp 182BA experimentation
« Reply #9 on: January 09, 2016, 11:24:04 AM »
Thats kind of an apple and oranges comparison, but i will say that it doesn't seem that even on the vaunted CG, that magnavox ever went all out on transformers. If you've seen(and i'm sure you have) the quality/size of hifi transformers that followed in the 60's on component units. They really upped the game.
I'd guess Magnavox made the usual compromise between quality and affordability, but i wouldn't
specifically choose an old Mag output to build ANY hifi if i were inclined to build one.
Fisher/HK/Dynaco/etc would be something i looked for.

And really while size DOES matter, its not about size specifically.
there's plenty of line and microphone transformers the size of a 10 stack of quarters where the specs are off the charts.
So something that small can reproduce the full spectrum and beyond what we can even really hear.
In this case it's more about efficiency. That little treble transformer may very well spec out to 20hz-20khz,
but there won't be enough iron/windings to actually pass much full range signal to a speaker.
And i'd imagine it would start to saturate pretty quickly at that.

If you visit the diy audio world(as i don't think anyone makes them commercially)
you'll see guys building SE EL84, or even lower output amps, using a good, but not huge OP transformer,
and raving how good/loud/punchy/deep they sound with a good high sensitivity speaker like a Heresey.
Even the Mag SE EL84 amps sound suprisingly half decent. And in those i've seen the oldest ones with SMALL OP transformers, and have seen the 60's ones where they went with larger ones.

For THIS project, i ended up purchasing the guts of an Imperial from a guy who trashed the cab.
So i'm looking for an empty Imperial or CG cab thats restorable. If i can't find one i may build a console type cab.
Either way, my though is to possibly  go TRI-Amp. Use the 182BA for mids/highs, and build a stereo amp for the low end at about 30-40ish watts per side using a pair of 6L6 per side
for the low amp and use a ribbon tweeter for the high end.
Not sure i can make that all work without an external crossover, but at least i've kinda figured out the math for the 182BA, so it s a start.
Since i probably won't find an empty Imperial or CG, it may take me a while anyways.


AlexanderMartin

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Re: Amp 182BA experimentation
« Reply #10 on: January 09, 2016, 11:36:07 AM »
You can actually do that, but tiny little treble transformers will not extend down to 100hz or below or even 500hz. You are claiming that the bigger transformers on the CG provide more bass, even though there are more 6V6's per woofer on a CG. A larger transformer does nothing except extend frequency response into sub regions, and provide higher power handling capacity, and if otherwise please provide some evidence proving so. Granted, this experiment isn't to get a 182ba to extend to say 30hz, but it DOES have low end that is being attenuated in circuit.
We are talking about how much bass this unit provides, not how low it can actually go. I've heard many tube based maggies with small-ish transformers that provide plenty of bass, as well as other tube based unit. I think you're getting confused with freq response and the actual amount of bass present.
Also, Vox is right on the money, when it comes to transformer standards Magnavox always seemed to skimp out, probably so things weren't insanely expensive.

AMP82-01-00

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Re: Amp 182BA experimentation
« Reply #11 on: January 11, 2016, 02:28:39 PM »
Ill try clarify my thoughts.
 
Thats kind of an apple and oranges comparison, but i will say that it doesn't seem that even on the vaunted CG, that magnavox ever went all out on transformers. If you've seen(and i'm sure you have) the quality/size of hifi transformers that followed in the 60's on component units. They really upped the game.
I'd guess Magnavox made the usual compromise between quality and affordability, but i wouldn't
specifically choose an old Mag output to build ANY hifi if i were inclined to build one.
Fisher/HK/Dynaco/etc would be something i looked for.

And really while size DOES matter, its not about size specifically.
there's plenty of line and microphone transformers the size of a 10 stack of quarters where the specs are off the charts.
So something that small can reproduce the full spectrum and beyond what we can even really hear.
In this case it's more about efficiency. That little treble transformer may very well spec out to 20hz-20khz,
but there won't be enough iron/windings to actually pass much full range signal to a speaker.
And i'd imagine it would start to saturate pretty quickly at that.

