Bottlehead Forum
General Category => Technical topics => Topic started by: debk on March 29, 2014, 01:37:55 PM
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Ok I know to some it is sacrilege to play in the sandbox. My latest project is a Pass Lab F4 clone. It is an interesting amp since it has unity voltage gain. I want to drive it with a SET amp.
So far I have built one channel in a parallel mono configuration. In this configuration it puts out about 50W.
Source--->Extended Foreplay III preamp modified for 6SN7's---> Paramount 2a3 amp --->F4 in parallel monoblock configuration.
I tried both the 8 ohm and 16 ohm tap on the output transformer and listened to both with a variety of resistors across the Paramout output (12R, 15R, 20R, 22R, all Mills 5 watt resisitors).
Not surprising the 16 ohm tap sounded better. As for which resistance across the Paramount worked best, I think the 20R or 22R sounded best but there was not a big difference between all four. When the second channel is built and listening in stereo I may be able to refine this more.
As for my listening impressions. First it had plenty of volume, louder than I would want to listen at. The F4 adds very little to the coloration of the sound, except more power and the bass was very noticbly more present. Still warm and very detailed, much like my SET amp on steroids.
I also listened to just the preamp--->F4 combination and found this worked well also but the sound was much more alive with the SET amp in the chain.
The entire system was dead quiet no hum at all, even at loud volumes.
I look forward to trying it in stereo in my actual system (BeePre and SR45amp)
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Debra
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Are those boards from the diyaudio store? I've been tempted to build one of those amps as they seem very popular on the forum.
Love the purple wiring by the way :)
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Yes they are the boards from the diyaudio store
Deb
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It really is a nice sounding amp especially when driven with a DHT tube amp.
Glad you like the purple wiring, I kind of have a thing for purple :)
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Really nice build Deb. Please let us know how it sounds once you get the other amp built. If it really does sound like a high power 45 amp when driven by your SR45 amps then it could be the best of both worlds. A SET amp sound with enough power for any rock or classical music. Very interesting.
Ken
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debK
If I may ask, what front panel switch did you use, and how did you wire it in? I.e. are you switching the mains directly?
bryan
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I got the switch from apexjr.com. I am switching the mains. There is also a mains switch on the back, but i wanted somehting up front also. The rails in the amp are 24V, perfect for the led ring light in the switch
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Hi Deb,
I'll admit to playing with some SS stuff too -- namely the Aleph J (in monoblock form) and I just couldn't pass upthe ACA amp -- another SE class A SS amp but this one with a single output device, and if you rebias it as per Nelson's instructuions, it's good for a clean 6 watts.
I do have a pair of F4 boards here too.
-- Jim
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Debra, Have you any idea what kind of voltage this amp is seeing on its input, i assume its way above line level being unity gain?
Reason i ask is i'm planning to refurb a pair of vintage speakers so i need an amp with ~25w per channel to drive them. I'm trying to work out if an F4 with a Bottlehead Preamp in front of it would be enough to drive a set of speakers from a line level input, or would i need a amplifier in front of it for a greater voltage swing. I have no idea what kind of voltages speakers usually run at.
Cheers,
Mark
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Ohms law says that 25W into 8 Ohms is about 14V.
A Crack might be a good choice to drive a unity gain amp that needs that kind of input voltage.
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Thanks Paul, didn't realize it was that simple to work out. I was thinking about the Smash kit but it seems 7vrms wont be enough in that case. Maybe i should just build a regular F5 and use a preamp in front of it, decisions decisions.
The blurb for the speakers says the requirements are 15-30w, with 15w into 8ohms producing 96db at one meter in anechoic conditions so 25w may be complete overkill.
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The F4 is a current amp only -- no voltage gain. Rule of thumb is that you need a preamp of 12-15 dB gain. That's a bit much for the bh preamps. The Aleph J is a much better amp than the F5 and is one of Nelson's personal favorites of all his designs. This is typically the amp that people who like SET/tube amps go to because of it's predominant second order distortion characteristic, and will work fine with BH preamps. I believe it is also easier to build than the F5, but I'm not sure about that.
