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Got the first of the 3 minis finished more or less (less case, etc.). Had it running on AC for about 5 mins or so. 255R bias resistors, +/-20V PSU... I'm only seeing around 170mV across the 20R resistors. Low, and seems strange with others getting 18mA with 220R, etc. As for adjustment (offset), I used the pots by the LEDs to get the offset between +/- for that channel centered around ground, then had dialed the individual offsets in using the other 2 pots. Anyone have a different adjustment method? I may play with the pot by the LEDs and see if that does anything to the bias current or not.

I suppose chassis ground would be to code, though from what I have seen no one who had built/cased one did that. Were you going to put holes in the bottom panel for feet? You could use the one closest to the IEC to run a ground wire. Make sure there isn't any interference from anything on the amp board. The RCAs (and the Neutriks) can be tapped. I just tapped an RCA for M3, and would think 4-40 would work as well. I prefer your v1 lettering above as well. EDIT: for grounding, the IEC has 2 mounting holes in the rear panel, which appear they require a screw/nut. As long as the screw contacts bare metal, those would work for the case grounding as well.

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Why do bodily parts start puckering up every time I hear the word “bursun”? Almost as bad as when I hear “bybee ” Sent from my iPhone using Tapatalk

^ Posted the gerbers in the GB thread, but here they are again as well... Bridge_Vert.zip

Some Gerbers... Schottky diode bridge board, vertical diode mtng: Potentiometer: TKD 4CP601 Only TKD 4CP601 / 4CP2500 TKD 4CP601 / 4CP2500 / Alps RK27 Quad GRLV 35mm SiC diodes https://www.head-case.org/forums/applications/core/interface/file/attachment.php?id=21170 Latest CFP2 https://www.head-case.org/forums/applications/core/interface/file/attachment.php?id=20304 Note for those wanting to do one of those balanced: you might want a uBal board to front end that. Bridge_Vert.zip TKD 4CP601 only final.zip TKD 4CP 2 pot final.zip TKD 4CP 3 pot final.zip EDIT: If you have either of the CP2500 boards run, make sure they thru-plate the slots.

I could be interested in going as well. 4 hour wait for a burger? Heh. Sent from my iPhone using Tapatalk

If they are DC servos, then no, they will not change the sound signature if the servo is implemented correctly. But as long as the opamps you are trying can handle the voltage requirements, who knows? The opamp in question is probably implemented with dual supplies. Most opamps seem to be rated for +/- 18V. The OP27 is higher (don’t recall what exactly) and the OPA445 higher yet (quite a bit). If the offset is low and stable, you could try it without the opamp(s) in place. I don’t have a copy of the Krell schematic though, so can’t say for sure. Sent from my iPhone using Tapatalk

I’d match for hFE, but also try to get Vf (also known as Vbe) as close as possible as well. I’d shoot for 5% if possible. Matching the N and P is often nigh impossible depending on device type. You just have to do the best you can. Sent from my iPhone using Tapatalk

Why would you want to do this? What do you hope to achieve with your “upgrade”? What voltages are you running your PSU at? Sent from my iPhone using Tapatalk

Yep. It is what it is. Nevermind...

I should temper that by saying this isn’t 10mm territory for this case with the panel mounted controls. 4mm might be too thick. Kerry would probably know better. I know John was good with the 2.5mm he used on the FPE case, and it sounds like their std. is close to that. Sent from my iPhone using Tapatalk

Thanks, was just wondering. They do show a Heavy option on their end plates, but don’t specify what it is. Sent from my iPhone using Tapatalk

TKD 4CP601, 10K Steve, Any interest in adding Kevin’s latest 35mm cap GRLV version to the GB? Also a use had asked me about the schottky rectifier boards that I did. If there is interest in those or in the potentiometer boards I did, I’d be happy to share the gerbers. Sent from my iPhone using Tapatalk

Do you know what the panel thicknesses are? Also, I liked the “super symmetry” on John’s design. Also, were you planning on countersinking the corner holes in the Fr/Rear panels, or doing an inset larger blind hole (for inserting socket-type screws)? Sent from my iPhone using Tapatalk

Sure! I’ll need to look at them however. Sent from my iPhone using Tapatalk

No I don’t, at least that I want to get rid of. Also, I’m interested in Kevin’s latest large cap version, which checks most of the boxes I was looking for. The SiC rectifiers used on that are Schottky... The larger diameter caps would allow much shorter (25-30mm) caps to be used, allowing something like a 1U chassis for a Dynalo Mk2, etc. Sent from my iPhone using Tapatalk Add what? Rectifier boards? Kevin’s latest large cap GRLV? The mid-size GRLV? Sent from my iPhone using Tapatalk

Ahh, that makes it clearer. The height issue is caused by the headers I am using (the plastic breakaway strip), so I can deal with that. I'll either get some nylon screws or drill and tap the heatsink for 4-40 or M3. The TO-220 silpads I have aren't quite long enough to cover the 3 annular rings, so I cut a strip and put it there so all is covered.

Question regarding the mini heatsinks in the BOM, Aavid 581002B02500G. I didn't realize these were tapped for 6-32, rather than something more rational, like 4-40. The screw head for a 6-32 contacts the regulator chip, which doesn't seem like a good idea. The TO220 mounting kits and parts I have are all sized for 4-40, including the various insulators I have. I noticed in Kerry's build that he used an insulator that covers the screw head... can't tell for sure what it is exactly. Additionally, Amb's o78/o79 are a bit taller than normal TO220s and with the Molex or 3M headers I used, sit a bit taller than the mounting hole. They also sit out from the heatsink at the bottom. In the image on Amb's site, it looks like he bent the pins slightly (but doesn't mention it). I guess the screw issue is the largest one. Any thoughts/suggestions? Not enough room between the fins for a nut.

Yep to both you and WInk, though my impressions of the Stanton vs. the Shure were reversed. I wish I wouldn't have tossed the Shure (maybe I didn't? Hmm, have to look). I always liked that cart on a Thorens (TD160... never tried it on the TD320 I have now). Back in the early '80s, when my wife and I had first married and moved to the Dallas area, I had brought my beloved (at the time) Infinity Monitors (Walsh tweeter) with me, but nothing to run them with. I went out and bought a Hafler amp/preamp (big stuff back then ). After going thru a crap Sony Linear turntable that liked to drag the cart across the grooves periodically, I bought the Thorens 320 (online out of NY). I bought a HO MC cart that I liked a lot, think it was an Apogee? Searching I find no such cart or info about it. At any rate, it was a good sounding cart, even thru the crap phono stages back then.

Cool. Just as a note, you might consider going a bit wider to allow a 0.25” or so gap along each side of the board. (I didn’t check or note the dimensions on your drawing) This would help with airflow/cooling (I think). There is an AC trace down one side of the board so you certainly do not want to use the case slots for the PCB. Sent from my iPhone using Tapatalk

There is a clearer drawing of the case layout on context engineering’s site here: contextengineering.com/desktop_enclosures.html Sent from my iPhone using Tapatalk

I could be interested in a 2CP2500 or 2511 in 10K as well.

Here is the latest CFP gerber file with the servo mod, along with the schematic: cfp2hmt.zip cfa2cmirror.pdf

The screws I was referring to are those that put the case together (front panel, rear panel, top and bottom panels. Sent from my iPhone using Tapatalk