What is the effect on noise of DC heater voltage tied to a DC standoff? This was what I was planning.
Hi Guys
As stated, any heater noise that might have been present will be reduced by 30db.
For general noise abatement and best note articulation, use the Galactic Ground illustrated in TUT3. This method can be applied to all technologies and any application as it is based on recognising and controlling circulating currents in the circuit. This layout technique incorporates distributed capacitance and decoupling to provide the lowest noise possible.
Grounding, for the most part, is very simple yet many builders find it mysterious. This is partly because no one bothered to explain it clearly before and others misdirected everyone to use a star ground. The star ground is the easiest to explain and the easiest to understand, so anyone can implement it. However, it is almost universally the worst (or second worst) ground scheme for audio and especially for tube circuitry. Galactic Grounding eliminates rectifier buzz and hum-modulation of signals. Proper wiring methods take care of signals modulating each other.
Once grounding and wiring technique is done properly, the only remaining noise will be thermal - hiss from resistors, tubes, etc - and from circuit design compromises.
Have fun
Kevin O'Connor
As stated, any heater noise that might have been present will be reduced by 30db.
For general noise abatement and best note articulation, use the Galactic Ground illustrated in TUT3. This method can be applied to all technologies and any application as it is based on recognising and controlling circulating currents in the circuit. This layout technique incorporates distributed capacitance and decoupling to provide the lowest noise possible.
Grounding, for the most part, is very simple yet many builders find it mysterious. This is partly because no one bothered to explain it clearly before and others misdirected everyone to use a star ground. The star ground is the easiest to explain and the easiest to understand, so anyone can implement it. However, it is almost universally the worst (or second worst) ground scheme for audio and especially for tube circuitry. Galactic Grounding eliminates rectifier buzz and hum-modulation of signals. Proper wiring methods take care of signals modulating each other.
Once grounding and wiring technique is done properly, the only remaining noise will be thermal - hiss from resistors, tubes, etc - and from circuit design compromises.
Have fun
Kevin O'Connor
Hi JFace, I respect all the previous posts by JMFahey and Struth..both have great insight and many years experience. Your design goals are good, I just have a couple of questions.
Are you intending to run the line out to a main mixing board/PA amp with ''flat'' response speakers, or to a dedicated bass power amp (example Mark2 etc..) with ''bass response'' speaker cab?
Are you adverse to some solid state early in the preamp stage (ie move TL072 or Fet/mosfet up to front end) prior to your tone stack/EQ? Or do you want to use tubes throughout?
In the possibility that you would consider reduction in tube count ( 1 or 2) and like struth mentioned add some tube flavor (which you wanted after the EQ).
Would you consider switchable between James stack / EQ / Flat Bypass instead of running them in series?
Those were just some ideas , and no it would not be the same as what you designed but similar functionality maybe simplified a bit. I would also agree that an output transformer is an advantage. Even with an active balanced line out driver,if the power to your preamp is not turned on, the mixer/power amp may hum very loudly. (from experience!) A transformer would completely isolate from any potential ground loop between the separate equipment.
Are you intending to run the line out to a main mixing board/PA amp with ''flat'' response speakers, or to a dedicated bass power amp (example Mark2 etc..) with ''bass response'' speaker cab?
Are you adverse to some solid state early in the preamp stage (ie move TL072 or Fet/mosfet up to front end) prior to your tone stack/EQ? Or do you want to use tubes throughout?
In the possibility that you would consider reduction in tube count ( 1 or 2) and like struth mentioned add some tube flavor (which you wanted after the EQ).
Would you consider switchable between James stack / EQ / Flat Bypass instead of running them in series?
Those were just some ideas , and no it would not be the same as what you designed but similar functionality maybe simplified a bit. I would also agree that an output transformer is an advantage. Even with an active balanced line out driver,if the power to your preamp is not turned on, the mixer/power amp may hum very loudly. (from experience!) A transformer would completely isolate from any potential ground loop between the separate equipment.
Hi Guys
Regarding the heater supply again:
If you DC the heaters, you get about 30db possible noise reduction.
If you use a DC-standoff, you get a 30db noise reduction even with AC heaters.
If you DC and use the standoff, you can get 60db noise reduction.
These figures assume that all other grounding and wiring is proper. If it is not, say you followed an original layout from the 1960s, then there will still be significant hum and/or buzz that has nothing to do with heater wiring.
