One thing not mentioned yet is the use if 110v primaries on these Chinese power transformers.
If your mains are 120v your B+ voltage is going to be higher. That may or may not be an issue. However it can be an issue when it comes to heater voltage.
If the heater winding is 6.3v changes are it's as high as 7+ volts.
This should be addressed to extend the life of the tubes. If there's no center tap for the heater winding a single resistor can be used to reduce the voltage.
I recently y built a preamp using a Zero Zone board. It came with an adjustable voltage regulator of the heater voltage. Many of these kits dont.
If your mains are 120v your B+ voltage is going to be higher. That may or may not be an issue. However it can be an issue when it comes to heater voltage.
If the heater winding is 6.3v changes are it's as high as 7+ volts.
This should be addressed to extend the life of the tubes. If there's no center tap for the heater winding a single resistor can be used to reduce the voltage.
I recently y built a preamp using a Zero Zone board. It came with an adjustable voltage regulator of the heater voltage. Many of these kits dont.
Ok, so it sounds like your preamp is working correctly, at least in this context. A lot of open loop gain, with all the noise to go along with it.
jeff
Make sure paint is scraped off where the grounding lug attaches to the chassis.
This is driving me nuts! I'm not well versed in a ton of this. I got to thinking perhaps it was the way I hooked up the crappy RCA input modules with their shared ground and then the input selector switch with the tiny circuit board to the volume control etc. Anyways, I disconnected all inputs except for 1. I wired it up to a brand new 100k Alps RK27. The pot is as smooth as can be but the problem still persisted. I have the source cranked full along with the amp and the pre. Sonically its nice but ... . Stupid question #99!! Could the preamp not like what I'm feeding it? Perhaps I should have mentioned I'm using a Portable lossless DAC player's headphone out as source. Single ended output rated at 70mw 32ohms. It does have a balanced output rated at more than double @ 190mw 32 ohms. I don't possess a cable for it but that can be rectified if it solves the problem. Seems oxymoronic(?) going through all this trouble to run a lossless digital player through a tube preamp and back into a digital amp. Again I thank everyone and hope that in the future I might be able to return the favor 🙂
That was the #1 thing I did right after reading a post on grounding here. I'm a commercial electrician by trade and seeing that made me cringe too 🙂 Thanks for the advice!
Wiring errors are always possible. It happens to everyone. Double-check the signal flow, make sure everything's connected correctly internally.
Have you gone through the schematic and measured voltages? It could be helpful if you can use a digital multimeter (DMM) to measure and post the following voltages:
Tube plates (anodes)
Tube grids
Tube cathodes
B+
Heaters
A balanced output from the source probably won't solve any problems into a preamp with unbalanced input.
Are you sure the noise you hear isn't coming from the headphone output? A headphone amp is a tiny power amp, designed to drive very low impedance loads (like 32 ohm headphones). Its gain could go way up driving a 100k ohm pot, which is a 3125x lighter load, possibly resulting in audible levels of hiss. Have you tried feeding this preamp from a different source, like a CD player's analog output, or the headphone jack from your smartphone, tablet or laptop?
I'm sorry I can't remember, but have you grounded the input and listened for that noise with nothing playing into the preamp? If it hisses then, then it's the preamp's problem, not any sources.
Does the level of hiss change when you turn down the preamp's volume control? Or does it remain the same at all settings of the volume control?
Is the hiss equal in level from both channels?
As has been pointed out in hundreds of threads here with similar questions about using line level preamps, your amplifier probably has more than enough gain to reach full power from the headphone output of a DAC, or anything else like that. Contemporary amplifiers have in the neighborhood of 26dB to 30dB of gain, all by themselves. The Behringer A800 has a whopping 40dB of gain from its RCA unbalanced inputs. With some weak sources it could be helpful to have a line amplifier with 2 or 3 times gain, but there's just about never a need for more gain than that.
Do you have the volume control on your Aiyima amp turned up all the way? What happens if you turn your amp's volume control down to about half-way, and use the preamp's volume control to control playback level? Does that result in less audible noise from the speakers?
