This has been talked a little bit around here before, but I could really use some help on this. I'm thinking of building an all tube bass amp for home recording, and thinking of loosely modeling it after the SVT. Planning on using the bandaxall EQ for low and high shelving. I want to keep the layout of the amp as simple as possible, but also allow for mids to be pushed or scooped, and adjust the frequency where it's pushed or scooped, and the bandwidth of that frequency.
I'd also like to keep the EQ parametric. I don't want to mess with anything graphic. Been reading up on gyators, but I'd like to keep the amp free of op-amps. Using an inductor sounds more appealing to me. But I'm a bit lost at the moment. I'd like to have a mid control that boosts at 1kHz, over a wide bandwith, 2 or maybe even 4 octaves.
Any help to point me in the right direction would be a great help.
I'd also like to keep the EQ parametric. I don't want to mess with anything graphic. Been reading up on gyators, but I'd like to keep the amp free of op-amps. Using an inductor sounds more appealing to me. But I'm a bit lost at the moment. I'd like to have a mid control that boosts at 1kHz, over a wide bandwith, 2 or maybe even 4 octaves.
Any help to point me in the right direction would be a great help.
All musical instrument amp threads belong in Instruments and Amps per forum directives. (See forum subheaders) Will move to I & A.You can't boost with a passive tone control/EQ , you can only cut , boosting a frequency requires amplification of that frequency which can't generally be done passively so if you want to boost the mids by say 12 DB you are pretty much relegated to going active ....
The other option is to go passive and cut the highs and lows which boosts the mids in relation to the highs/lows .....
What I did with a Tube guitar amp I built last year was use a standard 3 band tone control then put in a FX loop so I can run the preamp output into a 15 band graphic EQ (and other FX gear) .....
Cheers
The other option is to go passive and cut the highs and lows which boosts the mids in relation to the highs/lows .....
What I did with a Tube guitar amp I built last year was use a standard 3 band tone control then put in a FX loop so I can run the preamp output into a 15 band graphic EQ (and other FX gear) .....
Cheers
One way I could see you do it is by the use of one tube for bass, mid and highs. Frequency depended feedback controls the boost or cut. Rotary switches could be used for the mid frequency and bandwidth. Check figure 18 at this link: click. You'll probably be able to figure out the switchable caps.
If you're serious, you'll need a real killer output transformer. The last of the Trace Elliot V-6 and V-8 output transformers are on sale. They used 6 or 8 KT88 respectively, at high voltage pushing them really hard. But now you can use 6 or 8 KT120 for a lot better reliability than either an SVT or a V-8, better bass, and more power. The only catch is that you have to find your own bell-end covers as the transformers arrive with an open-frame taped winding. I used the bell-end covers from a 225-watt Peavey VB-2, which fit, but the V-6 and V-8 output transformers have iron laminations twice as thick.
I like the SVT layout with power amp below and preamp up top, as long as you cool it well. It puts the weight low and keeps the heat out of the power amp chassis. But then it really needs a chimney / separator between the power amp and preamp if you want to make one that's convection-cooled with air grates front and back instead of fans for recording and home use. In fact, I'd build a separate power amp and separate preamp on separate 19" chassis, and build a dual case that put the power amps below and controls above but in its own area with some insulation barrier. That way you could swap for an Alembic tube preamp or a Trace Elliot tube preamp. And if your project got sidetracked halfway thru you could still complete the power or pre section.
BTW look carefully at the tube compressor in the better Trace Elliot tube preamps, really handy for getting the optimum tube bass sound and a lot cheaper than adding a tube compressor afterward. I think the new Bassman 300 also has a compressor. The old SVT also has plenty of gain! I worked for a band in the early '70's that used SVTs for both guitars and the bass, and they were pretty darn amazing.
Do you really need 300 watts for recording at home? You might consider picking up a used Harman-Kardon Citation II with its really excellent output transformers and converting it to KT120's like Carver did, then adding a preamp with a variable compressor and variable gain, or even relays for switching between multiple preamps. That would give you the option of using stereo effects between the preamp and power amp.
Of course my dreams are not yours...dream on. All I mean to say is that for a tube bass guitar amp, you might start with the output transformer and the output tubes.
I like the SVT layout with power amp below and preamp up top, as long as you cool it well. It puts the weight low and keeps the heat out of the power amp chassis. But then it really needs a chimney / separator between the power amp and preamp if you want to make one that's convection-cooled with air grates front and back instead of fans for recording and home use. In fact, I'd build a separate power amp and separate preamp on separate 19" chassis, and build a dual case that put the power amps below and controls above but in its own area with some insulation barrier. That way you could swap for an Alembic tube preamp or a Trace Elliot tube preamp. And if your project got sidetracked halfway thru you could still complete the power or pre section.
BTW look carefully at the tube compressor in the better Trace Elliot tube preamps, really handy for getting the optimum tube bass sound and a lot cheaper than adding a tube compressor afterward. I think the new Bassman 300 also has a compressor. The old SVT also has plenty of gain! I worked for a band in the early '70's that used SVTs for both guitars and the bass, and they were pretty darn amazing.