As Shanx agrees, simpler is better for tube circuitry, especially if you want tube tone.
Have fun
Kevin O'Connor
Regarding the heater supply again:
If you DC the heaters, you get about 30db possible noise reduction.
If you use a DC-standoff, you get a 30db noise reduction even with AC heaters.
If you DC and use the standoff, you can get 60db noise reduction.
These figures assume that all other grounding and wiring is proper. If it is not, say you followed an original layout from the 1960s, then there will still be significant hum and/or buzz that has nothing to do with heater wiring.
As Shanx agrees, simpler is better for tube circuitry, especially if you want tube tone.
Have fun
Kevin O'Connor
This will be primarily amplified in PA systems. I would like to power a power amp into a bass cab, but this would be much less frequent. I realize I will probably need some hard coded high frequency filtering to take out some of the harshness that the PA will naturally amplify. Any suggestions are welcome.
For now my goal is to keep the audio path all tube. Not because of any tone snobbery, but more for the learning experience. I have a good amount of experience with solid state audio gear, so I'm venturing into the tube realm. I think once I get some years of experience with both, I can move towards the optimization of a hybrid setup that you mentioned.
One of the preamps that I studied extensively was the Fender tbp-1 (schematic available on their website). They had a good handle on the balance between tube circuitry (only two tubes) and solid state. I'm open to all ideas, but I'll likely stick to my design goals for the short term.
Hi JFace, That's sounds fair enough, keeping all tube on the preamp. I am not snobby about the all tube circuit or hybrid either. Both can do quite well to achieve what you want. A simple hi frequency roll off just before the output level control may be adequate, or you could go more towards a ''cabinet simulator'' filter network (maybe that is a circuit you could switch in/out for PA/Bass amp use). An output transformer could also useful in that respect.
I thought modern PA had digital EQ taking good care of such things 
anyway, going through PA, it will end up going through lots of IC's and whatever is used
anyway, going through PA, it will end up going through lots of IC's and whatever is used
I thought modern PA had digital EQ taking good care of such things
anyway, going through PA, it will end up going through lots of IC's and whatever is used
True. I have no problem with my signal going through ICs.
My experience has been the bass player is the last to get any attention for fine tuning the eq and compression. Often times I don't get that privilege. I want to give the best quality sound up front to ensure my sound won't be too overbearing due to a careless sound person.
btw, I think your Baxandal tone control was mentioned as being active
since its not in a feedback loop, its a passive tone control
but passive is ok too I guess, or maybe even better
you really should try the simulator on Duncanamps.com
great tool
and also really crazy to see how wrong it can go
since its not in a feedback loop, its a passive tone control
but passive is ok too I guess, or maybe even better
you really should try the simulator on Duncanamps.com
great tool
and also really crazy to see how wrong it can go
I want to do DC heaters, so I'm looking at two transformers to accomplish this (unless I can find a 230+8VAC transformer).
I estimate the B+ will be drawing ~7.2mA. How would I go about selecting a fuse for this? The transformer is rated for 25mA...do I just use a 25mA on the secondary before the rectifier?
I estimate the B+ will be drawing ~7.2mA. How would I go about selecting a fuse for this? The transformer is rated for 25mA...do I just use a 25mA on the secondary before the rectifier?
I'm thinking a 200-250mA slow blow on the primary, before the power on switch. This feeds both a 120:10 and 120:230 transformer. A PTC thermistor may be a bit more reliable for the B+ transformer secondary.
My thinking here is the B+ transformer will burn out way before the mains fuse will blow, so I'd like some extra protection for the small VA transformer.
My thinking here is the B+ transformer will burn out way before the mains fuse will blow, so I'd like some extra protection for the small VA transformer.
I suppose you have a few well functioning SS curcuits
I would use some of those for test runs of individual parts of your tube pre curcuit
I reckon you also know that once you start playing through such curcuits, it might work different than intended or expected
FWIW I wind my own transformers so in my tube rack preamps I make one with 3 secondaries: the HV one, a 6.3V one and a 14/15V one for any auxiliary Op Amp circuit I may need to add.
For the latter, CRC filters are more than enough.
The Marketing Dept. would call them "organic"
Not a tube "purist" by any means, in fact I moved forward *many* years ago, so I use them when they show their sonic imprint, generally when driven hard (not necessarily clipping, but hard: quite a few Volts RMS), so for "front ends" I often use SS, either a Fet or an Op amp.
