Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Stereomour => Topic started by: altec604e on May 29, 2014, 05:37:59 PM
-
Hello,
I have some questions regarding my Stereomour 2a3 tube amplifier.
1. How much noise is usually "accepted" or "normal" with the Stereomour amp:
Mine is not dead quiet - I use a pair of Altec 604E`s that are rated to 16 ohm operation.
And the speakers are rated at 100dB efficiency.
The output transformers are wired for 8 ohm operation right now, I heard a lot of difference from the 16 ohm wiring - the noise floor did go down, but it is still not as quiet as I want it to be. It does not have to be dead quiet, but a bit more would have been great!
The 4 ohm operation was even more quiet - but at the same time I lost a lot of information - especially vocals was lost ( I have not done a lot of testing , but this is how I heard it yesterday ).
Previously I have been recommended to lower the ohm setting on the output transformers because of the high efficiency speakers I`m using. 4 ohm is definitely the setting with the lowest noise floor, but I cannot find the sound convincing because of other things that are lost - based on your knowledge of these amps - is this loss of for example vocals just in my head??
One more thing on the subject: is there anything else I can do to lowering the noise floor on my Stereomour amp?
-
I'm going to agree that with 100dBW speakers noise will be hiding in the background.
You don't say how much noise it is. Is it only heard between tracks or is is heard during quiet passages? How loud do you listen, 60dB, 70dB, 80dB or higher? How big is your room? The larger the room the farther away you will probably sit (attenuating the noise).
There may still be a few tweaks to minimize the noise and PJ will probably come up with them.
-
Hi !
The noise is definitely present during quiet passages.
To answer you questions:
I do not know how loud I listen to when you're talking about dB - normally I use from the Stereomour from the 9 o`clock position to the 12 o`clock position . I`m guessing the loudness Im listening to is quite low to normal - not loud or extremely loud.
My room is roughly 30 square meters.
I`m sitting roughly 3 meters away from the speakers.
Thanks for your replay !
-
The Stereomour is AC heated, so some filament hum is to be expected.
Can you describe the nature of the noise itself? Is it a hum or a hiss?
It's also worth mentioning that the Paramounts are significantly quieter than the Stereomour.
-
If it's hiss, could be the bad batch of 431s.
-
The noise can best be described as a hiss.
What is 431s?
One more questions:
1. Right now I`m using my Svetlanas - the HUM-balance is set to as low as it gets with my Svetlanas - to 1.8 and 1.9 mV AC. When using my RCA-s I cannot get it lower than 2.3 or 2.2 mV AC.
It says in the manual that the HUM-balance varies between which tubes you use.
So my question is what does this HUM-balance do? - and what difference is it between using these two sets of 2a3 tubes I got ?
I mean one pair
the Svetlanas is right below 2.0 mV AC and
the RCA´s is right above 2.0 mV AC
- what difference does this make on the noise floor? - if any?
-
OK - just went through the manual - are you talking about the LM431 adjustable shunt regulators?
Then I got something to share -
1. When turning the amplifier on there is always a couple of seconds with both hum and hiss.
2. There were some points when doing the DC check when first firing the amp up that got me a little bit confused - especially the measuring points around the circuit boards...
I will attach all the DC voltage checkpoints in a PDF document - please let me know if you can see if there is a problem related to the items you are talking about....
-
That is the 431 (LM431) that they mean. They have new ones that meet the spec, the bad lot didn't. Just contact replacementparts (at) bottlehead (dot) com or fastest thing is to call Monday. They are very quick about getting parts out.
-
Regarding the 431's, you can look at the writing on the 431 to be sure. We received some 431 regulators labeled "WS" that entirely meet spec. If you have these 431's and sensitive speakers, you ought to replace them. If you don't have these 431's, then there isn't any need to replace them.
-
I have the 431´s with WS labeled on them.
I think something is missing in your post replay....
If I understand your post correctly - these WS labeled 431´s did NOT entirely meet the specs - and are from the bad batch of 431´s...
