An externally hosted image should be here but it was not working when we last tested it.
You should, however, "Support Your Local Sheriff"
(every time I think of Joan Hackett my heart cringes, a life lost too early!)
I can agree with that statement. I finished my preamp enough to have a listen, then just a few cosmetic items to take care of to wrap it up. A very nice sounding preamp.
There is zero 60 Hz hum, but just a slight hiss. My midranges are Audax PR170, about 96dB. It is independent of the volume control. At listening position you can't here the hiss. Is this normal, if it's not what can be done?
Since there has been some questions on tuning or loading for the Cinemag input transformer, here is what I found to work. With a 100K pot. a 10K ohm resistor by itself worked well enough. With the volume at maximum there was a slight peaking on the leading edge of a 10KHz squarewave. A 500pf capacitor would get rid of the peaking but in the end decided to leave the 10K resistor.
BDP
What sort of power amp are you using? It's possible that the gain is just too high for your setup. We can proceed from there.
(FWIW, mine was dead quiet when used with a tube amp having a gain of 6 (15 dB) and speakers having about 93dB/2.83V sensitivity)
(FWIW, mine was dead quiet when used with a tube amp having a gain of 6 (15 dB) and speakers having about 93dB/2.83V sensitivity)
I have a Bi-Amped setup with F3's through a MOX active X-over. Not much gain.
I didn't mount the heater ceramic disc capacitors C106, 107 at the socket pins. Could this be my problem? It will be the first change I make.
Thanks for the reply
BDP
I didn't mount the heater ceramic disc capacitors C106, 107 at the socket pins. Could this be my problem? It will be the first change I make.
Thanks for the reply
BDP
It can't hurt. I'd also double check the the FETs are all OK (they can get damaged and go noisy but still work after a fashion) and that you don't have a noisy (relatively) 6SN7.
The hiss is the same in both channels. You can start to hear it at about a meter away. The FETs are both right at 8ma. The boards are from Jackinnj, which came with the FETs already setup.
So it sounds like I should be able to reduce the hiss?
So it sounds like I should be able to reduce the hiss?
I'm sure you can. One other thing to check is the regulator- do you have a scope? If so, connect it to the reg output with a capacitor (0u1 will do just fine- value not critical) and see what the output noise is. The fact that the noise is the same on both channels potentially points in that direction.
I don't have a "hiss" issue on mine.
You can often knock down the noise of an LM317 regulator with some significant bypass on the Adjust pin -- and remember that it is significantly elevated above ground. I am just lifting a page from the "Last PAS" power supply of many decades ago in which the authors used 470n polypropylene in parallel with 330uF -- both probably rated 400VDC.
You can often knock down the noise of an LM317 regulator with some significant bypass on the Adjust pin -- and remember that it is significantly elevated above ground. I am just lifting a page from the "Last PAS" power supply of many decades ago in which the authors used 470n polypropylene in parallel with 330uF -- both probably rated 400VDC.
No significant noise on the regulated output. A Fluke meter showed 3 to 4 mV and the scope was between 15 and 20 mV peak-peak.
Yes, 47uF. I have extra zeners so I will try that ,then I have to order a regulator.
I can give that a try.
Even though it has a slight hiss it didn't prevent me from some listening🙂
Make sure that if you bypass the adjustment pin, you put safety diodes between adjust and out and between out and in.
I bypassed the adjust pin and the noise went down to 100uV RMS and my speakers are dead quiet. I used what I had on hand which was 5uf PP.
Thanks for the help and the comparison measurements.
BDP
Thanks for the help and the comparison measurements.
BDP
Nice work. much MUCH nicer than mine. Mine is still living on a piece of plexi held together with wire ties and hot glue. Singing like an angel none the less 🙂
Can we get a pic of the front to see what you have done there?
Can we get a pic of the front to see what you have done there?
The nice thing about the window is you get a view of the glowing parts inside.
Do you see the driver next to it. I just recieved my Sonido SFR200A and I ordered a couple pairs extra to distribute.
The part that surprised me about the ImPasse is not the midrange because I expected that, but the highs which are defined and delicate. The brushes on the cymbals are wonderful.
Do you see the driver next to it. I just recieved my Sonido SFR200A and I ordered a couple pairs extra to distribute.
The part that surprised me about the ImPasse is not the midrange because I expected that, but the highs which are defined and delicate. The brushes on the cymbals are wonderful.
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BDP said:
No, that's pretty fancy by my standards. Nice!
I guess you're using this to drive an F4 amp, as that's what SY designed it for?