The F4 is the amp to use if you have a SET amp and speakers that need more juice and you don't want to sacrifice your SET sonics. Also a great amp in it's own right.
-- Jim
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The Smash will have an upgrade package that should push the gain into that region.
-PB
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The Smash will have an upgrade package that should push the gain into that region.
-PB
Are we talking C4S upgrade?
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Yeah, when we wrap up shooting the manual and getting all the parts in, I will delve a bit more into what it will look like. As the stock circuit is designed, it would benefit greatly from a C4S.
-PB
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The F4 is a current amp only -- no voltage gain. Rule of thumb is that you need a preamp of 12-15 dB gain. That's a bit much for the bh preamps. The Aleph J is a much better amp than the F5 and is one of Nelson's personal favorites of all his designs. This is typically the amp that people who like SET/tube amps go to because of it's predominant second order distortion characteristic, and will work fine with BH preamps. I believe it is also easier to build than the F5, but I'm not sure about that.
The F4 is the amp to use if you have a SET amp and speakers that need more juice and you don't want to sacrifice your SET sonics. Also a great amp in it's own right.
-- Jim
Thanks Jim that's good to know, i was looking at the various boards and wondering the pros/cons were between them. The transparency of the F4 is what really caught my interest, i like the idea of using a tube amp with the F4 as an output stage to provide the power, i.e. the best of both worlds.
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The Smash will have an upgrade package that should push the gain into that region.
-PB
That is interesting to know. While it worked with the SET amp driving it, I still like the SET amp better alone. Maybe I just like the purity of it.
I am looking at a preamp to drive the F4's with. Maybe I will consider getting a smash with the C4S upgrade when it is available. I am also looking at the pumkin preamp, a SS preamp designed for driving the F4.
I really have way more amps than I know what do with :)
Debra
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similar to DebK, I built an F4 (only one in my case however)... Just finished said build and with limited listening time, I can say it seems pretty transparent running behind my paramounts. More experimentation ahead, but if nothing else, it was fun to build while waiting for the BH DAC. :)
Bryan
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Nice build!
Deb
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Just curious how you two are getting on with the F4, and what amps you have running infront of it?
I'm seriously considering building one but i need to work out what i need to put in front of it. A preamp like the Smash or Beepre, or a regular amp like the S.E.X. or Paramounts. Decisions decisions.
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Mcandmar
Mine are sitting gathering dust at the moment. I hope to build a preamp to drive them with this winter. I have most of ht eparts to build a Pumpkin preamp
I drove them with my 2a3 Paramounts, while it wokred with no problem, I really like the sound of my SR45/ BeePree combo the better.
As time permits I will play more with it.
Slan
Deb
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Have you tried the F4 with the BeePre? That might be interesting. I have an F5 which sounds OK when I need some more power. Pretty much the only SS amp I have been able to stand for any length of time. The SR-45 is hard to beat...John
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Ok stupid question time. What is the SR-45? I tried googling it and get a lot of hits for a Marantz amp which i assume is not what you are talking about?
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Ok stupid question time. What is the SR-45? I tried googling it and get a lot of hits for a Marantz amp which i assume is not what you are talking about?
Shunt Regulated 45.
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Gotcha, i've seen talk about BH working on a 45 amp, i assume a replacement for the Paramours?
I've gone ahead and ordered the F4, power supply, speaker protect, and soft start PCB's. Currently trying to put together a BOM in Mouser, then order a transformer and case. Anybody got any words of wisdom i should know about? .....a decent manual wouldn't go amiss for these, especially for sizing the power supply section as i'm having to scroll through hundreds of pages to pick out bits of information here and there. Why cant everybody do a kit like Bottlehead :)
Cheers,
Mark
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Mark
I didn't use a soft start board in my build. I think the thermistors do a good enogh job with any inrush current.
