Rare visitor in my workshop!
Finaly I have had a HK Citation12 in for repair, no more than 32 years of service, so much for indestructabilty!! Actually just a case of dried out electrolytics.
By the way, I have designed boards to build Mr Pass ´s Mosfet modification from scratch, niceboard based on up to date components, any one want a pair to try send me a note.
Ingvar
Finaly I have had a HK Citation12 in for repair, no more than 32 years of service, so much for indestructabilty!! Actually just a case of dried out electrolytics.
By the way, I have designed boards to build Mr Pass ´s Mosfet modification from scratch, niceboard based on up to date components, any one want a pair to try send me a note.
Ingvar
Citation 12
Hello Ingvar,
A friend of mine has a Citation 12, he has already stripped the pcb's and has asked me to find the necessary components. Now, for the most part I can find equivalents, but I'm still interested to see which components you chose (especially the semiconductors, of course).
Can you send me your partslist and schematic? I'll ask this friend of mine if he's interested in using new boards. How much do your boards cost?
Thanks,
Jarno
my email: Jarno dot verhoeven at planet dot nl
Hello Ingvar,
A friend of mine has a Citation 12, he has already stripped the pcb's and has asked me to find the necessary components. Now, for the most part I can find equivalents, but I'm still interested to see which components you chose (especially the semiconductors, of course).
Can you send me your partslist and schematic? I'll ask this friend of mine if he's interested in using new boards. How much do your boards cost?
Thanks,
Jarno
my email: Jarno dot verhoeven at planet dot nl
Citation12 mod.
Hello Jarno.
Glad to hear that Your friend is doing this mod, it makes a really good amp.
I´ll send You my schematic and partlist during the day.
The semiconductors i use are:
Output devices IRFP264, very good.
Input stage 2SK872G, among the best there is, a bit hard to find.
Driver stage Zetex ZTX653 / ZTX753.
My boards are high grade FR4 with solder resist and silkscreen.
Cost is 10 Euro /pair, (mono board).
I also bias the output stage a bit higher than the original.
Pls let me know Your progress.
Ingvar
Hello Jarno.
Glad to hear that Your friend is doing this mod, it makes a really good amp.
I´ll send You my schematic and partlist during the day.
The semiconductors i use are:
Output devices IRFP264, very good.
Input stage 2SK872G, among the best there is, a bit hard to find.
Driver stage Zetex ZTX653 / ZTX753.
My boards are high grade FR4 with solder resist and silkscreen.
Cost is 10 Euro /pair, (mono board).
I also bias the output stage a bit higher than the original.
Pls let me know Your progress.
Ingvar
Mr Pass!
Submitting details:
For a start, here is the boards for the citation diy. I kept them very small to keep wires around the mosfets as short as possible.
The output devices ar mounted from underneat with the pins bent 90 degrees forward, this allows for a 4mm thick alluminium plate with corresponding holes for the transistors as distance wich makes a very tight assembly on the heatsink and the boards need not be secured any other way.
Submitting details:
For a start, here is the boards for the citation diy. I kept them very small to keep wires around the mosfets as short as possible.
The output devices ar mounted from underneat with the pins bent 90 degrees forward, this allows for a 4mm thick alluminium plate with corresponding holes for the transistors as distance wich makes a very tight assembly on the heatsink and the boards need not be secured any other way.
Attachments
While we are waiting for update
http://babelfish.altavista.com/babelfish/urltrurl?lp=zh_en&url=http%3A%2F%2Fwww.diyzone.net%2Farticle.php%3Fsid%3D277
http://babelfish.altavista.com/babelfish/urltrurl?lp=zh_en&url=http%3A%2F%2Fwww.diyzone.net%2Farticle.php%3Fsid%3D357
http://babelfish.altavista.com/babelfish/urltrurl?lp=zh_en&url=http%3A%2F%2Fwww.my3c.net%2Fproduct%2Fdetail.asp%3Fky%3D%26pid%3D1492%26sgid%3D104%26gid%3D7%26gid2%3D%26Sort%3D%26Price%3D
http://babelfish.altavista.com/babelfish/urltrurl?lp=zh_en&url=http%3A%2F%2Fwww.diyzone.net%2Farticle.php%3Fsid%3D277
http://babelfish.altavista.com/babelfish/urltrurl?lp=zh_en&url=http%3A%2F%2Fwww.diyzone.net%2Farticle.php%3Fsid%3D357
http://babelfish.altavista.com/babelfish/urltrurl?lp=zh_en&url=http%3A%2F%2Fwww.my3c.net%2Fproduct%2Fdetail.asp%3Fky%3D%26pid%3D1492%26sgid%3D104%26gid%3D7%26gid2%3D%26Sort%3D%26Price%3D
Hi Mark
I´ll send You the gerber files, just have to browse through the computers to find latest version.
