Ok guys I don't post much here but I do a lot of reading and I would like some advice. I have done some preamp builds and various other products and done a lot of mods but this will be my first amp build.
What I have now are a pair of 5k James 50 watt output transformers. I found some nice aluminum cases that are 15.75 inches by 11.6 by 3 inches.
I am looking at 3 different amps and would like to know your opinions.
The first is the Millett Uniamp.
View attachment UNIAMP2_sch.pdf
This amp look fairly easy and I have some 5U4's waiting for a home. Pete said my James would be fine. I like the fact that it has the PCB to work from..
I also like Pete's PP-driver board. I like the fact it has the CCS and uses FET's for loads. I would need to build the power supply but the board does most of the rest. I don't know much about the tubes he uses in this build?
The last one I was considering at this time. That doesn't mean I'm closed to suggestions. It is Allen Wright's PP-2c. I would use Salas SSHV2 regulators if I did this build. This would be a little more work for me.
View attachment PP-2C_map.pdf
I would really like to get your thought and if possible personal experience with these designs. I will be back in the U.S. visiting family in June and I want to gather my supplies when I'm there.
The iron to finish these builds would be more or less the same cost. I contacted James for the Power transformers and Choke. I also contacted K @ K audio for the price of the Lundahl's in case I go with the PP-2. The PP-2 would cost more than the others but that isn't my biggest concern. I really want to build the nicest amps I can.
I will be using the amps with my Vandersteen 2 sig II and Aikido preamp. My room is not very big but I think 25 watts and above would be best. I would appreciate your thoughts.
What I have now are a pair of 5k James 50 watt output transformers. I found some nice aluminum cases that are 15.75 inches by 11.6 by 3 inches.
I am looking at 3 different amps and would like to know your opinions.
The first is the Millett Uniamp.
View attachment UNIAMP2_sch.pdf
This amp look fairly easy and I have some 5U4's waiting for a home. Pete said my James would be fine. I like the fact that it has the PCB to work from..
I also like Pete's PP-driver board. I like the fact it has the CCS and uses FET's for loads. I would need to build the power supply but the board does most of the rest. I don't know much about the tubes he uses in this build?
The last one I was considering at this time. That doesn't mean I'm closed to suggestions. It is Allen Wright's PP-2c. I would use Salas SSHV2 regulators if I did this build. This would be a little more work for me.
View attachment PP-2C_map.pdf
I would really like to get your thought and if possible personal experience with these designs. I will be back in the U.S. visiting family in June and I want to gather my supplies when I'm there.
The iron to finish these builds would be more or less the same cost. I contacted James for the Power transformers and Choke. I also contacted K @ K audio for the price of the Lundahl's in case I go with the PP-2. The PP-2 would cost more than the others but that isn't my biggest concern. I really want to build the nicest amps I can.
I will be using the amps with my Vandersteen 2 sig II and Aikido preamp. My room is not very big but I think 25 watts and above would be best. I would appreciate your thoughts.
Hello,
I had quite a few discussions with Allen before he sadly passed... I have accumulated most of the bits for the PP2 amp. I will be starting soon to build this. Allen was very adamant that this amp if built to exactly his design would be very, very good. I have his pre-amp cookbook too... This is a very entertaining read. One of the sweetest amps I played with was the Puresound A30. I replaced most of the parts in it with much better one's and it was superb. Hardwired it in triode mode. To my ears the imaging was far more stable.
I have all Shinko resistors, Mundorf SGO caps, Mundorf Tubecaps for the build of the PP2. Just waiting for the Transformers now.
Best of luck with your choice.
Regards
J
I had quite a few discussions with Allen before he sadly passed... I have accumulated most of the bits for the PP2 amp. I will be starting soon to build this. Allen was very adamant that this amp if built to exactly his design would be very, very good. I have his pre-amp cookbook too... This is a very entertaining read. One of the sweetest amps I played with was the Puresound A30. I replaced most of the parts in it with much better one's and it was superb. Hardwired it in triode mode. To my ears the imaging was far more stable.
