Peavey vk100 into some bassman like amp

[überfuzz]

Jazz P Bass - It's my way of gently saying, my crapper sounds better. :-)

[Jazz P Bass]

Have you 'checked out' the amp?

I had one in recently that sounded really bad.
It was a 2x12.

Half of the solder joints were 'crappy'.
I resoldered the whole amp.

Truly, I thought it sounded great.

Is this the head version?

[überfuzz]

Yes, this is a head.

This amp seems to be all about über-distortion. I'm not into that kind of sound.

[überfuzz]

I asked around in a bass players forum. They encouraged me to build an Ampeg like channel... Here's a first draft, please comment on faults or just weak spots in general.

[bea]

I would suggest to make C22 and C8 switchable to some smaller value yielding a 1st order high pass filter at around 70 Hz. That would reduce musically less important deep fundamentals.

[überfuzz]

I would suggest to make C22 and C8 switchable to some smaller value yielding a 1st order high pass filter at around 70 Hz. That would reduce musically less important deep fundamentals.

I think 70 Hz is higher than the lowest bass note on a normal 4-stringed bass. A 5-string with a low B string even lower. The highpass filters you refer to was designed to pass frequencies rendered by somewhat normal basses.

Thanks for the input! I'll double check all high-pass filters.

[überfuzz]

Correction
According to the all knowing internet the frequency of a standard tuned A-string is 55 Hz, B-string is 29 Hz. This would suggest that I shouldn't filter out these frequencies, i.e. the highpass filters you addressed should be as low as < 29 Hz. Right?

[Enzo]

Such filters are not brick walls. A rolloff under 70Hz does not mean that 69Hz won't come through. A 6db per octave slope means that if the rolloff starts at 60Hz, then 30Hz is only down 6db.

[bea]

Indeed, Enzo, and indeed, my suggestion explicitly and intentionally means to reduce the level of the deep fundamentals a bit (6dB / octave is a weak reduction, even at 30 Hz).

Reasons:

a) the tone of an electric bass guitar is dominated by it 1st harmonic, not by its fundamental. This holds even for extremely bassy instruments like the Gibson EB-0. Too much energy in the lowest registers will lead to mudiness and to conflicts with the bass drum.

b) most bass cabs are tuned to something around 55Hz. The majority of the bass drivers are not suitable for lower tunings, except of course, specially designed drivers. But those drivers are reduced in efficiency (unavoidably - the lower a speaker can go the lower its efficiency).
With a relatively small amp like this it is (IMO) preferable to use drivers with a good sensitivity.

c) the lowest registers eat up a lot of energy - with many bass cabs that energy is simply wasted to silently move air around (vented cabs driven below their Helmholtz resonance). Not good for the speaker and it reduces the headroom of the amp.

If You d not believe me - simply try it out. It'll cost You a few ct for one or two capacitors of a few nF.

[potatofarmer]

Indeed, Enzo, and indeed, my suggestion explicitly and intentionally means to reduce the level of the deep fundamentals a bit (6dB / octave is a weak reduction, even at 30 Hz).

Reasons:

a) the tone of an electric bass guitar is dominated by it 1st harmonic, not by its fundamental. This holds even for extremely bassy instruments like the Gibson EB-0. Too much energy in the lowest registers will lead to mudiness and to conflicts with the bass drum.

b) most bass cabs are tuned to something around 55Hz. The majority of the bass drivers are not suitable for lower tunings, except of course, specially designed drivers. But those drivers are reduced in efficiency (unavoidably - the lower a speaker can go the lower its efficiency).
With a relatively small amp like this it is (IMO) preferable to use drivers with a good sensitivity.

c) the lowest registers eat up a lot of energy - with many bass cabs that energy is simply wasted to silently move air around (vented cabs driven below their Helmholtz resonance). Not good for the speaker and it reduces the headroom of the amp.

If You d not believe me - simply try it out. It'll cost You a few ct for one or two capacitors of a few nF.

To add to this:

d) The Peavey OT was designed for guitar and it's a fair bet it lacks the primary inductance necessary to push significant power at those ultra-low frequencies, further limiting your headroom.

The Matamp/Orange "FAC" control is very useful for variable bass cut.

