Newbee question about impedance

[YardBirdFan]

I will introduce myself as Tony, AKA here as YardBirdFan. I am now the proud owner of a MetroAmp JTM50 that I stumbled into at a Music-Go-Round in the Twin Cities (Minnesota) area. I am truly amazed at this amp! I have recently acquired a "blessed" 95 Les Paul Standard, and knew I had to go "british" on my amplification. Yee-Haw!

So, I need some advise on how to run this.

I plugged the amp into my 2X12 Ampeg with a pair of 8 ohm jacks with two cables and the amp set to 4 ohms. It sounded SOOOOO good, but I am not sure my neighbors will like the sound as much as I do. So, an attenuator is my next investment. I am at a crossroads and need advice on what to do before I pull the trigger.

Option A) leave the cabinet alone and get a THD 4 ohm hotplate
or B) modify the cabinet and get a THD 16 ohm hotplate.

What differences can I expect in overall tone, tube life, noise levels... anything else to consider?

Thanks!!!!!!!!

YardBirdFan

[reswot]

I prefer 16 ohms....

[YardBirdFan]

I haven't bought an attenuator yet, but I did re-wire my cabinet from 8's in parallel (4 ohm) to series (16 ohm) and flipped the switch accordingly. It seems like I lost some of the "shimmering" highs. I play mostly clean, but overdrive on occasion. I am not really playing loud enough to make my final conclusions though. I happen to have two Ampeg 2x12's, one stock, one re-wired as mentioned. This weekend I should have the opportunity to explore more.

I am very interested in any reasons why you prefer a particular setting... whether that reason be technical or a certain sound characteristic or impact on playability.

A friend advised another option is to try the 8 ohm setting on the amp into my now 16 ohm cabinet. Reply quick if anyone disagrees with my friends advise that it is safe.

I just bought 8 small voice coil 8 ohm 12" speakers from a vintage organ that will give me the opportunity to go series parallel at 8 in an extra 4x12 cabinet I have in storage.

Thanks!

[toner]

First, don't buy a Hot Plate unless you can get a used one cheap. There are better attenuators, including Alex's (PM 908ssp for info) for not much more $.

The impedance mismatch thing has been debated a lot. Some say it's okay, some don't. Personally, I always match the amp to the cab just to be safe. Marshall's can be more sensitive to this than other amps.

Lastly, I have read that wiring speakers in parallel can increase the damping for a tighter response than series. I haven't experimented with this but it may be worth comparing.

[Vince Neville]

Hey Tony,

I usually match impedances as well, but it really depends on your output transformer and what kind of tone you want. Some are sturdier than others with mismatching. Hammond transformers are apparently good with mismatching, for instance, whereas, as Toner said, traditionally English transformers were not as well suited for mismatching the load (the speaker) and tap (the particular ohms setting chosen on the output transformer). Stephenson Amplification has an amp called the Standard Amp, and it has 4-8-16ohm outputs, but they are labelled 1-2-3. You can hook up any 4, 8, or 16ohm speaker to either 1,2,or 3 depending on the tone you want Here's the link:
http://www.stephensonamps.com/standard-amp.htm" onclick="window.open(this.href);return false;

Just a comment on attenuation: you do have to pay for loud tone at quiet volumes with dummy load attenuators. That is, you are driving your amp really hard (both the power tubes and your output transformer), and most of the power is converted into heat, i.e., waste. The end result is you spend more money replacing power tubes to use less power. If you do want to get a dummy load attenuator, get one that can match more than one impedance, simply for the flexibility. There is an option called Power Scaling, which was invented by Kevin O'Connor at London Power in Ontario, Canada (you may have noted that Marshall uses Power Scaling in their AFD100 and YJM100 amps, although they do not call it that). It is an electronic method of reducing output power by only producing whatever amount of power you need, as opposed to producing full power and dumping what you don't need into an attenuator box. People have their arguments for both physical attenuators and electronic ones, and I tend to stay out of it and listen to all sides. I just wanted to point out those few things.

And Toner is correct with regards to speaker damping. Speakers don't passively accept a signal from an output transformer, they push back, so to speak. If you hook up your speakers in parallel, your amp can deal with each one individually and control their motion better. But in series, you have speakers that are connected like when you line up single file in elementary school. The student closest to the teacher is easiest to control, but further on down the teacher can't exercise as much control on them (I think it's a decent analogy, and I'm sure there are flaws in it). The end result is you have a looser tone, which may be just what you want. And of course, with typical 412 cabs, you have a mixture of series and parallel wiring, giving you something in between. You would have two series-pairs wired in parallel, or two parallel-pairs wired in series.

