F3 mono blocks

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Member
Joined 2009
Paid Member
You should really look for a sound card solution to measure distortion.... No money!

Look if the sound card does 24bit and 48KHz.....

Use ARTA for windows

If you are Mac user use a thirty day demo of Electroacoustic toolbox....

To have prober wiring from amp to sound card PM me.....

More fun ....... And I am afraid nobody will know much more than Nelson, ZM and all the others said here.....
 
Wow

Thanks everyone for the tremendous response!

Nelson,
Thank you. Yes I went through the Idss exercise. The jfets are both 1.027 Vgs and I am currently using a 1.5ohm resistor for R3 (ZV9 schematic)
I am embarrassed to say that these jfets are from the original GRollins group buy :eek: Wow, I'm slow... The lot code from the jfets are all 0540G. I imagine that there are a lot of people with this same lot code jfet in functioning amps. FYI, all of my IRFP244 devices that I am using have a Vgs of approximately 4.44V

Zen Mod and Dzius both suggest that increasing bias should improve things, so I guess it won't hurt to change R8 (F3 schematic) back to 1ohm (from 2ohm - F3 schematic) to increase the bias to 2A and see what happens to the voltage across the jfet and the gain. I'll report back tomorrow and let you know what happens.

Generg,
I will send you a PM about using ARTA to measure distortion. I have actually been looking at this since I have been thinking about an active crossover to use with these new F3's and my Aleph-X. If I can use it to help with this then that would be great!:D
 
Updated voltages at 2A bias current

I increased the bias current to 2A and let the amp warm up for several hours. I have attached the schematic with the new voltages. Interestingly, the jfet now has about 2.6v across it. What a big difference a little more bias current makes. The hottest spot on my heat sink is 125F directly underneath Q3. Overall, the heat sinks are about 100F, but my shop is a little cooler than my living room will be.

JS-F3Schematicat2A_zpsf7f13a93.jpg


I was able to increase the gain to 14.5db within the range of P2 :)
I put dip switches on this board for both feedback and the Aleph current source so I can play around with turning those on and off. This should come in handy for setting the ACS.
With a 1Vpp sine wave input, I measure 2.65Vpp output with the ACS off (8.5db). Just to confirm, I should adjust P2 to give 5.3Vpp at 1Vpp input (14.5db) to achieve 50% gain via the ACS? Or to 4.3Vpp to achieve 12.75db (commercial F3)?

I will continue to try to try to find a way to measure the distortion at some point to do some final adjustments. And a lot of listening :cool:

Now on to the next issue, the square wave response...
On the scope the bottom trace is the input at 0.5v/d and the top trace is the output across an 8ohm resistor at 2.0v/d.
The first image is at 1kHz and the second image is at 10kHz

Anyone care to guess what is going on or what I should look at? I tried a 50ohm resistor across the amp input and without - no significant change.

1kHzsquarewave-F3_zps56b72f3c.jpg

10kHzsquarewave-F3_zps5ddb3236.jpg
 
Well, I fiddled with C9 and then removed it completely, but it didn't improve the square wave response.

I tested a different amp I have to be sure something wasn't wrong with my test setup and it worked fine at both 1kHz & 10kHz (actually it had a slight ringing on the leading edge).

I tested the amp with the feedback dip switch turned off completely. The bottom trace is the sine wave input at 0.5v/d and the top trace is the output across an 8ohm resistor at 5.0v/d (clipping with signal generator at minimum output)

I have C7 (F3 schematic) in circuit, but I don't currently have R22 or LED1 in circuit. Could this cause this type of issue with the square wave?

1kHzsinewavewithoutfeedback_zps3f0f0d13.jpg
 
Sweet sucess

After quite a bit of diagnosis, I finally found my wiring mistake that I made converting from the ZV9 to the F3. I am basically back to the original ZV9 (PD/Veteran boards). :eek: I still have the dip switches to play with turning off the ACS & feedback if I decide to.

wiringmistake_zps9e47ad9b.jpg


Once I got everything back together and adjusted (12.75dB gain), I got much better square wave results at 1kHz & 10kHz with 20pf cap. With a 5pf cap it still has some overshoot. I will fine tune this a little bit more...

1kHzsquarewave-ZV9_zps2b76c8f6.jpg

10kHzsquarewave-ZV9_zpse77e3bd3.jpg


When the amp was fully warmed up with the DC voltage at the output cap set to half of the Q3 drain voltage (41.4v/20.7v), I noticed that the sine wave clipped much sooner on one side).

I adjusted the output DC voltage until the output clipped at the top and bottom of the wave at the same time. This ended up being 23.85Vdc at the output with the drain voltage of Q3 at 41.4Vdc

The image below is 33v p-p with a 6.5 ohm load (41.4v supply voltage)

This is quite a bit away from 1/2 the supply voltage. Is this correct? or should I adjust it back to 20.7Vdc? Since I am trying to learn as I go, any additional feedback would be appreciated.

For reference, the voltage at the drain of the jfet is 3.56 & the source voltage is 1.13v with the 23.85Vdc at the output.

ZV9symetricclipping_zpsbb6c550d.jpg


I will continue to try to find a way to measure distortion to dial everything in...
 
Hi together,
Could i get help from you.
I made boards to build the ZV9 from Nelson Pass. After mounting all parts I detected that the F3 circuit has only a little difference in the circuit.
So I changed the circuit to F3.
My problem is, the voltage about Q2 is much more, about 30V, than the necessary 21V.
I build two boards. Always the same fault.
Have someone a tipp?
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.