I wanted a small bass amp that sounded like a vintage tube bass amp without the size, cost, heat or tube issues.
I selected the Marshall AVT20 as the reviews were very positive, they are very easily acquired at a low price on the used market, and it uses 10" speakers of which there are many to choose from in the Eminence bass guitar and pro sound lines.
A classic 60's/70's Marshall bass amp was a guitar head with Marshall G12H(55) speakers in a 4x12 cab. Jimi Hendrix used the G12H(55) speaker cabs in conjunction with G12M 4x12 cabs. A G12H and a G12H(55) are the same except for resonance frequency, in this case 55 Hz. HiWatt was also conspicuous in using similar heads for bass and guitar and changing the Fane speakers in the 4x12 cabs. Note Pete Townshend and John Entwistle and their HiWatt rigs of the 70's. The Partridge output transformers in HiWatt DR103 amps were of audiophile quality and made them very suitable for bass guitar (which is why audiophiles bought old HiWatt DR103 heads on the used market, removed the output transformers, installed something cheaper and inferior, and resold them on the used market....BEWARE of an old DR103 at a to-good-to-be-true price). The solid state output stage of the Marshall AVT20 gives extended bass and tight control of a speaker while the tube preamp stage gets good tube overdrive tone, so it's a natural for a guitar to bass amp conversion.
I installed a Philips JAN 12AT7A tube in place of the Marshall supplied Ei ECC 83 to drop the gain from 100 to 70 in order to have slower breakup and wider control range in the first gain stage. The Ei ECC 83 is a killer tube for lead guitar due to its high gain, quietness, and the fact it is a Telefunken ECC 83 copy.....no need to say more if you are an tube audiophile or lead guitarist. BUT, I think the Ei ECC 83 has too much gain for my Spector ReBop with active tone controls and high output DR Sunbeam strings and high output EMG HZ passive pickups.
The stock Celestion G10-30AVT is a piece of crap for bass guitar as it falls flat on its face at 80 Hz, and I have the proper test equipment (I'm a degreed biomedical engineering techie) to prove these points. It has a lot of suckout in the midrange for a scooped sound that guitarists like, but bassists have little need of. It farts when you try to get deep bass from it at an appreciable level. It will self destruct if you keep shoving it, so I pulled it out and intend to give it away to a friend's son who is interested in taking up guitar.
First speaker in was an Eminence B102 of 92 dB efficiency and excellent extension low and high with very linear response. The quality of sound was excellent with the flattest response of the three speakers I have used so far. The fly in the ointment is the low efficiency and the low 20-watt power of the AVT20 .These are solid state watts, not tube watts, equal to about 10 tube watts for comparison. I just had to have more volume, and the quality and range of tones I was getting from the AVT20 started me on a search for a more efficient speaker.
Searching the Eminence spec sheets for a day lead me to conclude that the Eminence Beta 10A was my best choice at my $100 or less price point. If I need to spend more than $100, then a bottle of Talisker and a bottle of Laphroaig for mixing my secret blended Scotch recipe into cheap grain Scotch gets me the best tone.....for a few weeks at least.
The Eminence Beta 10A in the standard pro sound line seemed the best choice. It is 95-97 dB efficient, depending on how you look at it. Would make the AVT20 sound like you had at least doubled the power relative to the B102. Resonance freq was 53 Hz, close to a Celestion G12H(55) from days past. 2" voice coil, bigass magnet, good response curve, good Xmax, and rated for bass guitar, keyboards, PA use. A giant killer at $70 delivered. Ordered one from Musician's Friend.
The Beta 10A arrived and I was impressed with the build quality. It has a vented pole piece/voice coil with protective screen. No squawker cone like on the B102, but with a presence peak at 3kHz in spite of that. But off axis, I expected the presence peak to be much diminished, and you generally are off axis from a combo amp speaker. I was expecting a flatter power response due to the presence peak, as it makes up for the narrowing of the "audio beam" at higher frequencies. This keeps overall total power into the room more constant, in spite of the peak on axis. Doing a LIAR test (listening in another room.... if you don't know audiophile speak) while I made the dog his dinner in the kitchen tended to bear that out. The B102 is 200watt rated, but the 250 watt rating (coupled with increased efficiency) of the Beta 10A means it can play about 3-5 dB louder if you have the power. This looks (and turned out to sound) like a killer bass speaker for the price.
