I tried the amp with a pair of speakers yesterday. Got very briefly sound on left side and then nothing. I have sound only on the right channel. The left channel biases properly, I get around 1.4v between T7-T8 and same on the other side. When connect speakers and send audio signal get no AC volatage between O-and O+
Power supply shows +31.5 and -31.5. I checked the Vfets and the are ok. Where should I look next?
Power supply shows +31.5 and -31.5. I checked the Vfets and the are ok. Where should I look next?
Rookie mistake. Had mixed up R2 and R1 values. Swapped them around and both channels are stable now. Been listening for the last 30 min or so.. The amp is sweet, my speakers are 91dB sensitivity and while not perfect, able to drive them well on low volumes can control them a ok. I love that fast attack and sweet high frequency of the V-fets. One only wish it had a little more watt. Looking forward to next design. Any other projects? 2SK180?
Should be fine.
You can always add a preamp with gain if you feel you need it, later on.
All values are original as per schematics. Is it a revision you are referring to?
This is a very good amp don't give up on it just yet.
If you have 32V rails then increase R15 and R16 to 47.5k or 48.7k, this will give you more voltage swing before clipping.
Essentially it will convert it to around a 25W amp.
If you have 31.5V rails use 47.5k
If you have 32.5V rails use 48.7k
We can also increase the gain a little bit but I don't think we need to go there just yet.
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I like the amp very much, guess just used to my other Vfet beasts. The Sit1 surely has a gorgeous sound.
I get around 31.5~but less than 32V on the power rails. Will try to change the resistors you mentioned and report back.
dc offset at the amp's output
just a question to the lucky people who are already enjoying the sound of the sony vfet amp; what is the change of the offset dc at the output of the amp when you cold start and after the amp is warmed up lets say 30 minutes? any reason to be worry that at the cold state the offset might be relatively too high to damage the speakers? any recommendation?
best regards
just a question to the lucky people who are already enjoying the sound of the sony vfet amp; what is the change of the offset dc at the output of the amp when you cold start and after the amp is warmed up lets say 30 minutes? any reason to be worry that at the cold state the offset might be relatively too high to damage the speakers? any recommendation?
best regards
In my case, it takes about 1.5hours of waming up for the DC-offset to settle down. As soon as the airflow around the headsinks changes or the lid comes off, the offset starts moving again. In order to dial mine in I made up a makeshift lid with holes to adjust the pots through. Eventually this got me close enough after about a week of fiddling.
I'm not sure why not more people have reported these kind of challenges. Maybe their component tolerances where better.
many thanks, stijn. would you please share the dc-offset values at cold state and after 1.5h warming up?
do you hear a difference in sound quality when the offset changes duo to the airflow condition?
best regards
Appologies for the delayed reply.
I measure:
L channel, @ cold start: 151mV, after 1,5hr -7mV
R channel, @ cold start 225mV, after 1,5hr 20mv
Sounds quality is subjective and I don't know to what extend this can be attributed to the DC-offset, I wondered about this myself. However I find the amp becomes smoother & more natural sounding after it's had time to warm up.