line preamp
Thanks, Salas and Merlin.
I had seen a post in the F5 power amplifier thread which states the the F5 does not need a preamp, depending on the input. Is the problem that there really isn't a defined standard output range from phono stage, line stage power stage, etc.?
I just did a calculation, and it looks like the F5 needs 2.43Vrms input for 25W output into 8 Ohms. Perhaps the F5 does not need a preamp when using a high output DAC or CD player.
At any rate I am looking at building the Pumpkin preamp, because I do like some volume occasionally.
Also, Thanks, Salas for pointing out the hyperlink in thread number 1. I had missed this before. I'll post my FET values soon, so that I can get started.
Andy
Thanks, Salas and Merlin.
I had seen a post in the F5 power amplifier thread which states the the F5 does not need a preamp, depending on the input. Is the problem that there really isn't a defined standard output range from phono stage, line stage power stage, etc.?
I just did a calculation, and it looks like the F5 needs 2.43Vrms input for 25W output into 8 Ohms. Perhaps the F5 does not need a preamp when using a high output DAC or CD player.
At any rate I am looking at building the Pumpkin preamp, because I do like some volume occasionally.
Also, Thanks, Salas for pointing out the hyperlink in thread number 1. I had missed this before. I'll post my FET values soon, so that I can get started.
Andy
60dB to 63dB is what is used by majority for Low MC and keeping hiss and internal transient over load at bay. That leads to 250-350mV RMS from a 0.25mV cart. Records do have modulations to track near enough some CD recordings for same volume position and ~300mV 0dB phono, mind you. Especially with 45RPM wide dynamic records. Its either you will make the pre-pre and HOMC combo from the PDF for 63dB but one more stage, or I can recommend you a quad K170 60dB gain one. With the Pumpkin it will suffice.
May I ask why balanced phono pres would only be interesting to moving-coil cartridge users? A moving-magnet cart still has a coil to generate the signal... can this not be wired in balanced configuration with all of the CMRR benefits that come with?
MM users also can do balanced, as MC all depends rest of stuf if it's balanced or not.
Hi all,
I finally had the parts arrive to enable me to start my phono. I'm using 60dB gain version with 45V supply and 8.5-8.7mA Jfets.
I've tried initially with a 36V supply from a Salas shunt, the LEDs initially light up but then dim and go off after a couple of seconds. I get no sound/hum and nothing is getting hot. Any ideas please?
I finally had the parts arrive to enable me to start my phono. I'm using 60dB gain version with 45V supply and 8.5-8.7mA Jfets.
I've tried initially with a 36V supply from a Salas shunt, the LEDs initially light up but then dim and go off after a couple of seconds. I get no sound/hum and nothing is getting hot. Any ideas please?
Attachments
That circuit says 45V. Why work OK with 37V. Provide 45V. http://www.diyaudio.com/forums/powe...-voltage-shunt-regulator-420.html#post2678743
While you are at it, make R7 ~1.5k (must), R6 33R (must), C3 15nF (flatter highs), and C4 47n if you got big speakers to save some rumble.
Yes it does say 45V but I thought I'd start on the low side to check for overheating parts or catastrophic failures. Thanks Salas, I will make the amendments you mention.
Is there anything that looks obviously wrong with what I have built looking at the pictures? I though the best option was to build one channel first, get it working OK and then build the other.
Is there anything that looks obviously wrong with what I have built looking at the pictures? I though the best option was to build one channel first, get it working OK and then build the other.
Its not a power amp or an OpAmp to have a range of rail voltages. If you go as low as you went, the cascode shuts down, the output shuts down, etc.
You did well to start with one channel. Can't say by just looking for connections, especially bcs its a stripes perf. But from looking the components side I have this suspicion that all fets and the cascode transistor may be reversed. Plus I don't see two fatter 1W resistors as noted. Do a recheck.
You did well to start with one channel. Can't say by just looking for connections, especially bcs its a stripes perf. But from looking the components side I have this suspicion that all fets and the cascode transistor may be reversed. Plus I don't see two fatter 1W resistors as noted. Do a recheck.
Attachments
The phono circuit is now getting 45V. It was just the BC550 that was the wrong way, the J-fets were ok. My CCS LED's now light up but I still get no sound or hiss, my LED string measures 6.9V.
I am still waiting for my 1W 3.9k and 8.2k resistors to arrive. Salas, are these tweaks to the circuit that will improve performance or adjustments that could stop it from working?
I am still waiting for my 1W 3.9k and 8.2k resistors to arrive. Salas, are these tweaks to the circuit that will improve performance or adjustments that could stop it from working?