I sent you a PM about some parts
Deb
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Thanks to your inspiration, advice, and parts donation i have finally finished building my own little sandcastle. It really is everything i hoped it would be, and by that i mean transparent to the point it sounds exactly like whatever you are driving it with. My speakers are a pair of large inefficient vintage KEFs from the 70's which can fill the house with authority powered by nothing more than a humble little Quickie so volume range is not an issue.
Vs the 5.1 Pioneer amp i was using before it really is astounding how much better the DAC/Quickie/F4 setup sounds, so smooth yet detailed, i cant wait to build a nice preamp for it now.
I still have plenty of experimentation to do with different sources to work out what gain and voltage levels i need for these speakers to operate in, given how well the Quickie drives the setup it appears they dont need very much at all. I am also really curious to try the S.E.X. amp in front of it so i need to make up a cable to make that happen. Out of interest have you tried running yours directly from the BeePre?
Thanks again for all your help Deb!
Mark
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Very nice build!
Deb
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If you are using the SEX amp as a preamplifier (which I am) try putting power resistors across the binding posts (I'm using 16 ohm Mills 12 watt resistors). I like the result with a load close to spec paralleling the power amp input. It works without, but it's nicer with.
Skip
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Interesting, i will give that a try.
Cheers,
Mark
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Would the Mainline be able to drive the F4?
If you're using a Bottlehead pre amp with an amp, is the voltage swing higher? Or is that limited by the amp?
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Would the Mainline be able to drive the F4?
The Mainline would be a good choice to drive the F4.
If you're using a Bottlehead pre amp with an amp, is the voltage swing higher? Or is that limited by the amp?
Unless the input impedance of the amplifier is very low (under 10K), then the voltage swing of the preamp is dependent on the output voltage of the source and the gain of the preamp itself.
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So if we assume a constant source voltage, adding a Smash into a chain that goes like this Source --> Smash --> SEX...raises the voltage output at the SEX outputs (Compared to Source --> SEX), right? Due to it seeing more than 2vrms at it's input? If this is true, does this affect the frequency response/distortion levels at the output at the SEX?
How can we figure out the voltage swing of the SEX given a 2v input? This is something I can't seem to figure out properly...
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It takes about 0.62 volts RMS to drive the SEX amp to full power, which is 2 watts. That is 4v at the output for an 8 ohm load.
If you put more voltage into the SEX, it will clip at the output, increasing distortion but not voltage or power. Well, actually, if you put a LOT more voltage in, the output will be square waves and you might get close to 4 watts - but it will all be distortion, not music.
A preamp does not change the amplifiers maximum output capability.
If you had a low-output source of less than 0.62 volts, then that source would not by itself be able to drive the SEX amp to full power, and a preamp could raise the voltage closer to the clipping point (0.62v input to the SEX) and thus get more power and voltage out of the SEX.
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How can we figure out the voltage swing of the SEX given a 2v input? This is something I can't seem to figure out properly...
You can work backwards by knowing power and gain. Power into 8 Ohms gives you voltage at the output. The gain specification will let you calculate what voltage would need to be applied to the input to get that voltage at the output.
If you want to do the calculation without the gain specification, you have to consider the mu of the tubes at their operating points, the step-down ratio of the output transformer and other losses.
-PB
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I have a Smash on the way, and I've got the parts coming for an F4 build. I'm eager to try this out, unfortunately I won't be able to grasp these concepts until I can actually play around with the hardware it seems... But thanks for the explanation you two, it will come in handy down the road.
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I have a Smash on the way, and I've got the parts coming for an F4 build. I'm eager to try this out, unfortunately I won't be able to grasp these concepts until I can actually play around with the hardware it seems... But thanks for the explanation you two, it will come in handy down the road.
Let us know how the smash works out with the F4. Then input of the F4 is ~47k ohms so its not really any more difficult to drive then the S.E.X. amp. Voltage level required for normal listening levels are surprisingly low, i have a pair of vintage KEF speakers connected to mine that are easily driven into uncomfortably loud territory with a Quickie. I measured my Quickie with ~4x gain, 2v rms in, 8v rms out. Normal listening levels are ~1/3rd volume on the Quickie. So in short if you have a source outputting ~4v into the F4 it will rock your socks off!