This is the answer to my problem then. Will write a email to the replacementparts email address.
Thank you !
-
Change those WS 431's! I did so and it made all the difference in the world!
-
Hello!
So I installed the new 431´s - with great improvement !
Thank you for all help with this issue.
One last question from me:
I´ve set the secondary windings on my output transformers to a 8 ohm impedance.
My speakers has a 16 ohm impedance.
So before making any new changes; will the speakers perform better ( sound more prominent in the room - raised from the background ...) if I set the secondary windings to a 16 ohm imperdance?
I have a sense that the sound has a veil over it...
I mean since I´ve now got a much more quiet Stereomour 2a3 amplifier and the noise floor question I started this thread with is now gone...
The popping when sometimes occurred when turning of my Stereomour is also gone...
GREAT!
Best,
Altec604E
-
Hi,
Got some more questions....
I do hope this is OK.
Here we go:
The secondary windings on the output transformers : if set to 8 or 16ohm operation should not have a great impact on sound since my speakers are rated to 100dB sensitivity- correct?
Noise: The 100K potentiometer in the 12 o`clock position is a source for noise. I usually use the volume knob set between the 10 o`clock and 2 o`clock position when listening.
Is there any high DC current at the input? I´m asking since I have been told that there are no input capacitors on my Stereomour.
If there is no high DC current at the input, then I can use any normal pre amp to control the volume of my Stereomour ( as long as the 100K pot is set to fully clockwise position ) - correct?
What output current should I choose on the Pre amp I now own. The 5mV, the 1.6V or the 5V output to use it as a volume controller for my Stereomour?
So my two 2a3 RCA tubes died yesterday. They did not last long, did I do anything wrong? They were supposedly to be NOS. Now they make this up and down hiss noise...
-
The secondary windings on the output transformers : if set to 8 or 16ohm operation should not have a great impact on sound since my speakers are rated to 100dB sensitivity- correct?
Nope, the damping, how well the amp holds your woofer, changes if you mismatch the load and OPT. But try it, you might like it.
Noise: The 100K potentiometer in the 12 o`clock position is a source for noise. I usually use the volume knob set between the 10 o`clock and 2 o`clock position when listening.
I'm not sure, are you saying 12:00 and above or only at 12:00?
Is there any high DC current at the input? I´m asking since I have been told that there are no input capacitors on my Stereomour.
Input DC would be from your source or preamp. There is no DC at the Stereomour input/12AT7 grid.
What output current (voltage) should I choose on the Pre amp I now own. The 5mV, the 1.6V or the 5V output to use it as a volume controller for my Stereomour?
Again, this is a try and find the best balance. The output of your preamp depends on the input voltage. So you don't always have those voltages available at the output of your preamp.
So my two 2a3 RCA tubes died yesterday. They did not last long, did I do anything wrong? They were supposedly to be NOS. Now they make this up and down hiss noise...
How old are they? Were they new? I'm thinking they may have been old, old stock if they failed this soon.
-
So my two 2a3 RCA tubes died yesterday. They did not last long, did I do anything wrong? They were supposedly to be NOS. Now they make this up and down hiss noise...
What do the voltages look like with those tubes installed?
[/quote]
-
Thank you for giving a replay for my last post !
I will try to give the best answers as possible.
Remember I´m a newbie- willing to learn!
OK.
So I think I got you regarding your first answer - will try to configure the OPT to 16ohm winding - will give a feedback when seeing this.
I think I remember the woofer going all crazy ( vibrating back and forth very fast) on high volumes when the OPT were set to 4ohm. ONLY when I was playing loud- stopped playing right away when seeing this - this was also when put it back to 8ohm configuration. So in real world terms I get what you are saying about how well the amp holds the woofer - If I am getting your point; that is.
I´ve been told that when the 100K pot is set to the 12 o`clock position the source resistance is 50K ; it is in series with the input.
This is not the best thing is it? So controlling the volume with a pre amp is a better option.
