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http://www.audio-gd.com/Pro/diy/DA01/DA01EN.htm a-gd has released their R2R module. NO digital filter included so it seems future promising when better filter is available. Kingwa said if there were enough people want this, he would also do the digital filter module, separate DSD DAC, and also PS for the whole thing. Please notice the last few lines:"The module had the DC offset , customer want to use the couple cap, or the DAC analog filter output had the couple caps or DC serve design. For the balance DAC design, the proper design can remove the DC offset in the analog filter amp output , without couple caps or DC serve design ". KG's unbaltobal seems to be a good chioce for the buffer or with SuSy dynalo to make a wonderful DAC/amp

green ones are prototype. red ones are final product. Just go for the red ones.

The picture is Denafrips DAC-1 PRO link here: https://item.taobao.com/item.htm?spm=a1z10.1-c.w4004-8327544200.2.yvBVss&id=520399273447 I read from a Chinese forum Hibiki sounds like TDA1541 while comparing to DAM1021 sounds like PCM1704. The Hibiki seemed to have some resolution problem.Of course this doesn't really make much sense because DA chip itself often doesn't have strong sound character. Maybe it's implying if the circuit was fine in the design, then maybe digital filter was not that good.

Bias current seems to have positive correlation with temperature. That means this amp may blow itself without adequate heat sink? Also, the performance will be different in winter or summer. Please describe the sound. Anyway, nice job. It's time for some fancy casework.

5V seems acceptable. I was thinking if someone was bad luck enough to have a bunch of sands far away from average hfe will be a pain to set the mid point. Is it possible to put a svr somewhere to do the trimming job?

Is there any problem to set the mid point?

https://world.taobao.com/item/525195615222.htm?fromSite=main&spm=a312a.7700824.w4004-12659368213.2.4SmcUz another discrete R2R module for you guys to play with.

The owner of Holo audio is now developing a new flagship above spring. The estimated release time was going to be next year. Another discrete R2R single board like dam1021 was called "hibiki" was also sold on Taobao. There are also a manufacturer called denafrips also making discrete R2R DACs. If people are interested I could post some more information. The main problem of those I think is those solutions couldn't achieve the noise level as low as single chip solution because of the accuracy and temp drift of the resistors. Correct me if I was wrong.

Err... so do you mean the amps having differential input (eg. 2sk170 pair) output balanced signal no matter input signal was balanced or not? And also if the above was true, what's the benefit of balanced input signal?

Why female only? I am now building a two box design, too. another question: is it necessary to separate filament and regulated PS into two wire? How much is the benefit?

can't catch up with the mafia... looks like a nice, low cost, all sand design.

I am in for SH's 25 pcs. Am I too late? The sheet was locked.

Is there any TOSHIBA substitute for 2SK170? Because this hard to buy LSK389/170 here. Some say 2SK366 is ok. How do you guys think?

A friend was building this amp and said something was wrong in the bias of 1000170D he's building, causing the regulation not working. Thus, the output voltage was around 457V. Few seconds later, the BC557 fried. If BC557 was substituted with some higher voltage sands (~100V), the circuit will be more fail-proof.

About GRHV. BC557 has -45V voltage limitation. If you use a way over spec trafo and unluckily enough to turn on the amp on the peak of AC, before the regulation starts working, the voltage crossing BC557 will be over 45V. This might be a long term problem. Or, when sth is wrong when assembling HVs, BC557 will be easily fried.

Changed several sands, and resulted in BC557s fried. Suspecting .047uf cap leakage because the voltage of 20K kept raising (~15V) and opposite side LT1021 voltage dropping. Will change all the sands and caps. I think this is the fastest way now for me could thought of. Luckily I still have same spare parts. How do you guys think?

Thanks. Do you mean there might be short between fets? I think I will replace STN9360, KSC5026, BC557 one by one. Unregulated voltage was fine(450V).

It's 10V not sth like 5v version. Switched Lt1021, nothing changed. LT1021, 10M90s, DN2540 already switched. Still the same. Voltage dropping speed became a little bit slower, but it's still not working. -400v was exactly the same circuit and was working perfectly. It's a little bit hard to measure because all the fets are directly mounted. After turned off, I couldn't feel any part is hotter than room temperature. I think it's because there's no current at all. (current limiter?)

Tried to turn up +400V several times, it always gave +403V in the first and quickly dropped to 300V. I hooked the fluke on LT1021 and found LT1021's voltage would slowly increase from 4V initially to about 4.5V when the output voltage dropped to 300V , which was obviously wrong. Where should I continue to check with? I am sure it was marked LT1021-10 on the chip. Did diode test on ksc5026, which seemed be fine. 6V on both sides and it was not shorted.

No, it's unloaded.

I tested +400V GRHV today and found it was not working. It outputted 403V immediately when powered up, and quickly dropped to about 200V after 5 seconds. It would continuously dropping and won't stop. Where should I begin to check with? -400V with same batch of parts work perfectly(-403V)

And when it starts to leak....... Sounds like a plan. A thick case will do the rest.

How a about using the whole case as heatsink? It's rather easy to calculate the distance between case and PCB. Customized aluminum block can do this job. Or, hollow the case to expose the heat sink. My concern is if the whole PCB is cased and heat dissipation will be a problem after hours of running.

Is there any benefit to raise rail voltage from 400V to 450V? Tubes are said to be more linear when the voltages are higher. Though 400V seems enough.

bui501 said AC420. And I thought 470V is way too high for rated 420V. Unloaded 470V for 450V rated is indeed just fine. Any reason for using 450V as sec? I thought 400-420V was already enough. How much voltage drop should I consider when ordering transformers?