A quick question for all the many members who have built this great amp. I am finally getting around to building one now - have ordered the store F4 pcb's. So my question is: on the schematic shown on the store order page, it shows parallel 0R47 3W resistors for the output Fet sources. However the BOM only shows a single resistor here and looking at a pic of the pcb, it seems there is only one position for these resistors and as well 6L6's build guide clearly shows only one 0R47 3W for each.
For a standard build of the F4 - do I need only one resistor on each output Fet source and ignore the second parallel one shown in the schematic?
For a standard build of the F4 - do I need only one resistor on each output Fet source and ignore the second parallel one shown in the schematic?
When in doubt go back to the original source: See the schematics on page 13 here: https://www.firstwatt.com/wp-content/uploads/2023/08/prod_f4_man.pdf
Ciao, ho appena finito di montare l'F4, chiedo gentilmente se posso abbinarlo al preamplificatore Aikido LV 48V con ecc88 (ne ho 4 da un vecchio SRPP) al posto di ecc99 e, in caso affermativo, cosa devo modificare nel relativo circuito? Grazie in anticipo per l'aiuto
Hi, I just finished assembling the F4, I kindly ask if I can match it to the Aikido LV 48V preamp with ecc88 (I have 4 from an old SRPP) instead of ecc99 and, if so, what do I have to change in the relative circuit? Thanks in advance for your help
@sergiog Please post in English, thanks much!! Per favore pubblica in inglese, grazie mille!!
🙂 🙂 🙂
You will need to swing 18V. I'm sure you know this?
I got a CJ driving an F4. That's 20Vrms max. Works fine.
I got a CJ driving an F4. That's 20Vrms max. Works fine.
Sorry for not seeing this when you posted… the Schematic you refer to is showing the two sets of resistor pads, provided for different lead spacings, in parallel. Only use one.
Hi, I just finished assembling the F4, I kindly ask if I can match it to the Aikido LV 48V preamp with ecc88 (I have 4 from an old SRPP) instead of ecc99 and, if so, what do I have to change in the relative circuit? Thanks in advance for your help
hi sergio, you have to change nothing, if your ecc88 aikido is able to output the minimum tension swing to correctly drive the f4.
The f4 is 23Vpeak, so you need at least 23Vp at the output of your ecc88 aikido, better something more (the f4 voltage gain is slightly less than 1, and the psu is +-23Vdc).
I believe the aikido is able to output the needed voltage with ecc88, but is better to ask in the aikido thread:
The f4 is 23Vpeak, so you need at least 23Vp at the output of your ecc88 aikido, better something more (the f4 voltage gain is slightly less than 1, and the psu is +-23Vdc).
I believe the aikido is able to output the needed voltage with ecc88, but is better to ask in the aikido thread:
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sergiog, are you asking what it takes to change the Aikido circuit from using ecc99s to ecc88s? If so, might be best asked in the vacuum tube forum,
Huh?
The peak rating for the F4 is 50 watts peak at 8ohms... that works out to 20 Vpeak. For rms, the rating is 25 watts rms, which works out ~17 Vrms.
I suppose you could ask for even a higher rms and peak power, but can the F4 even support that much current? And what would the distortion be then? Is that even practical?
From the F4 user's manual:
"...As a stereo amplifier with single-ended inputs and outputs, it will deliver up to 25watts into 8 ohms with a damping factor of 40. It will do 50 watts into 4 ohms,and as a mono-block amplifi er with parallel inputs and outputs, it will do about100 watts into 2 ohms.
As a mono-block amplifi er with balanced inputs and outputs the power outputrating is 100 watts into 8 ohms at 1%, and the damping factor is 20.
The amplifier operates Class A to 25 watts (50 peak),..."
BTW, thanks for the link.. I kept searching for info on that preamp... anything that will drive an F4 is of great interest...
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... but, the real question on everyone's mind is.... is there a "clunk" once it leaves the 25W envelope?
I have a 20Vrms tube preamp hooked up to an F4. Driving that I got a DAC that puts out a full 2V. Meaning that I can easily push the gain envelope and drive the F4 into an unrated world. Specially in the few times I've hooked up that front end with a pair of 83 db/w Maggies.... which suck power.
Even when playing loud, -trying to at least- I've never had the preamp at full blast... the sound becomes unpleasant as the amp runs out of power before the preamp runs out of power. I'm positive I've had that amp leave Class A many, many, many times. I couldn't hear distortion per se, but it sure sounded more like a soft clipping... gain compression and the soundstage did collapse. At lower levels, the combination sounds really good, but when it gets louder, forget it, the magic disappears. Nothing blows up, mind you, but it becomes something that is no longer enjoyable to listen to.
I figure that with a 20Vrms preamp, I have lots of dynamic overhead over the amp rating. Heck, for most people running reasonably efficient speakers, I've run that configuration with 90 db/w speakers, I never had to crank the preamp that loud... I don't think you'll ever run the amp into needing 23Vrms into its input. If your speakers are reasonably efficient (*) you will seldom ever run the F4 past its rated class A power.
Needless to say, if you want power in an F4, go bridged or get something else. In bridged mode you do get lower damping factor, but then you get power. POWER... The sound of the amp changes. In a good way, if you like bass.
