You have an amazing ability to innovate simple and practical circuits of improved performance.You could think of it as a Schade, but with high power supply rejection and
lower DC current.
It has been a couple months since you implemented this CCS, so do you have any updates regarding how the amp sounds with SE bias added? Have you tried increasing the amount of bias beyond the 60mA you quoted at the time?
My experiments have been with CCS of about 300mA, but I am still experimenting to better understand the role of the CCS in the circuit. Hopefully I will have something to report at a later time.
I have now after some month’s opinion about the Pass XA 60.8 and now also have also purchased the Pass XP 20. I had some troubles at begin with the sound of the new units compared to my Aleph P Pre and the DIY Aleph X 60W mono`s.
In compare it to my old system at first the bloom in midrange was gone. That was for me a very big disappointment at first, because I hear different thinks during the auditions at the shop with XP 10 and my XA 60.8 then my old Aleph P and new 60.8.
After 2 months of investigating why my new AMP was so different I have purchased the Pass XP 20 Preamp to see it had the effect in the better way. It was better space allocation but not the midrange bloom why I loved my Pass gear.
Then I realized that I had made some changes in my speakers before I bought XA 60.8. After the change reversed the sound was many times better but not the way I was familiar with from Pass. No charms from the Midds and Highs.
Then after someday ( one week ago) I realized that I switched my DIY XLR cables based on Klotz 5000 series to Mogami`s ( not sure what type ). So I changed it back 4 days ago. And , and , and my BLOOM was back !!!! Love was again sparkling from the AMP`s.
So, after some cables switch XLRs from Mogami to Klotz 5000 series ( I know very cheap ones
) the new set of mine is sublime !!! So everything I was worried about the sound I now for 100% gone. I`m now very pleased with the reality ( wat I was first looking for in the new set ) , the bloom, and space the new amp in combination with the Pre has to offer. Really the new .8 series ware the combination of typical Pass sound with the Spicy pinpoint reality with much wider stage as bonus !!
Now I can add 6K to upgrade from 60.8 to 100.8 , I do not need more power just a little more bass.
And my dealer and according the forums the 100.8 will just deliver that plus little warmer sound. Is there somebody familiar with those two AMP`s and the sound difference?
Can someone axplane the response from Pass Labs: sound is little fuller ( whatever that means
???? ) according to the response from Pass Labs:a The XA100.8 is a little fuller sound than the XA60.8 but the difference is small relative to other equipment. All the Point 8 class A amp have a similar sonic signature but all are slightly different because of the differences in rail voltage, bias current and no of output devices.tle
Last edited:
There is possibly a better solution. Keep the 60.8 and purchase some Zu Audio speakers or other decent quality speakers of similar efficiency.
Some testing results
Hi, I've been watching this forum for many months & trying myself build something like XA.8 amplifier. After months of simulating different circuits, i've got interesting results. Look at these simulations at 1W, 10W, 100W, on 4 & 8 ohm load. Circuit is assymetric power end with base current of 300mA per MOSFET (7/6; 6/7 MOSFETS) with two high precision CCS of 300mA replacing missing N & P - channel MOSFETS. Used UGS circuit for simulation is the secret (maybe patented), but I can reveal that is general a little simpler than that posted in #354 & has only two feedbacks one local with high freq comp. & the global one. I'm interested in your opinion. Here comes simulations:
Hi, I've been watching this forum for many months & trying myself build something like XA.8 amplifier. After months of simulating different circuits, i've got interesting results. Look at these simulations at 1W, 10W, 100W, on 4 & 8 ohm load. Circuit is assymetric power end with base current of 300mA per MOSFET (7/6; 6/7 MOSFETS) with two high precision CCS of 300mA replacing missing N & P - channel MOSFETS. Used UGS circuit for simulation is the secret (maybe patented), but I can reveal that is general a little simpler than that posted in #354 & has only two feedbacks one local with high freq comp. & the global one. I'm interested in your opinion. Here comes simulations:
Attachments
Solution of everything?
Hi again,
I think I found the secret of good sounding XA line.