The power and output connections on the board are designed for the exelent powerpole 30amp system but standard terminals for amp crimp cable termination works alright.
I designed power supply boards, also mono, with space for 2X100 000uF and surge arresters, i dont use them, dont like the idea of running this much current through 35u copperfoil.
If You want them i´ll mail these to
pls let me know progress
I´ll send You the gerber files, just have to browse through the computers to find latest version.
The power and output connections on the board are designed for the exelent powerpole 30amp system but standard terminals for amp crimp cable termination works alright.
I designed power supply boards, also mono, with space for 2X100 000uF and surge arresters, i dont use them, dont like the idea of running this much current through 35u copperfoil.
If You want them i´ll mail these to
pls let me know progress
I did the Pass IR mosfet mod and a complementary bipolar mod to the Citation 12 amp (for some reason I have a bunch of these, about 7). The bipolar sounded a lot better and had more output (less voltage swing wasted on biasing the mosfets). Sorry it's not gee whiz high tech, just plain Jane dependable and sweet sounding. The key thing with this amp is the power supply, it's way overdesigned for the job and lends itself to upgrading.
I'd recommend using complementary bipolars (although I did not think to try lateral mosfets, hmmm.....)
I'd recommend using complementary bipolars (although I did not think to try lateral mosfets, hmmm.....)
Inspired by the Pass upgrade article, years ago I did different mods to several different Citation 12s. This is a summary of the three variations. I like this amp as a starting point because it has a solid power supply, decent heat sinks, and overall a robust enclosure. I don't like to do the heavy iron bit myself, it's a lot of work to do it right and make it "pretty", and I'm better at the electronic side anyway.
First, I added only a 1N4001 Baxandall diode to the original circuit, in parallel with R15, a 10 ohm 1W emitter resistor for the PNP driver transistor. It utterly changed the character of the amp and was a tremendous improvement. This has been suggested by Donald Self and Randy Sloan as a perfectly adequate treatment for the Quasi-complementary output stage, and I'm sold on it. But, being curious, I kept experimenting.
On another Citation 12 I changed the output transistors to complementary mosfets, keeping the original drivers. I used IRF 130s and 9130s as I recall, but it could have been 230/9230s. I did not have any spare lateral mosfets at the time or I might have given them a try. I wanted to use TO-3 packages so it would look like the original. Pass suggested driving these without the drivers in an addena to his article, but that seemed silly to me since the drivers are already there. So I left them and implemented a CF output stage, which sounded very good. It definitely had better high frequency behavior than the original, just looking at square waves. But, to tell you the truth, I preferred the previous amp's sound (QC bipolars with Baxandall diode) over this mosfet implementation.
On a third amp I changed the outputs to complementary bipolars, actually just adding a PNP output to both output haves working as CF outputs. I used a crappy PNP, similar to the crappy NPN that was already there (I think it was an MJ2955 which was lying around). This sounded the best of all to my ear.
I did not expect this result, but it convinced me that for low power outputs, bipolars sound great. For really high power levels, Mosfets are so much more reliable that I would tend to use them.
The reason I go into this gory detail is to suggest that for a very small investment (one 1N4001 per channel), you can dramatically improve this amp. And it's reversible, if you feel you want to go back. On amps from the late 60s and early 70s, who knows they might be collectible some day. If I had to recommend a best mod for this amp, it would be simply that or the bipolar CF mod. It's easy, and it sounds dramatically better.
