Tube amp cathode follower compression For instance I outfitted my 60's Vox AC100 with separate resistor/cap on each output tube's cathode. With 100k cathode resistor less distortion, because there is less grid current pulled. Regarding the last gain stage and cathode follower regulator of this preamp schematic only 1 resistor value is different, the 560K from C/F grid to ground is changed to a 680K. Can the gain stage part of the The normal approach to volume compression (or expansion) is to run the signal into a detector and use the output of the detector to modulate an amplifier. This amp uses the cathode follower design because it is the lowest distortion amp for the easiest circuit topology. Welcome To the Hoffman Amplifiers Forum December 28, 2024, 10:55:40 pm: Welcome, Once I measured from the grid of the driver to the cathode of the follower the compression effect was clearly evident. Re: Pentode vs Cathode follower for compression Post by bepone » Thu Sep 14, 2023 5:07 pm those experiments you build on wooden plank for preamp and output and experiment how you want. Thanks to this, the amplifier sounds stronger and "wider" and also has a unique compression not found in Fender. Approximately 5 pei cent regenerative feedback is added from cathode to cathode, increas ing peak output and noticeably re ducing peak overall distortion. for_p1 Addicted Member. Bear in mind Valve wizard is explaining how to get the most linear out of a cathode follower and choose the Ecc82 for that purpose with a lower load on the cathode. Guitar amps are not exactly like HiFi equipment. The output stage of the circuit is a Cathode Follower and is suitable to drive a low impedance amplifier. R. My design calls for an output stage to be a 12au7 triode as a cathode follower into a 4:1 output transformer (9600 to 600 ohms). Andy Le Blanc Posts: 2582 Joined: Sat Dec 22, 2007 1:16 am FAQ and General Tube Amp Electronics Troubleshooting; ↳ FAQs; Shop Talk; ↳ Technical Discussion; ↳ Garage Talk; ↳ Speakers and Cabinets; ↳ PCB Design; The amp is much more approachable with more of the compression I was looking for to match leads to rhythm, and the overdrive lost the fuzziness. A tube amp builder's community Joined: Wed Jun 30, 2021 6:08 am. This assumes you are designing for minimum Choosing lower gain pre tubes such as 5751, 12AY7, 12AV7 may help. 2. Merlin explains this well. get an extremely powerful push-pull tube-amplifier simulator for On Sale only $19 . In a "Marshall" type amp (a circuit I'm much more familiar with) the supporting triode plate and the cathode follower cathode R are the same and this arrangement does achieve an acceptible bias. Can the gain stage part of the The first tube is a classic phase inverter. Hence, their popularity in the output circuits of many preamplifiers. I can do a test with my SSS feeding a signal in the PI and see I designed and built one guitar tube amp already, a very complicated 2 x 6L6GC amp with parallel effects loop, pentode-driven spring reverb, adjustable feedback loop with presence and resonance controls built in, and a number of other tone tweaking tricks gathered from Merlin's book and around the internet (scale control, bass/mid/bright boost crbowman wrote:I have a donor 2 holer chassis from a gutted Laney 30 watt ProTube that I'm thinking about building into a clean 50 watt amp. Jul 10, 2014 The 12A*7 tube family has a nice feature to easily inject filament bias voltage at pin 9 of the tube (because pin 9 is The idea is to "repurpose" V2 in that V2b (cathode follower in original circuit) becomes the "added" gain stage between V1b and V2a. Can the gain stage part of the My first attempt would be to set a cathode follower after the tone stack and fully bypass the third gain stage to recover from fx-level. Please login or register. -User Name-Password There also is a point where the cathode follower introduces some compression. He already installed an appropiate speaker, an old Carvin made by Eminence, that they used in their bass combos and stage monitors, really nice and woody sounding. This type of stage is effective for driving EQs and effects loops. On the Chinese tubes- they sound great in my Laney LC-30, ok in my Fenders, and awful in my Marshall- A: Yes, while the HMV2E will technically work in some other amp models, we’ve optimized and tuned this design specifically for Marshalls’ with master volume controls such as Thanks. most use a 12bz7 or 12bh7 or a 5751. Very great improvent adding the cathode The Marshall JVM 410 and 210 amps run two tone stacks off of one cathode follower with no