Bass Amp for a friend

[dorrisant]

What do you guys think about using a Dumble model as a base for such an amp?

I have been playing bass here in the shop band for the past 6 years now... I too am looking for something that will keep it together without farting out. I'm running a YBA (2 x EL34s) into an Ampeg 4 x 10 and an SWR Redhead combo with 2 x 10. My buddy who has played bass professionally for decades now is suggesting a new speaker... 1 x 18 + 4 x 10 in one cab. I like the concept, but I'll need a bigger amp to push it. I use a couple of four strings as well as a 5 and a 6.

I've read a post where the guy was floored by the capabilities of a Small Special as a bass amp while recording in a studio...

Has anyone ever traced a Winterland? Is this a call for it?

Btw, what are the sources for big iron like we are discussing here?

[Colossal]

I think Chris Squire used both a bass amp and a guitar amp with his ricky's stereo out, I look at it kind of like that

I believe that is correct. Geddy Lee did a similar thing, splitting his signal between low and high amplification. Interestingly he used a 2x15 loaded with EVs, as Stevem suggests.

There's a design for a 100W KT88 amp in the classic GEC book (as well as other tube amps up to 1100W.) For a bass amp, I wouldn't hesitate to use good quality "hi-fi" rated design and transformer. The extended frequency response is important.

http://www.tubebooks.org/Books/GEC_approach.pdf

Yes, I am very much planning a hifi-ish power supply and the OT will certainly be spec'd for bandwidth. Working backwards...so far I am thinking 4xKT88 in U/L for about 140W, a 12BZ7 cathodyne inverter with a DC cathode follower bolted on to the inverting side, a clipping stage just in front of the PI with an adjustable grid leak to control the onset of clipping, a tone stack recovery stage (the front half of the clipper), then the preamp and tone stack. For the preamp, either a 12AU7 input stage or maybe a cascode (?) into a James stack with an added mid control. The preamp could also be fun as octals (thinking 6SL7s). CLC filter in front of the OT supply. Hammond 158Q is 10H/53Ω at 500mA.

[ER]

What do you guys think about using a Dumble model as a base for such an amp?

Jackson Browne's Dumbleland 150 that Stevie Ray used on Texas Flood was Jackson's studio's bass amp, and Tommy Shannon played a Winterland 300 for many years if I remember correctly. I've played bass a bit through my 100 watt 70's amp and it sounded good with a pair of EVs, so I think it would be a great idea, especially with real bass cabinets.

I might go even simpler though, the Alembic F-2B is basically a showman, and those things are plenty piano like with the right bass.

My bass player played a 100 watt ampeg V4B with either a sun 6x10 or a single TL606 with an EV 15 forever and that had plenty of thump. That might be another Schematic to look at for inspiration. I think I would look to really efficient open sounding speakers rather than lug around giant iron. Remember a doubling of watts is around 3dB of volume, that's some heavy expensive iron that could be avoided with careful speaker selection and cabinet design.

[Stevem]

The large cone of a 18" driver is too slow to respond for much of my playing needs especially with anything faster then quarter notes.

I also have a 1971 Sunn Saro that I use for recording and light rehearsals and it's 60 watts of RMS KT88 power is perfect for that as long as I don't play one of my 5 strings.

For a live rock gig with a hard hitting drummer I would want no less then 150 watts RMS of tube power with a stiff power supply.
I would use 6550's since they cost way less then KT88s and 4 of them could get you that 150 watts .

Also build the amp with a line out in case he will gointo a sound system as all too many live sound guys will patch you into a DI box and then there lack of how a Bass should sound produces nothing out front but rumble out of the E and A string and the D and G string don't even eigist out front!

[Colossal]

For a live rock gig with a hard hitting drummer I would want no less then 150 watts RMS of tube power with a stiff power supply.
I would use 6550's since they cost way less then KT88s and 4 of them could get you that 150 watts

I have a quad of KT88 pulls coming from Xtian (thanks dude).

Here's what I am thinking:

Preamp
V1ab Input tube ideas:
1) 6SL7 parallel triode/common anode mixer
2) 6SL7 in cascode
3) 12AU7 parallel triode common anode mixer

Tone Stack
James stack 1MA Bass-120k-1M Treble, with added mid control -> Volume w/2-way bright
(similar values to Ampeg B-15)

Recovery and Clipping Stage
6SL7
V2b 180k/1k8/1uF -> Treble peaker w/variable grid leak Clipping control -> V2a 180k/39-56k cold clipper

Phase inverter
V3ab 12BH7 cathodyne with DC coupled cathode follower on inverting side

Power amp
V4-V7
4 x KT88 in U/L 40% taps
140-150Wrms into a 2k load
PT 350-0-350VAC SS rectified
100uF - 10H/53R - 100uF -> ~450-460VDC B+ under load -> OT tap
Fixed bias, each pair has its own bias pot

Ballparked B+ Voltages
B+1 450VDC - OT centertap
B+2 355VDC - Phase Inverter
B+3 320VDC - TS Recovery & Clipping stages
B+4 310VDC - Input stage
B+5 90VDC - Filament DC reference

Also talked to my friend. He is looking at building a pair of TL606s and sourcing a pair of EVM15Ls for this amp. He is quite excited and surprised. I need to nail down some transformers.

