I know I'm not reinventing the wheel here.
Today, I ran my VFET with some old '70s vintage, 3 way, inefficient, floorstanders. It sounded great of course, but it needed a little oomph to get to some listening by myself volume.
The other day I reread the First Watt F4 manual and remembered that in addition to being a great sounding amp, it's a power buffer and should be able to help the VFET with it's oomph issue.
I got the F4 out of the garage and hacked off the end of an old RCA cable. I added two banana plugs to the end of the cable and plugged them into the L/R positive terminals of the VFET with the RCA end to the input of the F4. The signal went- preamp/VFET/F4/speakers.
I checked my connections and crossed my fingers. These days I usually don't let the magic smoke out but mostly get the sound of silence, followed by a lot of cursing. I'll be dammed. It worked and sounded much better than expected. (Which is my usual feeling when I finally get my Papa projects to work.)
Anyone else using their F4 as a compliment to their VFET? Do you have a better way of connecting the signal between the VFET and F4?
Today, I ran my VFET with some old '70s vintage, 3 way, inefficient, floorstanders. It sounded great of course, but it needed a little oomph to get to some listening by myself volume.
The other day I reread the First Watt F4 manual and remembered that in addition to being a great sounding amp, it's a power buffer and should be able to help the VFET with it's oomph issue.
I got the F4 out of the garage and hacked off the end of an old RCA cable. I added two banana plugs to the end of the cable and plugged them into the L/R positive terminals of the VFET with the RCA end to the input of the F4. The signal went- preamp/VFET/F4/speakers.
I checked my connections and crossed my fingers. These days I usually don't let the magic smoke out but mostly get the sound of silence, followed by a lot of cursing. I'll be dammed. It worked and sounded much better than expected. (Which is my usual feeling when I finally get my Papa projects to work.)
Anyone else using their F4 as a compliment to their VFET? Do you have a better way of connecting the signal between the VFET and F4?
Attachments
with some tweakadoo, you can try driving mid+tweet with Vfet directly, and feeding F4 to drive bass
all you need is dividing input to bass xover from input to xover for Mid+tweet
as you connected it now, I can bet it'll sound better if you put some decent dummy load on VFet output ....... say something in range of 16R
all you need is dividing input to bass xover from input to xover for Mid+tweet
as you connected it now, I can bet it'll sound better if you put some decent dummy load on VFet output ....... say something in range of 16R
You could directly drive the F4 from the VFET front end card, since the front end's output swings SIGNIFICANTLY wider without clipping: the front end will swing more than 50 volts, peak-to-trough. But the VFET output stage can only swing 36 volts, peak-to-trough.
Why? Because the front end card can swing beyond the 36V supply rail, whereas the VFET output stage cannot.
Why? Because the front end card can swing beyond the 36V supply rail, whereas the VFET output stage cannot.
Hi wg45,
You have already 2 experts replying to your question on how to connect these devices best 🙂
As of me, I am somewhat confused by your aim to start with. My understanding is (reading your post, but I could be wrong), that you seek for more dB at the output of your speakers: you want them to play louder.
I haven't built an F4 and it has been over a year I looked into it for my power hungry LS, but if I recall well F4 is unitary gain re voltage, and basicaly an excellent power amp to make sure there are enough amperes at its output, enabling an excellent drive of difficult or heavily varying loads from the LS.
Because of that, I can't see how you fared better re dB only as the loudness you experienced should be roughly the same. Now, you might though perceive the sound as being better / faster / impactfull because the F4 has a better control over your loudspeakers, basicaly delivering perhaps more amps to the bass (if it is a difficult load) than the VFET can, and also having a better DF which affects sound perception aswell. Perhaps also the VFET suffers slightly less and produces less distorsions when confronted to the F4 high input impedance (vs a LS), who knows...
Either way, that sems to indicate to me that the VFET wasn't the right amp for these LS to start with - the VFET likes efficient LS with also their impedance curves not really going deeper than 4R IMHO.
So now you are using the VFET as a preamp. There are for sure better pres for that function alone, but then why not...
If so, I would follow Mark's advice, that is to connect the FE cards directly to your F4, so you get really at the end more volts out of the F4 which will translate in a louder output level from your LS as what you have now - If that's the initial aim, job done. Louder with the same control over the LS. You will though lose the "lovely sound coloration" brought by the VFET output stage, which might or not suit you.
