tech

I recently bought a 1982 Marshall 4210, the 1x12 combo version of the 2205 head. Both channels sound a bit too harsh or tinny, regardless of settings




I recently bought a 1982 Marshall 4210, the 1x12 combo version of the 2205 head. Both channels sound a bit too harsh or tinny, regardless of settings. I’ve tried varying the settings, the EQ, driving the power amp hard, the preamp hard, etc., and it always seems to lack that solid midrange punch that I usually expect from a Marshall. The speaker appears to be an original, an 80-watt, 15-ohm Celestion. What is your thought as to why the sound is like this? Could the speaker need to be replaced? Does it need new tubes (or at least a bias job)? It has 6550s in the power stage. Thanks for your time.

-Tom


Tom,
Since the amp is a 1x12 combo configuration, it’s never going to have the tone and feel of a head and 4x12 cabinet, but there are definitely a few items here we can look at to help better your tone.

First I’d consider replacing the output tubes. I believe most of the “solid midrange punch” of which you speak is typically generated by the tube that made the Marshall sound famous, the EL34. Years prior to the production of your amp Marshall had converted to the use of 6550s in export amps when they began to suffer reliability problems with the EL34s available at the time. Since the EL34s would not last through the warranty period, the warranty repair of export amps became increasingly costly and the decision was made to install the more rugged 6550 tube. On the upside, warranty claims declined. On the downside, the much-loved Marshall tone had changed. The tone signature of the newer 6550s contained more top and bottom end, and while eventually proving to be better suited for “heavier” music, the rich midrange content was now missing.

Sound familiar? Have a tech replace your 6550s with a nice set of EL34s and you should notice a substantial difference. Just know that he will need to replace a couple of components in the bias supply in order to bias the EL34s properly, so it’s a little more involved than a simple biasing. While you’re having the output tubes replaced, you should probably have the preamp tubes replaced as well. Since all preamp tubes have different tonal characteristics, tell your tech what you’d like to hear from the amp and hopefully he can suggest the best tubes for the tone.

Next I’d consider replacing the speaker. While there’s nothing wrong with an 80- watt Celestion, a 25-year-old version may be a little tired and in need of retirement. Replacing the speaker(s) in an amp can be one of the best ways to bring it new life, and luckily there are a plethora of speakers now available. I believe the biggest selection is now being offered by Eminence, whose Red Coat series is “British voiced” and would be well suited to your Marshall amp. Another option would be to drop in a Budda Phat 12, which is sonically a cross between a Vintage 30 and a G12-80 and would be a great match. While you’re at it, I would also suggest replacing the stock speaker cable with an upgraded cable. We recently began installing Monster speaker cables in our amps, and it definitely improved the bass and mid content.

One last item you might want to consider. Since your amp will more than likely be taking a trip to your local technician for an EL34 conversion, you might want to have him replace the capacitors in the power supply. A fresh set of filter caps in an amp of that age can certainly improve the tone and response of the amp. Incorporate all these upgrades and the amp should be a lot closer to what you expect to hear.

But you want it even better, you say? Okay, here’s a little extra mod for you. It may get a little technical, but a good tech will know exactly what I’m talking about. Replace the four .022uf signal caps in the Master Volume circuit with .047uf or 0.1uf caps. The Master Volume circuit in these amps is a post phase-inverter type which uses two .022uf caps in series for each half of the phase inverter signal. The problem with placing two .022uf caps in series is that the value then gets reduced to 0.011(0.01)uf, which will begin to attenuate some of the lower frequencies of the amp. Replacing them with .047uf caps yields a capacitance of .0235(.022)uf and using 0.01uf caps yields a .05(.047)uf capacitance, both of which will yield a fuller frequency response.

Now your tone can go to 11.

You want to be heard when you play!

As a musician, you want to be heard when you play. How loud you need to be to “be heard” depends on your style of music, the size of your audience, and venue.We buy amplifiers by the number of available watts, and expect that to translate to loudness. And it does, but in unexpected ways.

Our ears and brains perceive sound on a logarithmic scale. Here’s a table of examples adapted from Wikipedia (“Sound power”*) The middle column is the power of the actual air moving against your eardrums.We sense a doubling of power, which is a 3dB change, as a just-perceptible change in loudness. A sound that seems “twice as loud” has to be ten times the power, a 10db increase. That’s why the middle column of the SPLs is in powers of ten. Humans perceive a jackhammer as about twice as loud as a chain saw and a machine gun as about twice as loud as a jackhammer. A full-blown rock concert might only seem twice as loud as a machine gun.

Tech Views

The sound power is not the amplifier power you’d need to be that loud. Most amplifier power is wasted as heat in moving the speaker cone around; little of that gets radiated away as sound. The following table shows some speaker sensitivities as quoted by the makers, in sound pressure level (SPL) at 1W of amplifier power as heard one meter away from the center of the speaker, as well as the maximum amplifier power before they burn out. I computed the estimated maximum SPL column.

