always worth a shot !!
no trouble with the control , just the gain. It never occurred to me to look for higher gain tubes as the biggest challenge I have as a headphone amp is too much gain. I will get in some 6SL7s ,i think i have 12AT7's in my horde
thanks for the suggestion.
..dB
I have a bit of an ulterior motive. I'd like to know how the F4 works with Maggies. I'm not sure that I have an appropriate preamp in the house right now, and my plans will benefit from your experimentation.😉
F4 can send a lot of current to a speaker and Magnepans will be driven with poise, control, style and grace.
Pass DIY Addict
Joined 2000
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yep - I recognize those little tin foil and stickered "drug packets" - I've received lots of those as well 😉
Another F4 is born, I just finished it up today, but I have a problem. Build is using 18 vac, 400VA trafo, 60,000 uF per rail with a soft start, no issues with PSU. I needed to piggyback a 10K resistor on to R9 since I couldn't get enough bias, but once I did I had no problem biasing or nulling DC offset. I settled on a bias at 300 mA with offset ~ =/- 1 mV. Let sit powered up for ~ 2 hrs after final bias adjustments and the heat sinks were nicely warm, but not hot. I got the mosfets as a set from the DIYAudio store recently but none were marked with matching numbers. The jfets I had bought many years ago as spares. They were supposedly a matched set of toshibas from a reputable source, they look real, but it was quite a while ago.
Here is my issue. I did my test using an Aikido preamp that I use without problems with my Aleph J. When the F4 is powered up and connected to a preamp it is dead silent, no hiss or hum what so ever, but when I play music the sound is distorted and bit garbled. The preamp can drive the F4 to loud volumes and sounds great with the Aleph so something is amiss with my F4 build. I have included pics of my build. I am wondering if the jfets might be fakes. I would greatly appreciate any help or insight on a potential cause/remedy.
Here is my issue. I did my test using an Aikido preamp that I use without problems with my Aleph J. When the F4 is powered up and connected to a preamp it is dead silent, no hiss or hum what so ever, but when I play music the sound is distorted and bit garbled. The preamp can drive the F4 to loud volumes and sounds great with the Aleph so something is amiss with my F4 build. I have included pics of my build. I am wondering if the jfets might be fakes. I would greatly appreciate any help or insight on a potential cause/remedy.
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I would try a different source before I started tinkering with the amp , also make sure that your input and output wiring is accurate. Hard to think that an amp that biases and has stable DC offset is not electrically operational.
Nothing (that I can see) looks amiss in those photos.
That the amp biases and offset adjusts properly is a good sign.
Bias.. you are measuring 300mV across the resistors ? You say mA above, just verifying.
Where did you get the Jfets?
What is the preamp you are using?
That the amp biases and offset adjusts properly is a good sign.
Bias.. you are measuring 300mV across the resistors ? You say mA above, just verifying.
Where did you get the Jfets?
What is the preamp you are using?
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Your top of your jfets show the tiny slit typical of Toshibas so at least that looks ok.
(ie, doesn't look to be obviously fake.)
Does it only sound distorted when you start cranking up the volume?
Have you tried another source, or just connect a source directly to the F4?
(ie, doesn't look to be obviously fake.)
Does it only sound distorted when you start cranking up the volume?
Have you tried another source, or just connect a source directly to the F4?
Hi Guys,
Jim,
- I meant 300 mV across the source resistors.
- They've been sitting in my parts bin in my garage for many years, can't remember who exactly I got the jfets from but it was off of a seller who frequented Diyaudio and had a good rep, maybe Spencer, but too long ago to be sure.
- I tried it today using a dual mono Aikido tube preamp that I've had for several years. I tried it first with my Aleph J, sounded great, then removed the Aleph J and substituted the F4, sounds distorted.
dBel84,
- I have a couple of other preamps that I can try, a Waynes BA2018, a Salas DCG3, and an Aikido 9 pin all in one, all of the preamps have been used with great success with my other Pass amps (M2, F6, Aleph J). I will try another preamp and see what happens.
Dennis,
It sounds distorted from very low volumes to loud volumes, the level of distortion stays the same relative to the volume, it doesn't get worse as volume increases only louder.
Zenmaster Mod,
Schematic and BOM are from this thread. I tried to follow the build guide faithfully.
Paul
Jim,
- I meant 300 mV across the source resistors.
- They've been sitting in my parts bin in my garage for many years, can't remember who exactly I got the jfets from but it was off of a seller who frequented Diyaudio and had a good rep, maybe Spencer, but too long ago to be sure.
- I tried it today using a dual mono Aikido tube preamp that I've had for several years. I tried it first with my Aleph J, sounded great, then removed the Aleph J and substituted the F4, sounds distorted.
dBel84,
- I have a couple of other preamps that I can try, a Waynes BA2018, a Salas DCG3, and an Aikido 9 pin all in one, all of the preamps have been used with great success with my other Pass amps (M2, F6, Aleph J). I will try another preamp and see what happens.
Dennis,
It sounds distorted from very low volumes to loud volumes, the level of distortion stays the same relative to the volume, it doesn't get worse as volume increases only louder.
Zenmaster Mod,
Schematic and BOM are from this thread. I tried to follow the build guide faithfully.
Paul