I have all Shinko resistors, Mundorf SGO caps, Mundorf Tubecaps for the build of the PP2. Just waiting for the Transformers now.
Best of luck with your choice.
Regards
J
Nelson the autobias is very is very interesting. Never seen that one before. I think that will be part of the upgrade. I don't want to overwhelm myself on my first amp build.
I haven't seen any builds for the PP-2c yet .
As far as the Uniamp goes. I have a question. Sorry I'm always trying to tweak or improve things. Is there any reason why R9 couldn't be changed to a CCS? Also what about removing R4 and R5 and replacing them with some MOSFETs?
I haven't seen any builds for the PP-2c yet .
As far as the Uniamp goes. I have a question. Sorry I'm always trying to tweak or improve things. Is there any reason why R9 couldn't be changed to a CCS? Also what about removing R4 and R5 and replacing them with some MOSFETs?
I built the PP2C a while ago, using the Salas reg on the input stage and EH 6CA7s. Sounded good. Allen once ended a post with the something like "I want speed and I want definition" which gives you a good idea of the sound. I've recently changed the output tubes to 6B4Gs for even more dynamics. It's a clean, powerful sounding amp.
Hi,
I'm in similar route.
Almost ready with parts to build PP2-C ( I'm convinced that this design is from best PP designs)
So sadly that is not possible to ask directly Mr. Allen Wright for some details. Very, very sadly. Respect to him! Rest In Peace!
I read several times his Preamp Cook book, still have a ton of questions
But from long time ago I have a big affinity for transformer coupling.
I like a lot Linn Olson's designs, Mr. Kevin Carter's front-end design. Exelent!
So I start wounder why not possible to use this topology:
input transformer - diff. cascoded (by Allen Wright) driver - interstage transformer - output diff.stage
(pentode or not, CCSed or not, harmonic equalised or not (by WE), whatever you like)
Yes, I know Mr.Wright, that is against your religion....
Please, forgive me
I'm in similar route.
Almost ready with parts to build PP2-C ( I'm convinced that this design is from best PP designs)
So sadly that is not possible to ask directly Mr. Allen Wright for some details. Very, very sadly. Respect to him! Rest In Peace!
I read several times his Preamp Cook book, still have a ton of questions
But from long time ago I have a big affinity for transformer coupling.
I like a lot Linn Olson's designs, Mr. Kevin Carter's front-end design. Exelent!
So I start wounder why not possible to use this topology:
input transformer - diff. cascoded (by Allen Wright) driver - interstage transformer - output diff.stage
(pentode or not, CCSed or not, harmonic equalised or not (by WE), whatever you like)
Yes, I know Mr.Wright, that is against your religion....
Please, forgive me
Shoog,
for me no doubt that input transformer will make things better.
I have LL1544 and LL1676 and 74 all ready for experimentation.
I will use even with balanced preamp. ( my plan is to build Raven or Parafeed by Mr.Davenport design)
RTP3 by Allen, is excellent design but... "little" complicated for me, by now.
Anyway, main question to decide: possible to make cascoded diff. stage to be transformer loaded.
I read a lot diyaudio, lot of books - old and not so, still no answer.
Nowhere dont see this. May be I try to make things unnecessarily complex?
Who knows...
If this topology works - we will have a project called Wright/Olson driver stage
OK guys, I just trying to get good things from two worlds.
Unfortunately, for me is impossible task то make some simulation.
Must try on breadboard, but want to be prepared... don't be OUCH, right
for me no doubt that input transformer will make things better.
I have LL1544 and LL1676 and 74 all ready for experimentation.
I will use even with balanced preamp. ( my plan is to build Raven or Parafeed by Mr.Davenport design)
RTP3 by Allen, is excellent design but... "little" complicated for me, by now.
Anyway, main question to decide: possible to make cascoded diff. stage to be transformer loaded.