Hope that helps....
Mark
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Yeah that helps Mark, thanks. I was a bit nervous at one point there that I might not get the levels I want but I've got a very good idea of what to expect now. I will certainly post results. I'm ordering a set of load resistors for the outputs of the SEX but I'm assuming, since there are no output transformers in the Smash that it's useless to load the outputs there when it's powering an F4 directly?
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Okay I got it built. :)
The Smash with Smash-Up powers it just fine. Got it to go as loud as one would want it to go in a small room with the Orca Minis. I would have to imagine it wouldn't be up to snuff without the Smash-Up.
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Playing in the sandbox for beginners ::)
About a month back for a little project I decided to order the Nelson Pass ACA amp pcb boards from diyaudio. I put the two mono block amp sections in one diy enclosure and am using my Bottlehead Mainline for preamp and volume control,
Its a little pair of 6W single ended class A, mono block power amps Pass designed to be simple and inexpensive to build for newbies like me. I wanted to try it with some Fostex FX120 speakers but was also curious how it might work with my HE-6 headphones.
Its 6W is sounding good with the speaker set up so I built a little adapter and have been running the HE-6 off of the speaker taps with encouraging results. I'm going to try some tweaking and swapping out the electrolytic signal capacitors for some film ones next, but this inexpensive little amp I am sure with a little further tweaking is potentially going to make for a really sweet combo for the notoriously difficult to drive HE6 headphones. Its also sounding ok with the HD800 but have a little low level volume noise to chase down with it on them. I am pretty certain its from my unshielded adapter cabling picking up interference (I just used the cabling I had to hand in the parts box).
Its up and running but still requires some feet and a little finishing off plus some experimental tweaking I expect I will swap out the unshielded signal wires for shielded and try a few different film cap options. Any thoughts or tips on optimising and making a little more headphone friendly would be welcome.
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Been playing with the F4 again. This time with the SR45 (last attemp was with the 2a3 Paramounts). Had to play with resistor values to find the right combo, using 20R across the SR45 output terminals. So the chain is BeePre--->SR45-->F4-->speakers.
It sounds greats!. Just like the SR45 but louder. Drives my Orca's better than the SR45 alone, and loses little or none of the SR45 sound with no coloration from the F4. Really impressed.
The combo needs 15 to 20 minutes to warm up and sound it's best. And, as an added bonus for those in colder climates, this combination can probably heat a small room :-)
Debra
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The input of the F4 is ~47k ohms so its not really any more difficult to drive..... Voltage level required for normal listening levels are surprisingly low, i have a pair of vintage KEF speakers connected to mine that are easily driven into uncomfortably loud territory with a Quickie. I measured my Quickie with ~4x gain, 2v rms in, 8v rms out. Normal listening levels are ~1/3rd volume on the Quickie. So in short if you have a source outputting ~4v into the F4 it will rock your socks off! Hope that helps.... Mark
Thanks very much for those measurements in and out of your Quickie preamp, and what your volume setting was with the F4 driving your KEF speakers. Levels in the “….. uncomfortably loud territory…†with 2V in and 8V output. Very impressive.
But would you happen to know the model of those KEF speakers, and their actual sensitivity?
And would your listening room size be about 15 ft x 12?
Thanks again for this very valuable info!
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Speakers were KEF Cadenzas, but i am currently in the process of restoring a pair of KEF Reference 104ab's which use the same drivers but with a better crossover design. Looking forward to hearing how they compare. Room is probably around that size, but they would have no problem in a room twice the size. As for sensitivity the manual states "12.5watts into nominal 8 ohms produces 96dB at one metre and 400 Hz in anechoic conditions" so yeah, not sure what that tells you :)
I am also experimenting with 6A3 single ended amps and have been very surprised how well they drive them with a few watts. The F4 is more controlled in the low end which i assume is due to the better damping, but i don't find it wanting for power as long as you keep the volume levels sensible.
