PEAVEY Mark III vs Mark IV

[Obese Chess]

Doesn’t increase the power into 8 or 4 ohms, that is dictated by the power supply itself.

Interesting! I figured if the new power supply would increase power at 2 Ohms it would also increase it at 4 or 8. There's so much I don't know...

 

[agedhorse]

The power module used is independent of the power supply itself. 2 different parts of the amp.

 

[stefancaunter]

I've just purchased a mk3 Centurion and while I love the tone I am concerned it won't be loud enough - is the 400BH plug and play, or are there directions somewhere?

the mk3 centurion is only 130 watts into 4 ohms, it’s a valid concern - i find it somewhat underpowered for bass. but the centurion box is physically too short to mount a 400BH on it. different form factor.

 

[stefancaunter]

Doesn’t increase the power into 8 or 4 ohms, that is dictated by the power supply itself.

i was under the impression that it’s the output transistors on these peavey amps that determine the output power, is that wrong? the power supply is the real determining factor in output?

 

[agedhorse]

i was under the impression that it’s the output transistors on these peavey amps that determine the output power, is that wrong? the power supply is the real determining factor in output?

The power supply determines the output power provided there is adequate silicon (output transistor voltage, current and SOA) to support it.

 

[stefancaunter]

The power supply determines the output power provided there is adequate silicon (output transistor voltage, current and SOA) to support it.

ahh thank you. seems that peavey got it right with the 400BH. still useful after 40 years.

 

[Pontiac Thrasher]

ahh thank you. seems that peavey got it right with the 400BH. still useful after 40 years.

Does Peavey still provide (customer pay of course) service/repair for the Mark 3 and Mark 4?

 

[stefancaunter]

Does Peavey still provide (customer pay of course) service/repair for the Mark 3 and Mark 4?

yes
send it to Meridian with instructions - no RA needed - website breaks it all down for you
Invalid Link Removed

 

[Count Bassie]

Picked up a MK3 400BH today. It needs some service but it's in pretty clean shape. I'll report back when it's out of the shop.

I read the manual and it has some sneaky good features. Did you know that you can jumper from the bi-amp high out to the power amp in and use the crossover frequency control to adjust the rolloff point? Essentially a built in HPF? So that's about 40 years ahead of its time. Built-in HPF in '78. Not bad.

I did not know that! Wow- that's very cool! I'll go try that with my MK-III...

 

[byacey]

Picked up a MK3 400BH today. It needs some service but it's in pretty clean shape. I'll report back when it's out of the shop.

I read the manual and it has some sneaky good features. Did you know that you can jumper from the bi-amp high out to the power amp in and use the crossover frequency control to adjust the rolloff point? Essentially a built in HPF? So that's about 40 years ahead of its time. Built-in HPF in '78. Not bad.

Does it sweep low enough to be useful for a HPF?

 

[bigtone23]

Does it sweep low enough to be useful for a HPF?

The control sweeps from 50-500Hz, so yes!

 

[agedhorse]

The control sweeps from 50-500Hz, so yes!

Kind of, most sweep HPF’s go down to 25-30Hz.

Also, if it uses an LR alignment (for constant power summing), that would be the -6dB point rather than the more common-3dB point. This would raise the 50Hz number to ~75Hz for equivalent comparison.

I don’t know what alignment Jack used on this, but it was within the time period that crossovers were migrating to LR from BW.

The crossover function was not intended to be a HPF, this is an “off-sheet” application that may work, especially for smaller cabinets.

 

[jthisdell]

I remember using the crossover freq as a hpf at a basement dorm gig in 1981

 

[agedhorse]

I remember using the crossover freq as a hpf at a basement dorm gig in 1981

Sure, sometimes a hack like that is better than not having it.

 

[donahue]

^Okie Dokie there big boss. Why don't you take your own advice and read the manual? It's in there.

 

[agedhorse]

^Okie Dokie there big boss. Why don't you take your own advice and read the manual? It's in there.

I'm assuming that you aren't being intentionally insulting here, and maybe you are trying to be funny rather than rude?

This crossover uses a bi-quad circuit which was quickly retired only a few years later for a slightly more friendly version of the circuit in the Mark IV, but by 1986-87 Jack had switched over to a conventional HPF filter (with the ability to tune the Q) topology with the Pro Bass series which is still being used today. The bi-quad type circuit has significant limitations on the ability to tune the filter alignment, a HPF (and crossover circuits) do benefit from this control. It's part of the natural evolution of filters, something that I have studied for 40+ years. That's why nobody that I know of today uses these bi-quad filters.