A 10X (20 dB) gain clean, relatively noiseless , humless SS input stage will in practical terms push the "next tube" noise contibutions 20dB down , as far as useful signal is concerned.
I mean we are pushing hum/hiss/popcorn (burst) noise , all typical Tube problems, 20dB down: ***GOOD*** .
Besides, if we want "tube flavour" (non linearity/curve bending), we are getting much more of it, the more we hit the tube hard.
There's also another noise contribution we are pushing below the floor:
not a "tube noise problem" per se, but "typical of tube circuits" anyway: the first tube plate resistor is a noise machine:
* typically high value (100K/220K),
* passing an important DC current through it (important relative to the actual signal present there) , typically 0.5 to 1 mA
* dropping an *important* voltage across it (90 to 150V)
* last but not least: it works relatively hot.
All 4 characteristics contribute, in a larger or lesser degree, to noise.
Not bad in a conventional preamp (old Fender, Ampeg, even a Plexi, etc.) but murder in any modern high gain preamp.
Starting with Soldanos and their heirs, MBDR and such, selecting a relatively low noise tube for V1 (the first tube) is *paramount*.
And I'm not even mentioning a far worse enemy: microphonics.
And in even higher gain, full tube preamps, such a Peavey's 5150 and later, noise is unbearable and "must be accepted".... or so they say
Just read threads about Peavey 5150 (and later) owners.
So much so that they had to add a so called "noise gate", in fact a crude "squelch" circuit, based on diodes connected in series with the signal, to tame it down.
They could be avoiding a lot of this using a 10X clean noiseless (relatively to tubes) front end.
The function of the plate resistor in a tube stage, is fulfilled by the Op Amp feedback resistor, which may be high value but has no DC voltage across it nor passes DC current .
And if you insist on a FET there, to keep closer to tube "architecture", its drain resistor will probably be a lower value (4K7 to, maybe, 47K, usually 10 to 22K) and drop some 15V across it .... and no filament of course, nor microphonics.
EDIT: for those who wonder "isn't it complicated to wind a 3 secondary PT for a relatively small Rack Tube Preamp?" the answer is: the pesky one is the HV winding, many turns of very fine wire , the machine must be set to a lower speed and the operator must be careful; while the filament and 14V ones are 20 to 40 times less turns and 5 to 10X thicker wire: piece of cake
For the latter, CRC filters are more than enough.
The Marketing Dept. would call them "organic"
Not a tube "purist" by any means, in fact I moved forward *many* years ago, so I use them when they show their sonic imprint, generally when driven hard (not necessarily clipping, but hard: quite a few Volts RMS), so for "front ends" I often use SS, either a Fet or an Op amp.
A 10X (20 dB) gain clean, relatively noiseless , humless SS input stage will in practical terms push the "next tube" noise contibutions 20dB down , as far as useful signal is concerned.
I mean we are pushing hum/hiss/popcorn (burst) noise , all typical Tube problems, 20dB down: ***GOOD*** .
Besides, if we want "tube flavour" (non linearity/curve bending), we are getting much more of it, the more we hit the tube hard.
There's also another noise contribution we are pushing below the floor:
not a "tube noise problem" per se, but "typical of tube circuits" anyway: the first tube plate resistor is a noise machine:
* typically high value (100K/220K),
* passing an important DC current through it (important relative to the actual signal present there) , typically 0.5 to 1 mA
* dropping an *important* voltage across it (90 to 150V)
* last but not least: it works relatively hot.
All 4 characteristics contribute, in a larger or lesser degree, to noise.
Not bad in a conventional preamp (old Fender, Ampeg, even a Plexi, etc.) but murder in any modern high gain preamp.
Starting with Soldanos and their heirs, MBDR and such, selecting a relatively low noise tube for V1 (the first tube) is *paramount*.
And I'm not even mentioning a far worse enemy: microphonics.
And in even higher gain, full tube preamps, such a Peavey's 5150 and later, noise is unbearable and "must be accepted".... or so they say
Just read threads about Peavey 5150 (and later) owners.
So much so that they had to add a so called "noise gate", in fact a crude "squelch" circuit, based on diodes connected in series with the signal, to tame it down.
They could be avoiding a lot of this using a 10X clean noiseless (relatively to tubes) front end.
The function of the plate resistor in a tube stage, is fulfilled by the Op Amp feedback resistor, which may be high value but has no DC voltage across it nor passes DC current .