And with regards to those 'shimmering highs', you will get a tamer tone from a 16 ohm setting, at least that is my experience. Hooking up an amp at 16 ohms gives a breathier, less pushy sound than at 4 ohms. And if you love cranking your amp (I've certainly cranked my JCM Slash many a time), take care of your ears with those shimmering highs. We don't want anyone getting tinnitus.

That may have been too much for one comment, but I like contributing to this forum. I'm a newbie as well, and appreciate help from others.

[johniss0001]

thd i wouldn't waste my time with them as i've said in afew other posts i know some major flaws with them so not for me. I'd be more inclined to go for the weber mass as you can alter the impedance and last time i checked they had more features also I have been looking at the new rivera rock crusher

[neikeel]

Hey Tony,

I usually match impedances as well, but it really depends on your output transformer and what kind of tone you want. Some are sturdier than others with mismatching. Hammond transformers are apparently good with mismatching, for instance, whereas, as Toner said, traditionally English transformers were not as well suited for mismatching the load (the speaker) and tap (the particular ohms setting chosen on the output transformer). Stephenson Amplification has an amp called the Standard Amp, and it has 4-8-16ohm outputs, but they are labelled 1-2-3. You can hook up any 4, 8, or 16ohm speaker to either 1,2,or 3 depending on the tone you want Here's the link:
http://www.stephensonamps.com/standard-amp.htm" onclick="window.open(this.href);return false;

Just a comment on attenuation: you do have to pay for loud tone at quiet volumes with dummy load attenuators. That is, you are driving your amp really hard (both the power tubes and your output transformer), and most of the power is converted into heat, i.e., waste. The end result is you spend more money replacing power tubes to use less power. If you do want to get a dummy load attenuator, get one that can match more than one impedance, simply for the flexibility. There is an option called Power Scaling, which was invented by Kevin O'Connor at London Power in Ontario, Canada (you may have noted that Marshall uses Power Scaling in their AFD100 and YJM100 amps, although they do not call it that). It is an electronic method of reducing output power by only producing whatever amount of power you need, as opposed to producing full power and dumping what you don't need into an attenuator box. People have their arguments for both physical attenuators and electronic ones, and I tend to stay out of it and listen to all sides. I just wanted to point out those few things.

And Toner is correct with regards to speaker damping. Speakers don't passively accept a signal from an output transformer, they push back, so to speak. If you hook up your speakers in parallel, your amp can deal with each one individually and control their motion better. But in series, you have speakers that are connected like when you line up single file in elementary school. The student closest to the teacher is easiest to control, but further on down the teacher can't exercise as much control on them (I think it's a decent analogy, and I'm sure there are flaws in it). The end result is you have a looser tone, which may be just what you want. And of course, with typical 412 cabs, you have a mixture of series and parallel wiring, giving you something in between. You would have two series-pairs wired in parallel, or two parallel-pairs wired in series.

And with regards to those 'shimmering highs', you will get a tamer tone from a 16 ohm setting, at least that is my experience. Hooking up an amp at 16 ohms gives a breathier, less pushy sound than at 4 ohms. And if you love cranking your amp (I've certainly cranked my JCM Slash many a time), take care of your ears with those shimmering highs. We don't want anyone getting tinnitus.

That may have been too much for one comment, but I like contributing to this forum. I'm a newbie as well, and appreciate help from others.

I have to agree with nearly all of that although I find my JTM 45 runs with a bit more shimmer if I run it with selector on 16 and two celestion gold (16ohms) in series for 8ohms load.

Regarding the Hotplate.....I have one and use it on the bench and at gigs for second amp, with line to desk and maybe -8dB of attenuation. I run my main amp through my Motherload, again with line out to desk. There are better attenuators for sure and the Alex must be worth a trial at $370USD (I am in the UK and Alex is not permitted to send them to the EU). The others sound pretty spectacular in demos I have heard and it may be worth selling an amp to buy one (Faustine DX2 looks the most versatile but is $750USD and the Aracom is $700USD and that also copes with different loads).

Only my opinion of course.......... (and I did not mention Mr Ho's Ultimate either )

[robert]

Hi Neil,

you wrote: "...if I run it with selector on 16 and two celestion gold (16ohms) in series for 8ohms load."



Regards

Robert