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Been playing with the F4 again. This time with the SR45 (last attemp was with the 2a3 Paramounts). Had to play with resistor values to find the right combo, using 20R across the SR45 output terminals. So the chain is BeePre--->SR45-->F4-->speakers.
It sounds greats!. Just like the SR45 but louder. Drives my Orca's better than the SR45 alone, and loses little or none of the SR45 sound with no coloration from the F4. Really impressed.
The combo needs 15 to 20 minutes to warm up and sound it's best. And, as an added bonus for those in colder climates, this combination can probably heat a small room :-)
Debra
About your comments about your F4 and tube integrated heating up the room, you might find the following experiment very interesting, unless you already did it.
But first what is the sensitivity of your speakers? At least 89 to 90db?
And do you play them not much more than ~ 75db at 70Hz and 53db at ~7kHz at 11 ft away, as per the revised Fletcher-Munson equal loudness curves? See the curves in the wiki report.
If yes to both questions, try this sound quality vs. power consumption experiment: Turn down the bias on the F4 so that it stays in Class A for the first 10 to 12 watts/channel.
No doubt the chassis will feel a lot cooler. But will the sound quality suffer a lot? Again if you answered yes to both questions above, if you use one or two powered subs from about 70Hz on down and if your room’s not too big then you might be pleasantly surprised on both counts. That is, the slightly underbiased F4 amp will still be able to stay in Class A and will be running a nice bit cooler too.
One thing: You said that the combo needs 15 to 20 minutes to warm up to sound their best. That’s less than half the preferred warm up time stated in the F4 manual.
Did you build your F4 clone to do 25 wpc into 8 ohms and 40 wpc into 4 ohms, like a stock F4 amp does? If it puts out a lot less power than that then maybe you can’t do this experiment. Otherwise, why not give it a shot?
Btw, is this that "Simple 45" amp that you built to drive the F4 amp the same one that was reviewed at dagogo.com? Sorry, not allowed to post the link.
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Speakers were KEF Cadenzas, but i am currently in the process of restoring a pair of KEF Reference 104ab's which use the same drivers but with a better crossover design. Looking forward to hearing how they compare. Room is probably around that size, but they would have no problem in a room twice the size. As for sensitivity the manual states "12.5watts into nominal 8 ohms produces 96dB at one metre and 400 Hz in anechoic conditions" so yeah, not sure what that tells you....The F4 is more controlled in the low end which i assume is due to the better damping, but i don't find it wanting for power as long as you keep the volume levels sensible.
According to Pat D at audioreview.com's forum, the circa 1974 (?) Cadenza is 83db/1watt/meter. That’s not considered a sensitive speaker compared to Lowther, Azurahorn, Bastani, Audio Note and countless others in between. DebK’s Orca Deluxe that I just read about are 89db. That 6db difference quadruples the apparent loudness per meter compared to your 83db Candenzas, and for the same amount of applied power.
But the fact that the F4 can drive the Candenzas into the “…..uncomfortably loud territory…†in your room size with 2V in and 8V output applied to the F4 is excellent news. And that’s why I suggested that experiment to DebK. I’m in no position to guarantee anything, but it seems plausible that unless she ever intends to really crank up the Orcas volume (and her powered subs), that the bias on the F4 can be tapped down a bit to have a somewhat cooler amp-so long as there’s no perceived loss of sound quality (i.e. soundstage, depth, tonality, clarity, detail, imaging, micro and macrodynamics). Would you consider trying this?
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Hello?