And if you insist on a FET there, to keep closer to tube "architecture", its drain resistor will probably be a lower value (4K7 to, maybe, 47K, usually 10 to 22K) and drop some 15V across it .... and no filament of course, nor microphonics.
EDIT: for those who wonder "isn't it complicated to wind a 3 secondary PT for a relatively small Rack Tube Preamp?" the answer is: the pesky one is the HV winding, many turns of very fine wire , the machine must be set to a lower speed and the operator must be careful; while the filament and 14V ones are 20 to 40 times less turns and 5 to 10X thicker wire: piece of cake
Last edited:
I quite agree with it as that is what I have been doing and works well to increase relative S/N ( you can lower the volume on a tube amp) and drive the preamp tubes a tad more. Again being careful with grounding, a +20dB SS preamp can be dead quiet. WRT The first plate resistor: always a good candidate for a low noise type resistor with upgraded wattage.
Agree with your worry, but I think it will be very hard to find a such low current rated fuse.
Maybe NASA has them
, but that's far away from us mere mortalsI'd add a 1/8W resistor in series the +V rail, (by the way use it as part of filtering), rated so on any overload it burns open.
W= I^2 * R , so at 8 mA, a 1K5 1/8W resistor will dissipate 96 mW.
Will be hot to the touch, but within specs, less than the 125mW it's rated for.
At 25mA it will dissipate close to 1 W and quickly open.
Use a carbon film resistor, flameproof if available, and mount it with long legs (1 cm - 1/2") away from the PCB surface, so as not to "toast" it.
Hi Guys
Selecting fuse sizes is a rather simple process.
First point to remember is that every winding must be fused. A single mains fuse for everything provides next to zero protection. To properly protect the PT and the mains source, each secondary and each primary requires its own fuse. In general, the fuse value should be 1.25 times the load current to accommodate heating of the fuse itself.
Fuses in AC lines and ones that feed capacitors must be slow-blow.
Fuses that feed only DC, as for an OT, can be fast blow.
Selecting AC fuses is easiest. Say your heater load is based on the three 12A_7s in your schemo, representing either 750mA at 12V or 1500mA at 6V. A time delay fuse is a MUST as the inrush heater current is 4x the operating current. (measured values with real tubes). Keeping in mind that the fuse should be operated at 80% or its value as a maximum, we would use a 1A fuse for 12V or 2A for 6V, rounding to common values. As my previous post states, there are good reasons to avoid 6V operation of these tubes. TUT3 and TUT4 detail why, with TUT4 also showing how to mix 6V and 12V heaters as we do in our amps.
The use of a DC standoff makes no difference to the above fuse values.
If you were DCing the above heaters, you could try using the fuse values above but you might encounter nuisance failures. This is because the capacitor after the bridge rectifier has nothing to limit its initial charging current other than circuit resistances designed in or that are stray.
For example, suppose you have a 20V raw supply feeding the 12V regulator for the three tubes. Suppose the total circuit and winding resistance is 1R. The initial current pulse can be as high as 20A. If this was a 400V supply for plates, the current peak could be 400A. Such pulses are typical of real circuits and fortunately diodes are designed to accommodate these surges. The 1A 1N400_ -series has a pulse rating of 30A, so they are fine to use in the heater supply and in the plate supply if you add a series R ahead of the first filter cap - 22R will drop Ipk to <20A.
Your plate load of 8mA suggests an AC current about three times this value, using certain rules of thumb, or six times using other rules of thumb. The fuse value will be either 8x3x1.25=30mA, or twice that, 60mA. A very low value fuse by any account. Controlling the inrush current using series resistance also goes some way toward protecting the winding.
(Certain other comments above must be taken with a grain of salt - or some may need an entire shaker. There is no reason for a tube circuit to be noisy despite the fact solid-state can easily come in 20db quieter without much fuss. The noisy examples of product put out by manufacturers are only as noisy as they are because of economic design. Plainly, cheaping out. The PV 5150 is a dead copy of the SLO preamp, but has an intermediate-level effects loop following the preamp. The economic design imposes a 10db noise penalty on top of the sins committed laying out the preamp. Soldano committed the same sins, so their example of their own circuit is also noisy. Yet, neither has to be if the TUT3 methods are followed. High gain does not have to equate to high noise. That is just lethargy of design and maximising profits. Also note, the diode noise gate was never added to 5150, rather to the Tone King and similar based circuits (see TUT6). Really one should just keep comments limited to those relevant to the dude's preamp project....)