The Beta 10A was installed and secured with blue loc-tite and it was time for listening and testing. Early testing tended to support Eminence's published response curve. Quick bass guitar test proved it to be louder in bass response and much better sounding than the G10-30AVT. More loudness than the B102, if not better sounding. But then again, the B102 is used by audiophiles for making single driver wideband loudspeakers, and not likely to be bettered in sound quality in a lower priced speaker.
I needed a mono recording to test wideband sound quality, so out came the Beach Boys "Sounds of Summer" album. A CD player is a "flat" input, so it gave me a "flat" setting of my AVT20 tone controls. They are Bass 8, Mid 5, and Treble 0. Remember the Beta 10A has a presence peak, so treble will need a big rolloff. I prefer a bit of bass/midbass boost. This is "right" to my ears.
The first pass of the album definitely improved the sound, so I listened to the album again, and it improved some more, and I listened a third time. Yes, the Beta 10A is a good PA speaker for sure. It should be a good partner with the B102 in a 2x10 or 4x10 cab. Don't Worry Baby, everything will be all right. Yes....I Can Hear Music. Good Vibrations are going on here. It sounds good....In MY Room. We'll have FUN, FUN, FUN....till the neighbors call the cops.
There were some mods done to the cab to improve it for bass. I'm not a real fan of ported cabinets. My Polk HT bass-reflex speakers have open-cell foam resistive flow plugs shoved into their ports (just make your own and experiment), and by my sound level meter and my ears, it flattened the in-room response and gives a slower rolloff in the deep bass. The U2 and Santana concerts sounded better after that.
Resistive flow ports (aperiodic vents, also known as variovent) get rid of the unloading of bass drivers below port cutoff frequency and protect against overexcursion as is the case with bass reflex cabinets. It also gets rid of the high impedance at box resonance in totally sealed cabinets and without the need for as much acoustic fiberfill. It very closely approximates a transmission line speaker without the size and complex internal baffles and precise acoustic stuffing issues. It gives a more flatly resistive impedance curve that permits more speaker coil current near resonance and thus better driver control and a "tighter" sound. Should sound more "live" than a tightly stuffed acoustic suspension cabinet. A famous audiophile loudspeaker of the T-line design is the Vandersteen Model 1, if you get a chance to listen to a pair. They are killer for the price. Listen to something else around the $1200/pair price and then you decide. A famous loudspeaker of the aperiodic vent design is the old Dynaco A25 which sold about a million copies in the 70's and 80's. Known for monster bass extension in a bookshelf size cabinet and 10" woofer. Bass guitar cabs are living a few decades behind the times relative to audiophile loudspeakers in sophistication. The Nestorovic bass alignment in the Vandersteen Model 2 and Model 3 is another killer bass system (by Mile Nestorovic, past chief engineer at McIntosh Laboratory), but don't expect it to show up in bass guitar cabs anytime soon.
Anyway, Madisound or any good audiophile loudspeaker supplier can sell you a Scan-Speak or Dynaudio variovent. Shoving the proper density and thickness of foam in a bass-reflex cabinet can do a similar trick. You can staple 1/4" hardware screen over a cabinet cutout of the proper size, stuff it with fiberglass, then staple another piece of hardware screen on the other side of the cabinet wall to hold the fiberglass sheet in place. That is basically what a Scan-Speak vent is, but uses molded plastic instead of hardware screen. The Dynaco A25 used stapled hardware screen, so look it up on the internet to see what I mean. It's a classic and sure to be talked about in vintage audiophile forums. And it could make a good practice bass cab if you stumble across a pair at a garage sale....but the efficiency will probably even be lower than a B102, so expect a speaker changeout.
An aperiodic bass enclosure is usually filled about 2/3 full of acoustic fiberfill with a clear pathway to the variovent. Fill rates are 1# to 4# per cubic foot, and that's a matter of personal taste. For bass guitar cabs something closer to the lower figure will probably be to most folks taste.
Anyway, it's time to plug in the Stingray and ReBop and abuse the AVT20 and Beta 10A for a while before I give it a final response curve test. It's looking good so far. If you want something different, you just have to do it yourself sometimes. Not available in stores.