isolation. G. In a sea of microprocessor powered IC based gizmos this vacuum tube amplifier WON ONE OF THE CATEGORY PRIZES!!! It should be featured in the Circuit Cellar magazine, and on their web site in the near future. By way of background, I would like the preamp circuit to be that of a Marshall 1959 Super and my first diagram is the preamp section of the Marshall. Using Ra = 10K and B+ = 160V, plot load line. This unity-gain buffer is part of what I call the trinity of lazy push-pull Hoffman Amplifiers Tube Amp Forum, DC Coupled Cathode Follower ANOMALY - Help. In addition to the effects of the driver itself (AFAIK, use of a high plate resistance tube like 12AX7 is the source of the compression in the SSS), direct coupling avoids charge time associated with capacitor coupling resulting in a Hello, I am wondering if someone could look at the attached diagram of a circuit I have built based upon a design in a commercial boutique amp and offer any advice about the Cathode Bypass values. 11), which is a unity-gain (actually, a little less than unity) cathode follower (V2a) loaded Although the tutorials are using 6922 calculations, using the same formulas may assist you in designing an amplifier based on other triodes. With that context now established, I learned something interesting while chatting with this person: if one is aiming for maximum output or RMS watts, they should consider a Plate Fed tonestack vs a Cathode Follower. It’s called the cathode follower and it doesn’t amplify sh!t, at least not in the voltage embiggening Completely new Amp block cathode follower algorithm yielding more accurate results. I've heard that due to the spiral filiment, they shouldn't be used in the cathode follower/tone stack position. A conservative guess would be that 99. In indirectly heated tubes, the cathode is a sleeve surrounding the filament heating it; this mechanical separation helps prevent heater hum (50hz or 60hz AC) from entering through the cathode. " 16. Shop Talk. That whys Fender used the 12at7 as the PI tube a lot of times Design a cathode follower as a common-cathode amplifier, then move the load resistor from the anode to the cathode. 17. The AC input is divided by two with the two 470kΩ resistors and feeds the grid of the cathode follower bluesky636 wrote:I am not familiar with any amp that uses a cathode follower after the PI. It's the same problem like the Trainwrecks have as the distortion comes from the power amp what makes the fx loop somewhat useless. Replacing V1 with a 6U8, using the triode section as the cathode follower. instead of asking and loosing time The cathode follower, once again, does its job. I know that you said “low gain” but the cathode follower stage is such that even a 12AX7 at full output cannot overdrive the buffer. Moderators: pompeiisneaks, Colossal. 8 CATHODE FOLLOWER HARMONICS; 17 Power Supply parameters. FAQ and General If the cathode follower runs at 180V grid and 190V cathode, the grid is NEGative of cathode and draws negligible grid current. Complete schematic diagram of direct-coupled 6V6 cathode-follower amplifier. You need a low output A 1. In many ways it is the inversion of a cathode follower: where the A tube amp builder's community Joined: Wed Jun 30, 2021 6:08 am. A bit radical perhaps but it tamed the amp. ) The Sprague atom addition made the amp a lot cleaner too whereas before the amp could breakup rather soon. If wanting that mid gutted sound you get with a 33K slope resistor then you are pretty much forced to drive it with a cathode follower. I am aware that the cathode follower itself has a gain of less than unity. . M Hartman SSS#002 has the 12AX7. A high impedance tube (i. TCJ Push A robust tube, such as the 12BH7 or 5687, should be used in the cathode-follower position. The only reason I'd decided on the 12AU7 is that I had indeed read the 12AX7 made a crappy cathode follower; so if that's not the case I've definitely got no problem using the tube the PS and chassis were already designed to use. I also did not wish to use one tube for both amps to reduce crosstalk A classic example of class AB2 drive and biasing with a follower is the Heathkit W6A or W6M amp. The cathode follower was easy to do and anyone who has some amp building experience should be able to pull it off. Specifically, a 38Ω load (Sivga Luan pair of headphones). I prefer the DC driven in a totally clean amp due again to the added Bandwidth Clarity and singing sustain like compression 2. I've been using 20V germanium zeners (1N4747A), opposing pair, with resistance in front. I replaced it and the amp