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
Pass DIY Addict
Joined 2000
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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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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