I selected the Marshall AVT20 as the reviews were very positive, they are very easily acquired at a low price on the used market, and it uses 10" speakers of which there are many to choose from in the Eminence bass guitar and pro sound lines.
A classic 60's/70's Marshall bass amp was a guitar head with Marshall G12H(55) speakers in a 4x12 cab. Jimi Hendrix used the G12H(55) speaker cabs in conjunction with G12M 4x12 cabs. A G12H and a G12H(55) are the same except for resonance frequency, in this case 55 Hz. HiWatt was also conspicuous in using similar heads for bass and guitar and changing the Fane speakers in the 4x12 cabs. Note Pete Townshend and John Entwistle and their HiWatt rigs of the 70's. The Partridge output transformers in HiWatt DR103 amps were of audiophile quality and made them very suitable for bass guitar (which is why audiophiles bought old HiWatt DR103 heads on the used market, removed the output transformers, installed something cheaper and inferior, and resold them on the used market....BEWARE of an old DR103 at a to-good-to-be-true price). The solid state output stage of the Marshall AVT20 gives extended bass and tight control of a speaker while the tube preamp stage gets good tube overdrive tone, so it's a natural for a guitar to bass amp conversion.
I installed a Philips JAN 12AT7A tube in place of the Marshall supplied Ei ECC 83 to drop the gain from 100 to 70 in order to have slower breakup and wider control range in the first gain stage. The Ei ECC 83 is a killer tube for lead guitar due to its high gain, quietness, and the fact it is a Telefunken ECC 83 copy.....no need to say more if you are an tube audiophile or lead guitarist. BUT, I think the Ei ECC 83 has too much gain for my Spector ReBop with active tone controls and high output DR Sunbeam strings and high output EMG HZ passive pickups.
The stock Celestion G10-30AVT is a piece of crap for bass guitar as it falls flat on its face at 80 Hz, and I have the proper test equipment (I'm a degreed biomedical engineering techie) to prove these points. It has a lot of suckout in the midrange for a scooped sound that guitarists like, but bassists have little need of. It farts when you try to get deep bass from it at an appreciable level. It will self destruct if you keep shoving it, so I pulled it out and intend to give it away to a friend's son who is interested in taking up guitar.
First speaker in was an Eminence B102 of 92 dB efficiency and excellent extension low and high with very linear response. The quality of sound was excellent with the flattest response of the three speakers I have used so far. The fly in the ointment is the low efficiency and the low 20-watt power of the AVT20 .These are solid state watts, not tube watts, equal to about 10 tube watts for comparison. I just had to have more volume, and the quality and range of tones I was getting from the AVT20 started me on a search for a more efficient speaker.
Searching the Eminence spec sheets for a day lead me to conclude that the Eminence Beta 10A was my best choice at my $100 or less price point. If I need to spend more than $100, then a bottle of Talisker and a bottle of Laphroaig for mixing my secret blended Scotch recipe into cheap grain Scotch gets me the best tone.....for a few weeks at least.
The Eminence Beta 10A in the standard pro sound line seemed the best choice. It is 95-97 dB efficient, depending on how you look at it. Would make the AVT20 sound like you had at least doubled the power relative to the B102. Resonance freq was 53 Hz, close to a Celestion G12H(55) from days past. 2" voice coil, bigass magnet, good response curve, good Xmax, and rated for bass guitar, keyboards, PA use. A giant killer at $70 delivered. Ordered one from Musician's Friend.
The Beta 10A arrived and I was impressed with the build quality. It has a vented pole piece/voice coil with protective screen. No squawker cone like on the B102, but with a presence peak at 3kHz in spite of that. But off axis, I expected the presence peak to be much diminished, and you generally are off axis from a combo amp speaker. I was expecting a flatter power response due to the presence peak, as it makes up for the narrowing of the "audio beam" at higher frequencies. This keeps overall total power into the room more constant, in spite of the peak on axis. Doing a LIAR test (listening in another room.... if you don't know audiophile speak) while I made the dog his dinner in the kitchen tended to bear that out. The B102 is 200watt rated, but the 250 watt rating (coupled with increased efficiency) of the Beta 10A means it can play about 3-5 dB louder if you have the power. This looks (and turned out to sound) like a killer bass speaker for the price.