sounded much better. A tube amp builder's community. The plate follower (a. Marshall uses them in many of their circuits. I could estimate that well over 60% of the tube guitar amps on the market have a stage of this configuration. This . There is a 39k resistor between each treble wiper and volume pot, but I think that's to isolate the channel mute relay from the other channels, in Thanks! The DC coupling refers to the output of one tube passing directly to the input of the next stage without a coupling capacitor. Post by Tobyk » Tue Aug 15, 2023 7:25 pm. instead of asking and loosing time Re: Pentode vs Cathode follower for compression Post by bepone » Thu Sep 14, 2023 5:07 pm those experiments you build on wooden plank for preamp and output and experiment how you want. You overdrive the cathode follower and get a high gain sound without driving up the noise floor with more gain. Not sure where the EQ sits in the MP1 nor the exact values, but Output EQ type JMPre-1 should more or less be an active EQ. anode follower), like the common-cathode amplifier, is a much-too-overlooked circuit. I don't want to change the tone, just add more sustain. Well, at least this week's circuit continues the thread from my last post on cathode-follower You should be able to choose a value that suits your needs. The left hand triode is a cathode follower with a very steep dc load line (10kΩ). Rooster>I've enjoyed Merlin's book along with many others. It works well. OK, that makes sense that it would be a power supply issue. Quick links. Like the driver for the Fender Bassman tone stack, the cathode follower is DC coupled. Cathode follower compression A lot of guitar preamps use a cathode follower to softly clip the signal instead of driving a load like a tone stack. In the 5F6-A, there is an extra unused triode if you don't include the cathode follower. 9% of tube power amplifiers use the grounded-cathode amplifier configuration, with the load attaching at the plate, not the cathode; the output tubes working as amplifiers, not buffers. But this Hiwatt cathode follower is not DC coupled to driving stage bluesky636 wrote:I am not familiar with any amp that uses a cathode follower after the PI. A cathode follower performance can be improved by using a high transconductance tube, whether it is a triode, pentode, beam power, or beam tetrode (beam power) tube. This voltage is supplying the bias voltage divider/cathode follower. Is it as easy as simply dropping one leg each off of pins 3 and 8? Any input here would be greatly appreciated. 2 B+ TIME CONSTANT; The compression was due to the 100K cathode follower resistor measuring 880K. Thus, if the cathode must swing +/-150 volts, the grid needs to see +/-195 volts of swing, which means that the driver stage’s B+ must sport at least a +500V rail voltage in the form of a mono-polarity power supply or +/-250V in a bipolar The White cathode follower is no stranger to the Tube CAD Journal, having made many appearances here before. 25 volts (+4dBu). A schematic of the non-functional amp as it sits now is attached. Post by mhartman » Wed Jul 18, 2012 5:59 pm. I was curious to what you would expect the inclusion of that stage to offer in terms of both advantages and disadvantages, mostly relating to effect on potential output The cap I was talking about was the "bootstrapping for gain" cap that runs between the split plate resistors on V1b and the tube side of the cathode resistor of the follower. 2 at cathode follower at idle. 20 posts 1; 2; Next; Tobyk Posts: 101 Joined: Wed Jun 30, 2021 6:08 am. This circuit can be as Tube amp kits, tube amp books, tube guitar amps by Kevin O'Connor. This balanced signal would be used either as a DI or as the signal to a power amp for personal monitoring. Cathode follower's output impedance is lower, which makes it behave more like an ideal voltage source, and it can often also source more current to the load. In a directly heated tube, on the The problem is when using the 12AX7LPS in a "cathode follower" type stage. Fig. instead of asking and loosing time Was just re-examining the math- the real trick to making a cathode follower work correctly, is having a LOW ENOUGH PLATE IMPEDANCE tube, so that you don't run out of "drive". So cathode bias would seem more forgiving to varying tube substitutions than a circuit that is designed to a Re: Cathode follower for compression Post by cdemike » Tue May 28, 2024 10:25 pm Tobyk wrote: ↑ Mon May 27, 2024 10:59 am Does anybody know if this ’Direct DC coupled cathode follower’ setup for compression can be done with transistors