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Dirty-South Blues Harp forum: wail on! >
Amp Mods - in Laymans Terms?
Amp Mods - in Laymans Terms?
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MindTheGap
611 posts
Jun 17, 2015
12:00 AM
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I often read about people modifying their amps to be more harp friendly. I understand the one about using a lower gain preamp tube, and why you might want to do that.
For the other things like changing a speaker, or other components, what are the features of the amp you are looking to change? Is it trial and error or is there a plan? Do you aim to radically change the characteristics, or is it a tweak?
I've some electronics background, so feel free to write technically. But I'm more interested in the motives.
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rogonzab
750 posts
Jun 17, 2015
8:06 AM
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In my experience, whe you change the speaker is a more dramatic change than replace some tube for betters ones.
If you go from 8" to 12" that is a big change, just like going from ceramic to alnico.
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Sorry for any misspell, english is not my first language.
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arnenym
352 posts
Jun 17, 2015
11:31 AM
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For me is tweaking when i change some tubes or a speaker.
Modify a amp includes some resistor changes or cap changes to new values.
I have a plan when i modify a amp. It vary from just get it resistant to feedback to do a clone of a existing, good harp amp. When i do it for a customer i often just do some modifications to get it feedback resistant.
I do not do every amp i do just amps i know and am certain to get a good result.
I look for better bass and and cut harsh treble.
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dougharps
945 posts
Jun 17, 2015
2:54 PM
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There are circuit mods for some amps that are said to improve specific amps for harp. There are tube swaps to decrease gain and make the amp more manageable with the stronger signal of a harp mic. There is the basic and (I think necessary for safety) mod to older amps of changing to a grounded cord. There is the speaker replacement mod.
I have a 1961 Gibson Explorer GA-18T that was pretty good for harp, but tended to be to strong on the high frequencies. I talked with a tech about circuit mods to shift the range of the single tone control toward more bass. He said he could do it or perhaps I should try a different speaker. I installed a darker toned speaker, the Eminence Lil' Buddy. It made the amp sound much better for harp.
Techs on the forum can better explain circuit mods specific to amps.
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Doug S.
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indigo
126 posts
Jun 17, 2015
3:16 PM
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Beer glass circles and cigarette burns only in the earlier days.
Since then i have changed preamp valves to lower values etc
because i thought it was the thing to do.A recent thread gave some good reasons why it isn't always a good idea(especially on less powerful amps).It can be a complicated this Mod thing.
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SuperBee
2687 posts
Jun 17, 2015
3:36 PM
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A good question which has potential to provide an enduringly useful thread. There are some members with detailed knowledge on the topic.
I can't add much arm to the comments already made, but I'm watching in hope that someone will explain about input impedance resistors and the how and why of catering for crystal microphones
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Barley Nectar
832 posts
Jun 18, 2015
8:54 AM
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First off you need to have the ability to utilize the amps capabilities. No amp is going to make you sound good. You must sound good on your own! Next you must decide how you want the amp to sound. You have a sound in your head that you are striving for. Remember, the mic is important in this scenario also. The features to consider are many. Is the amp, dark, bright, to small, to big, no cut with a band, muddy, noisy, squeely, to clean.... Where will it be used, bedroom, low level coffee house accoustic gig, studio, busking, blues band, loud ass rock band, loud ass jam, pro tour, big room, small room, soft room, hard room, outdoors....There is no amp that will cover all situations.
There is a lot of trial and error when you start modding. After a while you get to know how to acheve your goals. It takes time and practice to develop these skills. I've been at it about 15 yrs as a hobby and just now starting to get things figured out. I have a good backround for this type of thing and that has been very helpfull.
One other thing is this, learn to utilize an amps strong points. They are like people, thay have their own personality that will shine when given a chance. Tube amps sound best on a full moon!!!...Goose
Last Edited by Barley Nectar on Jun 18, 2015 8:57 AM
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1847
2455 posts
Jun 18, 2015
10:05 AM
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the guy to ask would be mark overman
not only is he a mic. builder extraordinaire
he has done every modification on a bassman known to man. ok well not every mod. for that you would need to talk to john kinder. rod was one of the first to have
amp mods done
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1847
2477 posts
Jun 19, 2015
3:54 PM
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my amp has a bias pot installed so i guess that is a mod?
i do not switch out power tubes it is there just in case it is needed
i have changed speakers because they do not last forever
i used 4 10 inch mojo tones for a very long time, one was damaged so it was replaced with a 10 inch jensen p10q
the newer reissue. it sounds fantastic so i took a blown vintage p10q and had it re-coned
so now i have 2 mojo's and 2 jensens, just because.
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MindTheGap
617 posts
Jun 20, 2015
12:01 PM
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Interesting info so far, and I'd love to hear more detail. When you change a speaker from 8" to 10" what effects are you looking for? What have you found in practice? Louder? Warmer?