Do you really need 300 watts for recording at home? You might consider picking up a used Harman-Kardon Citation II with its really excellent output transformers and converting it to KT120's like Carver did, then adding a preamp with a variable compressor and variable gain, or even relays for switching between multiple preamps. That would give you the option of using stereo effects between the preamp and power amp.
Of course my dreams are not yours...dream on. All I mean to say is that for a tube bass guitar amp, you might start with the output transformer and the output tubes.
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Cycle, thanks for your informative input! One of the biggest problems with tube bass amps is that they aren't all that reliable, and they're heavy. Having internal fan cooling can also cause issues for home recording, or any recording environment. But what occurs to me is that with more and more guitarists playing or recording at home with tube amps that are 1 watt to 20 watts, I imagine one could build a tube bass amp that doesn't weigh a ton, is pretty reliable, and is loud enough to compete against 20 watt guitar amps, but quiet enough for getting a good sound for home recording.
I thought you said modeled on an SVT, which has 6 output tubes and 300 watts output.
Indeed, that's for filling a large stage outdoors without instruments thru the monitors, not for recording at home.
Seriously, consider a stereo tube power amp and separate preamps then. Though more and more people run a smallish amp into an absorptive isolation speaker box with a microphone, then use transistor amps as necessary for monitoring and coverage.
Bass power amps just have bigger output transformers and bigger interstage coupling caps, as compared to guitar power amps. A hi-fi stereo power amp (not ultralinear) without too much feedback works surprisingly well.
There's also things like the Peavey Classic 120 rack-mount mono power amp, with a bunch of 6L6s in it. Decent bass guitar power amp for really cheap.
I'll hold any comment or advice until you reveal more about what you're lusting for.
Indeed, that's for filling a large stage outdoors without instruments thru the monitors, not for recording at home.
Seriously, consider a stereo tube power amp and separate preamps then. Though more and more people run a smallish amp into an absorptive isolation speaker box with a microphone, then use transistor amps as necessary for monitoring and coverage.
Bass power amps just have bigger output transformers and bigger interstage coupling caps, as compared to guitar power amps. A hi-fi stereo power amp (not ultralinear) without too much feedback works surprisingly well.
There's also things like the Peavey Classic 120 rack-mount mono power amp, with a bunch of 6L6s in it. Decent bass guitar power amp for really cheap.
I'll hold any comment or advice until you reveal more about what you're lusting for.
Funk, that's a lot of what I'm thinking. I'm not really wanting to build a clone, so much as just get a tube bass amp sound that's ideal for recording. Lower wattage has another advantage in that it makes the amp cheaper to build, it makes it lighter, more reliable, you can even omit fan cooling. They're pricey for power tubes, but I've been reading some very good things about KT120's. I'm thinking a tube bass amp in the 50 watt to the 150 watt range would be ideal.
I'm very interested in the Trace Elliot V Type compression circuit, but I haven't had much success finding a readable schematic. If someone has one and could post it, I will be eternally grateful. I'm considering using an optical tube compression circuit, much like what was used on some Teletronix circuits from days of yore. I have no idea if this is similar to the Trace circuit.
Back in the late 90's I bought a solid state Trace. I picked it over a V-Type. At the time I thought, "what is this junky V-Type amp?!? It doesn't even have a graphic EQ!" Man, am I ever kicking myself for that now. Now that I'm older and wiser, I've noticed that every single tube bass amp I've ever heard, be it an SVT, or a Marshall VBA, or the new Fender Bassmans, or those Trace V amps, all of them sound ungodly good, and leaps and bounds better than any solid state bass amp I've ever heard. Sadly, they either cost a fortune or are difficult to find.
I'm very interested in the Trace Elliot V Type compression circuit, but I haven't had much success finding a readable schematic. If someone has one and could post it, I will be eternally grateful. I'm considering using an optical tube compression circuit, much like what was used on some Teletronix circuits from days of yore. I have no idea if this is similar to the Trace circuit.
Back in the late 90's I bought a solid state Trace. I picked it over a V-Type. At the time I thought, "what is this junky V-Type amp?!? It doesn't even have a graphic EQ!" Man, am I ever kicking myself for that now. Now that I'm older and wiser, I've noticed that every single tube bass amp I've ever heard, be it an SVT, or a Marshall VBA, or the new Fender Bassmans, or those Trace V amps, all of them sound ungodly good, and leaps and bounds better than any solid state bass amp I've ever heard. Sadly, they either cost a fortune or are difficult to find.
Another thing I've been pondering is whether to include switching for passive or active pickups. Many older amps just had a built in attenuator on the input to switch between different input impedances.
Since this is just a simple pad, the thought occurs to me that it might be interesting to have a few different options. I'm just not sure of what values to use.
Since this is just a simple pad, the thought occurs to me that it might be interesting to have a few different options. I'm just not sure of what values to use.