instead, with the same compression result? Re: Cathode follower for compression Post by cdemike » Tue May 28, 2024 10:25 pm Tobyk wrote: ↑ Mon May 27, 2024 10:59 am Does anybody know if this ’Direct DC coupled cathode follower’ setup for compression can be done with transistors instead, with the same compression result? Re: Cathode follower for compression Post by cdemike » Tue May 28, 2024 10:25 pm Tobyk wrote: ↑ Mon May 27, 2024 10:59 am Does anybody know if this ’Direct DC coupled cathode follower’ setup for compression can be done with transistors instead, with the same compression result? Re: Cathode follower for compression Post by cdemike » Tue May 28, 2024 10:25 pm Tobyk wrote: ↑ Mon May 27, 2024 10:59 am Does anybody know if this ’Direct DC coupled cathode follower’ setup for compression can be done with transistors instead, with the same compression result? Hoffman Amplifiers Tube Amp Forum, Following EF86 V1 w/ Cathode follower and TMB? EF86<Cathode follower<TMB stack<Cold clipper<triode gain stage< PI etc. I chose to use the cathode follower because I am driving two tone stacks from this one stage. I'm dubious that the lower plate resistance of the triode section would produce the compression from the cathode follower I'm hoping for, so it's possible that idea 1 would be better in this regard. if not a tech should be able to do it for you and it wouldn't be that expensive. The effect caused due the biasing of a standard cathode follower yields a compressed signal of the positive half cycles but not the negative halves which yields 2nd If the DC-coupled CF is in the preamp (like a 5F6A, where it is coupled to a preceding driver stage, and where there is also another gain (input) stage in front to boost the Anyway, cathode follower and common cathode circuits inherently react somewhat differently to reactive loads, such as a highly capacitive "tonestack". 2021 6:08 am. a. Many find it the most musical breed of tremolo available, arguably the best type ever built into a Re: Pentode vs Cathode follower for compression Post by bepone » Thu Sep 14, 2023 5:07 pm those experiments you build on wooden plank for preamp and output and experiment how you want. "Mid gutted" suggests to me that the tone stacks in question have a "slope resistor" value that's too high. As such, the preamp is totally free of blocking Seeing as we now have a pretty good idea of what the SSS post PI cathode follower looks like, I was wondering what changes would need to be made to implement this in a 50 watt output stage. Skip to content. 7 CATHODE FOLLOWER COMPRESSION; 16. The second tube is cathode follower, which is connected directly to grid of power tubes. We'd need to add yet another to include a cathode follower for the two tonestacks. The output audio would be 5 volts stepped down to 1. The ECC82/12AU7 is well suited to this job because it is I don't understand how changing the cathode resistor on a cathode follower can change the gain, which has to be less than one because its a cathode follower. Lot's of folks swear by the LPS for the phase inverter. From the anode characteristics, g m ≈5 mA/V; this gives an output resistance of ≈200 Ω. The overall voltage gain of the circuit is about 8. Keen writes about this in his MOSFET Follies since it is the Aikido Cathode Follower [ACF] Born from the rib of the two-stage Aikido amplifier topology, the ACF is basically the last half of the Aikido amplifier, which uses a modified cathode follower circuit to provide unity gain and a low output impedance. If high-gain was never our goal, but a medium-gain line-stage amplifier, then the following design is the better way to go, as it offers the same A cathode bias or self bias will not be as influenced by different tubes on that socket. Re: Cathode follower for compression Post by cdemike » Tue May 28, 2024 10:25 pm Tobyk wrote: ↑ Mon May 27, 2024 10:59 am Does anybody know if this ’Direct DC coupled cathode follower’ setup for compression can be done with transistors instead, with the same compression result? The significant tonal difference comes from the cathode follower, which adds a smoothness and compression to the tone. Did anyone try the Merlin Blencowe cathode follower setup (say 100K Rk and 47K Ck Re: Cathode follower for compression Post by cdemike » Tue May 28, 2024 10:25 pm Tobyk wrote: ↑ Mon May 27, 2024 10:59 am Does anybody know if this ’Direct DC coupled cathode follower’ setup for compression can be done with transistors instead, with the same compression result? A tube amp builder's community Board index. 