If you visit the diy audio world(as i don't think anyone makes them commercially)
you'll see guys building SE EL84, or even lower output amps, using a good, but not huge OP transformer,
and raving how good/loud/punchy/deep they sound with a good high sensitivity speaker like a Heresey.
Even the Mag SE EL84 amps sound suprisingly half decent. And in those i've seen the oldest ones with SMALL OP transformers, and have seen the 60's ones where they went with larger ones.

For THIS project, i ended up purchasing the guts of an Imperial from a guy who trashed the cab.
So i'm looking for an empty Imperial or CG cab thats restorable. If i can't find one i may build a console type cab.
Either way, my though is to possibly  go TRI-Amp. Use the 182BA for mids/highs, and build a stereo amp for the low end at about 30-40ish watts per side using a pair of 6L6 per side
for the low amp and use a ribbon tweeter for the high end.
Not sure i can make that all work without an external crossover, but at least i've kinda figured out the math for the 182BA, so it s a start.
Since i probably won't find an empty Imperial or CG, it may take me a while anyways.





This is what i was meaning well said voxACthirtee!  also i think 6l6 tubes will give a good punch for your bass channel. Your tri amp idea is awesome.

I at times have a complex of the "if a little is good then more is better" years ago my first tube amp was a 8601 SE 6bq5 Magnavox amp. it amazed me on how much sound came out of roughly 3-5 watts a ch. So then I wanted a Amp 175 thinking it would be better. it had more bass but wasn't really any louder. Next I hear about concert grands and how great they are. so i got a set of amps off ebay and was not impressed at all so i sold them. later on im told they need a very strong preamp signal to sound good. then feeling like a idiot i buy another set of amps. and ran a mcintosh mx112 through them and i was amazed! and hooked! then i actually get a real CG and go through this limitations of the tuner/preamp. It took awhile to understand what a Cg needs to sound good and produce deep bass.

Room acoustics and placement make a big difference in how you hear a radio.

AlexanderMartin 
I was comparing it it the 81 series that's in the imperial consoles not the concert grands. The BA182 and 81 series are very similar except the output trans are different.   
Problem is a amp 182ba has small output transformers for the bass channels compared to the later updated imperial 81 series amplifiers. I was never impressed with mine. It takes big transformers to give you bass that can rattle stuff on the walls.

Guys i hope i didn't come across rude i truly enjoy all tube amps. plus after hearing the BA182 will be highs and mids changes my opinion greatly. my continental had a BA182 and i didn't care for it too much at the time because i had a 9300 stereo 6BQ5 amp that to me sounded better.

I often wondered why magnavox didn't use a pair 6l6gc for the bass ch in concert grands. but seeing 8 6v6 tubes glowing is cool i guess. Im told by some guitar guys 6v6 are more musical.

oh well happy monday all! This is a great thread covering the crossover network of bi amped or dual frequency amplifiers.
David        "If it ain't interesting, its really just boring"

Pat L

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Re: Amp 182BA experimentation
« Reply #12 on: January 11, 2016, 03:54:41 PM »
Guys, we've discussed this issue in other threads, but I'd like to bring it up here. Lots of people use the tape or MPX inputs as their source. If you connect anything to these units you must use the phono inputs for proper bass response. It has an extra stage of amplification that the other inputs lack. They were designed for components like RTR's and MPX decoders that also amplified the signal. Trust me on this, use a switch tied into the phono input so you can use it for all your sources. The bass will come alive.

Pat L

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Re: Amp 182BA experimentation
« Reply #13 on: January 11, 2016, 03:57:21 PM »
The 9300 is blown away by the Imperial amp when driven through the correct inputs as I stated above. All the Magnavox bi-amp instruments have this in common, including the Concert Grand's. You will be amazed.

AlexanderMartin

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Re: Amp 182BA experimentation
« Reply #14 on: January 11, 2016, 04:25:07 PM »
That doesn't detract from the fact that you can hook up a 2.1v source right into the amp and tell immediately using an equalizer that the bass has been artificially attenuated, and seeing some of the stuff in the front end it's obvious. There is absolutely no reason for a single ended treble stage to be louder then a push pull stage using a 15" woofer. There is something going on here and I will solve it.