For the tube preamp project outlined here, two or three tubes even used all as gain stages do not have to result in a noisy finished product. Keep it purely tube to maximise the tube flavouring. You might want to try an incremental approach to the build, however, to get a feel for what is offered by each circuit portion. This will also aid in assessing how much treble roll off to make "fixed" and how much to be variable, if you decide on using any at all.
If you wish to knock down noise from Rs, best to avoid carbon everywhere in the build. Use metal film in the audio portion and metal oxide (flame proof) wherever a power device is needed. The latter can also be made up from series-parallel MFs. Carbon adds significant distortion of various types, both correlated and uncorrelated to the signal. Just because the economically driven designs use carbon does not mean you have to settle for such junky parts in your own project. As we say in our books and on our site, we select circuits for tone and components for reliability.
Have fun
Kevin O'Connor
Selecting fuse sizes is a rather simple process.
First point to remember is that every winding must be fused. A single mains fuse for everything provides next to zero protection. To properly protect the PT and the mains source, each secondary and each primary requires its own fuse. In general, the fuse value should be 1.25 times the load current to accommodate heating of the fuse itself.
Fuses in AC lines and ones that feed capacitors must be slow-blow.
Fuses that feed only DC, as for an OT, can be fast blow.
Selecting AC fuses is easiest. Say your heater load is based on the three 12A_7s in your schemo, representing either 750mA at 12V or 1500mA at 6V. A time delay fuse is a MUST as the inrush heater current is 4x the operating current. (measured values with real tubes). Keeping in mind that the fuse should be operated at 80% or its value as a maximum, we would use a 1A fuse for 12V or 2A for 6V, rounding to common values. As my previous post states, there are good reasons to avoid 6V operation of these tubes. TUT3 and TUT4 detail why, with TUT4 also showing how to mix 6V and 12V heaters as we do in our amps.
The use of a DC standoff makes no difference to the above fuse values.
If you were DCing the above heaters, you could try using the fuse values above but you might encounter nuisance failures. This is because the capacitor after the bridge rectifier has nothing to limit its initial charging current other than circuit resistances designed in or that are stray.
For example, suppose you have a 20V raw supply feeding the 12V regulator for the three tubes. Suppose the total circuit and winding resistance is 1R. The initial current pulse can be as high as 20A. If this was a 400V supply for plates, the current peak could be 400A. Such pulses are typical of real circuits and fortunately diodes are designed to accommodate these surges. The 1A 1N400_ -series has a pulse rating of 30A, so they are fine to use in the heater supply and in the plate supply if you add a series R ahead of the first filter cap - 22R will drop Ipk to <20A.
Your plate load of 8mA suggests an AC current about three times this value, using certain rules of thumb, or six times using other rules of thumb. The fuse value will be either 8x3x1.25=30mA, or twice that, 60mA. A very low value fuse by any account. Controlling the inrush current using series resistance also goes some way toward protecting the winding.
(Certain other comments above must be taken with a grain of salt - or some may need an entire shaker. There is no reason for a tube circuit to be noisy despite the fact solid-state can easily come in 20db quieter without much fuss. The noisy examples of product put out by manufacturers are only as noisy as they are because of economic design. Plainly, cheaping out. The PV 5150 is a dead copy of the SLO preamp, but has an intermediate-level effects loop following the preamp. The economic design imposes a 10db noise penalty on top of the sins committed laying out the preamp. Soldano committed the same sins, so their example of their own circuit is also noisy. Yet, neither has to be if the TUT3 methods are followed. High gain does not have to equate to high noise. That is just lethargy of design and maximising profits. Also note, the diode noise gate was never added to 5150, rather to the Tone King and similar based circuits (see TUT6). Really one should just keep comments limited to those relevant to the dude's preamp project....)
For the tube preamp project outlined here, two or three tubes even used all as gain stages do not have to result in a noisy finished product. Keep it purely tube to maximise the tube flavouring. You might want to try an incremental approach to the build, however, to get a feel for what is offered by each circuit portion. This will also aid in assessing how much treble roll off to make "fixed" and how much to be variable, if you decide on using any at all.
