Good morning,
Haveing my USSPA up and running for a couple of hours and I can say, I am very happy with it. My setup is simple, just one Zigma22 PSU; Yesterday I reduced gain by paralleling feedback resistors. Gain is now low enough, and it seems that I have to let it run in again.
Before the change tone was, rich, detailed and smooth, big stage, gentle. After changing the fb res stage has become smaller. Hope it widens again. Gain should be at about 1.6 now.
Thanks a lot!
Cheers, Ernst
Haveing my USSPA up and running for a couple of hours and I can say, I am very happy with it. My setup is simple, just one Zigma22 PSU; Yesterday I reduced gain by paralleling feedback resistors. Gain is now low enough, and it seems that I have to let it run in again.
Before the change tone was, rich, detailed and smooth, big stage, gentle. After changing the fb res stage has become smaller. Hope it widens again. Gain should be at about 1.6 now.
Thanks a lot!
Cheers, Ernst
USSPA
Hi Ernst
I am glad you like the sound ( with the higher gain...)
Interesting your findings...
I have never tried and listen to gain less than about 2.7 for this pre-amp.
This is a low feedback design thus feedback factor (open loop AV/closed loop AV) is more affected by closed loop gain value... it is strange that only sound stage would be different...
Right now I use about 3.5 in the USSPA2 and I like it that way. Changing the gain proportion between the pre-amp and power amp in the whole gain of the system can make a difference on the overall sound character...
You can keep your original preamp gain and increase attenuation at input...
Keep us posted on your findings.
Fab
Hi Ernst
I am glad you like the sound ( with the higher gain...)
Interesting your findings...
I have never tried and listen to gain less than about 2.7 for this pre-amp.
This is a low feedback design thus feedback factor (open loop AV/closed loop AV) is more affected by closed loop gain value... it is strange that only sound stage would be different...
Right now I use about 3.5 in the USSPA2 and I like it that way. Changing the gain proportion between the pre-amp and power amp in the whole gain of the system can make a difference on the overall sound character...
You can keep your original preamp gain and increase attenuation at input...
Keep us posted on your findings.
Fab
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You can keep your original preamp gain and increase attenuation at input...
Keep us posted on your findings.
Fab
Fab, maybe this is what I am doing at a later time in putting a voltage divider in place or maybe a 4:1 trafo ;-)
There might be more differences, but the flatness of the scene is the most obvious for me. Haven't done enough listening for a really qualified writing.
I do have a few preamps, and I like an old and simple tubed one most as well as your USSPA in higher gain setup.
And I want to build the Superbuffer....
In summer, summer is more important, so I am sloooww.
Cheers
Ernst
USSPA
Real gain having the 0.8 correction factor. 100 ohms for each 4 resistors or even 150 ohms (in my latest USSPA2). Overall my actual system has a very satisfactory sound stage (for me) but it may also result from the combination of all parts...
Good if you can manage the gain. Anyway the are often 12db difference between average recording level between albums...
If the Superbuffer is the one from Erno Borbely I would expect it to be surely pretty good. However, there are several pairs of rare jfet to match and even maybe select IDSS range for each stage...
Happy good summer
Fab
Hi Ernst
Real gain having the 0.8 correction factor. 100 ohms for each 4 resistors or even 150 ohms (in my latest USSPA2). Overall my actual system has a very satisfactory sound stage (for me) but it may also result from the combination of all parts...
Good if you can manage the gain. Anyway the are often 12db difference between average recording level between albums...
If the Superbuffer is the one from Erno Borbely I would expect it to be surely pretty good. However, there are several pairs of rare jfet to match and even maybe select IDSS range for each stage...
Happy good summer
Fab
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Hi Do, my USSA-5 was finished. I dismantled PSU these days in order to improve it. I just had 20 V [emoji809][emoji810] and now I am going to have 23.5V per rail. Totally new PSU and I expect a different signature. Was a bit on the bright side.
My USSPA is running in my system with 100R feedback resistors very well with a single Sigma 22. Absolutely low distortion, nice H2 and a tad lower H3. Maybe some day it will get a second PSU. Will see.
Maybe some pics later.
Cheers, Ernst
My USSPA is running in my system with 100R feedback resistors very well with a single Sigma 22. Absolutely low distortion, nice H2 and a tad lower H3. Maybe some day it will get a second PSU. Will see.
Maybe some pics later.
Cheers, Ernst
USSA5 has been my favourite power amp so far, totally happy with its powerful, clean crisp sound delivery. I have ordered a presumably better PSU (SLB) for it.
I hope this new psu can improve the USSA5 to another level, depending on the choice of the transformer sec voltage you choose, mine will ends up having +/- 27 Vdc rails which i think may squeeze out a few more watts.