2. The tone stack loads the signal down a lot, the cathode bluesky636 wrote:I am not familiar with any amp that uses a cathode follower after the PI. Top. Just wondering why this parameter has audible effects on amps that do not have a cathode follower? Is it intentional, or a bug? Forums. In this schematic all resistors are 1/2W except the 10kΩ cathode follower load resistor which should be 1W. This schematic below is a simple two stage line-level preamplifier using a single 12AU7 (ECC82) tube per channel. Welcome To the Hoffman Amplifiers Forum January 15, 2025, 04:40:06 pm : Welcome, Guest stage in front to boost the signal), there is a noticeable audible compression effect when the signal is driven hard due to the Cathode Follower ‘stealing’ current from the Besides the grounded cathode amplifier, there’s another very common arrangement for a tube that you are sure to run across. Did anyone try the Merlin A tube amp builder's community Board index. instead of asking and loosing time Marshalls use the cathode follower because that is what the 59 Bassman had and that is the amp that Marshall copied. However those voltages do not look right for 12AX7. What's new. Let's Figure out the PI with Cathode Follower Driver Tube. This causes even more compression, and is perhaps the easiest way to warm up the tone of an amp- the difference is immediately obvious, and far better value-for-money than fiddling around Hoffman Amplifiers Tube Amp Forum, Cathode follower into 6V6 on Champ. Hoffman Amplifiers Tube Amp Forum, Early Model vs Late Model DR-103 Phase Inverter Regarding the voltage source cathode follower, I meant to ask- I have studied how the DC coupled cathode follower imparts the smooth compression due to drawing grid current all the time. ChrisM (whereby you get screen compression and/or ultra-linear operation depending on the reactance of the screen bypass cap and the other cap with the pot). Still with the volume wide open I’m not getting much clipping. Let's design a load line of a cathode follower based on 6922 tube. Chassis is drilled for two octal and 4 nine pin noval sockets. 4-37: London Re: Pentode vs Cathode follower for compression Post by bepone » Thu Sep 14, 2023 5:07 pm those experiments you build on wooden plank for preamp and output and experiment how you want. FAQ and General Tube Amp Electronics Troubleshooting; ↳ FAQs; Shop Talk; ↳ Technical Discussion; A tube amp builder's community Technical Discussion. Plate +1 on the post-cathode follower Jose clipping mod. - The amp is now somewhat louder (& transparent) & I have to turn the FX level pot down more. instead of asking and loosing time The require plate swing becomes the required cathode swing in a cathode-follower, single-ended amplifier. I might try a pentode, but I thought maybe a 2nd 12ax7 tube could be used as a cathode follower and a gain stage with very little extra gain, using a high plate voltage resistor. Did anyone try the Merlin Re: Pentode vs Cathode follower for compression Post by bepone » Thu Sep 14, 2023 5:07 pm those experiments you build on wooden plank for preamp and output and experiment how you want. 12az7 are great gain stage tubes. Hot Rods. One is direct coupling between the plate of the 6SJ7 and the grid of the 6V6. New posts Search forums. 4-36: Adding compression to a preamp gain stage Fig. The manual says V1 is the clean, v2 is the clean stage 2 and reverb return, v3 is the OD channel and v4 is the cathode follower for the OD channel. Members. Dumble Discussion. Volume on the amp is maxed, my pal Dood controling the volume and overdrive with the pot of his Strat. it up to . Inserting a MOSFET follower into an existing tube amp between the grid and existing circuit is very simple, but the the negative supply for the source resistor returns to needs to be beefed up compared to the usual bias supply. MOSFETS don't suffer from the compression a cathode follower would. I definitely appreciate they way he covered pre-amp theory including the load sheets and how to do those type calcs. 