more of good engineering practice ....... 300k + 100K pot for biasing net
1k gate stoppers I understand it is too high, but for biasing net why 300k is too high? It isn't in the signal path. What is the highest value you recommend? And reasonable value of coupling cap? My dac is rated 2vrms on a 10k load
Thick film resistors are cermet (ceramic and OXIDE), not metal film. The same confusion was perpetrated in that other thread as well. Thin film = metal film, thick film != metal film. Now you are telling people that a metal film resistor caused your H3 when it was a thick film - please do not perpetuate misunderstandings.
I suppose my underlying question is whether gate stoppers for mosfets should be non-inductive.
ray
Yes, sorry about that but I meant metal oxide thick film. I have not tested metal thin film SMT but bet that it would be fine, which is why I said thick film resistors.
Thin and thick film >> Resistor Guide
for cmpression driver 600Hz upwards, better bulb or inductor?
I con't care about voltage swing or efficiency as I need only 1W of output power
I can not tell you for sure because :
- My taste and "sound better" definition could be similar, but could be totally different than yours.
- All compression drivers are not built the same way.
- All inductors are not built the same way.
- Mr. Pass explained about some amount and negative phase of second harmonic distortion has a signature he preferred. For some people, but not all, a bit higher distortion (not too much) of an amplifier actually sound better. 6L6 has a youtube video here.
- The late Eduardo de Lima of Audiopax published a white paper claiming that when single ended amplifier (like the MoFo) is used with a widebander (like your compression driver) connected at a certain polarity, measured distortion at listener position is lower compared to a very low distortion amp. But a lot worse distortion when speaker polarity is reversed.
A lightbulb does not cost a fortune, why don't you try it first. You can always try the inductor later if you don't like it. In my experience, light bulb load gives more "air" while inductor gives more "slam" with "a little subdued high". But I tried with nemesis type circuit and my diy inductor is made with non oriented core, not a real good quality one. However, nobody can guarantee that a certain inductor with better specification or more expensive will sound better to me on my setup in my listening room. Our Mr. MR tried a lot more options compared to my very limited experience, perhaps he could chip in his experience.
In short, "better" is a very complicated issue. Simply try it and have a good diy journey, it's a fun journey for all of us.
Nothing wrong with lightbulbs, except that you may need high wattage ones that are getting a bit more diffucult to obtain (leds everywhere), and/or you may find that a higher psu supply is needed, since for a proper headroom, you will want to drop around 2/3rds of the supply voltage through the lightbulb, and 1/3rd across the mosfet. With 19 v supply, it won't be enough for anything useful, but you can try. That also means readjusting the voltages on drain/source...
See what a DeLite-MoFo looks like
See what a DeLite-MoFo looks like
Attachments
I have the same light bulbs, 1000W 220v
will try with 19v PSU, 12V on the bulb, 7V on the IFRP, it will bias around 0.8A
And thanks to the trick of reversing polarity!
It means that the distortion will change if I output referenced to the + or the - ?
Parallel to the bulb will sound differently than parallel to the IRFP?
my compression driver is JBL 2446
for the bass (2226) I plan to use F4 buffer, for bedder damping factor
Directly feed from DAC, no preamp, 2.2V RMS is plenty for high sensitivity speakers.
Next I will replace bulb by 2.5mH air core inductor and compare
will try with 19v PSU, 12V on the bulb, 7V on the IFRP, it will bias around 0.8A
And thanks to the trick of reversing polarity!
It means that the distortion will change if I output referenced to the + or the - ?
Parallel to the bulb will sound differently than parallel to the IRFP?
my compression driver is JBL 2446
for the bass (2226) I plan to use F4 buffer, for bedder damping factor
Directly feed from DAC, no preamp, 2.2V RMS is plenty for high sensitivity speakers.
Next I will replace bulb by 2.5mH air core inductor and compare
Yes, but to a lesser degree.
What I meant was simply reversing speaker cable connection, connect the - polarity speaker lead to the point previously connected to the + polarity lead, and + polarity speaker lead to the point previously connected to the - polarity lead. This way, phase of 2H amplifier generated distortion will shift 180 deg relative to the speaker's.
Be careful, you cannot just swap the lightbulbs and the inductor. You have to adjust the proper Bias for each of them, since there should be much lower voltage across the inductor than the lightbulb...
Almost finished with my Big MoFo build, still have a few details to button up. This is probably the quietest amplifier I own!! Absolutely no noise of any kind with my ear pressed up to a very efficient set of Klipsch speakers.
Thanks Michael Rothatcher!!
Thanks Michael Rothatcher!!
Attachments
Quick question on best practices for grounding (an apologies but I also posted in the PSU section, but realized that this might be a better place to get a response as so many comment on lack of noise on this amp.
if using one or more laptop bricks that are floating +/- rails, how best to address earth connections to minimize earth loops etc?
connect earth via resistor and parallel cap to nearest appropriate rail?
run an earth back to the wall socket?
sorry to divert...
if using one or more laptop bricks that are floating +/- rails, how best to address earth connections to minimize earth loops etc?
connect earth via resistor and parallel cap to nearest appropriate rail?
run an earth back to the wall socket?
sorry to divert...