If you wish to knock down noise from Rs, best to avoid carbon everywhere in the build. Use metal film in the audio portion and metal oxide (flame proof) wherever a power device is needed. The latter can also be made up from series-parallel MFs. Carbon adds significant distortion of various types, both correlated and uncorrelated to the signal. Just because the economically driven designs use carbon does not mean you have to settle for such junky parts in your own project. As we say in our books and on our site, we select circuits for tone and components for reliability.
Have fun
Kevin O'Connor
Last edited:
Noisy examples of commercial products certainly exist because of economics and design. But how many stages need to be put in versus how much wasteful gain throwaway, picking up noise each stage. It happens in SS amps and in tube amps. It's (sometimes bad) design and economics. Couple of stages less means can afford to put higher quality components..harder sell for the commercial guys I guess. But that's the good part of DIY , you get to decide yourself. I was going to mention the series/parallel MFs ..good point. That is getting studio/hi fi grade..again a design purpose choice. I would have figured two 12AX7 was more than enough for a bass preamp going from instrument level /selectable eq/line out.
Hi Guys
Most bass preamps use only two triode stages. With a guitar signal, this would result in mild overdrive, assuming standard voltages. With a bass, the distortion level is higher due to the higher output most basses have - passives, not including actives - but the sonic impression is still of overdrive.
For guitar, modern metal tones are easily derived from four stages. The reason you see five+ is from the lethargy of the early modifiers who decided to add another tube to a stock amplifier rather than re-assign functions of the existing preamp stages.
There are multiple points to work through and balance when designing any tube preamp or amp. First, you define the tone that is required.This might imply a tube budget and even possible topologies to consider. Next you define fixed aspects you want in the design, like the inductor mid control. These fixed items impose their own restrictions and requirements.
Interstage attenuation is a must even with only two stages, although in this format a proper grid-stop will suffice on the second grid. Each tube provides a veil of tube character at all signal levels. You do not have to slam the tube hard for its character to be revealed. However, tubes respond to small signals differently than they do to large signals, which is the basis of "touch response" and a means to achieving whatever tone you require. It also means that fewer stages can be used for a given task if you are willing to refine a design rather than use a brute force approach.
Our books kicked off the boutique amp industry, giving a lot of tinkerers the courage to embark on commercial ventures. We show options without restriction other than what causes burnt circuits. Ampeg followed hifi rules when designing all of their vintage equipment. You can as well, or you can follow tube safety rules which allow greater latitude. In a preamp, there is no real distinction except that you allow the signal to go beyond the strictly linear part of its swing. All guitar and bass tube preamps do that when pushed harder than the "fifties intention".
The veils of tube tone are harmonics added. Harmonic buildup leads to compressed and distorted tones that do not rely in any way on clipping or cutoff.
Have fun
Kevin O'Connor
Most bass preamps use only two triode stages. With a guitar signal, this would result in mild overdrive, assuming standard voltages. With a bass, the distortion level is higher due to the higher output most basses have - passives, not including actives - but the sonic impression is still of overdrive.
For guitar, modern metal tones are easily derived from four stages. The reason you see five+ is from the lethargy of the early modifiers who decided to add another tube to a stock amplifier rather than re-assign functions of the existing preamp stages.
There are multiple points to work through and balance when designing any tube preamp or amp. First, you define the tone that is required.This might imply a tube budget and even possible topologies to consider. Next you define fixed aspects you want in the design, like the inductor mid control. These fixed items impose their own restrictions and requirements.
Interstage attenuation is a must even with only two stages, although in this format a proper grid-stop will suffice on the second grid. Each tube provides a veil of tube character at all signal levels. You do not have to slam the tube hard for its character to be revealed. However, tubes respond to small signals differently than they do to large signals, which is the basis of "touch response" and a means to achieving whatever tone you require. It also means that fewer stages can be used for a given task if you are willing to refine a design rather than use a brute force approach.
Our books kicked off the boutique amp industry, giving a lot of tinkerers the courage to embark on commercial ventures. We show options without restriction other than what causes burnt circuits. Ampeg followed hifi rules when designing all of their vintage equipment. You can as well, or you can follow tube safety rules which allow greater latitude. In a preamp, there is no real distinction except that you allow the signal to go beyond the strictly linear part of its swing. All guitar and bass tube preamps do that when pushed harder than the "fifties intention".
The veils of tube tone are harmonics added. Harmonic buildup leads to compressed and distorted tones that do not rely in any way on clipping or cutoff.
Have fun
Kevin O'Connor
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.