Also I just noticed that the schematic is missing a reservoir cap and the screen supply filter cap is on the low side.

I'd move C64 and C65 to the grids, "after" the grid stoppers.

[g1]

I like the bass sound I hear from an old AM radio in a car with a small in-dash speaker. It's coherent and intelligible, punchy, and it stands out for me. But to a certain extent I have no use for sub-woofers.
So this is the difference between having all the fundamentals there or not, as I think Bea is suggesting. I believe the same holds true for the popularity of 8 inch drivers with bass players.

[überfuzz]

Correction
According to the all knowing internet the frequency of a standard tuned A-string is 55 Hz...

Thanks for the input bea, seems internet was right all along, according to you. :-)

Enzo - I know how filters affect the frequency sweep. More particular in this case where bea addressed a first order filter. However, thanks for reminding me. :-)

Edit - PS
If this set up result in wonky bass tone, i.e. bad low frequency behaviour, I think I might tinker with the bypass capacitors of the pre amp gain stages. This would be to sort of nip it in the bud. Next step would be the high-pass filters suggested by you bea.

[km6xz]

Bea makes a very good suggestion.

What sort of sound are you looking for? The HP filtering is a great way to generate tight articulate bass that is easier on speakers and listeners....plus is a lot louder. As G1 noted, in the radio and vinyl days, the low fundamentals were filtered out from the cutting head or modulator and no one every complained there was not enough bass. In fact it was easier to dance to because the peaking at 70 or so hertz, emphasising the second harmonic gave all the brain needed to know the note bases on the harmonic series and our brain's ability to complete sequences given any portion of it. 32hz will rob any headroom, tax speakers and muddy the tone but it became popular with the advent of the first disco era in the 70s. Musicality is not diminished, but enhanced by rolling off the lowest portion of the spectrum. Did you ever try dancing to older live shows or records and have a problem hooking up to the rhythm section? It was easier than when large systems focused on thundering subsonics came into vogue.
So it depends on your intent, but don't underestimate how much tighter and more impact every note has by emphasizing the second harmonic.
Remember how JBL was really popular in home stereo in the era of separate components, 1970s? Salesmen always commented that customers said the JBL speakers had the best, tightest bass. Bass, "tight", sorry, they do not go together. Doing a measurement of the speakers all theirs had poor deep bass, and all those models that sold so well like the L100 had drivers with a lower free air resonance than the cabinet. So they had less bottom but a peak in the 65-75 range that emphasized the second or third. The brain synthesized the fundamental from the harmonic series but since the speaker, amp, listener's ears and room was better suited to 60-100 hz than 30hz the impression was tight powerful bass, each note being articulate, even if not very accurate in reproduction. All depends on your goals.If you want the bass line to be heard distinctly, a bass player would normally set the bass response to not have so much gain in deep bass. Besides, with as inefficient rooms and speakers are at 32 hz, you probably do not have enough power to reproduce it well anyway. 1000 watts at 32hz has a much lower perceived loudness than 1000 watts at 64 hz, you would never need that power at that frequency in fact, but never have enough for 32.

[Enzo]

I still have a pair of L100s.

Recording studios always have a pair of small speakers to listen to, because no matter how wide ranging the original material is, it also must sound good on typical car radio speakers, and there are no 15" woofers there. Guys put big subwoofer systems in cars to listen to the artificial low end on rap music, but now we are getting away from any sense of tone.

[km6xz]

We started using small 5 in speakers in mix for balance but the most important reason was have small essentially point source speakers at arms length so stereo image could be heard with minimal impact by the room acoustics and reflections. Two cheap speakers within 2 feet of you gives a better representation of the image than any large room monitors. So when tracking we used big speakers that were often built in to the walls over or just to the sides of the window into the main room. Those were used for full tone range and imagining was not important, and would not have been good any for it any way. The small speaker also gave a better accounting of the rhythm section since just upper harmonics of the bass and kit were heard but that was fine since those additional harmonics could be heard even at low volumes very distinctly. Nowadays people with project studios usually have a small 2-3 way monitor mounted close but imaging is not good because of the multiple drivers, and they are to small for full spectrum. They add a sub often which in turns creates mixes that are too light in the bottom. Subs are almost never adjusted so they fit into the system well, nor are time aligned.