Pro audio folks talk about 'gain staging', or how to set levels in each device in a signal chain so they all work at optimal levels (neither working with signals that are too weak nor overloading on signals that are too strong). https://www.google.com/search?q=gain+staging
Have you gone through the schematic and measured voltages? It could be helpful if you can use a digital multimeter (DMM) to measure and post the following voltages:
Tube plates (anodes)
Tube grids
Tube cathodes
B+
Heaters
A balanced output from the source probably won't solve any problems into a preamp with unbalanced input.
Are you sure the noise you hear isn't coming from the headphone output? A headphone amp is a tiny power amp, designed to drive very low impedance loads (like 32 ohm headphones). Its gain could go way up driving a 100k ohm pot, which is a 3125x lighter load, possibly resulting in audible levels of hiss. Have you tried feeding this preamp from a different source, like a CD player's analog output, or the headphone jack from your smartphone, tablet or laptop?
I'm sorry I can't remember, but have you grounded the input and listened for that noise with nothing playing into the preamp? If it hisses then, then it's the preamp's problem, not any sources.
Does the level of hiss change when you turn down the preamp's volume control? Or does it remain the same at all settings of the volume control?
Is the hiss equal in level from both channels?
As has been pointed out in hundreds of threads here with similar questions about using line level preamps, your amplifier probably has more than enough gain to reach full power from the headphone output of a DAC, or anything else like that. Contemporary amplifiers have in the neighborhood of 26dB to 30dB of gain, all by themselves. The Behringer A800 has a whopping 40dB of gain from its RCA unbalanced inputs. With some weak sources it could be helpful to have a line amplifier with 2 or 3 times gain, but there's just about never a need for more gain than that.
Do you have the volume control on your Aiyima amp turned up all the way? What happens if you turn your amp's volume control down to about half-way, and use the preamp's volume control to control playback level? Does that result in less audible noise from the speakers?
Pro audio folks talk about 'gain staging', or how to set levels in each device in a signal chain so they all work at optimal levels (neither working with signals that are too weak nor overloading on signals that are too strong). https://www.google.com/search?q=gain+staging
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Thank you Lavane! I did in fact just measure it right after reading your post. 6.6v is what I see. There isn't a center tap. The 270v lines are both reading almost 10 volts over and the 3.14v feeds are at 3.34v
I apologize if I came across as having excessive noise (even though my wife says I make enough of it 🙂). That's not the case at all. I'm not having hiss problems or humming or buzzing. When plugged into my cheap little hybrid preamp, the portable drives the little amp and rattles the living room. Plugging the same device into this preamp and hooked up to the same amp literally cuts the volume in 1/2. Sonically it's really nice and it reaches a comfortable level
but that's it. To be honest, I haven't had a stereo system since the late '80s until now. I got nailed with cancer a couple years ago and have been enjoying myself with more sedentary activities and hobbies and latched onto this one. I'll hit up some friends and find another source to play with and get some measurements done. Yes the Aiyima amp is up all the way as I usually run it at around 80%. The hybrid preamp never gets past 12 o'clock and I can crank the portable's headphone outs up to about 80% as well cleanly. There are 2 x 120k resistors across left and right RCA output jacks. Can these be manipulated to have any effect?
Ya, that isn't bad at all. I just finished a Chinese made tube guitar amp kit.
It's a decent kit. The B+ was up a bit but nothing to worry about. But the 6.3v heater voltage is 6.7v. That's just a little too close to the max for me, so a resistor will be added to each of the two 6.3v windings to bring it down closer to 6.3v.
I apologize for getting that mixed up. OK, just low output from the preamp. That's strange, because according to the schematic, the preamp should have almost 8x gain, so it should make the signal a lot louder if it's working correctly. The preamp must not be working correctly.
The 120k ohm resistors you mentioned should connect from the signal output to ground. They're load resistors, meant to present a load to the output stage even if the preamp's not plugged into anything.
