Almost finished rebuilding the amp after all the problems that I had exterminating P channel VFETs.
I had multiple further issues as I went along, 1 of my Cinemag transformers had a short between windings which meant the 2SJ28 bias on one channel was flowing to ground. This wasn't really picked up when using the LM317 bias regulators as they can supply a fair amount of current - enough to ruin a 30VA R-Core mains transformer! When trying to bias with the TL431 I couldn't do it as the circuit was drawing all the current that it could supply and this was running through the 3K3 resistors and dropping the voltage. This is now the stock CSX1 circuit with IRFP240/9240 main regs and TL431 bias.
Hopefully the problems are all in the past. I now have both sides up and running at 1.2A to be on the safe side. Plenty of time to push the bias higher in future. I need to put new speaker protection in (blew the original speaker protection boards somehow too) and tidy up the wiring, but other than that and upping the bias it is pretty much done.
Oh I need a new rack to fit it in, but I haven't mentioned that to the wife just yet 😉
How does it sound - very nice indeed. My perception may be coloured by the painful process building this amp has been (all the blown 2SJ28s, the bias, the R-Core xformer, the shorted Cinemag xformer etc, etc). It is absolutely quiet, no mechanical hum at all and I cannot hear any circuit hum with my ear next to the speaker cone.
I have a weakness for female vocals, and there I could not be any happier! Really a joy to listen to. Maybe the bass is not as taught as my F6, but I can always bi-amp with a B4 DIY and some FAST type speakers in future - definitely have not mentioned that to the wife at all...
I have added a few pictures too.
I had multiple further issues as I went along, 1 of my Cinemag transformers had a short between windings which meant the 2SJ28 bias on one channel was flowing to ground. This wasn't really picked up when using the LM317 bias regulators as they can supply a fair amount of current - enough to ruin a 30VA R-Core mains transformer! When trying to bias with the TL431 I couldn't do it as the circuit was drawing all the current that it could supply and this was running through the 3K3 resistors and dropping the voltage. This is now the stock CSX1 circuit with IRFP240/9240 main regs and TL431 bias.
Hopefully the problems are all in the past. I now have both sides up and running at 1.2A to be on the safe side. Plenty of time to push the bias higher in future. I need to put new speaker protection in (blew the original speaker protection boards somehow too) and tidy up the wiring, but other than that and upping the bias it is pretty much done.
Oh I need a new rack to fit it in, but I haven't mentioned that to the wife just yet 😉
How does it sound - very nice indeed. My perception may be coloured by the painful process building this amp has been (all the blown 2SJ28s, the bias, the R-Core xformer, the shorted Cinemag xformer etc, etc). It is absolutely quiet, no mechanical hum at all and I cannot hear any circuit hum with my ear next to the speaker cone.
I have a weakness for female vocals, and there I could not be any happier! Really a joy to listen to. Maybe the bass is not as taught as my F6, but I can always bi-amp with a B4 DIY and some FAST type speakers in future - definitely have not mentioned that to the wife at all...
I have added a few pictures too.
Attachments
That's looking better than your last picture....
Glad you solved it! You have had a lot of strange problems indeed.
What are you driving the CSX-1 with, preamp ? Do you use the JFet buffer ? I think I see them at the back...but there are two blue trimpots....
Curious what are your voltages of REF1 and 2 for the 1.2 Ampere ?
Glad you solved it! You have had a lot of strange problems indeed.
What are you driving the CSX-1 with, preamp ? Do you use the JFet buffer ? I think I see them at the back...but there are two blue trimpots....
Curious what are your voltages of REF1 and 2 for the 1.2 Ampere ?
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A 5U case is enough for this amp? Sure would simplify my case search/construction. If I use one, I will probably offload my toroids/PSU to a separate case.
The CSX-1 is driven by a Pearl 2 into a TVC and then this amp. I am using the simple 2sk170/2sj74 buffer as well in front of the splitter transformer. The 2 trimpots are for adjusting the pos and neg supply to the buffer with some big 1K8 resistors to drop the 24V regulated supply to between 14V and 10V.
I haven't measured the values of the bias voltages yet. I'll have a look this weekend and report back.
Cool! I got sony silicon + Jensen transformers early on after BAF. Got Permender's PCBs from the first group buy. Most recently ordered a pair of Plitron transformers for this amp along with some 30 VA toroids for my current DDDAC project. (Took all 4 transformers to break the $300 minimum at Plitron)
I don't think I can fit 2 power supplies into a case with caps, and thos PCBs. They stick aways into the case. Amp Case + PSU case vs. some sort of DIY monoblocks. Guess you could use 2x 5u case as monoblocks, but that's 2 wasted heat sinks, and big boxes. Could easily do the PSUs in a 2-3U case to match the modu-shop 5u case.
Thanks for response ZM!
Haven't compared to the Jensen and I had problems with 1 of my Cinemag transformers so I have not listened to alternatives in this amp. I use the Cinemag in my F6 and I have found it to be very good.
I do like Lundahl transformers though. I use an MC xformer of theirs as a step up in my Pearl 2 and I have used their tube output transformers before. In this application, after only a few hours of listening I have no regrets going down the Lundahl route.
It does have a higher primary resistance than the Jensons - ~42R instead of ~25R, not sure if this will cause me problems anywhere?
The LL1864 would be another alternative, similar to the LL1527 (but not physically a drop in replacement unfortunately). This is an amorphous C-core and is supposed to be very good - alas the price is too rich for me, a pair costs more than a 5U chassis. If anyone does try them I'd be interested in their experience!
Up and Running
I finished my second channel and did a couple of hours of listening to the CSX1. This build uses the Permaneder boards; the boards worked flawlessly and were easy to implement using the Jensen transformers. While this is a new amp and needs breakin time, it has a harmonic signature similar to my 845 PP transformer coupled DHT amps, very open and airy. In comparison to my F6 (R100), it’s less controlled on the bottom and more pleasing to listen to overall. I’m using horns so I’m not driving it very hard, your mileage, with low efficiency speakers, may vary 🙂
I finished my second channel and did a couple of hours of listening to the CSX1. This build uses the Permaneder boards; the boards worked flawlessly and were easy to implement using the Jensen transformers. While this is a new amp and needs breakin time, it has a harmonic signature similar to my 845 PP transformer coupled DHT amps, very open and airy. In comparison to my F6 (R100), it’s less controlled on the bottom and more pleasing to listen to overall. I’m using horns so I’m not driving it very hard, your mileage, with low efficiency speakers, may vary 🙂
Hello Botte. Please show schematic of 845 PP transformer coupled DHT amp; if available. Thank you.
Perhaps that's the truth... Yesterday I have been listening in a good HIFI shop to their 33.000 Euro active crossover loudspeakers with several amps. And the bass I heared from that "reference"system is exactly as what I hear with the F5Tv3.
So the bass I hear with my CSX-1 isn't that good with my 4 Ohm, 10 inch woofer. The damping factor is obviously too low.
BTW: I wasn't exactly stunned, listening to their most expensive DAC and reference system, with DIY you can get to high levels😀
Thanks to mister Pass!
Here are a few, I don't have the outside of the box done.
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for those like me who don't use the input buffer, for increasing the input impedance of the Jensen transformer is it worth to replace the two 1k input gate resistor with 10K ? 
Nice, thanks that's a tube style mono amp? What is the huge sleeved cable a mains PSU cable? Did you make it yourself?
Walter
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