There's a ton of stuff you can do between the guitar and that first stage. I'm no guru but here's some thoughts from another newbie.
If you wanted just an L-pad or T-pad, you could look up or calculate the values. But the load on the guitar changes the sound significantly with passive pickups (not with active) , and how hard you hit that first grid makes a big diffference too. So you might consider making the two legs of an L-pad seperately adjustable but adding some resistors to keep the ranges reasonable. Usually there's about 1M to ground then 27K to 64K to the grid. The only problem is only you will know how to work it the 'load' and 'drive' knobs; here's some guesses for values:
1- (a 200K resistor and 2M audio taper pot in series) hot to ground (parallel with the guitar input), adjustable from 200K to 2.200M. This can make a difference if you have high-value pots in your passive guitar, or volume and tone bypass in your passive guitar. If you get hum in the middle area of the pot range, try a lower-value pot. You don't want to completely short the output of an active pickup, so there's that range-limit resistor.
2- (a 1K resisor and 100K pot in series) hot to first stage grid (series with the #1 above) adjustable from 1K ohms to 101K. Try dfferent things here.
You can also switch an isolation coupling cap in for active guitars. With the cap on, maybe you can switch in a bit of DC bias on that grid.
You can also switch a "bright" cap, (or even two switches with different value caps) across the #2 resistance leg above. While Fender put 'bright' switches across the volume between 1st & 2nd stages, Peavey sometimes had a cap across a resistor somewhere between the pickup and the first stage.
In that first stage, you can vary the resistor from cathode to ground, and you can switch caps across it for a deeper or brighter sound. You can vary the value of the coupling cap out the plate.
It might get ridiculous with too many switches, you might just experiment and leave what you like for the guitars you use.
But some of this stuff makes the difference of how some good amps and some good guitars work really well together (or don't).
Work won't let DIYAUDIO download an attachment to this post, but give me your email address and I'll send the v-8 service manaul with the preamp and compressor schematic. Or maybe I can load it from home later.
Have fun!
If you wanted just an L-pad or T-pad, you could look up or calculate the values. But the load on the guitar changes the sound significantly with passive pickups (not with active) , and how hard you hit that first grid makes a big diffference too. So you might consider making the two legs of an L-pad seperately adjustable but adding some resistors to keep the ranges reasonable. Usually there's about 1M to ground then 27K to 64K to the grid. The only problem is only you will know how to work it the 'load' and 'drive' knobs; here's some guesses for values:
1- (a 200K resistor and 2M audio taper pot in series) hot to ground (parallel with the guitar input), adjustable from 200K to 2.200M. This can make a difference if you have high-value pots in your passive guitar, or volume and tone bypass in your passive guitar. If you get hum in the middle area of the pot range, try a lower-value pot. You don't want to completely short the output of an active pickup, so there's that range-limit resistor.
2- (a 1K resisor and 100K pot in series) hot to first stage grid (series with the #1 above) adjustable from 1K ohms to 101K. Try dfferent things here.
You can also switch an isolation coupling cap in for active guitars. With the cap on, maybe you can switch in a bit of DC bias on that grid.
You can also switch a "bright" cap, (or even two switches with different value caps) across the #2 resistance leg above. While Fender put 'bright' switches across the volume between 1st & 2nd stages, Peavey sometimes had a cap across a resistor somewhere between the pickup and the first stage.
In that first stage, you can vary the resistor from cathode to ground, and you can switch caps across it for a deeper or brighter sound. You can vary the value of the coupling cap out the plate.
It might get ridiculous with too many switches, you might just experiment and leave what you like for the guitars you use.
But some of this stuff makes the difference of how some good amps and some good guitars work really well together (or don't).
Work won't let DIYAUDIO download an attachment to this post, but give me your email address and I'll send the v-8 service manaul with the preamp and compressor schematic. Or maybe I can load it from home later.
Have fun!
cycle, I was thinking a lot of the things you were. I was thinking of using a rotary switch where I could put a lot of different values. I think the parts count would be well worth it.
Some of the old Ampegs used a normal and bright input, and sometimes even used a 0ohm resistor on the grid. A few solid state bass amps used 1k. Marshall's used 33k or 68k. Most Ampegs settled on a 48k. They even put a 5.56M resistor to ground. I'm not sure what their reasoning for this was, other than possibly keeping noise out of the amp. I figured it might be interesting to use a pot here to adjust different values, but I figure using a rotary switch would end up sounding a lot better. I'm just not sure what kind of rotary switch to use.
I will message you!
Some of the old Ampegs used a normal and bright input, and sometimes even used a 0ohm resistor on the grid. A few solid state bass amps used 1k. Marshall's used 33k or 68k. Most Ampegs settled on a 48k. They even put a 5.56M resistor to ground. I'm not sure what their reasoning for this was, other than possibly keeping noise out of the amp. I figured it might be interesting to use a pot here to adjust different values, but I figure using a rotary switch would end up sounding a lot better. I'm just not sure what kind of rotary switch to use.
I will message you!
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