I read a lot diyaudio, lot of books - old and not so, still no answer.
Nowhere dont see this. May be I try to make things unnecessarily complex?
Who knows...
If this topology works - we will have a project called Wright/Olson driver stage
OK guys, I just trying to get good things from two worlds.
Unfortunately, for me is impossible task то make some simulation.
Must try on breadboard, but want to be prepared... don't be OUCH, right
I think it theoretically possible, but probably not worth the effort. The obvious way still requires cap coupling to the IT - which to my mind is just adding complexity without any technical gain.Shoog,
for me no doubt that input transformer will make things better.
I have LL1544 and LL1676 and 74 all ready for experimentation.
I will use even with balanced preamp. ( my plan is to build Raven or Parafeed by Mr.Davenport design)
RTP3 by Allen, is excellent design but... "little" complicated for me, by now.
Anyway, main question to decide: possible to make cascoded diff. stage to be transformer loaded.
I read a lot diyaudio, lot of books - old and not so, still no answer.
Nowhere dont see this. May be I try to make things unnecessarily complex?
Who knows...
If this topology works - we will have a project called Wright/Olson driver stage
OK guys, I just trying to get good things from two worlds.
Unfortunately, for me is impossible task то make some simulation.
Must try on breadboard, but want to be prepared... don't be OUCH, right
Personally I would just stick with the input transformer. If I was going to try anything it would be DC coupled.
Shoog
Yes, with cap and IT may be will work, but this is not so elegant
No sense...
So, if we cannot avoid cap in cascoded diff. stage, stay only with cap.
Bob, sorry for my mini-theme - I don't want mess, just to add more details in big pictures.
Finaly - my judgment and advice:
Go your attention to PP2C, or Kevin Carter designs (more expensive option I think)
What about Output stage: if we use pentode.
I know that with DHT is the best option for driver and output, but for me it is too early
Made a decision
Thanks for the input!
I decided to build the uniamp. I think I will build the PP-2c down the road sometime. I think the uniamp will be easier for my first build.
I'm going to use James iron throughout. Except the input transformer. I got quotes from Sowter for the 3575 $170 shipped to the U.S. or China where I'm living. The other option is Lundahl LL1690 but these are $140 each plus shipping. I have read the input transformer is very important. Anyone have any opinion on these two?
I've ordered these cases. They are 17" *12" *3". They should match the black James transformers.
Thanks for the input!
I decided to build the uniamp. I think I will build the PP-2c down the road sometime. I think the uniamp will be easier for my first build.
I'm going to use James iron throughout. Except the input transformer. I got quotes from Sowter for the 3575 $170 shipped to the U.S. or China where I'm living. The other option is Lundahl LL1690 but these are $140 each plus shipping. I have read the input transformer is very important. Anyone have any opinion on these two?
I've ordered these cases. They are 17" *12" *3". They should match the black James transformers.
Attachments
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We'll I'm finally back to my projects. I had a couple people write and ask me how the amps were doing. I took a contract in Western China and couldn't finish everything. Now it's time to finish.
I found out a few things while doing these builds. I built the first amp and turned it on and everything seemed fine. But the power supply ripple was unacceptable. I hooked up a test speaker and I was getting some motor boating. I pulled the driver first and that was where my problem seem to be. I tried turning the choke and that didn't help.
The James output transformer is positioned horizontally in an encapsulated case. I thought I had it positioned properly but as usually my assumption was wrong. Rotated the output transformer and all is well.
I'm doing a few more test and will check the o scope signal before hooking up my speakers. I'll post some pictures soon. The black aluminum chassis look good. Cutting the holes in the thick aluminum chassis was also a lot of work.
I found out a few things while doing these builds. I built the first amp and turned it on and everything seemed fine. But the power supply ripple was unacceptable. I hooked up a test speaker and I was getting some motor boating. I pulled the driver first and that was where my problem seem to be. I tried turning the choke and that didn't help.