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Would you consider trying this? Nope :)
Running below the stock bias setting of 200mv increases distortion rapidly, and going higher will reduce distortion, hence the 200mv measured across the source resistors was the chosen sweet spot for the circuit in terms of performance, and heat dissipation per device. From memory i ran mine slightly hotter at 225mv which is ~450ma per device for 50c on the heatsinks as i really didn't care about the heat dissipation. Have a read of the 2nd post from 6L6 in this thread for more info and measurements http://www.diyaudio.com/forums/pass-labs/234355-guide-building-pass-f4-amplifier.html (http://www.diyaudio.com/forums/pass-labs/234355-guide-building-pass-f4-amplifier.html)
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Have a read of the 2nd post from 6L6 in this thread for more info and measurements http://www.diyaudio.com/forums/pass-labs/234355-guide-building-pass-f4-amplifier.html (http://www.diyaudio.com/forums/pass-labs/234355-guide-building-pass-f4-amplifier.html)
Yes, the Impasse http://www.audioxpress.com/article/The-ImPasse-Preamplifier
and also the Aikido are probably the two most popular DIY tube preamps that F4 users go for http://glass-ware.stores.yahoo.net/listheam.html
But what’s the best preamp that you’ve used? What did it do for the F4’s performance-particularly its soundstage? Is it now much deeper?
And wider, both horizontally and vertically?
Did the F4’s tonality and imaging also benefit from this new preamp?
Which make and model preamp?
And its output voltage?
Was it also driving those KEF Cadenza speakers?
http://
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The F4 doesn't really have a sound of its own, it just sounds like whatever you put in front of it.
I built my own preamp using 4P1L tubes similar to Moglias design here http://www.bartola.co.uk/valves/2014/04/21/4p1l-dht-preamp-siberian-gen3-finished/ (http://www.bartola.co.uk/valves/2014/04/21/4p1l-dht-preamp-siberian-gen3-finished/) using Rod Coleman regulators in a filament bias configuration, but instead of an output transformer i used a Bottlehead style constant current source and capacitor coupled output. I've not heard it myself but i would expect the Bottlehead Smash +smashup upgrade would sound very similar. The 4P1L is a lovely tube for preamp stages, the only downside is it can be microphonic.
The Bottlehead Quickie + PJCCS for $120 would really surprise you too, amazing performance for the price. On the other end of the spectrum i would love to try the Bottlehead 300B BeePre kit, maybe some day..
I have also experimented with many other tubes layouts, some push pull configurations, and even some solid state designs but i always come back to single ended DHT tubes, they just have a sweet and delicate sound that i love. Experiment a little and see what works for you, different speakers and tastes will prefer different things.
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as design here http://www.bartola.co.uk/valves/2014/04/21/4p1l-dht-preamp-siberian-gen3-finished/ (http://www.bartola.co.uk/valves/2014/04/21/4p1l-dht-preamp-siberian-gen3-finished/) The 4P1L is a lovely tube for preamp stages, the only downside is it can be microphonic....... I have also experimented with many other tubes layouts, some push pull configurations, and even some solid state designs but i always come back to single ended DHT tubes, they just have a sweet and delicate sound that i love. Experiment a little and see what works for you, different speakers and tastes will prefer different things.
Please excuse the length, but these things are hardly ever simple, and everything counts. Thanks for an informative helpful and candid reply, and for confirming what all users have said about the F4; ultra transparent to whatever preamp is driving it.
And I take it that to date the F4 has been your sole, if not frequently used output stage? And that you’ve fed it with two or more preamps that you’ve built over the years?
Incidentally, you may or may not be interested in reviews, but here’s probably the best known published one of the F4. http://www.6moons.com/audioreviews/firstwatt6/f4.html
Though your speakers may be much different than Srajan Ebaen’s, it would be interesting to learn where your opinions or experience with the F4 may agree or differ.
In his reply to my inquiry about preamp recommendations, Srajan seemed to agree with you, or at least suspect, that single-ended DHT preamps might be ideal candidates to drive the F4.
“Given your speaker's sensitivity and desired SPL, you don't need additional voltage gain so using the F4 as an amp follower is unnecessary. Now it's down to a preamp…… To my mind, the F4 would be an ideal candidate to experiment with a DHT preamp which, admittedly, are rare beasts. Basically, the sound of the F4 will be what precedes it. I would go after an active circuit not because you need the gain but because the F4, if I remember correctly, has a very relaxed character. If preceded by a passive to rely exclusively on source output voltage (sufficient in your case), I'd expect too mellow a sonic presentation.â€
Sadly, the finicky drivers I’ll be using surely won’t tolerate that 4P1L tube’s monophonic behaviors. Indeed, Gary Dahl, who co-designed the speakers, placed the crossover boards on top of the sealed midwoofers boxes rather than inside them to prevent cap microphonics.
