mwl168

May I suggest moving the build notes and related discussions to the build thread?

I did successfully build both GR78 and GR79 using the GB boards. First of all, you need some capacitance on the output for the regulators to work. That's the first thing I would try. I did have an issue with GR78 at first and finally figured out I used the wrong part (used HN4A51J instead of HN4C51J). But try adding some capacitance on the output ends first.

IIRC, significant voltage is dropped in the chain of R26 and VR1 and I am wondering, depending on where VR1 value is set, if one of them is overly stressed beyond its rating and causing some issues.

Also, I think the frequent point of failure of such device has been the contact points of the switch itself. If they are not of high quality, they'll develop noise in the long run.

Hmm, what’s the voltage drop and dissipation on R26 and VR1 when you adjusted the offset to 0V?

Ok, that makes sense. When you increase the output device bias current, you need to tweak the offset adjustment chain (R26 and VR1 - 2K and 1K respectively in the schematic) so you can adjust the offset close to 0V. The easiest thing to do is to decrease R26 but make sure the voltage drop is somewhat even between R26 and VR1 so they are not stressed. I posted earlier in this thread of a similar effort I made on my build: https://www.head-case.org/forums/topic/8327-im-on-a-roll-the-kgsshv/page/187/ The goal is to get the offset and balance close to 0V as possible. They will drift a bit and that's normal.

Thanks James. Corrected.

I've asked this question before - what's the lowest offset voltage you can adjust to with the higher bias current of the output devices (lower R5, R6 values)? I would first get the offset and balance to reasonable range and see if that affects the distortion issue you are experiencing. If the amp is set up properly you should be able to get both to below 1V easily. If the amp was originally set for lower bias, increasing the bias current may cause the amp to run out of offset adjustment range without making change to the offset adjustment circuit.

I was not able to PM you so had to message you here. Please PayPal me $8.4 US for the shipping cost. @Orso_Aquilano: please check PM for shipping of your package.

Does McIntosh continues to use output transformers in all their amps?

All GB packages have been shipped as of today except for two. One of the two is pending the participant's response to my shipping payment request. Most of you have PayPal'ed me the shipping cost. Thanks! For those who have not yet PayPal'ed me the shipping cost please check your PM or PM me. I have been keeping track but there were 50 packages so may have missed a few. Shipping cost for US address is a flat rate of $8.4 US. For non-US address it depends on the location and weight and I added $1 US for the bubble envelop used. This GB is now officially closed. Happy building!

Sounds like you and I are keeping BDent's business afloat!

I am not sure if there is a "target" biasing. I've tried between 150mA to over 200mA and settled on 180mA IIRC.

Before you start replacing the sands, I suggest you do a diode-test on each of the transistors on the board and compare the result between the working and malfunctioning boards.

Two suggestions: 1. clean the solder flux on both side of the boards. 2. check to see all parts, especially the sands are the correct ones and inserted correctly.

40V offset is quite high. Is this the lowest offset you can adjust to? If your KGSSHV has offset servo, you will need to deactivate the servo before you adjust the offset. Get the offset close to 0V first (it will drift a bit) and then engage the servo.

I included an extra 1.6mm PSU main board in some packages mostly for extra protection of the assembled GRHV boards. It’s great if you can find use for it 🙂

I built a Ventus EZ (Ventus was out of stock) years ago for my father-in-law using very similar set up and it was hum and noise free. IIRC, there are pots on the amp boards to zero-out the output offset and I did not need to add coupling caps to the output. Hard to tell what's going on from the pictures. Looks like you shorted the inverted input to the ground on both channels but why do you have two ground wires coming out of one board and none for the other? May be check the wiring and ground scheme?

You have not missed anything. I am just not working very fast 🙂

A few packages went out this late afternoon but I think I missed the last truck out from the post office today.

