Hi DJ.
The amp didn't cost much to build - I used spare / salvaged parts wherever I could. The main construction costs were: the heatsink (from RS), the PCBs from Rod, the toroidal transformer (very cheap from Rapid Electronics), the reservoir caps (budget types from Rapid again), and the chips themselves (from RS). A lot of the components, like the bridge rectifier, connectors, limiter circuit, etc. were taken from my failed Velleman kit.
All in all, if I were to make the amp again, it would probably cost me around £120-130UK.
Cheers,
Tim.
The amp didn't cost much to build - I used spare / salvaged parts wherever I could. The main construction costs were: the heatsink (from RS), the PCBs from Rod, the toroidal transformer (very cheap from Rapid Electronics), the reservoir caps (budget types from Rapid again), and the chips themselves (from RS). A lot of the components, like the bridge rectifier, connectors, limiter circuit, etc. were taken from my failed Velleman kit.
All in all, if I were to make the amp again, it would probably cost me around £120-130UK.
Cheers,
Tim.
trwh
you said you were never able to get the velleman kit stable. Is this even when connected to the speaker?
I suppose being surrounded by valve amps has brought me to expect needing a speaker load. Personally I have found amp designs that were marginally stable to sound better with flatter frequency response.
you said you were never able to get the velleman kit stable. Is this even when connected to the speaker?
I suppose being surrounded by valve amps has brought me to expect needing a speaker load. Personally I have found amp designs that were marginally stable to sound better with flatter frequency response.
My parents had a very old very low quality turntable (bettor) that broke each time it ran unloaded.
The effect was fast and we had several repairs when one of the channels did a bad contact after cleaning it. The last time it failed the guy at the technical service said he could not repair it because he could not find spare transistors, so they probably were germaniums and the amp perhaps was trasformer-coupled push-pull. I doubt it was class A as it did not get very hot.
In class A single ended the dissipation on the active transistor can double if the amp is unloaded.
The effect was fast and we had several repairs when one of the channels did a bad contact after cleaning it. The last time it failed the guy at the technical service said he could not repair it because he could not find spare transistors, so they probably were germaniums and the amp perhaps was trasformer-coupled push-pull. I doubt it was class A as it did not get very hot.
In class A single ended the dissipation on the active transistor can double if the amp is unloaded.
How should this be? Even if there's a load connected, there's no current through it (with no input signal) - so effectively (without input signal) the currents with and without load are the same.
Otherwise you would burn dc through the speakers.
Or are you talking about transformer coupled designs?
All the best, Hannes
I'm going to resurrect this thread because I'm planning on trying something similar, but I wanted to run it past everyone, just in case.
I have a 7 channel Onkyo receiver and I'd like to experiment with some EQ on my center channel, but unfortunately, it lacks pre-outs.
What I'm planning to do is use a basic L-Pad of resistors to convert the output to line level, so I can connect this to an external DSP and amplifier, but this resistance would be all that's across the output of the center channel, something like 10k ohm.
Anyone think this would make the receiver grumpy?
I have a 7 channel Onkyo receiver and I'd like to experiment with some EQ on my center channel, but unfortunately, it lacks pre-outs.
What I'm planning to do is use a basic L-Pad of resistors to convert the output to line level, so I can connect this to an external DSP and amplifier, but this resistance would be all that's across the output of the center channel, something like 10k ohm.
Anyone think this would make the receiver grumpy?
I would not expect it. The SS amps I know run the headphones off the power amp through series resistance or voltage divider and work perfectly with speakers disconnected. OK, resistance is a little lower than 10k, but I don't think that makes much difference.
I must say that I like AndrewT's idea of intercepting the signal where VAS and power amp (CAS?) interconnect, though.
Agreed, that would be ideal. There's enough room on the back to have 2 rows of 8 rca jacks for pre out, amp in that could be jumpered or not, but I think that would require some fairly hefty surgery on the receiver.
I'm not against trying I suppose, maybe I'll pull the top off in the next couple of days and see, perhaps I'll get lucky and the power amp board is connected to the rest of it with cables that can be easily tapped.
You'd be a trillionaire with such a DSP because you'd have to go back in time 
DSPs generally queue up the sound in order to process it properly considering the time domain, then perform their 'trick' and make sure the result is aligned time-wise before it goes into the DA converter. Only if all channels are delayed by inserting a digital time buffer, you could achieve negative delay for one by extending the delay for others. It's all about relativity, even time-wise.
DSPs generally queue up the sound in order to process it properly considering the time domain, then perform their 'trick' and make sure the result is aligned time-wise before it goes into the DA converter. Only if all channels are delayed by inserting a digital time buffer, you could achieve negative delay for one by extending the delay for others. It's all about relativity, even time-wise.
You'd be a trillionaire with such a DSP because you'd have to go back in time
The MiniDSP I'm planning to use has ~1.5ms delay. I can counteract that by changing the "distance" setting in the AVR higher by 2 feet and moving them around a tiny bit, or just re-running Audyssey and letting it re-adjust the speaker delay, which is what I did to get my subs (which also go through the MiniDSP) back in phase/time.
I think you've misunderstood what I have to work with. I've got an AVR (Onkyo TX-NR609) which gets signal from HDMI and has only speaker level outputs. My plan was to use a pair of resistors to pad down the speaker output (because there's no other output) to line level, run it into one of my MiniDSP's unused channels, do a little processing and then feed it into an external amplifier.
If the AVR had pre outs, this would be a non issue, but what I'm planning to do would mean that the center channel section of the amp in the AVR is only seeing ~2k ohm rather than the 6 ohm center channel speaker it has on it's outputs now.
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