There I got my answer regarding no high DC voltages at the input. Good. Will try my Quad44 pre with my Stereomour shortly; will give a feedback to you on how this goes too.
To answer both of your questions regarding my 2a3 tubes. They were supposedly to be NOS, but I also have a feeling that I got old stock tubes since they run out so fast.
The voltage readings were the same as before they started hissing; around 2.6 down to 2.0 ...
Questions from me:
1. What tubes should I consider now if I want to do a tube roll? Is till got my Svetlanas, what about the 12AT7 tube- what impact does this tube has on the sound? Should I consider doing a tube roll on this tube too?
Thank you again for your replay!
Really do appreciate it.
-
In theory the 16 Ohm tap should sound best. I would suggest trying the 8 Ohm tap as well. It may lower noise and have enough damping to control the woofer.
The source will always see a 100k Ohm input for the Stereomour. The variable resistance is to the grid of the 12AT7.
If you want to use your preamp just set the Stereomour volume control to 100%. That effectively takes the pot out of the audio path.
PB/CB was asking for the plate, grid & cathode DC voltages measured to ground. You can measure the voltage on both of the small tube pins and one of the large ones. The large ones are the cathode/heater.
I have used a pair of NOS RCA, the stock Sovtek and the Shuguang 2A3C. The old RCA are very nice. The 2A3Cs replaced very worn Sovteks and were a big step up from the worn tubes. So I can't really compare those.
I believe that the 2A3C sound better than fresh Sovteks. They are ~$110/matched pair delivered from China. The NOS RCA beat out the 2A3Cs in detail and soundstage. But I only drag them out for special occasions.
-
Hi ;)
OK- understand.
Will do the plate, grid & cathode DC voltages measured to ground quite soon with the RCA's installed.
Found these 2a3 tubes at tubedepot:
https://tubedepot.com/products/2a3-us-made
Should I consider buying these? If so which brand?
Any point of investing in a tube tester? Quite an expensive instrument.... Even if you buy a portable or low budget one ( compared to the really professional ones )
Maybe a good idea to find a firm with a quality tester instead?
What is the purpose of the 12AT7 tube in the Stereomour?
-
Last question first:
the 12AT7 has all the voltage gain of the amplifier. The 2A3 is the current into the OPT. (I think that is right, pretty sure)
Moving back, tube testers come in all kinds of "flavors." Not all of them test the same things. I have one that I have never used. I just trust in the tried and true sellers I have used.
Tube Depot is one of the tried and true sellers. I am partial to Sylvania tubes. I have used them in my Foreplay, Seduction, Eros and as drivers in my Paramours. I have never had Sylvania output tubes. I can only guess they would appeal to me.
BTW, I sold the Thorens TD 124 MKI and the SME 2009 MKII back in the 70s. Great combination!
-
I am late to this conversation, but here are my remarks, from input to output:
The potentiometer is usually best set at 100% if you are using an external level control. For the preamp with a choice of outputs, I suggest you try the 1.6v and 5v outputs and see which works best - the biggest difference will be where you set the control. Only in certain circumstances will it be necessary to change the balance between preamp gain and amp gain to obtain the best performance. I do not think you have this problem, I just mention it for completeness.
The 12AT7 is the main voltage gain stage. Your voltage measurements indicate that you have a weak tube (the plate voltage is higher than ideal). It is within an acceptable range for performance, but a fresh tube may make an audible difference. (If it does not, then at least you will have a spare on hand!)
The 2A3 is the power output stage, it provides some voltage gain but all of the output current. Your voltage measurments show that it is operating correctly, so there is no circuit reason that I can see for a short life. Most likely the tubes were worn when you got them. (In the unlikely event that this happens again, post back and we'll explore other possibilities.) The filaments of this tube are powered with AC in the Stereomour, and the hum balance pot allows you to cancel the 50- or 60-Hz hum; the exact setting will be different for each individual tube. There is a residual hum at twice the frequency, which usually amounts to about 1mV RMS at the 8-ohm output (1.4mV at 16 ohms, 0.7mV at 4 ohms). This will vary with different tubes. Remember, few meters will be very accurate at this low voltage.