[didit]

Hello Dave —

As previously posted, would recommend higher plate voltage and primary impedance. Also a larger first filter. Something at or above 380VAC into SS rectifier and 2.2-2.4K Ohms on output transformer, and with at least 220uF initially. Others of course may have other advice as there is no set formula, just different response dynamics.

Best .. Ian

[sluckey]

Have you considered the Sunn 2000S? Very simple. Very powerful.

https://el34world.com/charts/Schematics ... _2000s.pdf

[Colossal]

Hello Dave —

As previously posted, would recommend higher plate voltage and primary impedance. Also a larger first filter. Something at or above 380VAC into SS rectifier and 2.2-2.4K Ohms on output transformer, and with at least 220uF initially. Others of course may have other advice as there is no set formula, just different response dynamics.

Best .. Ian

Hi Ian,

I would like to get a bit more than 100W out, so want to utilize a quad in U/L. 380VAC under load would probably be something like 500VDC, and then another small drop across a CLC, right? Was that what you were suggesting with the Dynaco A451 OT? At this point, I've got a schematic together but tweaking values. I want to do a CLC in front of B+1. Will up C1 to 220uF.

Have you considered the Sunn 2000S? Very simple. Very powerful.

https://el34world.com/charts/Schematics ... _2000s.pdf

Steve,

Thanks for the suggestion. The power amp I'm thinking of looks a lot like the S2000. I have been perusing a lot of schematics and cobbling together some ideas. Will post a schematic soon.

[roberto]

Are 100W enough for bass? I would suggest to use a quad of inexpensive GU50s for it.
There was an design working in AB2 class on some forums that used a sextet, IIRC.

[norburybrook]

I routinely record bass through a #102 and EV 1x12 cab in the studio. It's lovely sounding amp on bass. I was surprised when I tried it as an experiment.




M

[didit]

[I would like to get a bit more than 100W out, so want to utilize a quad in U/L. 380VAC under load would probably be something like 500VDC, and then another small drop across a CLC, right? Was that what you were suggesting with the Dynaco A451 OT? At this point, I've got a schematic together but tweaking values. I want to do a CLC in front of B+1. Will up C1 to 220uF.

Yes -- a quad of KT88s running UL and those transformer specs will make better than 100W out.

Ian

[Leo_Gnardo]

The one bass amp I built from scratch for a friend, a local blues bass player: Preamp design borrowed from Fender's white/tan early 60's Bassman, bass channel of course. Power amp 4 x KT88 or 6550 developing 120-140W thru a Hammond 1650T OT. Power transformer Hammond 378CX 400-0-400 V 534 mA. Way over spec'd for the application, it doesn't sag. Simple design, uncompromising power.

Choice of speaker is of course important. There's not much point using inefficient, undersized speakers. (Yeh I know, but SVT uses 10's... * see below)

Rare as it is for me to get out of the workshop and actually hear my customers in concert, 2 years ago this guy's band was playing only a quarter mile away. So, I hiked over there for a listen. Outdoors, the toughest test of all. Through a single EV 15", at 100+ feet away he sounded clear as you could ever want. Granted, not chest-crushing volume, who would expect that at a distance. OTOH he never got "lost in the mix." Wasn't put through the PA either - just a pair of speakers on sticks for the vocals. A second (and third, fourth, etc) speaker cab similarly equipped could only help. Onstage, this has been his standard rig for years. For his purposes, just one 15" speaker's enough for any club.

If you want to hear that B string sing, go for an 18", don't mess around. Still want "clank" from the upper frequencies, treat the speaker system like a PA : A 2x10, 4x10, even a PA horn atop your 18" cab(s). DO block lowest frequencies, even on the 10's, with a series capacitor. Why stress the poor little guys? My friend, playing basic blues, has no need for these tricks. But that's no reason to not include them in a good full range bass system.

* SVT fans will note that one of the amp's most famous users, Jack Casady, played usually through a stack of 18's in the 1970's. No complaint about his sound! Though it may have taken a truck & a team of burly guys to set up the rig. Nothing second best there.

[Colossal]

[I would like to get a bit more than 100W out, so want to utilize a quad in U/L. 380VAC under load would probably be something like 500VDC, and then another small drop across a CLC, right? Was that what you were suggesting with the Dynaco A451 OT? At this point, I've got a schematic together but tweaking values. I want to do a CLC in front of B+1. Will up C1 to 220uF.

Yes -- a quad of KT88s running UL and those transformer specs will make better than 100W out.

Ian

The one bass amp I built from scratch for a friend, a local blues bass player: Preamp design borrowed from Fender's white/tan early 60's Bassman, bass channel of course. Power amp 4 x KT88 or 6550 developing 120-140W thru a Hammond 1650T OT. Power transformer Hammond 378CX 400-0-400 V 534 mA. Way over spec'd for the application, it doesn't sag. Simple design, uncompromising power.

Choice of speaker is of course important. There's not much point using inefficient, undersized speakers

Thanks for the specs, gents. Very helpful. I am working up a schematic and will post for comment soon. Looking at transformers. I want to see if Heyboer offers an A451 clone. I have a quad of Winged =C= 6550s for this project. My friend is planning to build a couple of TL606s.

[sluckey]

Here's some old Dynaco transformer info you may find interesting. It covers the 451. Pretty expensive back in the day.

[roberto]

This is the thread I was talking about:
https://music-electronics-forum.com/sho ... hp?t=28617