USSPA
yes it is a Kozmo mainly because I wanted an R2R volume with remote control and display of source and volume. I had already installed an Ebay Chinese kit to one of my friend but got many problems (high pitch sound, changed volume by itself) to solve....
My 2 cents....:
Each preamp attenuator has its own pros and cons. For the R2R the small con is the mechanical clicks that can be heard when relays change state while volume is low.
For LDR the distorsion is higher at low volume but seems to not affect the overall sound results based on my friend preamp that I have heard.
I already had a muse volume but did not like the sound for an undetermined reason. Maybe other muse implementation are better.
For the simple passive log pot you must have short length of wire to the preamp or amp circuit and pot quality is important.
You also have TVC but I have never tried it so far.
Attenuation in the digital domain is possible but must be bit perfect. Even then I heard clicks when changing the volume...
Fab
yes it is a Kozmo mainly because I wanted an R2R volume with remote control and display of source and volume. I had already installed an Ebay Chinese kit to one of my friend but got many problems (high pitch sound, changed volume by itself) to solve....
My 2 cents....:
Each preamp attenuator has its own pros and cons. For the R2R the small con is the mechanical clicks that can be heard when relays change state while volume is low.
For LDR the distorsion is higher at low volume but seems to not affect the overall sound results based on my friend preamp that I have heard.
I already had a muse volume but did not like the sound for an undetermined reason. Maybe other muse implementation are better.
For the simple passive log pot you must have short length of wire to the preamp or amp circuit and pot quality is important.
You also have TVC but I have never tried it so far.
Attenuation in the digital domain is possible but must be bit perfect. Even then I heard clicks when changing the volume...
Fab
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Hello all,
Thanks to all the members ( tomtest and others) for acknowledging my contribution for the success of your builds (with regard to psu pcb supply and now USSPA). I havent been visiting this thread very often due to some apparent reason.
nevertheless, i do acknowledge your appreciation for my little contribution and rest assured, I will keep on contributing to this forum as a whole in some way or other.
regards
prasi
To Fab;
I have been getting some enquiries that if I can supply pcb for USSPA. I cant!.
I kindly request you to take it up on a bigger scale in GB thread and satisfy the hunger of DIYers (if its possible for you).
I am sure , along with USSA amp combined with USSPA, it will become the best diy effort that anyone can possibly build. All the best!
Thanks to all the members ( tomtest and others) for acknowledging my contribution for the success of your builds (with regard to psu pcb supply and now USSPA). I havent been visiting this thread very often due to some apparent reason.
nevertheless, i do acknowledge your appreciation for my little contribution and rest assured, I will keep on contributing to this forum as a whole in some way or other.
regards
prasi
To Fab;
I have been getting some enquiries that if I can supply pcb for USSPA. I cant!.
I kindly request you to take it up on a bigger scale in GB thread and satisfy the hunger of DIYers (if its possible for you).
I am sure , along with USSA amp combined with USSPA, it will become the best diy effort that anyone can possibly build. All the best!
Hi Prasi
I can surely authorize you to do group buy of the USSPA pcbs if you want to do it. I do not have much time these days for that ....a lot of activities in my job... just contact me through personal message or email to discuss details before doing so.
In the mean time I still have a few remaining pcbs of USSPA.
Fab
I can surely authorize you to do group buy of the USSPA pcbs if you want to do it. I do not have much time these days for that ....a lot of activities in my job... just contact me through personal message or email to discuss details before doing so.
In the mean time I still have a few remaining pcbs of USSPA.
Fab
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USSPA
Hi Fab, I do have a perfect matched 8ma K170/J74 quad. Would such perfect matched pairs would be best for the Preamp or would a slight mismatch be preferred? If yes, how big should the mismatch be?
If it is best, how would you start with the H2 (R19/R20) adjustment? First R19, or better R20?
Cheers
Ernst
Hi Fab, I do have a perfect matched 8ma K170/J74 quad. Would such perfect matched pairs would be best for the Preamp or would a slight mismatch be preferred? If yes, how big should the mismatch be?
If it is best, how would you start with the H2 (R19/R20) adjustment? First R19, or better R20?
Cheers
Ernst
USSPA
Hi Ernst
Is 8ma IDSS value or ID value with 22 ohms as RSource like in the USSPA?
Even if IDSS or ID operating point is matched, the transconductance of the 2SJ74 is lower than 2SK170 so unbalance will occur at a certain extend. There should already be H2 present but you need a thd analyser to confirm that.
In fact, the goal of the R19/R20 adjustment is more to reduce H2 - if required....In general, reducing R20 value will lower H2 and R19 reduction will do the opposite. However, going to low value on either side can do the reverse...this is tricky because you will not see a real effect until going close to the point it reverses the effect. From limited experience you can start with 2k ohms for either R19/R20 and go lower if needed.