Or from ceramic to alnico? I've read about people a mix of speaker types in their 4x cabinets, as 1847 says. What's that all about?
How about SuperBee's question of catering for crystal microphones?
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5F6H
1885 posts
Jun 21, 2015
8:05 AM
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I prefer 8" for recording & practice, can get a bit lost on stage, though can be mixed with 10". 10" will typically sound a little tighter/crisper, useful when with a full band.
Ceramic speakers all sound different to each other, as do Alnicos, good options in both, look at speaker models as just that - individually - rather than trying to group them into families by magnet material. Mixing speakers can make a more complex sound, some for volume/punch/bass, others for character/breakup? Again, there are great sounding amps with a mix & those with all the same speaker, again asses individually & note that a speaker may sound awful in one amp & great in another, speaker & circuit may balance each other, or tip each other over the edge?
Crystals & ceramics like big impedances (5Meg?), but also consider the sound of a harp - it doesn't have the big peak of a plucked string followed by decay (most of the note with guitar), it has a flatter profile in regards to amplitude, whatever mic you use, a higher value input resistor helps with sensitivity of the input circuit, generally a good idea for stage amps, not essential for smaller amps as it may/may not help with the aggressiveness of the sound. Some folk like to use the lower gain (but still technically hi impedance @ 50Kohms-100Kohms) inputs for a less aggressive/brash sound & more sweep on a volume control.
There are a few generally good methods/ideas, but also few "one size fits all" as amp designs vary wildly and you may be trying to accentuate, or not, different characteristics from one amp to the next.
As Barley Nectar says, it's better to start with a known good/'nearly there' amp that already shows promise & desirable traits.
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www.myspace.com/markburness
Last Edited by 5F6H on Jun 21, 2015 8:07 AM
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LSB
156 posts
Jun 21, 2015
8:21 AM
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If you want to start to get an idea about how different speakers can change the sound, go to the Eminence speaker website and start going through the speaker sound samples. Try listening to just one sample, say the overdriven lead sample, for all the 10" speakers, one after another. You might be surprised. Do the same with the 12's, it's startling how different some speakers sound from others.
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MindTheGap
618 posts
Jun 22, 2015
1:51 AM
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Thanks 5F6H and LSB and all. This is just the kind of info I was looking for - a little insight into the mind and motives of an amp technician. The speakers do sound very varied, from those clips. Looks to me like trying different speakers would be a low-risk way to dip your toe in the water.
Last Edited by MindTheGap on Jun 22, 2015 1:51 AM
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MindTheGap
619 posts
Jun 22, 2015
2:04 AM
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...one last thing. I read about people trying different tubes of the same type, but different makes and sources. They say each one has a character. What would be your comment on how much sound variety is available there - vs the variety of tones you can here in those eminence speaker sound clips? Subtle or radical?
(I note rozongab's comment on this).
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5F6H
1886 posts
Jun 22, 2015
4:02 AM
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Different tubes, of the same "type" even from the same manufacturer can sound different in the same amp. At the same voltage & bias, different brands can sound different...but, bear in mind some people play in a way that emphasise those differences, others play in a way that mitigate those differences.
Tubes like anything else are built to slightly different specs & subject to manufacturing tolerances.
Some tubes (pre & power) have a lot more gain for the same tube type (12AX7, 6L6 etc), this can impact in the sound and in usefulness (volume before feedback).
Changing preamp tubes (in the 12A#7 range) to models of a different spec will make a dramatic difference, this requires no monitoring of the circuit, or rebiasing, there are a few potentially risky choices (very low gain tube replacing 'Phase Inverters' in high power/voltage amps), but the tone benefits may win out & the worst case scenario is having to have a resistor replaced after a few years of use.
Good speakers (sound nice, not too prone to feedback) are a good way to adjust the sound, but especially in multi speaker cabs can be the most expensive components in your amp.
Tubes, speakers are easy/accessible ways too play with your sound, but the tubes are affected by the voltage & currents they see, this affects frequency response & harmonics, which are also shaped by the speaker...in amps that are "nearly there" they might get you to Nirvana...in other cases tweaking voltages & bias in the amp itself can make a significant difference that can help the tubes & speakers you have shine, or less suitable tubes/speakers may never deliver full potential even with circuit mods.
Circuit mods obviously require working around potentially lethal voltages, so are not for those who don't want to be bothered with observing safety protocols (discharging power supply caps etc.)
It's really best, when discussing amps & mods to really focus on a model/type (single ended champ style, cathode biased 50's PA type, fixed bias push-pull Fender type) to reduce variables & capitalise on others' experience.
Tone is also subjective at the end of the day, but the mechanics of tweaking it are pretty repeatable if you can describe what you want & if it is a practical call (e.g. I wouldn't try to make a brown Concert sound like a Masco, nor vice versa).
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www.myspace.com/markburness
Last Edited by 5F6H on Jun 22, 2015 4:04 AM
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