April 16, 201412 yr Lower output voltage swing perhaps, but I've never run my original KGSS (350V) past 1/2 output so I doubt output voltage is a big concern. The KGBH only runs on a +/- 400V supply. I've lost track of half of the thread, so I don't remember if the FET outputs had any meaningful change on the sound of the amplifier. The reason I asked is I remember the 2sa1968 used to be quite expensive, and FET outputs just seemed like a fun change from the classic KGSS I already have. I see sanyo 1968LS in stock for under $10 now, so it may not be as big of a concern as it used to be.
April 16, 201412 yr Author birgir and I have ordered 300 pieces of the new Motorola part. We expect that this part is going to be much better sounding than the ixys parts for the gain and output stage. 2sa1968 still more temperature stable than the ixys part and always will be. Also hopefully we have ordered significant quantity of 1200 volt bipolar.
April 16, 201412 yr I have a few questions regarding the dual transistor kgsshv board recently posted by Kevin. I am drawing a slightly modified board and putting together a schematic. First, what is the voltage rating requirement for the 1 uF capacitor in the servo ? Does it need to be 1000V ? Second, what are the devices next to the two 2SA1486 ? They do not appear to connect to anything electrically. Also. are the pads next to them just voltage reference points ? Thanks again for your help.
April 16, 201412 yr Author needs to be a mylar cap. so the 1uf/1000v cap works and fits fine and is cheap. But really you need a 30v cap. next to the 2sa1486 are stn9360. use one or the other, not both. stn9360 is surface mount.
April 16, 201412 yr Lower output voltage swing perhaps, but I've never run my original KGSS (350V) past 1/2 output so I doubt output voltage is a big concern. The KGBH only runs on a +/- 400V supply. I've lost track of half of the thread, so I don't remember if the FET outputs had any meaningful change on the sound of the amplifier. The reason I asked is I remember the 2sa1968 used to be quite expensive, and FET outputs just seemed like a fun change from the classic KGSS I already have. I see sanyo 1968LS in stock for under $10 now, so it may not be as big of a concern as it used to be. The whole goal of the KGSSHV was never the high voltage, that was just a side product of the parts available. The main focus was the new PSU design and indeed the CCS for the third stage where the old KGSS had resistors as current sources. Given that we could push to +/-500V we did it but there is nothing wrong with +/-400V. The higher the voltage swing, the further away from the limits of the circuit is the "normal" listening volume and the circuit is thus more linear. Now if 4686A's were still in production then it wouldn't be a problem to run at +/-450V but they are already in short supply so we need to look ahead. The fets do work but very high input and output capacitance makes them a less than ideal choice for this role. The new Moto part is promising and I'm looking everywhere for high voltage BJT's and might have some news on that front soon. It will cost me more than a BHSE to secure them (f it is even possible) but it will also mean a lot of new KGSSHV's can be built. I'm a pragmatic man though so with parts like the Fairchild F5027 in current production it makes sense to extend down to +/-400V with no performance hit.
April 19, 201412 yr Prototype nr. 2 of the tiny HV up and running. Different output devices, pcb's mounted closer to the sinks, different assembly technique, new chassis feet plus a lot of holes drilled into the bottom plate to see how much cooler inside is. It isn't SRM-T2 hot but then again the T2 didn't have electrolytic caps inside the amp section. I'll send the first prototype to the US next week to see how it plays in a warmer climate and for some measurements. These small amps seem to be multiplying like rabbits though... It is Easter after all. Speaking of Easter, it marks the anniversary of me giving up on making new offboard PCB's for the HV so to celebrate I've started work on them again. Glutton for punishment here...
April 19, 201412 yr Birgir. Those amps are quite nice. And there is a market for them. I wish you could outsell the Cavally crap.
April 19, 201412 yr Seriously making me want to start buying parts Though I'll probably want to replace my sr007 first, damn thing's unrepairable at this point. Edited April 19, 201412 yr by DouglasQuaid
April 20, 201412 yr Is that second prototype running at 9mA as well? Seeing these tiny (very nicely done) builds is starting to make my huge hv feel unnecessary.
April 20, 201412 yr Yup, the small one is at 9mA and the smaller one on the left runs at 11mA. Well it will once I get more transformers...
April 20, 201412 yr Really digging the new form factor! Especially the 2 on the left. Are you going into production mode and going to start selling KGSSHV's? Would really nicely fill in the gap with Justin's stuff whereas he has the Aristeus and BHSE. Now all we need is somebody making Megatron's and T2's. Edited April 20, 201412 yr by DefQon
April 20, 201412 yr The two on the left are one-off's so more won't be made. Simply not happy with the chassis... I will make a few of the smaller one when I have time. Parts have been ordered and boards assembled for some of them but it will take a while to source the parts. Nobody will ever make a T2 so that's out and the Megatron is way too complex.
April 21, 201412 yr The small ones on the right are awesome! I would love to have something like that for the office.
April 21, 201412 yr I was thinking that he could buy one of your prototypes when you finally sell them.
April 21, 201412 yr Can the KGSSHV be tuned for 16mA? Think I read reports somewhere on the other site while ago that the KGSSHV can be set at 16mA to match the BHSE? Edited April 22, 201412 yr by DefQon
April 22, 201412 yr Yeah, major misunderstanding of what is going on here. Let's just make one thing clear, running the KGSSHV at the same current as the BHSE will not make them sound close, let alone identical to one another. Major difference in terms of circuit design which has a clear impact on the final output. Even if we did a Blue Hawaii with sand instead of tubes it still wouldn't sound the same. As for the question, yes the KGSSHV can run at 16mA but there are other things to consider. First of all, why on earth would you want to do that. There are certainly no benefits to speak of and those talking about "major improvements" must be smoking something. I'd certainly love to see some date to back up these claims but there are naturally none to be found. There is a subtle change when moving from 5.5mA to say 10mA but after that it is all diminishing returns. Now say you have taken leave of your senses and want to pursue the magical 16mA then there are three major issues you need to tackle, what is the maximum power rating of the output device, do you have sufficient cooling and can the PSU supply the extra current.
April 23, 201412 yr How viable would it be to set up an amplifier to have multiple bias current settings? The mechanics would be pretty simple, assuming the existence of small rotary switches that are rated for the voltage. I'd like to assume that a 6-12" run of wire to a switch and back wouldn't cause any noise or instability, but I've seen lesser things cause problems. I'd also be curious if zeroing the dc offset would be required for every bias change. This would mainly just be to tune down the current when the weather starts to get hot and nasty, then turn it back up when things cool down. I have the feeling I'm grossly overestimating how big of a change in total power usage and heat generation this would actually make.
April 23, 201412 yr Massive issues with anything like this. While it is certainly possible to use adaptive biasing (i.e. Krell with sustained plateau bias and the new iBias) simply cobbling together a switch with some wires and resistors would never work properly.
April 23, 201412 yr Perhaps the usage was misinterpreted. It wasn't meant to be continually toggled while the amp is powered up. Likely just used prior to powering up to run the amp at a lower bias for the angry summer months. Though I suppose a jumper on the pcb would be much more effective. Edited April 23, 201412 yr by DouglasQuaid
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