So look at the first simulation - "symmetrical" asymmetric 4/5; 5/4 MOSFETS like XA30.8 at 1W on 8ohm output with no CCS at all - dominant 2nd harmonic. On the next pictures until 5th simulation you can see the same circuit with increasing CCS current. As you can see 3rd harmonic is totaly independent of CCS (depends only of global/local feedback) but a miracle is of 2nd one. At 413 mA per branch 2nd harmonic is getting strictly parallel to 3rd by a distance of about 8dB. This distance is reducing along with the increase in the output power, but stays parallel.
So, can we increase/decrease distance between the harmonics? The answer is yes !!! Look at simulation 6th & 7th. I've throw away next MOSFETS so we get "symmetrical" asymmetric 3/5; 5/3 MOSFETS at the same output conditions as above. 6th without CCS - as previously dominant 2nd harmonic but at 7th throwing away MOSFETS & increasing the CCS current by factor of 2 leads again to parallel 2nd & 3rd harmonic with distance between them of about 13dB !!! Moreover this parallelism is preserved with increasing in the power output - sim. 8th. Think, this little amplifier can work at 10W like SE !!!
Conclusions:
1. 3rd harmonic only depends of bandwith / feedback balance,
2. 2nd harmonic is dependent of deep of "symmetrical" asymmetry, higher asymmetry in N/P channel MOSFETS leads to bigger 2nd harmonic (adwerse effect is bigger THD of course)
3. CCS can modulate parallelism of 2nd & 3rd harmonics. Decreasing MOSFET count, needs same increasing of Iccs. So missing one MOSFET per branch I=Iccs, missing two -> I=2xIccs, three I=3xIccs etc. Throwing away all lower/upper MOSFETS in the branch and relatively multiplying Iccs leads to Xs amplifier?
4. Getting 2nd & 3rd harmonics parallel probably leads to proportional delay of frequencies and maybe this is the miracle of good sounding amplifiers.
Uff, so should I get a Nobel price? Is it patended?
The saddest thing, is that I've never heard original XA... amplifier
Hi again,
I think I found the secret of good sounding XA line.
So look at the first simulation - "symmetrical" asymmetric 4/5; 5/4 MOSFETS like XA30.8 at 1W on 8ohm output with no CCS at all - dominant 2nd harmonic. On the next pictures until 5th simulation you can see the same circuit with increasing CCS current. As you can see 3rd harmonic is totaly independent of CCS (depends only of global/local feedback) but a miracle is of 2nd one. At 413 mA per branch 2nd harmonic is getting strictly parallel to 3rd by a distance of about 8dB. This distance is reducing along with the increase in the output power, but stays parallel.
So, can we increase/decrease distance between the harmonics? The answer is yes !!! Look at simulation 6th & 7th. I've throw away next MOSFETS so we get "symmetrical" asymmetric 3/5; 5/3 MOSFETS at the same output conditions as above. 6th without CCS - as previously dominant 2nd harmonic but at 7th throwing away MOSFETS & increasing the CCS current by factor of 2 leads again to parallel 2nd & 3rd harmonic with distance between them of about 13dB !!! Moreover this parallelism is preserved with increasing in the power output - sim. 8th. Think, this little amplifier can work at 10W like SE !!!
Conclusions:
1. 3rd harmonic only depends of bandwith / feedback balance,
2. 2nd harmonic is dependent of deep of "symmetrical" asymmetry, higher asymmetry in N/P channel MOSFETS leads to bigger 2nd harmonic (adwerse effect is bigger THD of course)
3. CCS can modulate parallelism of 2nd & 3rd harmonics. Decreasing MOSFET count, needs same increasing of Iccs. So missing one MOSFET per branch I=Iccs, missing two -> I=2xIccs, three I=3xIccs etc. Throwing away all lower/upper MOSFETS in the branch and relatively multiplying Iccs leads to Xs amplifier?
4. Getting 2nd & 3rd harmonics parallel probably leads to proportional delay of frequencies and maybe this is the miracle of good sounding amplifiers.
Uff, so should I get a Nobel price? Is it patended?
The saddest thing, is that I've never heard original XA... amplifier
Attachments
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.