The matched impedance of the output transformer (16 ohm setting with 16 ohm load) produces the most power. With 100dB speakers at moderate loudness, you probably don't need the maximum power even in your fairly large room, but keep that in mind as you listen - rooms and speakers vary greatly. The higher ourpur impedance also has the lowest damping factor, which will affect the frequency response of the speaker - not a lot, but it may be audible. This effect is strongest in the bass, which is also most affected by room placement, so the only way to judge is careful listening to each setting.
-
Again, thanks for the replies!
Will definitely check out the Sylvania tubes from tubedepot.
Will never ever buy tubes from a not trusted or really well known seller again.
Will not buy myself a tube tester.
Cool that you also used to have thorens td124 with a SME tonearm Grainger49 ;)
Your voltage measurements indicate that you have a weak tube (the plate voltage is higher than ideal). It is within an acceptable range for performance, but a fresh tube may make an audible difference. (If it does not, then at least you will have a spare on hand!)
Paul Joppa; are you talking about the sheet with DC measurements I attached earlier in one of my posts?
Info:
These DC measurements are from the first time I fired up my Stereomour. I had the stock 2A3 Svetlanas tubes installed when measuring these checkpoints.
Should I do a second round with these DC measurements?
Do you think the bad 431's had a great effect on these DC measurements?
-
Ooohhh - good catch!
Yes, re-do the measurements, specifically the OA and OB voltage of the C4S board, which go to the plates of the driver.
It is not uncommon for a fresh tube to have a high plate voltage, and then drift down to a lower, stable value as the cathode finishes forming - usually in 50 to 200 hours, depending on the particular tube. Your original measurements showed a slightly high voltage. If you have run the amp for 50 to 200 hours and that voltage has come down, then the tube is fine.
The 431 will not affect that measurement.
-
Hi,
I have redone the checklist.
You`ll find the checklist attached.
Checkpoint 4 is really off from the manual.
I was to replace the resistor that goes from A3 to T4. I have a already a spare on hand.
First time installing this resistor it a little bit of the resistor fell off from the body- used a tweezer too hard I guess... Do you think this is causing the off measurement?
Anything else I should look into further based on the numbers attached?
PS: Just ordered the Sylvania tubes from tubedepot !
-
I'm not sure where in the circuit checkpoint 4 is. It is likely a grounded terminal. If so 14mV indicates that it needs the screw tightened.
Give that a try and see what happens.
-
Hi again ,
So I tightened the screws on all three terminal strips ( each with 5 terminals) in the front of my Stereomour.
It is Terminal 4 and Terminal 12 that do not have a 0 V DC reading. These two terminals mirror each other- Both are connected to same terminal to the 2a3 sockets on each side with a resistor - A3 and C3.
I also resoldered all four of the points without any new/good results with my multimeter.
Any idea on what to do next?
-
Checkpoint 4 is really off from the manual.
0.014V is not really off from 0V. Terminal 4 is not an issue.
A3 can't be 24V with the rest of those conditions, I'm guessing 24mV?
Your 12AT7 is reading a bit high, and may not be the quietest of tubes. Trying a spare isn't a bad idea.
Wiring the output transformers for 4 Ohms will yield the lowest noise floor, highest damping, least distortion, and least power into 16 Ohm speakers. If you have ~100dB efficient speakers, this is the way to go.
-PB
-
oh man... ;)
my fault... got a bit carried away there.
24mV is correct.
I just ordered a new 12AT7 tube when I ordered new 2a3 tubes ...
Thanks!
-
hi,
I´m having trouble with my stereomour...
so the issue is that one channel ( the left channel ) in my stereomour is making a mechanical noise- it vibrates.
in addition: when adjusting the volume knob the noise I´m making when moving the dial is reinforced in the left speaker.
the mechanical background noise that is always present has a much lower noise than when turning the volume knob or touching the chassis of my stereomour amp...
anyone got a clue what`s causing this background noise?
