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Can be from multimeter calibration difference 0,5 V is not critical.
You can verify vfet's bias value and output offset.
Normaly with the trimmers and DMM you can find if all is perfect ?
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I finally finished my vfet build. Nothing very different. I used the deluxe steel 4U chassis which looks nice with the handles. What took me so long was trying to figure out how to get the nuts attached to the perf mounting plate under those pcb's that stick out so far. I used an Antek AS-4222 with the old style PS boards from the diy store, which I could fit in the space. To get more capacitance, I soldered the caps with some space off the pcb so that I could solder two 10 mF on top and one 15 mF on bottom for each quarter to total 70 mF per rail. I used hot glue to hold the caps more stable. I followed the directions exactly and even though it was a lot of work, everything went smoothly and as expected. Sound will be described in next post.
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I wanted to set up a second system to try out new builds with so I rebuilt some old speakers. A little digression...in the 1990's a company bought out the Dynaco speaker name and offered two speakers, a 6" 2 way and an 8" 2 way. They called the 8" the A35 model, which sold for about $400 back then and sounded good for that price point. After 20 years the woofer foam surround was cracked and a paper cone tweeter had a small hole. I called Madisound and we found an 8" Silver Flute woofer and a Morel tweeter for reasonable cost that were direct drop-ins to the existing holes. They also provided a crossover schematic which I used. So for reasonable cost I ended up with some great sounding speakers. Only the cabinets stayed the same, but I can say I have Dynaco speakers (in front on the stool). After about a week of the amp and speakers breaking in, I sat down to some very enjoyable listening sessions. Everything sounds fantastic, the lows, mids and highs. This amp is definitely a keeper! Many thanks to Nelson, 6L6 and the diy audio store.
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Given that the amp does 15W rms into 8R and has a closed loop gain of 16dB, I'm guessing the input sensitivity is about 1.7V rms.
That's very nice.
Thank you. All your hard work paid off for many of us!
I guess is for better match with your audio source and adequate preamp choice for vfet amplier.
Technical words can easy make me confuse : nominal input voltage = amp input sensitivity
I guess is for better match with your audio source and adequate preamp choice for vfet amplier.
Technical words can easy make me confuse : nominal input voltage = amp input sensitivity
Absolutely, my preamp does not have enough gain for the Vfet amp.
Potentiometer to bottom, the amp does not develop all its power.
This is an DIY active tube preamp SE 5687 with Lundhal transformers LL1689
and I adjusted the gain at 6dB. It combines very well with a DIY SE 845 amp.
I think that with a setting to 12dB the association will be better.
Nota: With a preamp Luxman CL 360,the amp works perfectly and develops its full capacity with the pot to 80%.
Thanks ColinA123 and LUX35 interesting point.
Personally i am always excited by new diy build of particular amplifier with triode semiconductor
or line jfet preamp without feedback or another DHTubes preamp with thoriated thungsten filaments. But....
last days reveal my lack of knowledge about right specyfications to know
for proper correct use of new interesting diy amplifier i build.
That mean :
- do i need more gain and how much from preamp line stage ?
One example amp have 16 dB another amp have 20 dB of gain.
- if non so i can go passive preamp = attenuator
( potentiometer, resistive steped attenuator, light depended resistor, Autoformer Volume Control etc, )
+ buffer for correct impedance match from audio source output
( CD-Player , Audio Sound Card , DAC or OPPO ) to amplifier impedance input ?
- what preamplifier| amplifier combo if speaker drivers are ~ 90 dB efficient or less | impedance 8 Ohm ?
Room speace is 30 meters square
- what preamplifier | amplifier combo i need if speaker drivers are ~ 98dB | impedance 8 Ohm ?
Room speace is 30 meters square
What audio chain elements is to avoid if we don't want ruin some cool class A amplifiers ?
Kindest regards
Personally i am always excited by new diy build of particular amplifier with triode semiconductor
or line jfet preamp without feedback or another DHTubes preamp with thoriated thungsten filaments. But....
last days reveal my lack of knowledge about right specyfications to know
for proper correct use of new interesting diy amplifier i build.
That mean :
- do i need more gain and how much from preamp line stage ?
One example amp have 16 dB another amp have 20 dB of gain.
- if non so i can go passive preamp = attenuator
( potentiometer, resistive steped attenuator, light depended resistor, Autoformer Volume Control etc, )
+ buffer for correct impedance match from audio source output
( CD-Player , Audio Sound Card , DAC or OPPO ) to amplifier impedance input ?
- what preamplifier| amplifier combo if speaker drivers are ~ 90 dB efficient or less | impedance 8 Ohm ?
Room speace is 30 meters square
- what preamplifier | amplifier combo i need if speaker drivers are ~ 98dB | impedance 8 Ohm ?
Room speace is 30 meters square
What audio chain elements is to avoid if we don't want ruin some cool class A amplifiers ?
Kindest regards
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Thanks Ichiban i know this one is highly useful article
....but i ask about your " first ears" personal experiences
and preamps right choices for the Sony DIY Vfet amplifier ?
What you Diyers use with push-pull 2SJ28| 2SK82 ?
....but i ask about your " first ears" personal experiences
and preamps right choices for the Sony DIY Vfet amplifier ?
What you Diyers use with push-pull 2SJ28| 2SK82 ?