I wish I could share all this in schematic form, it's the best way. But I don't have a schematic capture package. I can take photos and scan hand drawn schematics, if there is interest in these projects.
First, I added only a 1N4001 Baxandall diode to the original circuit, in parallel with R15, a 10 ohm 1W emitter resistor for the PNP driver transistor. It utterly changed the character of the amp and was a tremendous improvement. This has been suggested by Donald Self and Randy Sloan as a perfectly adequate treatment for the Quasi-complementary output stage, and I'm sold on it. But, being curious, I kept experimenting.
On another Citation 12 I changed the output transistors to complementary mosfets, keeping the original drivers. I used IRF 130s and 9130s as I recall, but it could have been 230/9230s. I did not have any spare lateral mosfets at the time or I might have given them a try. I wanted to use TO-3 packages so it would look like the original. Pass suggested driving these without the drivers in an addena to his article, but that seemed silly to me since the drivers are already there. So I left them and implemented a CF output stage, which sounded very good. It definitely had better high frequency behavior than the original, just looking at square waves. But, to tell you the truth, I preferred the previous amp's sound (QC bipolars with Baxandall diode) over this mosfet implementation.
On a third amp I changed the outputs to complementary bipolars, actually just adding a PNP output to both output haves working as CF outputs. I used a crappy PNP, similar to the crappy NPN that was already there (I think it was an MJ2955 which was lying around). This sounded the best of all to my ear.
I did not expect this result, but it convinced me that for low power outputs, bipolars sound great. For really high power levels, Mosfets are so much more reliable that I would tend to use them.
The reason I go into this gory detail is to suggest that for a very small investment (one 1N4001 per channel), you can dramatically improve this amp. And it's reversible, if you feel you want to go back. On amps from the late 60s and early 70s, who knows they might be collectible some day. If I had to recommend a best mod for this amp, it would be simply that or the bipolar CF mod. It's easy, and it sounds dramatically better.
I wish I could share all this in schematic form, it's the best way. But I don't have a schematic capture package. I can take photos and scan hand drawn schematics, if there is interest in these projects.
I do agree that a classic like the Citation12 would be worth keeping in original shape, if only for nostalgia or collection purposes, allthough my ears find the Pass mod far superior in everything but the bottom end.( My Accuphase P300 stays original but would shurely gain from quite extensive redesign)
My wiev was more on the diy matter as i think the mosfet citation makes an excelent amp at low buildexpenses and easy enough to put together even as first diy-project.
My pcb layout is available for anyone wishing to make own boards, just give me a note.
My wiev was more on the diy matter as i think the mosfet citation makes an excelent amp at low buildexpenses and easy enough to put together even as first diy-project.
My pcb layout is available for anyone wishing to make own boards, just give me a note.
Pass-designed complementary HK12!
Nelson did design a complementary version of the HK12. He sent a letter to Audio Amateur describing the changes accompanied by a schematic. It is the lowest parts count amplifier design I have ever seen.
Unfortunately, Nelson did not add the schematic to the HK12 PDF file.
For anyone who is interested, I have the original Audio Amateur issue and have scanned the relevant page. Send me an email and I will be happy to send back the file.
Brian
P.S. Nelson, if you are reading this, I would be happy to send it to you for addition to the HK12 pdf file.
Nelson did design a complementary version of the HK12. He sent a letter to Audio Amateur describing the changes accompanied by a schematic. It is the lowest parts count amplifier design I have ever seen.
Unfortunately, Nelson did not add the schematic to the HK12 PDF file.
For anyone who is interested, I have the original Audio Amateur issue and have scanned the relevant page. Send me an email and I will be happy to send back the file.
Brian
P.S. Nelson, if you are reading this, I would be happy to send it to you for addition to the HK12 pdf file.
Thanks to Brian i now have the schematic for the complementary version. Layout will be done tonight, the result will be posted here.
Design will be doubblesided as i want plated throug holes, solder result is far better that way. For those who want to make own boards, You only need the solderside, no jumpers needed, i use componentside only to increase area of power and output wires.
Design will be doubblesided as i want plated throug holes, solder result is far better that way. For those who want to make own boards, You only need the solderside, no jumpers needed, i use componentside only to increase area of power and output wires.
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