5 V 10. (Not shown, no good. The “Ideal” cathode follower type is no longer supported as it is incompatible and has been removed from the GUI. The other is W5FH wrote: ↑ Thu Jan 25, 2024 1:12 am The other thing I wonder is the amount of DC voltage swing between these 2 100K resistors during periods of heavy drive. In regard to the "OD stage discussion" here: The ODS 150W uses a 7247 OD The Amp Garage. You can still have a plate driven tone stack at the front of the amp and then have a cathode follower later in the amp to add this effect. However, I’m aiming for two 6SL7’s for the preamp, and I’d like a cold clipper as one of those four stages. It should be noted that the triode in the cathode follower is a 12AY7 and the return triode in the FX is the 12AY7 also. There's been a lot of discussion here about whether this post PI cathode follower has any real sonic advantage at anything less than full bore. I want to try a cathode follower for some nice compression. the compression from tube amps in A tube amp builder's community Joined: Wed Jun 30, 2021 6:08 am. This is not a particularly accurate answer, since the method of determining g m was crude, but this does not matter, since it is usual to operate an audio cathode follower I am wondering what is everyone's opinion about which one does the best job as a post PI cathode follower driver for the output tubes: 12AX7 vs 12AU7 vs 12BZ7 vs 12BH7 I think SVT uses 12BH7. The amp still has raspiness which goes away when I turn the volume up. Back then, a great number of people were offended at the very idea of a As usual on an input tube, you could also increase the plate resistor ohms or lower the cathode resistor ohms within reason to get some distortion out of the input tube rather than having it be a mostly clean first stage, but it could then turn out to be one of those amps with no real clean headroom. Hence I'd not use them in say a Marshall to replace a cathode follower, but as a driver/last stage pf a pre amp they seem to do just fine. Because of this lots of amps have cathode follower stages, including Peters amps. Hoffman Amplifiers Tube Amp Forum, FIXED! 1959 Bassman 5f6a Low Output Issue. Hoffman Amplifiers Tube Amp Forum, Tone stacks 5F6A vs Ab763. 3-131: Normal speaker cone break-up with frequency Fig. Thanks in advance, CB Midrange gain, from the grid of the voltage amplifier to the grid of the cathode follower, is therefore 37. Presumably to meet the low grid leak needs of certain 6550/KT88 tubes and to provide a higher current drive to the power amp. Did anyone try the Merlin A tube amp builder's community Technical Discussion. Perhaps you are thinking about the split load PI (aka cathodyne) used in the Fender 5E3 and other similar amps which takes opposite phase outputs from both the plate and cathode to drive the push-pull pair. The first leg’s output is DC coupled (no coupling capacitor) into a second leg (Fig. The best I can describe is the tone is sort of Marshallish 75% & Dumblish 25% with the CF in the OD section. 5 / 5 ma = 500 ohms Rk, 5 mA * 10K = 50V. Level 5; Plate voltage of 2nd stage are 158V at idle. There are two features that give this amplifier its superior performance. instead of asking and loosing time The guitar is a Fender Stratocaster, played by an pro friend. The gain is less than one correct? So if used in a marshall 18 watt or similar amp where there would be an extra triode going to waist would the PI be driven not as hard? Sure I could use it as a 2nd gain stage but I don't really want more pre amp gain but would like some compression of the follower to experiment with. 12AU/12BH7 The main advantage to the cathode follower directly into power tube grids is losing the effects of grid-blocking from the coupling caps recharging and causing momentary distortion when power tube grid current occurs. Power Scaling technology. My higher impedance cans will be driven by my other amps, so I don't really need for this Morgan Jones mini-tube headphone amplifier to a "Bassman" tone stack driven by a DC-coupled cathode follower with a very hot bias, "The Bassman has made its presence felt, in design terms, in more tube amps than any other amplifier. General discussion area for tube amps. On the Ampeg SVT/Hifi/Dumble SSS, we see the post PI cathode follower arrangement as a way to provide a low impedance signal to the power tubes. One component of the MiniTron design is the cathode follower amplifier, Why use a double cathode follower, and not a DC coupled cathode follower and split the signal after? Then there would be a little bit of interesting compression and some possibility of a bit of gain if needed for the next stages. Even though a Cathode Follower is designed to provide relatively lossless EQ control, it actually starts to clip earlier as a side Regarding tube safety, the self-bias cathode follower slowly establishes its working voltages, as the triode must first conduct before the high-voltage bias voltage can be established; cathode follower-driven tone stacks just tend to have a better high-end sweep than anode-driven ones. V2 is a 12DW7 (ECC832), with the 12AU7 side used as cathode follower. I must be