Hello!
The time has finally come for me to stop lurking around and officially join this forum.
I figured since this is my first post I should write a short introduction of myself.
I'm a student from Sweden who two years ago made the choice of studying economics instead of engineering. While i really enjoy it I have always been fascinated by electronics and physics overall.
Long story short i ordered Morgan Jones Valve Amplifiers, 4th Edition a couple months ago and have been studying it and educating myself on the subject since.
The amplifier:
I have decided on an integrated class A/AB pp amplifier.
As far as the power tubes goes i have fallen for the KT88s due to their characteristics(as described by others) and the fact that they are interchangeable with 6550s and the EL34s with minor adjustments.
I just realized that i haven't really looked into any other transformers than the Hammond, they seem to have whatever i would need. I actually took a peak at the Piltron toroidals aswell, there seem to be a limited amount of amps with toroidal transformers... is the price the only reason for this?
Luckily i won't have to look far and wide to find a fitting chassis with diyaudiostore.com great variety
I have looked at quite a few kt88s schematics but haven't found "the one" yet.
I recently looked over lampizator.eu's modifications of different Chinese amps, specifically Music Angel XD 800 MK III and the Bewitch 6550. Both of these match my description and i though why not build the modded version directly from the schematic online?
The feedback for their mods varies so I would like to hear your opinion on them aswell.
I will most likely add treble and bass control to the amplifier aswell.
"Why don't you just buy the amplifier?"
I want the "I build this" feeling again and you have to build it to know it
If you got this far I hope you get the picture, I probably forgot about a gazillion things i wanted to say but hey, one thing at a time.
All replies are appreciated, the more opinions the better!
The time has finally come for me to stop lurking around and officially join this forum.
I figured since this is my first post I should write a short introduction of myself.
I'm a student from Sweden who two years ago made the choice of studying economics instead of engineering. While i really enjoy it I have always been fascinated by electronics and physics overall.
Long story short i ordered Morgan Jones Valve Amplifiers, 4th Edition a couple months ago and have been studying it and educating myself on the subject since.
The amplifier:
I have decided on an integrated class A/AB pp amplifier.
As far as the power tubes goes i have fallen for the KT88s due to their characteristics(as described by others) and the fact that they are interchangeable with 6550s and the EL34s with minor adjustments.
I just realized that i haven't really looked into any other transformers than the Hammond, they seem to have whatever i would need. I actually took a peak at the Piltron toroidals aswell, there seem to be a limited amount of amps with toroidal transformers... is the price the only reason for this?
Luckily i won't have to look far and wide to find a fitting chassis with diyaudiostore.com great variety
I have looked at quite a few kt88s schematics but haven't found "the one" yet.
I recently looked over lampizator.eu's modifications of different Chinese amps, specifically Music Angel XD 800 MK III and the Bewitch 6550. Both of these match my description and i though why not build the modded version directly from the schematic online?
The feedback for their mods varies so I would like to hear your opinion on them aswell.
I will most likely add treble and bass control to the amplifier aswell.
"Why don't you just buy the amplifier?"
I want the "I build this" feeling again and you have to build it to know it
If you got this far I hope you get the picture, I probably forgot about a gazillion things i wanted to say but hey, one thing at a time.
All replies are appreciated, the more opinions the better!
If you live in Sweden, don´t look farther than Lundahl transformers, made in Sweden. They are excellent, and don´t cost more than Hammond in Sweden. They have an excellent article by Claus Byrith on their webpage, about a Mullard variant with Lundahl iron. Other good suppliers of iron in EU are Indel and Toroidy from Poland, very good prices compared to the quality.
Using toroids as output transformers is problematic as the easily saturates with any imbalance of a pushpull pair. C or E cores ( lundahl) is much more forgiving in that respect.
Irrespective of that, matched output tubes are always needed in high quality amps, and that means both similar bias at working voltages and similar Gm.