But if a DHT single-ended preamp using another tube (?) is the ideal sonic signature to be expressed through the F4, then precisely what kind of speakers should or should not be used?
Here’s what’s become a truly hellish predicament, as I wade through countless commercially built and DIY line stages. As I had explained to Srajan Ebaen, I am cloning Gary Dahl’s Azurahorn 425/Radian 745 Neo Be/GPA Altec 416 system. http://speaker system The speakers were the result of one of several previous Gary
Dahl and Lynn Olson collaborations http://www.nutshellhifi.com/
Gary’s speakers are at least 94db sensitive, my room is 16 ft x 14 x 8 and I’d only need the F4 to drive the midwoofers down to 70Hz at ~ 72db, since I’d want 70Hz to be equally loud to my ears as a pure tone level at 1Khz is at ~ 50 phon, as per the (2003 revised) Fletcher-Munson curve.
https://en.wikipedia.org/wiki/Fletcher%E2%80%93Munson_curves
http://hyperphysics.phy-astr.gsu.edu/hbase/sound/eqloud.html
https://www.osha.gov/dts/osta/otm/noise/health_effects/physics.html
Gary put each Altec 416 in a sealed box to deliberately cut off the drivers below 70Hz, to minimize IM distortion. My pair of Rythmik 12" sealed powered subs take over below that. So as the F4 has nothing to drive below 70Hz, I may only need ~ 8V input for enough power from the F4.
Gary also added a passive EQ circuit to the passive crossover, which tremendously flattens the Radian driver’s otherwise ragged response, and further extends it, albeit out to only 13kHz. See crossover and EQ here
http://www.diyaudio.com/forums/multi-way/100392-beyond-ariel-1295.html
From the beginning, Gary used a pair of Lynn’s 300B push-pull mono integrated amps that Gary cloned himself from Lynn’s design
http://www.nutshellhifi.com/IT-Triode-Amp.gif The diagram does show the 300B
tubes to be directly heated, yes?
For a quite some time Gary was very pleased with the overall sound. But when he recently completed his build of his friend Gary Pimm’s unique integrated amp he was amazed at the improvement in the Radian drivers’ response performance.
Though both amps use a transformer output and of very similar quality (Lundahl) and also used Pimm’s constant current biasing, they believe that, unlike Lynn’s 300B amps, it is the absence of interstage transformer coupling in the Pimm amp that to at least some degree accounts for its “clean and strong control†of the equalized Radian compression drivers. Said Gary, “The tube amp’s IT-coupled input stage is quite good but not nearly as clean and strong as the Pimm amp’s input stage.â€
Indeed, one would-be Amity amp builder also said that the 300B amp (at least PP types), while able to deliver beautifully rich and even 3D sound quality are not ideal for horn speakers: â€â€¦â€¦..I don't agree with Lynn Olson is putting 300B push pull amp and mate with very sensitive horn speaker. It sounds a bit edging on several different horn systems (from Western Electric type to Homebrew electromagnetic system). Maybe his Avangarde behave differently. However, I insists a good 300B / KR300XLS in SE type circuitry after so many years of work on DHT push pull.†http://www.audioasylum.com/cgi/vt.mpl?f=tubediy&m=201099&VT=T
As for the Pimm amp, while details are currently unavailable, it has balanced and unbalanced inputs. I believe is has only two stages and that the driver stage may be cascoded JFETs. And the output stage may be a MOSFET-based Pentode circuit. It does have that one transformer at the output and the entire amp is solid-state.
Question: What, if any, benefits would a Pentode and transformer output stage, made from MOSFETs (?) have over the F4 follower amp’s MOSFET output?
Question: While sound quality is the primary concern, I am curious: Assuming the above description is correct, if the all solid-state Pimm amp is push-pull, biased Class A and can deliver at least 25 wpc, will the amp run about as hot as the F4?