Tech Views

[N.B. - These are not necessarily representative of all the speakers from the manufacturer. For instance, all Jensens are not always the quietest and all Fanes are not the loudest speakers. Due to overloading and other factors, these speakers may not sound exactly as loud as this projection shows.]

Remember that 3dB is just noticeable and it takes 10dB to be a factor of twice as loud. So at 1W, the most efficient Fane is not quite twice as loud as the lowest efficiency Jensen P12R, differing by +8dB SPL. If we wanted to make the Jensen sound as loud as the Fane is at 1W, we would need to drive the Jensen with +8db of power, which is 6.3 times the power, or 6.3W (trust me, that’s the way the math works out). The Jensen is loudest at its max of 25W: 109dB SPL. The Fane produces 109dB when driven with 4W. So if you replace a Jensen P12R in a cabinet with a Fane AX.12.150, the amp now sounds like it is now six times the power as it was before.

And that gets us down to watts and loudness.Watts don’t make loudness alone; the amplifier power and the speaker efficiency together make loudness. You can make an amplifier sound like it has more watts by using a more efficient speaker; or like it has fewer watts by using a less efficient speaker.

If you simply must have the tone of an inefficient speaker, be prepared to buy a bigger amp to keep your loudness the same, or to use multiple speakers and amps to get the loudness back. If you must have more loudness and don’t want to change your amp, consider more-efficient speakers. Greater efficiency doesn’t always mean better tone; it just gives you more volume.

Keep speaker efficiency in mind when you’re wondering about watts – you might make that 50W amp sound like it has 100W … or 25W.

*article found at: http://en.wikipedia.org/w/index.php?title=Sound_power&oldid=82695953


R.G. Keen
Cheif Engineer
Visual Sound
www.visualsound.net

I have an amp that’s been sitting in the closet until recently

 I have an amp that’s been sitting in the closet until recently. It all began as I was in need of a bench amp, so I bought this a year back, based on a fond memory of those tiny Gallien Krueger 250ML 50-watt combos from the late ‘80s, early ‘90s. I hopped on eBay and found a GK ML/S 100-watt head – which was also made as a combo, although I had intended to find an ML/E which has built-in/adjustable delay/chorus. When I first received it, I plugged it into a 4x12 cab and it was real wimpy but loud; I thought that was just how it was, and that maybe it would be a pedal amp.

Mene Gene I planned on building a tiny combo out of it and started looking for some speakers. I sketched me up baffle boards to cut on the CNC. I started comparing specs of a Celestion Vintage 30 12-inch as my benchmark – having a frequency range of 70 - 5000 Hz – with that of various 6.5 inch speakers.

The GK is a 100-watt head, so I needed speakers that could handle it; I initially thought of 2x6.5 speakers, then opted for 4x6.5. The combined wattage equaled 300+ watts total, so I figured we’d be safe. Keeping with the mini GK theme, I used two Eminence Legend 675 speakers – built for small amps, rated at 75 watts, with a sweet midrange and frequency range of 180Hz - 4.5kHz. The other two I selected were Goldwood 6.5 woofers, with a freq range of 60 - 3,000 Hz, rated at 90 watts and they pumped up my low end nicely. The test was to see if we could get four 6.5s to sound anywhere near that of a single 12. The funny thing was that all four speakers cost the same as the Vintage 30 – roughly $110.

Keeping with the GK metal cabinet theme, I planned to dig up some light gauge steel and have it bent to create the bottom and two sides. Being a budget project, I was calling in favors and willing to use remnant materials to build it. My buddy Scott scavenged up some ¼” aluminum diamond plate, so bending it became out of the question, but the cool factor skyrocketed, so we cut three pieces for the bottom and two sides. The front and rear baffles were made from MDF with pine braces which connected the front and rear.

We were blown away; first, I found the wimpy gain problem was a cold solder joint on the input jack – once it was fixed, the ML/S had gain for days! I couldn’t believe how loud the “LMF” was and tonally, compared to a 1x12 combo, it hung in there just fine, and even bigger in our ears. Clean tones were beautiful and it didn’t fart out as I had worried.

Mene Gene Bear in mind the entire cabinet is only about 14” square and 7” deep, although with the extra mass of the aluminum and the magnet size of the speakers, it now probably pushes 40 to 50 lbs, like a stout mini fridge. But all in all, it was a fun distraction on a tiny budget.

The best yet has been sending the preout into a Yamaha SPX90, set for a 280 mill slap back, fed into the return on a Randall MTS 18-watt 1x12 combo; the two together could handle any job clean and easy. Talk about a fun day in the shop. It all makes me feel like the Mythbusters guys, tinkering with ideas – I guess it just goes to show that size doesn’t always matter and some pretty hip things can come in small packages. Not to mention, it’s fun to do something for yourself now and then to inspire new creations.



Gene Baker
Any questions or comments visit www.finetunedinstruments.com www.meangene.org or email me at info311@verizon.net Fine Tuned Instruments LLC, home of b3 instruments.


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