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Old 5th January 2013, 08:05 PM   #151
redjr is offline redjr  United States
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Bob -

I just had a strange thing happen.... I was listening to my 7294 and source (my Zune) ended. I didn't immediately jump up and turn the amp off. After about 15 minutes I heard a loud pop, and then audible hum coming from the speakers. Didn't smell anything though. I took it around to my bench and opened it up to take a look. Nothing out of the ordinary. Nothing charred, no burnt odor. Haven't turned it back on yet, but will try and trouble shoot later tonight. Check PSU voltages, etc. This was the first time this happened. Odd. Is there some kind of standby mode the amp goes into automatically if it does not receive a signal after a preset time limit? Even so, it shouldn't make a loud pop when doing so!

Rick
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Old 5th January 2013, 08:31 PM   #152
KSTR is offline KSTR  Germany
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Originally Posted by gootee View Post
I used the "toner tranfer" type of method, usually with two-sided PCBs. I eventually found out how to do it using locally-available supplies, as much as possible, so that I only had to ensure that I had PCB blanks on hand, because I never wanted to have to wait for anything to be shipped to me (and it was much cheaper). The only other real problem was making sure that I had the correct paper to use for the transfer. I found a very good-working one that was carried by the local Staples office-supply store. But they kept changing it, almost yearly.
Tom,

At the moment I don't have PCB capabilities at home but I hope to change that soon, as I perfectly agree to start right away with a real PCB rather than bread-boarding. The more complex the total circuitry has grown (damn scope creep ) the more it pays off. I may do simple CNC-milled PCBs at work, occasionally, and did that before. Or just order, pay and wait for profesional proto boards, it's not that expensive.

For this amp, though, I think dead-bugging on copper GND plane and the mentioned capacitor strips plus some p2p wiring will do and is quite quick and easy, too (I hope to get there by tomorrow). Impedance, resistance and loop characteristics are about the same and should transfer well to a real PCB. Time will tell...
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Old 5th January 2013, 08:39 PM   #153
gootee is offline gootee  United States
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Originally Posted by KSTR View Post
Tom,

At the moment I don't have PCB capabilities at home but I hope to change that soon, as I perfectly agree to start right away with a real PCB rather than bread-boarding. The more complex the total circuitry has grown (damn scope creep ) the more it pays off. I may do simple CNC-milled PCBs at work, occasionally, and did that before. Or just order, pay and wait for profesional proto boards, it's not that expensive.

For this amp, though, I think dead-bugging on copper GND plane and the mentioned capacitor strips plus some p2p wiring will do and is quite quick and easy, too (I hope to get there by tomorrow). Impedance, resistance and loop characteristics are about the same and should transfer well to a real PCB. Time will tell...
Very good.

But that reminds me of another option: Since not many people make their own PCBs, and since professionally-manufactured PCBs are pretty cheap if a lot of them are ordered at once, then if this project eventually has a PCB made available, through group buys or whatever, why would we not want to use a multilayer board with at least four layers? (Or, maybe that could just be another future version.)
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Old 5th January 2013, 08:57 PM   #154
KSTR is offline KSTR  Germany
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I would think that the cost-up for 4-layer is better redirected into 105u (3x) copper, two-sided. I won't mind a few copper jumper wires or copper foils if I run out of layers anywhere. For lowest inductance 0.5mm base epoxy is nice but rather floppy in mechanical properties.
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Old 5th January 2013, 09:18 PM   #155
bcmbob is offline bcmbob  United States
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Originally Posted by redjr View Post

........In all honesty, the sound with my current 7294 build amp has a lot of overall presence - which I like. While over the long haul it can be a bit fatiguing and somewhat harsh to listen to, I find I enjoy the dynamics of it's range over that objection. Music and vocals are crisp and clear across the range with a modest amount of bass from the 350's passive 8" woofer/baffle..........I like it when I can hear the fingers slide on a guitar, or the vocalist take a breath! ............I might (and hope) be pleasantly surprised! I would like to do some serious A/B comparison between the stock amp sound and a redesigned amp. ........... so I'll just have to trust my ears!

Rick
So glad to get a matching subjective review. You called out the exact features that impressed me. That dynamics/presence trade-off is what I've been calling the need to clean up the top end. I have some side sound absorbency panels along both walls and I set the blinds as to not allow reflections. Opposite the speakers (~ 12 ft.) is a long overstuffed couch and as a result experience little or no ear fatigue with the stock build.