The James output transformer is positioned horizontally in an encapsulated case. I thought I had it positioned properly but as usually my assumption was wrong. Rotated the output transformer and all is well.
I'm doing a few more test and will check the o scope signal before hooking up my speakers. I'll post some pictures soon. The black aluminum chassis look good. Cutting the holes in the thick aluminum chassis was also a lot of work.
Help with this problem
Hi guys, I need a little help. I have been away from home for a year and I've just returned to my project. I thought my problem was fixed but it is not. I've attached the pictures from the scope. When the driver tube is plugged in you can see the AC ridding on the B+. When I pull the driver tube the problem goes away. I thought it was the output transformer.
When I rotated the output transformer it seem to go away. Actually I lifted one of the eyelets for the driver heater. I really don't like heaters on the PCB'S.
I have also rotated the choke and that didn't make any difference. I have not rotated the choke again after I rotated the output transformer.
I strapped a big film cap near the driver B+ and it improves but there is still AC present. Suggestions will be most welcomed. This is my first tube amp build and I'm pretty bummed.
I am thinking this is something to do with my layout or orientation of the transformers?
Hi guys, I need a little help. I have been away from home for a year and I've just returned to my project. I thought my problem was fixed but it is not. I've attached the pictures from the scope. When the driver tube is plugged in you can see the AC ridding on the B+. When I pull the driver tube the problem goes away. I thought it was the output transformer.
When I rotated the output transformer it seem to go away. Actually I lifted one of the eyelets for the driver heater. I really don't like heaters on the PCB'S.
I have also rotated the choke and that didn't make any difference. I have not rotated the choke again after I rotated the output transformer.
I strapped a big film cap near the driver B+ and it improves but there is still AC present. Suggestions will be most welcomed. This is my first tube amp build and I'm pretty bummed.
I am thinking this is something to do with my layout or orientation of the transformers?
Attachments
Wow, 400mS/division... this is very low frequency motorboating!
Change R11 to 4.7k, and R21 to 1k. That should help a lot.
Also, depending on your output tubes, you may very well need to reduce the value of R7 and R18. I found with some new KT88's this needed to go as low as 47k to stabilize the bias, as the tubes pulled a little grid current. This can contribute to the motorboating.
Pete
Change R11 to 4.7k, and R21 to 1k. That should help a lot.
Also, depending on your output tubes, you may very well need to reduce the value of R7 and R18. I found with some new KT88's this needed to go as low as 47k to stabilize the bias, as the tubes pulled a little grid current. This can contribute to the motorboating.
Pete
Thanks Pete,
I will pick up some resistors tomorrow. I've tried a couple different sets of KT88 and I have some EL34 in there now. Not much difference.
I thought about changing R11 and R21 but I thought it was my set-up or layout. I haven't read many issues with people building this amp. Is this have anything to do with the James iron I am using?
I'll make the changes and then post.
I will pick up some resistors tomorrow. I've tried a couple different sets of KT88 and I have some EL34 in there now. Not much difference.
I thought about changing R11 and R21 but I thought it was my set-up or layout. I haven't read many issues with people building this amp. Is this have anything to do with the James iron I am using?
I'll make the changes and then post.
Replaced R11 and R21 to values you suggested. Motorboating stopped and the amp is stable. I haven't yet tried to decrease the resistance yet to find out where it becomes unstable.
I put a 1k square wave through it and there is ringing. The square wave looks pretty bad.
I believe this is where C14 and C15 come in? What are suggested values to start with on C14 and C15?
I added the schematic and wiring diagrams
View attachment UNIAMP2_sch.pdf
Thanks,
Bob
I put a 1k square wave through it and there is ringing. The square wave looks pretty bad.
I believe this is where C14 and C15 come in? What are suggested values to start with on C14 and C15?
I added the schematic and wiring diagrams
View attachment UNIAMP2_sch.pdf
Thanks,
Bob
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