(*) I've been thinking... when amp designers spend their days working with High Efficiency speakers..... Now, I'm positive that Nelson and Co have some 83 db/w speakers around to test their behemoths... but perhaps we ought to have a DIY Audio fund to get ZM a pair of Maggies to test his amp designs with. Make sure he tests his SET/SITs on Maggies... ;-)
Even when playing loud, -trying to at least- I've never had the preamp at full blast... the sound becomes unpleasant as the amp runs out of power before the preamp runs out of power. I'm positive I've had that amp leave Class A many, many, many times. I couldn't hear distortion per se, but it sure sounded more like a soft clipping... gain compression and the soundstage did collapse. At lower levels, the combination sounds really good, but when it gets louder, forget it, the magic disappears. Nothing blows up, mind you, but it becomes something that is no longer enjoyable to listen to.
I figure that with a 20Vrms preamp, I have lots of dynamic overhead over the amp rating. Heck, for most people running reasonably efficient speakers, I've run that configuration with 90 db/w speakers, I never had to crank the preamp that loud... I don't think you'll ever run the amp into needing 23Vrms into its input. If your speakers are reasonably efficient (*) you will seldom ever run the F4 past its rated class A power.
Needless to say, if you want power in an F4, go bridged or get something else. In bridged mode you do get lower damping factor, but then you get power. POWER... The sound of the amp changes. In a good way, if you like bass.
(*) I've been thinking... when amp designers spend their days working with High Efficiency speakers..... Now, I'm positive that Nelson and Co have some 83 db/w speakers around to test their behemoths... but perhaps we ought to have a DIY Audio fund to get ZM a pair of Maggies to test his amp designs with. Make sure he tests his SET/SITs on Maggies... ;-)
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And you shouldn't need to... ever... with anything reasonable like above 86dB/1W/at 1m. I was alluding to Papa Pass idiom/trademark word: "clunk" 🙂 in an attempt to be funny... lol.
Magnepans are reasonable speakers... once you realize that Nelson forgot about us..
the First Ten Watts crowd.
AKA... PL.
HOWEVER... sometimes, even with efficient speakers... like back in 1980, when a friend of mine had rented a summer place on the beach facing the Olympic Mountains... he had his big Cerwin Vegas, big Pioneer receiver, Dodge Charger RT with MT4 and a fine ZZ Top collection. Speakers on the windows, sitting outside on the backyard, watching the sunshine on Hood Canal, drinking cold beer... neighbors were reasonably far away, it was good time to be young, carefree and with 110db playing behind you.
panama red, panama red
he'll steal your woman, then he'll rob your head
panama red, panama red
They say sound travels far over water?
the First Ten Watts crowd.
AKA... PL.
HOWEVER... sometimes, even with efficient speakers... like back in 1980, when a friend of mine had rented a summer place on the beach facing the Olympic Mountains... he had his big Cerwin Vegas, big Pioneer receiver, Dodge Charger RT with MT4 and a fine ZZ Top collection. Speakers on the windows, sitting outside on the backyard, watching the sunshine on Hood Canal, drinking cold beer... neighbors were reasonably far away, it was good time to be young, carefree and with 110db playing behind you.
panama red, panama red
he'll steal your woman, then he'll rob your head
panama red, panama red
They say sound travels far over water?
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HI, sorry about 25W, I forgot to say that the F4 I made has about 8.5W output (only one pair of output transistors) for my needs it sounds loud even like that. Thank you for the explanations.
I was working from the ratings..... 50wpc peak.
At 23Vp, we calculate 66wpc.
Could it be that we current limit at 20Vp... or most likely, the distortion numbers are not linear and rise quickly?
At 23Vp, we calculate 66wpc.
Could it be that we current limit at 20Vp... or most likely, the distortion numbers are not linear and rise quickly?
What I was thinking, and I got lazy and didn't make it clear, sorry about that... is that the output distortion for the Vrms input rating is lower than the output distortion rating for the corresponding Vpeak input. As you said, it's clipping.
So the peak rating for the amp, is lower than the corresponding rms.
I mean, if you rated the amp at 25 wpc rms and 50 wpc peak, that corresponds to 14Vrms and 20Vpeak.
Oh wait! I screwed up... my notes are wrong about those 17Vrms... for 25 wpc at 8 ohms, the voltage is ~14Vrms... so the peak is ~20Vpeak.
So, still, don't know where the 23V peak came from... that would have to be at a much higher wattage point: 66 wpc...
Fundamentally, then, I wonder if "amplifiers" like the F4 should be measured in "current" instead of "power"? We want to know how much current the amp can drive, then the power is derived neatly from the load impedance.
So the peak rating for the amp, is lower than the corresponding rms.
I mean, if you rated the amp at 25 wpc rms and 50 wpc peak, that corresponds to 14Vrms and 20Vpeak.
Oh wait! I screwed up... my notes are wrong about those 17Vrms... for 25 wpc at 8 ohms, the voltage is ~14Vrms... so the peak is ~20Vpeak.
So, still, don't know where the 23V peak came from... that would have to be at a much higher wattage point: 66 wpc...
Fundamentally, then, I wonder if "amplifiers" like the F4 should be measured in "current" instead of "power"? We want to know how much current the amp can drive, then the power is derived neatly from the load impedance.