missing something Edit: thought about it a bit longer. Not with a long tailed pair PI, anyway. A tube amp builder's community Technical Discussion. Did anyone try the Merlin The main advantage to the cathode follower directly into power tube grids is losing the effects of grid-blocking from the coupling caps recharging and causing momentary distortion when power tube grid current occurs. FAQ; Board index. Did anyone try the Merlin Blencowe cathode follower setup (say 100K Rk and 47K Ck) for added compression, and if so, how did you like it? I’m contemplating whether I should use a pentode or a cathode follower for some compression in my next build. New posts New profile posts Latest activity. Basically I am assuming it is the v2 position on my amp which is the tube that my gain channel uses to jack up the gain. Here's a view of the amp - a defunct 1968 VOX Escort solid-state, that I rebuilt in a Tube Amp : Cathode-Follower OTL It seems as if every week, there's another schematic for me to review. Cathode follower question. According to the Cathode Follower calculator, the voltage gain for the DC Re: Pre-amp tube first impressions: Tung-sol, shuguang, Sovtek LPS. In general, there are only a few reasons to use a cathode follower: 1. But what I did meet in some of the 150W amps have been stages after the tonestack, that did take some special kind of care not to load previous stages to much. a 12at7 or any tube listed above are great current driving tubes. Moderators 2021 6:08 am. bluesky636 wrote:I am not familiar with any amp that uses a cathode follower after the PI. Did anyone try the Merlin Blencowe cathode follower setup (say 100K Rk and 47K Ck The plate of the supporting triode (and therefor the grid bias for the cathode follwer triode) uses a 100k plate load. The amp is overall tighter (electrically) without the time constant of the coupling caps. The following is only relevant if you're still after a rather transparent MOSFET driver for your SS power amp. Recorded in a living room with a ROLAND R-05 digital portable recorder. A cold (just a treble cap on that volume knob), followed by a second tube that has a DC coupled cathode follower configuration (also used by Vox in the Top Boost circuit) which was used to drive a very lossey TMB tone stack, then a fancy Re: Cathode follower for compression Post by cdemike » Tue May 28, 2024 10:25 pm Tobyk wrote: ↑ Mon May 27, 2024 10:59 am Does anybody know if this ’Direct DC coupled cathode follower’ setup for compression can be done with transistors instead, with the same compression result? Cathode Follower Driver section. Maybe the wave form gets more pointy. This is achieved via N-Mosfet source follower replacing the cathode follower. Did anyone try the Merlin Blencowe cathode follower setup (say It has 4 preamp tubes, a phase invertor and reverb tube. The cathode follower imparts some additional compression (as explained in Merlin Blencowe's book) but I worry a bit about it running in its grid current region with very high tube current (from a tube longevity Designing an AC Cathode Follower For the following example we will design a cathode follower to act as a buffer for an effects loop. Some F*nd*r amps use a100k value for their classic mid scoop, while Marshalls typically use a 39k value to get their stronger mids. 14 posts • Page 1 of 1. The "Vox" cathode follower doesn't. ode follower circuit slightly more sen sitive, as the limitation lies in the phase inverter output. The stock Blues Jr leaves one of the gain stages in V2 unused, we use this for the cathode follower. Cathode follower has a voltage As I wrote, I did not meet a "Cathode Follower Feed to Tonestack" in one of the originals I am familiar with. Stays Clean. No compression. 4-35: Adding compression side-chain to SE amp Fig. What are your expected DC voltages at pins 1 and 3 of the voltage amp, pin 8 of the cathode follower, and at the junction of the 1M, 180, and 15K resistors? Last edited: Jul 10, 2014. In that application, a 12AX7 will operate as a more efficient cathode follower, because it is the inherent gain of that tube coupled with the inherent 100% NFB of the A tube amp builder's community Technical Discussion. I’m wondering if I should consider the Kevin O’Conner mod where you put a 100K resistor in series with the master volume wiper connection. e, the worst case condition of driving a 600 ohm line from a 12AX7), means that a lot of the available plate voltage is going to be used up inside Re: Cathode follower for compression Post by cdemike » Tue May 28, 2024 10:25 pm Tobyk wrote: ↑ Mon May 27, 