From trials with my USSA3 amp having a pot for that purpose I can not say that I prefer sound with much high level of H2 but it is only my personal preference. ..
Fab
Hi Ernst
Is 8ma IDSS value or ID value with 22 ohms as RSource like in the USSPA?
Even if IDSS or ID operating point is matched, the transconductance of the 2SJ74 is lower than 2SK170 so unbalance will occur at a certain extend. There should already be H2 present but you need a thd analyser to confirm that.
In fact, the goal of the R19/R20 adjustment is more to reduce H2 - if required....In general, reducing R20 value will lower H2 and R19 reduction will do the opposite. However, going to low value on either side can do the reverse...this is tricky because you will not see a real effect until going close to the point it reverses the effect. From limited experience you can start with 2k ohms for either R19/R20 and go lower if needed.
From trials with my USSA3 amp having a pot for that purpose I can not say that I prefer sound with much high level of H2 but it is only my personal preference. ..
Fab
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Good morning Fab, 8mA is IDSS. Thank you! I remember some readings from member EUVL. He recommended some slightly different IDSS plus additional resistance on the j74 side. Seems that I should look for that.
Fab, yesterday I tried to go a confirmation run with the USSA amp in order to have a stable ID. I saw that I don't have a stable power ground 0V if I don't keep power ground and ground connected.
Since there are two different grounds, which are connected by a resistor, I guess, I should not connect them in the finished amp, should I?
Ernst
Fab, yesterday I tried to go a confirmation run with the USSA amp in order to have a stable ID. I saw that I don't have a stable power ground 0V if I don't keep power ground and ground connected.
Since there are two different grounds, which are connected by a resistor, I guess, I should not connect them in the finished amp, should I?
Ernst
I mounted the USSPA with jfet in grade V because I did not have them in BL rank, I have a power supply in +/- 12V, I made adjustments just for my tests and I must say that I I am quite surprised by the quality of this project.
Personally I am not sure that you have to go to eliminate absolutely any H2 if you do not have specific material and if your project sounds good.
When all my elements will be in place in the box I will seek the most precise settings possible and I will see for the H2 but I can say that currently with the starting values of the manual is excellent.
Fab can tell us what he thinks about this H2 and it is essential to eliminate as much as possible.
Personally I am not sure that you have to go to eliminate absolutely any H2 if you do not have specific material and if your project sounds good.
When all my elements will be in place in the box I will seek the most precise settings possible and I will see for the H2 but I can say that currently with the starting values of the manual is excellent.
Fab can tell us what he thinks about this H2 and it is essential to eliminate as much as possible.
While all things considered in my very own opinion some H2 seems suitable (but that goes together with level, other Hs, soundfloor etc.) it is interesting to note that some trusty builders may want to eliminate H2.. while others tend to play with it, increasing or even reversing it à la Pass...
Who knows what sounds better, and in what combination... comparing the Korg, this pre, a passive LDR... and a LDR fitted as "volume adjuster" inside a Korg or inside this pre will be for sure a very interesting project to help finding your perfect combo. Sometimes less is more...
Very interesting thread
Claude
Who knows what sounds better, and in what combination... comparing the Korg, this pre, a passive LDR... and a LDR fitted as "volume adjuster" inside a Korg or inside this pre will be for sure a very interesting project to help finding your perfect combo. Sometimes less is more...
Very interesting thread
Claude
Coupled with the "Arduino based ldr volume source selection controller" I get something really good and as I said above without any particular research on settings.
For power supply the Salas UltraBIB has been really effective compared to a serial model, the transformer is an old ILP very famous for the audio that dragged in my drawers for a good thirty years.
I still have no work to finalize this project but it is worth it.
For power supply the Salas UltraBIB has been really effective compared to a serial model, the transformer is an old ILP very famous for the audio that dragged in my drawers for a good thirty years.
I still have no work to finalize this project but it is worth it.
Attachments
Hi Ernst
I once tried the « EUVL approach « for jfet as input but has not noticed a special sound difference. Also not so easy to “match” the so “complementary” jfet pair...
For the USSA amp, yes you have to connect both ground to PSU. See sketch below.
Fab
Attachments
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In fact, my serial power supply works very well and is very quiet and is a good choice for the USSPA but the problem was that I did not have sufficient voltage transformer and VA for serious operation and I did not want to invest in this component.
For the UltraBIB the operation is different and the transformer that I owned is perfect for her.
I confirm that listening to the difference seemed flagrant but it can be as suggestive.
For the UltraBIB the operation is different and the transformer that I owned is perfect for her.
I confirm that listening to the difference seemed flagrant but it can be as suggestive.