The Beta 10A was installed and secured with blue loc-tite and it was time for listening and testing. Early testing tended to support Eminence's published response curve. Quick bass guitar test proved it to be louder in bass response and much better sounding than the G10-30AVT. More loudness than the B102, if not better sounding. But then again, the B102 is used by audiophiles for making single driver wideband loudspeakers, and not likely to be bettered in sound quality in a lower priced speaker.
I needed a mono recording to test wideband sound quality, so out came the Beach Boys "Sounds of Summer" album. A CD player is a "flat" input, so it gave me a "flat" setting of my AVT20 tone controls. They are Bass 8, Mid 5, and Treble 0. Remember the Beta 10A has a presence peak, so treble will need a big rolloff. I prefer a bit of bass/midbass boost. This is "right" to my ears.
The first pass of the album definitely improved the sound, so I listened to the album again, and it improved some more, and I listened a third time. Yes, the Beta 10A is a good PA speaker for sure. It should be a good partner with the B102 in a 2x10 or 4x10 cab. Don't Worry Baby, everything will be all right. Yes....I Can Hear Music. Good Vibrations are going on here. It sounds good....In MY Room. We'll have FUN, FUN, FUN....till the neighbors call the cops.
There were some mods done to the cab to improve it for bass. I'm not a real fan of ported cabinets. My Polk HT bass-reflex speakers have open-cell foam resistive flow plugs shoved into their ports (just make your own and experiment), and by my sound level meter and my ears, it flattened the in-room response and gives a slower rolloff in the deep bass. The U2 and Santana concerts sounded better after that.
Resistive flow ports (aperiodic vents, also known as variovent) get rid of the unloading of bass drivers below port cutoff frequency and protect against overexcursion as is the case with bass reflex cabinets. It also gets rid of the high impedance at box resonance in totally sealed cabinets and without the need for as much acoustic fiberfill. It very closely approximates a transmission line speaker without the size and complex internal baffles and precise acoustic stuffing issues. It gives a more flatly resistive impedance curve that permits more speaker coil current near resonance and thus better driver control and a "tighter" sound. Should sound more "live" than a tightly stuffed acoustic suspension cabinet. A famous audiophile loudspeaker of the T-line design is the Vandersteen Model 1, if you get a chance to listen to a pair. They are killer for the price. Listen to something else around the $1200/pair price and then you decide. A famous loudspeaker of the aperiodic vent design is the old Dynaco A25 which sold about a million copies in the 70's and 80's. Known for monster bass extension in a bookshelf size cabinet and 10" woofer. Bass guitar cabs are living a few decades behind the times relative to audiophile loudspeakers in sophistication. The Nestorovic bass alignment in the Vandersteen Model 2 and Model 3 is another killer bass system (by Mile Nestorovic, past chief engineer at McIntosh Laboratory), but don't expect it to show up in bass guitar cabs anytime soon.
Anyway, Madisound or any good audiophile loudspeaker supplier can sell you a Scan-Speak or Dynaudio variovent. Shoving the proper density and thickness of foam in a bass-reflex cabinet can do a similar trick. You can staple 1/4" hardware screen over a cabinet cutout of the proper size, stuff it with fiberglass, then staple another piece of hardware screen on the other side of the cabinet wall to hold the fiberglass sheet in place. That is basically what a Scan-Speak vent is, but uses molded plastic instead of hardware screen. The Dynaco A25 used stapled hardware screen, so look it up on the internet to see what I mean. It's a classic and sure to be talked about in vintage audiophile forums. And it could make a good practice bass cab if you stumble across a pair at a garage sale....but the efficiency will probably even be lower than a B102, so expect a speaker changeout.
An aperiodic bass enclosure is usually filled about 2/3 full of acoustic fiberfill with a clear pathway to the variovent. Fill rates are 1# to 4# per cubic foot, and that's a matter of personal taste. For bass guitar cabs something closer to the lower figure will probably be to most folks taste.
Anyway, it's time to plug in the Stingray and ReBop and abuse the AVT20 and Beta 10A for a while before I give it a final response curve test. It's looking good so far. If you want something different, you just have to do it yourself sometimes. Not available in stores.