The V1.2 MyRef experience was similar but I am totally thrilled at how Dario, linuxgury, Uriah and others brought the entire presentation to a level far above my expectations with their mods and parts selection. It looks like that same level of development is going to take place here.

I built a sub (rather two subs - both sealed and reflex) using a Hi-Vi driver with a 68 pound magnet and a 500W bash sub amp. I haven't even turned it on once the improvements to the MyRefs were completed. I'm sure the "gurus" here will be able to tune in the bottom of the TDA7294 to everyone's satisfaction. It's my personal view that a woofer surface area equaling at least 8" is necessary to produce what high quality chip base amp is fully capable of.

I have never experiences anything like you describe as a standby shutdown. There have been some strange noises, but in my case are due to hiccups in the JRiver player. Maybe what you heard was the Zune going to sleep. Hope you have some junk speakers around for the next power-up.

Thanks again for the review.
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Last edited by bcmbob; 5th January 2013 at 09:37 PM.
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Old 5th January 2013, 10:55 PM   #156
Jay is offline Jay  Indonesia
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Originally Posted by bcmbob View Post
The V1.2 MyRef experience was similar but I am totally thrilled at how Dario, linuxgury, Uriah and others brought the entire presentation to a level far above my expectations with their mods and parts selection. It looks like that same level of development is going to take place here.
I think it was mentioned that the MyRef was originally designed with TDA7294 but later found that 3886 was more suitable. I do think that the TDA needs the same approach as MyRef to be improved.
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Old 5th January 2013, 11:27 PM   #157
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Originally Posted by redjr View Post
I was listening to my 7294 and source (my Zune) ended. I didn't immediately jump up and turn the amp off. After about 15 minutes I heard a loud pop, and then audible hum coming from the speakers.
Probably the Zune went off.
But you could check the amplifier's speaker jack for DC, just in case.
P.S.
I always use speaker protection of some sort with my chip amplifiers. Some output caps are most fun for bass extension tuning, but speaker protector kits work too.
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Old 5th January 2013, 11:50 PM   #158
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Originally Posted by KSTR View Post
Alternate Local Decoupling.
Really interesting, similar to AN-202 regarding feed forward decoupling.

Quote:
Originally Posted by gootee View Post
Actually, there is almost no similarity to a stacked film cap.
(...)
A stacked film cap is a single cap with some known "bad" issues for audio, and more inductance than the entire 100000uF array. How could there even be a comparison?
A stacked film cap in practice is a parallel of hundreds of plain caps.

Quote:
Originally Posted by Jay View Post
I think it was mentioned that the MyRef was originally designed with TDA7294 but later found that 3886 was more suitable. I do think that the TDA needs the same approach as MyRef to be improved.
I don't know if it were the TDA7294 but for sure from the TDA series.

I'm not sure the TDAs are well suited as current pumps.
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Old 6th January 2013, 12:43 AM   #159
redjr is offline redjr  United States
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Quote:
Originally Posted by danielwritesbac View Post
Probably the Zune went off.
But you could check the amplifier's speaker jack for DC, just in case.
P.S.
I always use speaker protection of some sort with my chip amplifiers. Some output caps are most fun for bass extension tuning, but speaker protector kits work too.
I think that might have been what happened, unless it was possibly heat related. But with no signal, I would suspect that the amp would not continue to heat up. I checked the voltage on both channels. 1.5 and 1.6mV respectively. I've never used coupling caps on the outputs of any of the amps I've built other then what's included on the standard schematic. (Should I be?) I've always felt they've 'messed' with the sound a bit.
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Old 6th January 2013, 10:36 AM   #160
KSTR is offline KSTR  Germany
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Dario,

That AN-202 is a classic and my oldest reference to that idea.

TDAs did well in some standard "current pumps" and mixed output impedance amplifiers I designed. Howland type is critical because common mode voltage is high (67% of the output voltage in the MyRefs) and could exceed chip limits, which are unknown for the TDAs other than that the input stage cuts off when pulled to V-. True usable input CM range is something I want to find out in detail sometime, in comparison to the LMs. Both have not specified this parameter in their datasheets so we can only assume a guaranteed range of no more than about 1/10th of the ouput voltage plus some unknown headroom, depending on supply voltages and their balance.
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