jboehle

I just saw this on The Verge as well, I can't imagine this is going to sell well...

Get off my lawn!

Sounds great! Tried my cheapo Monoprice 8323 first, I get a little hiss at 50%+ volume with those, but I'm pretty sure that's coming from my computer or the pupDAC. Listening now with Senn HD650, I'm jamming!

I bet! I was just trying to make sure nothing was getting too hot (beyond operating specs) while the case was on.

After biasing to 125mV at cold startup, then warming up with the case lid on, ch 1 settled to 104mV and ch2 settled to 100mV. I turned down ch 1 to 100mV. Amp heatsinks range from 45-50 deg C. I am using the 2" heatsinks. The PSU TO-3 cases are at 55 deg C, PSU Opamps at around 50 deg C, amp Opamps at around 35C. Looks to be running good! Now to hook up a source & some 'phones!

Prometheus OST.

Thanks for posting this. Of course I had heard some of their work in the past but did not know who the artists were. I'm really loving this! Also been listening to some of Rodrigo y Gabriela's older stuff, it's all great.

Got the replacement 1N914 diodes installed, DC offset is now less than 1mV DC in both channels with opamps in. Letting it warm up now. Gotta get back to work, will listen to it later. Really hope that's all it was!

GrindingThud, thanks for the suggestion! I pulled the 1N914 diodes out of both channels so I could compare the good to the bad. Both of the channel 1 diodes were bad as you suggested. Both of my channel 2 ones were still good. Luckily my local Rat Shack stocks 1N914 diodes (at least according to the website), so I will be picking some up first thing tomorrow. Thank you so much!

It won't be fun but I guess that's the only way to go. What all should I replace? Just the stuff in the red box? Or should I replace any of the stuff in the yellow or blue boxes as well?

Looks like spritzer has some of the original style psu boards still available:

Okay, I left the amp on for 15 min or so, adjusted the bias on channel 1 to 99mV. I believe I read earlier in the thread that the bias should be 125mv cold, or 90-100mV after warmed up. To get channel 1 to 99mV, I had to turn the bias pot all the way down (counterclockwise), so that was as low as I could get it. On channel 2, I was able to adjust the bias down to 95mV without reaching the limit of the bias pot. This gives me pretty much the same DC offset in each channel, without opamps installed, as I posted last night. Channel 1 = 6mV, channel 2 = 56mV DC offset. I also get the same results as last night if I turn the amp off, install the opamps, turn it back on, then my DC offsets are channel 1 = 60mV, channel 2 = 0.4mV. Are there any measurements I can make to verify each output transistor is working correctly?

So, got the Brown Dog adapters in today for the OPA445AU chips I have. In channel 2 of the amp (the one I did not short out the opamp on), I get 57mV DC offset w/o the OPA445, and 0.3mV DC offset with the opamp installed. Does that seem reasonable? Does the servo usually do that well? In channel 1 of the amp (the one I did short out the opamp on), I get 5.9mV DC offset w/o the OPA445. But I get 64mV DC offset with the opamp installed. That doesn't seem right, does it? That the DC offset would go UP 10x with the opamp installed? Any ideas what else I may have damaged in channel 1? Should I replace the output transistors? Or is this expected behavior when the channel starts with a low DC offset to begin with? I feel like I'm so close to getting this working!

Holy crap, I bet that was scary!

Well I guess it would help if I was using opamps rated for the voltage they are seeing. Next time I need to read the spec sheets a little more carefully. The OPA227P is only rated for +/-18V. Who knows if that is causing an issue as well or not. I have some OPA445AU but ran out of SOIC to DIP converters, so I won't be able to do anything more with this until next week....sigh.

So, I put the op-amp from the other channel into the channel where I had shorted +In & V- last night, got the same results, 7-12mV DC offset after warming up, whereas I used to get ~0.1mV DC offset on that channel before I shorted those pins together. So, I guess I fried something else in that channel? What should I look at first? Any test points I can check to give some ideas?

Got everything wired up in the case, powered up, was doing some final checks with my meter. Thought I'd check the V+/- voltage at the op-amps one last time. Fudged my test lead and bridged pin 3 & 4 (+In, V-) on one of the op-amps. I was using OPA227P. Now that channel that used to be at ~0.1mV DC offset, is anywhere from 7-12mV DC offset. So, other than the op-amp, did I ruin anything else? Without the op-amp, the channel still measures ~5mV DC offset, which is what it measured before I did this.

Come on, the braided, multi-colored cotton around the cable really accentuates the highs, brings the mids forward, and the bass, OMG the BASS, it's so tight and punchy...

Latest status. Getting there, slowly but surely.

Powered up the amp for the first time last night! After adjusting the trimmers, without the op-amps in, I had ~55mV offset on channel 2 and ~5mV offset on channel 1. With the op-amps in, it drops to ~1mV on channel 2 and ~0.1mV on channel 1. I have a few questions. 1) Are there any other "first power on" checks I should do before hooking up a source and headphones? 2) The TO-3 heatsinks in the PSU got up to ~60C, and the PSU is currently uncased. What are the max heatsink temps for the PSU & amp before bad stuff starts happening? I am using the 2 inch heatsinks (the ones with the single hole, from Newark) in the amp. Just wanted to know what temps are okay so I can double check once I get it cased up. Now to get it cased up. Unfortunately I still haven't figured out I want the final casing to be, but I have a 16x16x4 Par-Metal case I am going to put both the PSU & amp into for now. 3) How should I do the grounding when putting everything into one case? AC safety ground tied to enclosure Signal input ground tied to enclosure through ground loop breaker (0.1uF X/Y-rated cap in parallel with 10 ohm 5W resistor)? Input RCA jacks isolated from enclosure Volume pot tied to enclosure? Output jack isolated from enclosure Output ground connected only to output jack, never connected to enclosure Does the 0V line from the PSU just float, or is it tied to the enclosure through a ground loop breaker? If not floating, can 0V line from PSU and input signal ground be tied to enclosure through the same ground loop breaker? Should output ground on the output jack be tied to the output ground on the amp board, or go directly back to the 0V line from the PSU?

Okay, so I looked at the specs and it says the temp coefficient of the 3299W-1-501LF is 100ppm/C. So that would mean that even if the heatsink (and thus the resistor) went from 22C (room temp) to 65C, the resistance would only increase by ~2.15 ohms. Anything to worry about?

Trying to finish up my amp board. Was doing a test fit of the heatsinks with the trimmer resistor between them and the Bourns ones that were spec'd earlier in the thread from Mouser are a little wider than the ones I've worked with before. You can see in this pic, that on each side of the board, the side of the resistor is right up against and touching the side of one of the heatsinks. http://imgur.com/s6EKcY4 Will that be a problem?

I am using the newer one. I have one of the older boards with the error but currently have no plans to build it. PSU seems to be working great! I am using BB OPA227 op-amps. Measuring some temps around the board, the op-amps are the warmest at ~50C. Probably a useless measurement since the PSU is not under any load right now. The TO-3 cases are ~27C. Going to let it run for a bit and check voltages again. After about 5 minutes I had +23.12V, -22.94V on the outputs. Using a SumR tx 50VA 2x27V secondaries. EDIT: After running for a while longer, I saw +23.26V, -23.11V at the outputs.

Finally got my SumR transformer. Any precautions powering up the new PSU to test? Any problems testing it unloaded (not hooked up to the amp)?