Irrespective of that, matched output tubes are always needed in high quality amps, and that means both similar bias at working voltages and similar Gm.
I was thinking about low number of stages, and good quality without global fb. Answer is Schade fb, with help of mosfets low Rout of driver is possible.
Chances that I will build PP are close to zero, so may somebody else benefit from it. Slightly higher Ra-a than "normal" opt are preferred in this fb system.
In case tube gain is not enough, you can wire input tx to 1:2
With grid choke and good selection of anode capacitor value, you can get clean mid and treble, with some "boost" of bass. (amount of fb changes by freq) ; also grid choke has low dcr which is strong benefit
Chances that I will build PP are close to zero
, so may somebody else benefit from it. Slightly higher Ra-a than "normal" opt are preferred in this fb system.In case tube gain is not enough, you can wire input tx to 1:2
With grid choke and good selection of anode capacitor value, you can get clean mid and treble, with some "boost" of bass. (amount of fb changes by freq) ; also grid choke has low dcr which is strong benefit
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1st, search the archives for "modern mullard". A lot in that thread will be of benefit to you.
2nd, there is really no good reason, these days, for vacuum rectifiers in a tube power amp. High PIV Schottky diodes are every bit as quiet.
Instead of the hybrid bridge shown, use 4X Schottkys in your B+ PSU and have done with the matter.
2nd, there is really no good reason, these days, for vacuum rectifiers in a tube power amp. High PIV Schottky diodes are every bit as quiet.
Instead of the hybrid bridge shown, use 4X Schottkys in your B+ PSU and have done with the matter.
Thanks for the pointer on the schematic and rectifier rubes
I've been looking around for a new schematic, searching for "modern mullard" gave alot of hits with various results.
Seems to me that its not that popular to design DIY integrated amps, most I find are power amps.
Maybe it's better to build a pre and power amp under the same roof instead of taking a shortcut looking for an integrated amp schematic?
The Oddblock kt88s monoblocks have fantastic reviews and seem very simple. There are also other projects where they fit it in one chassis. There was some discussion about whether they should use 2x PTs(exactly like 2 monos) or one.
Can i fit these as stereo plus a preamp into a 40*40*20 ish cm chassis(Dissipante/Pesante 5U from diyaudiostore) without cramping it in?
Would you recommend this?
I haven't read up that much on standalone preamps but the "Forewatt" seems to be quite popular aswell and i assume they make a good fit.
I haven't made my output decision 100% but its pointing towards Lundahls if possible, I will take those toroidals into consideration though!
I really appreciate the help getting started
I've been looking around for a new schematic, searching for "modern mullard" gave alot of hits with various results.
Seems to me that its not that popular to design DIY integrated amps, most I find are power amps.
Maybe it's better to build a pre and power amp under the same roof instead of taking a shortcut looking for an integrated amp schematic?
The Oddblock kt88s monoblocks have fantastic reviews and seem very simple. There are also other projects where they fit it in one chassis. There was some discussion about whether they should use 2x PTs(exactly like 2 monos) or one.
Can i fit these as stereo plus a preamp into a 40*40*20 ish cm chassis(Dissipante/Pesante 5U from diyaudiostore) without cramping it in?
Would you recommend this?
I haven't read up that much on standalone preamps but the "Forewatt" seems to be quite popular aswell and i assume they make a good fit.
I haven't made my output decision 100% but its pointing towards Lundahls if possible, I will take those toroidals into consideration though!
I really appreciate the help getting started
flatscreened:
you might consider buying a kit as your first amp, say a vta-70 from tubes4hifi. Buying tubes locally will save tons of money , and by purchasing a kit you will get all parts and the end result will be a good amp that in addition could be sold if and when you decide to build another one.
you might consider buying a kit as your first amp, say a vta-70 from tubes4hifi. Buying tubes locally will save tons of money , and by purchasing a kit you will get all parts and the end result will be a good amp that in addition could be sold if and when you decide to build another one.
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