Question: Would know of John Tucker’s designs? Along with Gary Pimm and others, he apparently had co-designed the “Simple 45†http://www.dagogo.com/the-simple-45
John mentioned that it was he who first suggested to Gary Pimm to use constant current source/sink biasing.
He has this expensive preamp http://www.exemplaraudio.com/preamplifier-sel.html
Somewhat strangely, his integrated amp has a 6H6P gain stage and is capacitor coupled to a LM3886 chip output stage.
John also does custom design work.
In any case, Gary Dahl recently said that Gary Pimm isn’t taking customer orders for this amp, due to output transformer unavailability and/or other reasons.
Therefore, in order to closely approximate the sound that Gary Dahl enjoys from his Radian drivers, it’s obviously essential that the preamp’s input and driver stage must NOT include any interstage transformer coupling. And that it includes constant current biasing?
And from pushpulltriode’s statement above, should we conclude that a 300B SE DHT preamp-or a hybrid or solid-state preamp with a similar sound-would be best for the F4, particularly when driving horns to handle the mids and highs?
The trouble is due to a number of family and career issues, I no longer have time for any further DIY experimenting. I must either purchase a premade commercial line stage (no phono stage needed), or go with a proven design that someone can build for me to drive F4 amp.
Or even an integrated amp-one as close as possible to Gary Pimm’s deign-to drive Gary Dahl’s speakers.
http://www.diyaudio.com/forums/tubes-valves/192284-pcb-gary-pimms-ccs-ss-pentode.html
While budgeting for such a high performance preamp or low power integrated amp is not the problem, spinning my wheels over finding the best and most speaker system compatible design is extremely frustrating and time wasting.
I can’t be sure if I should pursue whichever is the right preamp for the F4 or to try to find some Integrated amp as close to Gary Pimm’s design-or replicating the sound of it-as possible for driving Gary Dahl’s speakers.
Which way to go?
Thanks for your input.
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I'll do my best to answer some of your questions here, but admittedly, I will intentionally also not answer some of them.
But if a DHT single-ended preamp using another tube (?) is the ideal sonic signature to be expressed through the F4, then precisely what kind of speakers should or should not be used?
Use the speakers you like the most that will work with the available power and damping.
Question: What, if any, benefits would a Pentode and transformer output stage, made from MOSFETs (?) have over the F4 follower amp’s MOSFET output?
There are some unusual semantics here. A mosfet is a mosfet, and a pentode is a pentode, one is a solid state device, and one is a vacuum state device. Having said that, the characteristic curves of mosfets and pentodes look similar if you ignore the scales on each axis.
Pentodes (when run as pentodes) and mosfets suffer from similar perils when used as voltage amplifiers, where their poor linearity requires feedback to obtain reasonable operation as an audio frequency amplifier. In a purely Fet follower amplifier, voltage gain is obtained from the preamp, and the fet follower provides current amplification, which circumvents this issue and allows the fet follower to operate acceptably with no feedback.
Mosfet amplifiers with transformer coupled output stages are quite rare for the reasons listed above.
Question: While sound quality is the primary concern, I am curious: Assuming the above description is correct, if the all solid-state Pimm amp is push-pull, biased Class A and can deliver at least 25 wpc, will the amp run about as hot as the F4?
If you have two class A amplifiers that each are putting out approximately 25 WPC into 8 ohms, both installed into identical enclosures, it's reasonable to infer that they will both run at similar (but undoubtedly not identical) temperatures.
And from pushpulltriode’s statement above, should we conclude that a 300B SE DHT preamp-or a hybrid or solid-state preamp with a similar sound-would be best for the F4, particularly when driving horns to handle the mids and highs?
Your statement above only excludes passive preamps and indirectly heated tube preamps as good matches? That seems overly broad, and I believe you would benefit enormously from hooking up with some locals in your area who can help you audition some gear.
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This whole conversation belongs on some other forum. It really has nothing to do with our stuff.