Maybe we should quantify the problem first. How much noise on your 100+ dB speakers are you experiencing, and how much do you think you should be experiencing?
L'Amp: A simple SIT Amp
- Thread starter ra7
- Start date
Michael
as first step, don't you think it is better to quantify (eg measure) the resulting AC directly on the psu?
Franz
as first step, don't you think it is better to quantify (eg measure) the resulting AC directly on the psu?
Franz
Sure Franz, why don't you walk him through that.
the noise comming from the speaker is very strong , i 'am used with hum as i have a DIY tube amp making some hum noise too on the medium and woofer but nothing compare to the SIT .. a friend of mine tell me that the transfomer could have a problem , so i will try two 300VA R-CORE in place of my 800VA tordoid to see.. and if the problem is still there i will ask for some help with my pocket osscilloscope 🙄
long is the road...
long is the road...
Even without measuring, I can tell you "very strong" is probably not normal. Let me know when you've measured it.
By comparison, I have 98 dB speakers. From 8 feet away, I can't hear any hum, from 4 feet away I can begin to detect a little, and with my ear at the speaker I can hear it clearly. It sounds like your expectations are realistic based on your experience with tube amps, so I think you should be able to achieve a satisfying, but not altogether silent result.
My amps don't have isolation transformers, snubbers, or anything else other than what you see in the schematic I posted so, the question is: What's different?
Please start by telling us what you've done to the amp since you last reported.
For example:
1. Did you move the power resistors to the outside of the enclosure, or are they still cooking the transformer inside the chassis?
2. You mentioned something about using an isolation transformer. What did you mean? Audio isolation? AC mains isolation?
3. You mentioned your transformer is 800VA. From the pictures, it appears to be about the same size as my 400VA transformers. Out of morbid curiosity, what does it weigh?
4. 95% of my "mystery" hum problems, come from faulty construction, bad connections, bad solder joints, messy wiring. Have you gone through all of your connections?
5. What color are your speakers?
I'll check my notes later, but as I recall I measured <100uV noise, and Part Deux was 30uV
By comparison, I have 98 dB speakers. From 8 feet away, I can't hear any hum, from 4 feet away I can begin to detect a little, and with my ear at the speaker I can hear it clearly. It sounds like your expectations are realistic based on your experience with tube amps, so I think you should be able to achieve a satisfying, but not altogether silent result.
My amps don't have isolation transformers, snubbers, or anything else other than what you see in the schematic I posted so, the question is: What's different?
Please start by telling us what you've done to the amp since you last reported.
For example:
1. Did you move the power resistors to the outside of the enclosure, or are they still cooking the transformer inside the chassis?
2. You mentioned something about using an isolation transformer. What did you mean? Audio isolation? AC mains isolation?
3. You mentioned your transformer is 800VA. From the pictures, it appears to be about the same size as my 400VA transformers. Out of morbid curiosity, what does it weigh?
4. 95% of my "mystery" hum problems, come from faulty construction, bad connections, bad solder joints, messy wiring. Have you gone through all of your connections?
5. What color are your speakers?
I'll check my notes later, but as I recall I measured <100uV noise, and Part Deux was 30uV
Last edited:
I agree, they're candidates, and tell us more about that soft-start thingy, i.e. how it is connected.
hi michael:
1 ) i plan to move to 500W thick film on heatsink so the heat will not be a problem any more . put a wood isolation between the case and the transfo for the heat.
2 ) i have a 1600VA main isolator ( noise is the same with or without )
3) yes it's a 800VA 40V , i have order 2 R-CORE of 300VA to try the difference
4) i'am waiting new Bridge rectifiers as my fancy shottky ones exploded this morning with a bad operation from mine😀
5) my speaker are Red..🙂
the softsart has 2 AC main input and 2 AC main output with a start/stop plug
1 ) i plan to move to 500W thick film on heatsink so the heat will not be a problem any more . put a wood isolation between the case and the transfo for the heat.
2 ) i have a 1600VA main isolator ( noise is the same with or without )
3) yes it's a 800VA 40V , i have order 2 R-CORE of 300VA to try the difference
4) i'am waiting new Bridge rectifiers as my fancy shottky ones exploded this morning with a bad operation from mine😀
5) my speaker are Red..🙂
the softsart has 2 AC main input and 2 AC main output with a start/stop plug
Last edited:
sorry i don't understand ? the bias PSU is a lttle 1,5A 2X 12V and i have a the 12V AC wire in a shield cable. ( the rectifier diodes of the BIAS are on the little regulator card).
the POWER cAPS are double mono like in the michael fig. 37000uf/1ohm/37000uf each side. where to put the 0,1Uf caps?
More cowbell, maybe.
Hi tea-bag,
they are Vishay, I cannot get them here in 100W so I took 50W and 4x10 Ohm in series and parallel gives 10 Ohm and one 2,2 Ohm and one 1 Ohm and I get the chain of 13,2 Ohm I need with the 45-48V DC an 2x18V AC xformer from my FW PSU can make......
the sound its really a big change now I can understand the BTW was speaking of "tube rolling" ; I made resistor rolling........
my battle between resistor solution and Mufollower is still not decided ...
not to speak of the Salas CCS..
RTO 50F 47 - Dickschichtwiderstand 50W TO220 47 Ohm, 5 - Dickschichtwiderstände TO220 bei reichelt elektronik
juanitox,🙂🙂🙂
I am sorry to hear about your hum, after I got away from the + -24V arrangement from the First Watt PSUs, and built it like Mike suggested with 48V I have no hum, only going to the speaker very close I can hear a little bit....
unfortunately i have no good idea what you should do,
when the hum is induced by the bias voltage you could try a nine Volt block instead for a moment, may be the hum is over.....
you will be happy about your thick film resistors....
and there must be a simple solution for your hum.....
I am sorry to hear about your hum, after I got away from the + -24V arrangement from the First Watt PSUs, and built it like Mike suggested with 48V I have no hum, only going to the speaker very close I can hear a little bit....
unfortunately i have no good idea what you should do,
when the hum is induced by the bias voltage you could try a nine Volt block instead for a moment, may be the hum is over.....
you will be happy about your thick film resistors....
and there must be a simple solution for your hum.....
Take your time. It's a journey. 🙂 We'll all still be here.
Yes, I can send you two from Germany maybe faster....
I have an idea, I would build only one channel with no extras, only main function to isolate the guilty part.
Oh rereading your posting you did not kill the SIT, but the bridge rectifier.... So no need to send you a part I suppose...
I have an idea, I would build only one channel with no extras, only main function to isolate the guilty part.
Oh rereading your posting you did not kill the SIT, but the bridge rectifier.... So no need to send you a part I suppose...
Last edited:
I pulled up my notes:
The resistor / lightbulb version measured 70 nanowatts noise + hum. With 101 dB speakers @ 2 meters distance that would be around 23 dB, or somewhere between a really quiet room and a faint whisper.
Forgive me for quoting the wrong units earlier (uV). I was away from my underground lair.
The resistor / lightbulb version measured 70 nanowatts noise + hum. With 101 dB speakers @ 2 meters distance that would be around 23 dB, or somewhere between a really quiet room and a faint whisper.
Forgive me for quoting the wrong units earlier (uV). I was away from my underground lair.