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tube preamp makes rushing noise at speakers
tube preamp makes rushing noise at speakers
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Old 23rd November 2020, 02:57 AM   #101
Rick PA Stadel is online now Rick PA Stadel  United States
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OK, good -- on the Mouser.

Here's the schematic - no great big deal.

Depending on your relay's current demands, one transistor may be adequate. But even all -C suffix devices may NOT have high enough current gain. The 22k resistor will have very little voltage across it as the relay(s) approach(es) full voltage, and therefore only providing a dabble of Base current for the transistor(s) -- 32uA unless I've booted the arithmetic. That's only 13,4mA even at the median beta of 420, which is higher than the lower half of the pool of -C devices -- by definition. Further complicating things, specs for beta are typically at a higher Vce, usually 10V or so. All BJTs are less conductive as the Vce drops; these will only have 1,3V across them if the supply is 6,3V, less if it droops.

Cheers
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Old 23rd November 2020, 03:56 AM   #102
gregas is offline gregas  Canada
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Rick,


Thanks for taking the time out of your day to sketch up the

muting relay schematic. My parts order selection is coming along.
I was thinking of using this relay DS2Y-S-DC5V Panasonic Industrial Devices | Mouser Canada
should be good?

I'll order an extra to keep around if one goes bad.
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Old 23rd November 2020, 05:23 AM   #103
Rick PA Stadel is online now Rick PA Stadel  United States
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Yes, the DS2Y-S-DC5V from Panasonic should be fine, with a couple minor caveats:

- a little more current hungry than we'd prefer -- but we can work with it

- it is a Not Recommended For New Designs, which is a bad news / good news thing: If a replacement is ever needed, a 'direct' one may not be available; but the price is likely better.

Oh, and before I forget again: Practically any diode will work for the 1N4148's -- even most of the 1N400x family, or about any other 1A rectifier you might have handy.

Regards
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Old 23rd November 2020, 03:42 PM   #104
gregas is offline gregas  Canada
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Rick,


Thanks for the clarification. I've wondered about the "not recommended for new design thing". Now it makes sense. yes this was the cheapest 5v relay from Panasonic.
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Old 23rd November 2020, 11:42 PM   #105
gregas is offline gregas  Canada
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Quote:
Originally Posted by Mark Tillotson View Post
What type of resistor are R12 and R16? Should definitely not be carbon comp...



You know your mono switch is shorting the inputs together? - not friendly to the source.

Just wondering what is a better option to get mono output.
I want to use it to setup the cartridge on my turntable.
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Old 26th November 2020, 07:59 AM   #106
Rick PA Stadel is online now Rick PA Stadel  United States
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Perhaps a 220R resistor from one volume wiper -- the source-side of C10 -- to the other. But I'd rather defer to the many wiser folks on this site for a proper answer to that question.

Also, 20V C10 needs to be a higher voltage. Since C9 comes from the great beyond, good practice would probably suggest a higher voltage rating for it, too.

Would still like to persuade you to consider omitting, or substantially re-biasing, the 6SL7. As a Cathode Follower, its job should be to lower impedance. It can't do that with a 110k load; unless I mis-read the graph, that places the current in the low 300's uA range. Worse, being DC-coupled to the next stage forces it into yet another non-ideal operating point.

Stage by stage the impedance just keeps going higher and higher ..

Regards
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Last edited by Rick PA Stadel; 26th November 2020 at 08:23 AM.
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Old 26th November 2020, 09:20 PM   #107
gregas is offline gregas  Canada
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Hopefully someone chimes in on the mono switch.

Thanks for your input Rick. Once we sort out the bugs we can setttle on final circuit topology/values. At that time we can see much better without the various noises obscuring things on the instruments. That's my friends perspective.
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Old 3rd December 2020, 05:41 AM   #108
gregas is offline gregas  Canada
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Hey Guys,


Jean-Paul
I got my parts order in today.
So as a first step to quiet the noise you suggested to add a .1uf cap from the drain to ground of every fet.

So i added them, I only did one channel as a test.

Unfortunately it hasn't made any difference at all in the noise i still hear the same static sounding noise from both channels.






Quote:
Originally Posted by jean-paul View Post
Gregas, .... 0.1 uf decoupling caps direct from the drain pins of the FETs to GND. .
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Old 3rd December 2020, 05:52 AM   #109
jean-paul is offline jean-paul  Netherlands
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All the steps necessary must be done. It is a combination of factors. There is a set of standard things to do to prevent circuits going wild. Decoupling power supply lines is a part of that. On itself it can today help and tomorrow it may not. No decoupling simply is below the minimum standard.

Normally circuits have been tested and proven to be stabile/not oscillating etc. Nowadays many first simulate to known what will happen. The cycle of building and trying out on the fly is not the way to do things properly so the first advice many experienced people will give are the standard things. They also had the issues and learned to tame circuits as anyone of us has built an amplifier that became an oscillator and vice versa.

When the circuit then still is not OK then it is a wrong design. The road to well performing circuits when you are not experienced is to build proven circuits first. The road of just building and paying attention to the parts themselves is not. It may also lead to frustration and time loss.
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Last edited by jean-paul; 3rd December 2020 at 06:04 AM.
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Old 3rd December 2020, 05:54 AM   #110
gregas is offline gregas  Canada
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Jean-Paul. thanks for the response. I will continue to add the parts you suggested. I will keep you posted.
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