I'm confused by what you wrote about volume settings on the headphone amp and your Aiyima amp. They're both turned 80% up? Have you tried any signal sources other than the headphone output from that DAC? What is that DAC anyway? I'm wondering how you can be using the Aiyima amp with its volume control up to 80% of maximum without it being painfully loud. Those little class D amps usually have a lot of gain.
What kind of speakers are you using? How far from them do you sit when you're listening?
From your description of your setup, there's no reason for inserting a preamp. If the headphone amp drives the speaker amp to clipping then there's no good reason for any more gain. All you will accomplish by adding unnecessary gain is adding some extra cabling, power usage, noise and distortion to what you already have.
You mentioned you were using a 'passive preamp'. Why? If the headphone amp has a volume control and the Aiyima amp has a volume control, then there's no reason for another volume control in the setup. You really only need one.
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No headphone amp involved 🙂 Here's what I have prior to using the new preamp
My Source
https://www.hidizs.net/products/ap8...Nf6SuPVOSas-zGky-TX-QHbhH6Eoxwx4vgAUtL9zktwtF
My Hybrid Preamplifier
https://fosiaudio.com/products/fosi...LAJd4VJVVfast1Esaq8vTxoD1rtUBX_QVl_DTPKbqOMAA
My Amplifier
https://www.aiyima.com/products/aiy...1HSpK1ayEg33TC24NzaaXbwObJ0R4ckUApuS7ERY2cqs6
I feel like a billboard for ChiFi! Anyway, all 3 devices have volume controls. I set the amp to 80% aprox. The preamp varies depending what I'm doing and the source volume I usually bring up fairly high as well. I like it to bump!
I'm going to put this to rest for a bit until I get a few things in. Then it will be a re-do
My Source
https://www.hidizs.net/products/ap8...Nf6SuPVOSas-zGky-TX-QHbhH6Eoxwx4vgAUtL9zktwtF
My Hybrid Preamplifier
https://fosiaudio.com/products/fosi...LAJd4VJVVfast1Esaq8vTxoD1rtUBX_QVl_DTPKbqOMAA
My Amplifier
https://www.aiyima.com/products/aiy...1HSpK1ayEg33TC24NzaaXbwObJ0R4ckUApuS7ERY2cqs6
I feel like a billboard for ChiFi! Anyway, all 3 devices have volume controls. I set the amp to 80% aprox. The preamp varies depending what I'm doing and the source volume I usually bring up fairly high as well. I like it to bump!
I'm going to put this to rest for a bit until I get a few things in. Then it will be a re-do
You didn't need my advice-you knew what the deal was on that. Safety with things electrical is alway a good first concern.
Hi Everyone,
Just a big, warm thank you to everyone that responded to my inane questions. Tonight (literally 45 minutes ago) I put the last screws in and powered it up.
I ended up stripping the whole thing down to sockets, less the feeds from the transformer. This thing has all the gain I could ever want and then some. I don't know what I did wrong before but tonight Norah Jones brought tears to my eyes and Ike Quebec made me hear things I've never heard before 🙂, I had a tiny bit of buzz when I first turned it on but that went away fairly quickly. I don't have the experience to say whether or not these tubes are bad as they really sound nice to me at this point. I'll use them for awhile and treat myself to some 'upgrades'. Here's a peek at the internals as they are now. A bit of a dog's breakfast
but it works!
Just a big, warm thank you to everyone that responded to my inane questions. Tonight (literally 45 minutes ago) I put the last screws in and powered it up.
I ended up stripping the whole thing down to sockets, less the feeds from the transformer. This thing has all the gain I could ever want and then some. I don't know what I did wrong before but tonight Norah Jones brought tears to my eyes and Ike Quebec made me hear things I've never heard before 🙂, I had a tiny bit of buzz when I first turned it on but that went away fairly quickly. I don't have the experience to say whether or not these tubes are bad as they really sound nice to me at this point. I'll use them for awhile and treat myself to some 'upgrades'. Here's a peek at the internals as they are now. A bit of a dog's breakfast
but it works!