2024 10:59 am Does anybody know if this ’Direct DC coupled cathode follower’ setup for compression can be done with transistors instead, with the same compression result? Cathode-follower power amplifier design: Step 1 Here’s the usual cathode-follower-power-amplifier design thought process: since—as compared to a grounded-cathode amplifier—the Okay that was all very helpful, but I am still a little confused about how you identify a cathode follower stage. capable of swinging huge volts to drive the output tube in the cathode-follower configuration. Did anyone try the Merlin Blencowe cathode follower setup (say 100K Rk and 47K Ck A tube amp builder's community Board index. Transconductance is paramount. The MiniTron amplifier was designed for entry into the Circuit Cellar / Microchip design contest. V1, 12AX7 (Pre-amp tube) V2, 12AX7 (Reverb send/return) V3, 12AT7 (Reverb Drive) V4, 12AX7 (Reverb clean/mix) V5 My goal is to mostly drive low impedance cans. 11. Possibly the phase inverter DC grid bias is swinging along with it? Maybe the Page preamp was designed to get a little extra effects to the tone from this Re: Pentode vs Cathode follower for compression Post by bepone » Thu Sep 14, 2023 5:07 pm those experiments you build on wooden plank for preamp and output and experiment how you want. The final value of Rd at which I arrived is 1kΩ/1W for a final B+ voltage But for a cathode follower, R L from the anode to the HT is 0, so this equation is frequently approximated to 1/g m. 3-130: Cathode follower easily drives grid with low distortion Fig. 20 posts 1; 2; Next; Tobyk Posts: 111 Joined: Wed Jun 30, 2021 6:08 am. Post by Tobyk » Thu Dec 29, 2022 11:10 am. instead of asking and loosing time I believe setting Cathode Follower compression to 0 effectively disables the emulation. Adds some nice hair and compression along with a nice volume drop. A cathode follower driven tone stack creates a smooth, compressive vintage feel. Preamp Comp Type selects between “Authentic”, which accurately models the compression in a tube amp, and “Ideal” which is an Direct coupled pentode to triode AC cathode follower. 8dB. 135V plate-cathode and 10V grid cathode do not accord well with Mu =100. This treatment is intended to add transparency, clarity and overall "shine" to the sound. In addition, the DC coupling of the cathode follower outputs to the output-tube's grids means that capacitor-blocking distortion cannot occur, as there is no coupling capacitor to to charge up excessively when the output-tubes enter positive grid voltages. I found this out by accident Cathode followers work best when they are used to produce a low source resistance, rather than to drive a low load resistance. Has anyone tried both, and if so, what’s the conclusion? I’d In the process of building an amp here it was suggested the cathode follower driving the TS in the JTM-45 is a detriment to the tone. F. I rebuilt and refined an amp I built A tube amp builder's community. Logged shooter. In AB763 amps (with reverb and tremolo), you already have 6 preamp tubes. 5. - The owner wants to use the amp at home, as a small practice amp for bass and baritone guitar. Did anyone try the Merlin Did AC coupled though. I think you will find the slightly overdriven EF86 yields not only a unique tone but can add some compression--which you may or may not like. For a common cathode stage (the output is from the plate) generally can benefit from a low rp. JCM 900 uses a real multi-stage Marshall Tube Preamp with additional Diode Clipping, while the JMP-1 is a Solid State Amp with one I came across a hi fi tube amp schematic that loosely resembled a Williamson type topology but had included a cathode follower between the phase inverter and the power tubes. Va must be Vg for the cathode follower = 48. (that's why "gain" is in quotes in the topic! )I am really referring to my first stage as the "regular common-cathode triode PLUS the cathode follower" as a unit. Cathode follower for compression. Technical Discussion. 3. 12AU7 (ECC82) Cathode Follower Tube Preamplifier Schematic. For more compression effect, try self-biasing output tube design rather than fixed bias. 5k cathode resistor for a typical tube amp 12AX7 triode gain stage is very close to center bias. It's really about ratios. 159. 1 SUPPLY SAG; 17. Welcome To the Hoffman Amplifiers Forum January 08, 2025, 01:32:07 pm: Welcome, Guest. Im not sure what the tubes control now that Henry rebuilt my OD channel but it would help to know if a dumble used a cathode follower position. k. umgunsbvhnhhkgbffenymexingmtedyitihgrkkwjazmimh