If it suits you and you follow your reasoning until the end, you might then consider driving your F4 from 2 separate FE cards in a box rather than wasting an entire VFET for it. At which stage we are back to my previous statement and you might just aswell drive your LS from a pre with a high voltage swing (which Mark's FE cards are) + F4.
If you really want the VFET sound and using the VFET entirely as a pre to drive a F4, but struggle re max dB, then you need to multiplicate the voltage at the VFET output before driving the F4. That can be done as the VFET output impedance is very low for a pre function and the F4 input impedance rather high of course. You could put some line transformers at the VFET outputs to multiplicate the voltage seen at the F4 inputs, but these are likely to colour the sound and they won't come cheap.
At which stage you might just think again "different preamp than VFET". If you love negative H2, what about a B1 Korg (limiting its ouput to 2V to avoid too much distorsions IMHO) followed by one of Mark's FE cards with high gain? Alternatively, although not as qualitative IMHO but to gain a non expensive feel of it, replace in the above the B1K by the simple H2 Box. In fact, you could start a pre with Mark's card and if missing the negative H2 add a H2 box or B1 Korg upstream your pre.
I hope this helps and sorry for the long post
Claude
You have already 2 experts replying to your question on how to connect these devices best 🙂
As of me, I am somewhat confused by your aim to start with. My understanding is (reading your post, but I could be wrong), that you seek for more dB at the output of your speakers: you want them to play louder.
I haven't built an F4 and it has been over a year I looked into it for my power hungry LS, but if I recall well F4 is unitary gain re voltage, and basicaly an excellent power amp to make sure there are enough amperes at its output, enabling an excellent drive of difficult or heavily varying loads from the LS.
Because of that, I can't see how you fared better re dB only as the loudness you experienced should be roughly the same. Now, you might though perceive the sound as being better / faster / impactfull because the F4 has a better control over your loudspeakers, basicaly delivering perhaps more amps to the bass (if it is a difficult load) than the VFET can, and also having a better DF which affects sound perception aswell. Perhaps also the VFET suffers slightly less and produces less distorsions when confronted to the F4 high input impedance (vs a LS), who knows...
Either way, that sems to indicate to me that the VFET wasn't the right amp for these LS to start with - the VFET likes efficient LS with also their impedance curves not really going deeper than 4R IMHO.
So now you are using the VFET as a preamp. There are for sure better pres for that function alone, but then why not...
If so, I would follow Mark's advice, that is to connect the FE cards directly to your F4, so you get really at the end more volts out of the F4 which will translate in a louder output level from your LS as what you have now - If that's the initial aim, job done. Louder with the same control over the LS. You will though lose the "lovely sound coloration" brought by the VFET output stage, which might or not suit you.
If it suits you and you follow your reasoning until the end, you might then consider driving your F4 from 2 separate FE cards in a box rather than wasting an entire VFET for it. At which stage we are back to my previous statement and you might just aswell drive your LS from a pre with a high voltage swing (which Mark's FE cards are) + F4.
If you really want the VFET sound and using the VFET entirely as a pre to drive a F4, but struggle re max dB, then you need to multiplicate the voltage at the VFET output before driving the F4. That can be done as the VFET output impedance is very low for a pre function and the F4 input impedance rather high of course. You could put some line transformers at the VFET outputs to multiplicate the voltage seen at the F4 inputs, but these are likely to colour the sound and they won't come cheap.
At which stage you might just think again "different preamp than VFET". If you love negative H2, what about a B1 Korg (limiting its ouput to 2V to avoid too much distorsions IMHO) followed by one of Mark's FE cards with high gain? Alternatively, although not as qualitative IMHO but to gain a non expensive feel of it, replace in the above the B1K by the simple H2 Box. In fact, you could start a pre with Mark's card and if missing the negative H2 add a H2 box or B1 Korg upstream your pre.
I hope this helps and sorry for the long post
Claude
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The transformers have 2 advantages though:
Have fun either way
Claude
- they can be external and easy to try without fiddling (but then this is a DIY forum LOL)
- more importantly perhaps, the VFET likes to see loads between 4R and 12R, so you could load it in a much better way than with the high F4 input impedance as you do now
Have fun either way
Claude
^ This. The VFET output stage will sound better when it is operating at its sweet spot.