-
How are your voltages?
What do you mean that the left channel vibrates? A vibration would suggest that the amplifier itself is vibrating, and this would generally be tough to localize to just one side.
-PB
-
I checket the hum balance last week - they were almost the same. low.
I have not done any voltage checks since last time I posted my second voltage list.
As far as I see it my left speaker is reinforcing a vibration sound from my stereomour.
I cannot feel that my stereomour is vibrating, but for example when turning the volume knob the sound from turning the volume knob is reinforced through my left speaker....
HOLD ON ! - I may have not put back the lock washer on one of the two screws ( holding the left output transformer in place ) - is this causing the issue?
If it is ... I´m so sorry for bugging you...
-
I'd triple check the voltages. The Stereomour shouldn't vibrate unless the iron is being drastically overstressed, which would show up in the voltage checks.
-
Will do!
can't do it until tomorrow though- it´s late in the evening here over the pond...
-
Do you mean microphonics?
-
hi,
what do you mean by microphonics?
when tapping the stereomour the sound is reinforced through the left speaker - I´ll guess like a microphone....
-
That is microphonics. Many tubes are microphonic, some more than others.
-
Hi,
I still got issues with noise from my left speaker.
Today I did the checklist of AC and DC measurements described as in the Stereomour manual.
I`m attaching two files in this replay:
Checklist 2 Voltages is from before I got the issues with noise from my Stereomour in the left channel.
Checklist 3 Voltages is from today.
Can anyone read anything strange / different / off - "THE PROBLEM" - from these two lists?
All help will be appreciated.
-
I think you have a loose heater wire on your 12AT7 (pins 4/5), or back where those wires connect to the power transformer.
Your first test reveals a 12AT7 that is just gasping for breath in terms of operation. Your second test reveals a 12AT7 that is working very well.
Since both halves exhibit the same issue, it is most likely a loose heater wire.
-PB
-
Hi !
I´ve just sat down to rearrange some of the wires in my Stereomour after reading your answer to my previous post replay.
I was wondering what you mean by "loose":
My interpretations of the term...
1. The wire is not connected at all in one of its ends.
2. The wire is not well enough soldered ( bad soldering ) at one of the two points connected.
3. The wire is not well enough twisted around other wires going the same way ...
Thank you for your answer !
Really do appreciate it!
-
1. The wire is not connected at all in one of its ends.
2. The wire is not well enough soldered ( bad soldering ) at one of the two points connected.
It's really #1 and #2. I would revise #1 to be that the wire passes through the terminal, but may not be soldered at all.
For #2, it would just be a solder joint that isn't shiny, and maybe has a lot of excess solder lumped up onto it.
-PB
-
Hi !
So I´ve gone through my Stereomour amplifier and resoldered all joints that where not shiny.
The red wire from IA soldered to HV+ in my Stereomour was loose at the PCB board.
When doing the fourth measurement of the DC measurements ( not attached this time ) I also saw that I had red light shining on the little circuit board - something I can not remember I saw last time I did these measurements.
The microphonic reinforcement is still there, but it is now in two channels instead of one. (for example when turning the volume knob the sound is reinforced through the speakers ) - as you guys previously told me this often depends on the tubes used I guess.
The other strange vibration sound through my left channel is gone.
There is a little hum from both channels when not playing music - this sound I`m familiar with ... it´s all good!
Thanks for the help!
-
I'm glad you got it all nailed down. No doubt the amp will sound a bit better too!
-PB
-
Hello,
I bought a Stereomour second hand a year and a half ago and I realized that the hiss was a little too loud but I thought that is the way it is suppose to work. Reading this post I realized that I needed to check the LM431s which I did and they are indeed the WS ones. Is thre any chance you might have a good set lying around? I was planning on ordering 2 bottlehead badges so if you still have a pair of LM431s can you please through them in as well. I can pay for them there is no issue there.
-
replacementparts at bottlehead dot com is the best contact address for replacement parts.