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Messages - Steve Dalllman

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Amplifier Discussion / Re: Upping caps Peavy M2600
« on: March 19, 2013, 08:00:10 PM »
I have a lot of old PV amps, and the main filter caps do have a limited life. I usually go 10,000 or 12,000uF. More capacitance yields better headroom. Since modern caps are generally smaller in size than the originals, one can go with higher value caps. I have replaced caps in Mark III, Mark IV bass amps, XR600, and M3000. All had nothing wrong with them other than filter caps.

FWIW, a bad filter cap in the XR600 caused DC to kill 6 old EV SRO speakers (not all at once.) It would intermittently spit DC which would freeze the speakers (overexcursion). Fine after the cap change.

Amplifier Discussion / Re: Peavey Blazer 158 Silver Stripe
« on: March 19, 2013, 07:52:39 PM »
I have a Rage (same amp without the reverb) and love it. I did a lot of tweaking. I listened to what I liked about the clean and distortion and what I didn't and changed a couple values, added a couple caps, and was pleased with the results. I let a little more low end and added a bright cap to the master for the distortion to sparkle the distortion up at high gain levels. I added a switch to the distortion channel to change from a vintage toned overdrive to a scooped mids modern sound, copying the circuit from the next generation of Rage amps.

I added a parallel effects loop, and changed the wimpy 8" speaker to a 10", which improved it a lot. I used an 8 ohm speaker and added an ext speaker jack to run another 8 ohm extension speaker.

I found an old ART, compact multi-effects unit, and put it in back of the amp, patched into the effects loop. I put an AC socket under the chassis for the AC adapter for the ART. There is a reverb program that works perfectly.

I wired the amp to use a footswitch for channel switching, putting a relay in place of the channel switch, and put an LED in the switch hole. The footswitch also has an LED.

I think I replaced the TDA2040 with a TDA2050, improved the heat sink and put in larger filter caps, not to increase power but to increase reliability and headroom.

It's a little beast. I love it. The best mod is I replaced the grill cloth.

Amplifier Discussion / Re: Watts vs Volume (db)
« on: March 19, 2013, 07:38:33 PM »
Many if not most of modern guitar speakers are in the high 90's to low 100's in dB's. Even high excursion bass speakers are usually in the high 90's but the compromise is usually less highs.

This is for 12's and 15's. As you go smaller, especially with 8" and 6 1/2" speakers, the sensitivity is often lower, in the 92dB range.

Most manufacturers will not only give all the specs, but will include a frequency graph. Every speaker will have a rather shallow low end rolloff, relatively flat across the mids, and then have a large peak between 2 and 4kHz followed by a treble rolloff that may extend gracefully to 5-6kHz or beyond, or be rather ragged.

A guitar pickup is similar, with it's "resonant peak" producing a characteristic tone.

Bass and PA speakers will usually use a crossover selected to be below that large peak, bass less so.

Tube VS SS endless argument. Let me give my take. When you reach the limits of a SS amp, there won't be much beyond it's limits. A 100watt amp may be rated 100 watts @ .05% distortion. Once the rails are hit, there may be nothing much left above a certain point.

With a tube amp rated at 100watts @.05% distortion, may be capable of 200 watts @ 30% distortion and sound great doing it.

The tube amp may keep putting out far more than it's rated power, at a very high distortion level, but still sound good. With the SS, the possible output will be limited by it's power supply limits, and at high distortion, may not sound very good.

My 12 watt Princeton Reverb will put out a lot more than a 15 watt SS amp using a TDA2030 power amp chip...a LOT more.

The info given is good. It isn't the amplifier but the cabinet that is important. An open back has no internal air cushion to limit the excursion of the speaker. The speaker matters as well. Guitar speakers do not have the excursion needed for the lower bass notes. The higher the excursion, (Xmass) the better for bass. The cabinet should be designed with the intended speaker in mind. Most speaker manufacturers give the specs on their speakers so the box size, and the port size (if ports are desired) can be calculated.

As for the amplifiers...bass amps generally require more power and headroom than guitar amplifiers. Guitar amps often have the low end restricted for tonal reasons, and that may not sound great for bass. A guitar amp will not be hurt by using bass.

The tone controls of a bass may be tuned lower. Individual amplifier stages will have larger coupling caps. The filter capacitance may be much higher.

In bands today, amplifiers from 15 to 100 watts are generally used, with the trend being toward smaller amps, which are often mic'd. 300 watts is considered the lowest power for a gigging bassist, with 500-1000 watts being common.

Trends change with all instruments. 100 watt stacks were common decades ago, but today, only metal and hard rock bands use amps that big. PA's have improved over the decades.

With bass, large cabinets were the norm. Today, with better speakers and good design, smaller cabinets are common. 10's (in multiples) are the most popular bass speakers. 12's are becoming very popular, giving 10-like highs and 15-like lows. 15's are still popular, but often in single 15 cabinets.

Foster/Fostex horn tweeters were and are still popular, although a trend has begun of using midrange cone drivers instead of tweeters, or with tweeters. Popular speakers for gigging bass players are often a 15 or 12 with a 6 1/2" midrange, crossed over between 800 and 1000Hz.

Vertical speaker placement is becoming very popular, rather than side by side speakers. This is to improve horizontal dispersion and limit phase problems in the audience. The same trend has happened in PA's with line arrays being very popular. Same principal with bass. Two 2X10 bass cabinets stacked vertically is preferred to a typical 4X10 cabinet.

But I ramble.

In Fender amps, when the switch gets dirty, the pop gets loud. Cleaning does not help.

The fix in a Fender (and I'm assuming the PV is similar) is to replace the switch, and then solder a cap across the switch. .01uf is fine, at least 630v (1k or 2kv even better).

Tubes and Hybrids / Re: Peavey Mace Question ?
« on: December 12, 2010, 12:29:29 PM »
I recently obtained a Peavey Bravo 112. I put a switch across the diodes and listened to it carefully for a while. (BTW, I am an amp tech, authorized by many companies like Line 6, Fender, etc.)

The diodes only work when the gain boost is on, and they do work well. I can hear no discernable difference with the diodes working or shorted in the guitar tone, but the noise is unbearable with the diodes shorted. The decay is as smooth with or without the diodes. I hear no gating action.

I'm quite happy with this simple circuit.

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