The load resistors could be placed inside either the VFET or F4 chassis and bolted to the base plate to enhance thermal dissipation. Yes the gold color power resistors will be needed for this. 30W to 50W
The load resistors could be placed inside either the VFET or F4 chassis and bolted to the base plate to enhance thermal dissipation. Yes the gold color power resistors will be needed for this. 30W to 50W
Thanks, ZM for the ideas.
I do have a crossover and I'll try that idea next. I tried the F4 first with the VFET instead of using the crossover, since I wanted to see if that combination would work. I'll also try adding some resistance to the VFET outputs. Something to add to my seemingly weekly parts order.
Thanks, Mark.
That's another good idea that I did not imagine. I recently finished my Dreadnaught cards; now might be a good time to try your suggestion before I install the new cards and have the VFET opened up.
A power buffer after the VFET would give adjustability in the harmonics by varying the load on it.
Thanks, Claude.
Overall, the goal of my posting was to get a discussion started. I couldn't find much info on using an F4 in this way, even though it had been described by Papa in the F4 manual.
I think I got a bit of luck in getting well thought, interesting ideas from ZM, MJ and you. I also wanted to see if I could start using the equipment that I had which ZM often describes as "papablocks" in different combinations. A power buffer seems to be a rare type of amplifier and I wanted to see if I could use it in another way.
In getting more oomph from the speakers, yes, I'd say it's looking for a combination of volume and bass.
I am using the ACP+ as a preamp. It goes ACP+/VFET/F4/speakers. I'm not sure what to call the VFET in this group. Maybe it still thought of as a preamp?
Yes, the VFET by itself might not be the best amp match for my speakers. I do love the sound it produces and it's one of my favorites along with the F2J. Both amps are not the best match for the speakers. I normally use Aleph 2 monoblocks with the speakers.
I had the same thought about Mark's FE cards this morning. Why not use them as a high voltage swing preamp in a separate chassis? I'm sure Mark had mentioned that purpose in his VFET FE introduction. Maybe I should put those Dreadnaught cards into a preamp and try that combination.
I do have an H2 preamp and I'll try that suggestion today with the F4, replacing the ACP+ and VFET.
Lot's of Papablocks combinations to try.....
Thanks, TungstenAudio.
Well noted. I'll have to do some research on higher watt resistors. I know which ones you mentioned.
Thanks, Papa.A power buffer after the VFET would give adjustability in the harmonics by varying the load on it.
I'll have to think about that. If I added the 16R resistors ZM suggested for the VFET output to the F4 output instead, would it have the same result of getting the VFET to it's sweet spot?
nope
you need load at VFet output to get it not flappin' in da breeze, unloaded
then - how you are going to torture F4 output, another chapter
though, it is not easy task - torturing F4, tough cookie
you need load at VFet output to get it not flappin' in da breeze, unloaded
then - how you are going to torture F4 output, another chapter
though, it is not easy task - torturing F4, tough cookie
Sounds like good plans, let us know your findings!
Note regarding the H2, you would still need some voltage gain, so Mark's FEs in a separate box is something coming back again...
Re the 16R resistor I will let the Master reply, but my understanding is it needs to be either at the VFET output or at the F4 INPUT. Can't see how it would work at the F4 output for the intented use...
Good luck
Claude
Note regarding the H2, you would still need some voltage gain, so Mark's FEs in a separate box is something coming back again...
Re the 16R resistor I will let the Master reply, but my understanding is it needs to be either at the VFET output or at the F4 INPUT. Can't see how it would work at the F4 output for the intented use...
Good luck
Claude
Thanks, Claude.
Yes, you and ZM agree that it needs to be on the VFET and not the F4.
I'll have to think more about Mark's VFET FE as a preamp. I'd need 36v to the FE, so it takes me out of the normal preamp power filtering and 24v supply.
Yes, you and ZM agree that it needs to be on the VFET and not the F4.
I'll have to think more about Mark's VFET FE as a preamp. I'd need 36v to the FE, so it takes me out of the normal preamp power filtering and 24v supply.