This use of the crossover filter as a HPF was a crude way to do something a little outside the box at the time, a bit of an afterthought but even at that time it was recognized that there might be value in the basic concept of the HPF. Of course, the crossover eventually went away on their amps (and most amps actually), once higher order and higher Q filter topologies became easier to design. The Mark III and Mark IV op amps were very slow, and low gain-bandwidth product (plus bipolar input) really limited the ability to do anything really aggressive because there wasn't enough open loop gain to feed back with at higher frequencies.

I am very familiar with Jack Sondermeyer's work as an engineer, he wrote many audio application notes while he worked for RCA, and any engineer taking this field seriously read what he wrote. He was at one time one of the leading designers of solid state power amps, that's what he specialized at while with RCA before moving to Peavey where he finished his career after another 30+ years of work. I met him several times over the years, he was really an engineer's engineer.

 

[stefancaunter]

I'm assuming that you aren't being intentionally insulting here, and maybe you are trying to be funny rather than rude?

This crossover uses a bi-quad circuit which was quickly retired only a few years later for a slightly more friendly version of the circuit in the Mark IV, but by 1986-87 Jack had switched over to a conventional HPF filter (with the ability to tune the Q) topology with the Pro Bass series which is still being used today. The bi-quad type circuit has significant limitations on the ability to tune the filter alignment, a HPF (and crossover circuits) do benefit from this control. It's part of the natural evolution of filters, something that I have studied for 40+ years. That's why nobody that I know of today uses these bi-quad filters.

This use of the crossover filter as a HPF was a crude way to do something a little outside the box at the time, a bit of an afterthought but even at that time it was recognized that there might be value in the basic concept of the HPF. Of course, the crossover eventually went away on their amps (and most amps actually), once higher order and higher Q filter topologies became easier to design. The Mark III and Mark IV op amps were very slow, and low gain-bandwidth product (plus bipolar input) really limited the ability to do anything really aggressive because there wasn't enough open loop gain to feed back with at higher frequencies.

I am very familiar with Jack Sondermeyer's work as an engineer, he wrote many audio application notes while he worked for RCA, and any engineer taking this field seriously read what he wrote. He was at one time one of the leading designers of solid state power amps, that's what he specialized at while with RCA before moving to Peavey where he finished his career after another 30+ years of work. I met him several times over the years, he was really an engineer's engineer.

I was going to say there’s no way that the Peavey crossover does the job that your Mesa D800+ HPF does (I gig a Mesa Subway as well as many SS Peaveys). Nevertheless the fact these Peaveys are still working well for players after 40 years speaks for itself.

 

[agedhorse]

I was going to say there’s no way that the Peavey crossover does the job that your Mesa D800+ HPF does (I gig a Mesa Subway as well as many SS Peaveys). Nevertheless the fact these Peaveys are still working well for players after 40 years speaks for itself.

Of course not, the newer HPF's are typically 24dB/octave (4th order) Sallen Key filter topology with much higher Q, whereas the old bi-quad filters (with those IC's) are typically 12dB/octave (2nd order) with low Q.

I used to design active crossovers for the pro audio world, including rack gear and powered speakers. There are very significant differences between (good) crossover filters and good HPF's, including how they are specified. Crossover filters are specified (these days) for constant power summing which means that the filter frequency is specified at -6dB rather than for constant voltage summing which is specified at -3dB. This is because of the squared factor in the power equations, and since SPL is directly related to power, this prevents an unwanted bump in the acoustic response at the crossover point.

The products that Jack designed were very thoroughly engineered, the fact that they lasted this long reinforces my opinion that a good design is inherently reliable when well manufactured.

 

[ryco]

I played and prefered the Mark III for years. I jusrtprefered the front panel control layout a lot more than the IV - which I also had. Was pretty much my main thru the 80/90s with a Sunn Concert 215. good times!
The footswitch peal does not *pop* between function selections.

Wondering why the keyboard playin' OP of 2014 wouldn't go for a Peavey KB-300 which is designed for keyboard use. 300w w/ 3 channels. My keyboard playin' wife used one for years. Good amp, solid, HEAVY (yes - I had to roadie it for her :/ ), and designed to run three keyboards. I use it now to run a drum machine and two channels for either a MacBook or iPod.

 

[bigtone23]

The 70s era Peavey Bass head had a "Slope" control in the master output section. It was described in the manual as an "extreme low frequency roll off." I would guess that was some sort of HPF of the time?