All boards are here and I am ready to start shipping the boards to the GB participants. I'll be using USPS Priority Mail for all US participants. All US GB participants please PayPal me $8.40 for the shipping charge. For international participants I will PM you the shipping charge after I have the package weighted at the post office. I have used first class mail without insurance and tracking in the past. Please let me know ASAP if you want to add tracking and/or insurance but be warned they are quite expensive options. I'll ship the package when I received your shipping payment. When you PayPal me, PLEASE INCLUDE YOUR SHIPPING ADDRESS and HEAD CASE ID if you have not done so when you PayPal'ed me the cost for the boards.

470uf/400V

This post is about the auxiliary power supply for the timer circuit. Kerry designed the board to accept an external +5VDC supply for the CD4093BM based timer. After Kerry and I discussed we agreed that there are 3 options: Option 1: For the purist, use an external +5V supply as designed. Note that C17 will see almost the entire voltage drop of the supply so it needs to be rated for 5V or higher. Option 2: Jumper a wire directly from GR78 output to the +5V pin of the Aux - Pwr pads. If you do so, make sure C17 is rated for the GR78 output voltage AND change R1 and R2 from 3K to 10K. For this option, the highest value we could find for C17 in 1210 package is 100uF/16VDC. Combined with 500K for R22, the delay is about 55 seconds give or take a few seconds. I tested this option by rigging in through-hole parts for C17 and R22 and it worked fine. I also added a 12K resistor in series to the LED indicator but this may or may not be needed. Option 3: Solder a 7805 regulator directly in the Aux-Pwr pads and feed theGR78 output to it. I came up with this option mostly because the parts I happened to have on hand and it's what's shown in the pic below. You'll need some capacitance between the Vout and GND pins of the 7805 for it to work (I use a 47uf cap). I also soldered in a 1N4007 zener between Vin and Vout pins to protect the 7805 regulator. I use 330uF/6.3V tant capacitor for C17 and 182K for R22 and the delay is about 75 seconds (I prefer a longer HV delay). You need to jumper a wire from the Vout of the GR78 to the Vin pin of the 7805 (the purple wire in the pic). Options 2 and 3 are easy to do because there is extra hole for the GR78 Vout on the board.

Here are a few pics of my test build. GR78/GR79 are set for +/-15VDC, GRHV set for +237VDC/-247VDC. I did not build out the bias supply on this board. I use 182K for R22 and 330uF for C17 which results in timer delay of about 75 seconds. I also tested a 500K/100uF setup which results in about 55 seconds delay. The 100K/470uF combination in the BOM provides about 50 seconds delay. Not these numbers will vary a bit mostly due to the tolerance of the capacitor (see more details in the next post). The PSU main board is of a modular design (see the schematic). It contains the following circuits: 1. A set of GR78/GR79 low voltage regulators. 2. A set of GRHVxx high voltage regulators (B+ and B-). 3. A CD4093BM trigger based timer control (need to provide aux-power, see my posts below). 4. CPC1117N based soft-start for the GRHV. 5. A configurable headphone bias supply (2 outputs are provided - Bias H and Bias L). Note that C1, C2, C3, C4 are pre and post regulation filter capacitors and their values and voltage rating need to be picked based on your needs. The pitch for the pins are all 10mm. C1, C2 diameter need to be 35mm or less and C3, C4 need to be 22mm or less. Pick caps with smaller diameters if you don't like the caps physically touching each other when installed. I mounted the pass transistors of the GRLV in a goofy way and it's not what Kerry has intended. For a normal person, the pass transistors should be behind the PCB

Hi All: This is the build thread for the Kerry design PSU. I posted BOM and schematic with Kerry's permission here and will be posting more information including photos of my test build. My test build use the partially-assembled GRHV boards. I soldered in the the pass transistor and the resistors to set up my desired output voltage. The voltages, timer all tested as expected without load. Fire up your soldering irons and happy building! GRHVBase-v2-production.pdf GRHVBase-BOM - V2 production.xlsx