I hope this new psu can improve the USSA5 to another level, depending on the choice of the transformer sec voltage you choose, mine will ends up having +/- 27 Vdc rails which i think may squeeze out a few more watts.
Sure, wil be happy to share my findings on SLB psu with USSA5.
As for the USSPA, i have collected all the parts but no time to assemble them yet, and since i have not decided on a psu for it, and my YARRA pre modular with custom casing just arrived. i may use the YARRA psu on the USSPA too.
As for the USSPA, i have collected all the parts but no time to assemble them yet, and since i have not decided on a psu for it, and my YARRA pre modular with custom casing just arrived. i may use the YARRA psu on the USSPA too.
USSA-5 Mosfet temperature
Hello Fab, I reworked my USSA-5 as I removed the Cap MX PSU and replaced it by a F7 style mono stereo PSU. The Cap MX lowered the voltage to about 21.5 which I finally thought, might be too low considered that I run the amp at about 1A only. Today I did finetune P1/P2 and found out (again) that one of the mosfets. in the negative side is running hotter on both channels, even at almost 0 mV across the ls terminals. Is this as it should be? Btw, they draw the same current and they are symmetrical on the heat sink, mounted in the same way???
Cheers, Ernst
Hello Fab, I reworked my USSA-5 as I removed the Cap MX PSU and replaced it by a F7 style mono stereo PSU. The Cap MX lowered the voltage to about 21.5 which I finally thought, might be too low considered that I run the amp at about 1A only. Today I did finetune P1/P2 and found out (again) that one of the mosfets. in the negative side is running hotter on both channels, even at almost 0 mV across the ls terminals. Is this as it should be? Btw, they draw the same current and they are symmetrical on the heat sink, mounted in the same way???
Cheers, Ernst
Hi Ernst
I do not understand the 0mv condition you mention.
The mosfet temperature should be similar for all mosfet in same conditions but a difference of 5-7 deg C is not a big deal and quite acceptable. Even 10c difference is not major. Heatsink surface flatness is important and thermal grease can compensate for that to a certain extent. Also you need a sufficient torque on the mounting Screws. The thermistors must be installed very similarly on both positive and negative sides. You can tweak the thermistors position related to mosfet location or distance from heatsink by checking dc offset direction while mosfet temperature rises after power up.
Maybe a picture would help to notice anything special.
Fab
I do not understand the 0mv condition you mention.
The mosfet temperature should be similar for all mosfet in same conditions but a difference of 5-7 deg C is not a big deal and quite acceptable. Even 10c difference is not major. Heatsink surface flatness is important and thermal grease can compensate for that to a certain extent. Also you need a sufficient torque on the mounting Screws. The thermistors must be installed very similarly on both positive and negative sides. You can tweak the thermistors position related to mosfet location or distance from heatsink by checking dc offset direction while mosfet temperature rises after power up.
Maybe a picture would help to notice anything special.
Fab
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Hi Fab, thanks for the reply. I guess the difference is below 10 K. So I don't have to worry.
The 0 mV were in regard the DC at the speaker terminal. I tried and could bring it down below 1 mV, so I have about 0,8 mV under my test conditions after an hour.
All Fets are mounted in the same way, and yes the sink has got the same temp overall.
One fet I can touch permanently with my finger, on the other one it would hurt after a short while. I'm gonna measure it.
Both channels show the same behavior.
Yes, I'll post a shot, as I almost finished it.
Cheers, Ernst .
The 0 mV were in regard the DC at the speaker terminal. I tried and could bring it down below 1 mV, so I have about 0,8 mV under my test conditions after an hour.
All Fets are mounted in the same way, and yes the sink has got the same temp overall.
One fet I can touch permanently with my finger, on the other one it would hurt after a short while. I'm gonna measure it.
Both channels show the same behavior.
Yes, I'll post a shot, as I almost finished it.
Cheers, Ernst .
Hello everyone,
Where is the enthusiasm that you showed in the beginning?
Now i imagine that there are many who build this amplifier.
I am in a vacation and i had enough time to listen to USSA5 amplifier.
I am not good at english to make a review so i purpose to you a score that you can give to this amplifier, like bad-mediocre-
good-very good- excellent
What is your opinion?
filenet- excellent+
Where is the enthusiasm that you showed in the beginning?
Now i imagine that there are many who build this amplifier.
I am in a vacation and i had enough time to listen to USSA5 amplifier.
I am not good at english to make a review so i purpose to you a score that you can give to this amplifier, like bad-mediocre-
good-very good- excellent
What is your opinion?
filenet- excellent+
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