Hey Tajzmaj,
That seems to have done the trick. It is playing fine now. I went ahead and added a 1000p to b-c on both sides of the amp just to be sure. The output coil is no longer running hot. I don't have it on a proper heatsink yet so I was only able to play it for a short time but it sounds pretty good. Quiescent current is 112mA per rail. I can see just a slight node at the crossover point on the scope. I'm not sure how the bias adjustment works on this type of amp. Maybe it's fine.
Blessings, Terry
That seems to have done the trick. It is playing fine now. I went ahead and added a 1000p to b-c on both sides of the amp just to be sure. The output coil is no longer running hot. I don't have it on a proper heatsink yet so I was only able to play it for a short time but it sounds pretty good. Quiescent current is 112mA per rail. I can see just a slight node at the crossover point on the scope. I'm not sure how the bias adjustment works on this type of amp. Maybe it's fine.
Blessings, Terry
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I'm glad to hear this.
I would suggest to remove cap from ''positive'' side. I would suggest checking it by scope. It might be responsible for that crossover node. There still might be some oscillation.
Things are going to improve if you mount amp in proper case etc. Good wiring is essential especially grounding.
I'm not sure about idle current but 112 mA seems reasonable. If you want know more about 606 check this.
http://www.desmith.net/NMdS/Shack/Bernd Ludwig 405 Modifications V13.pdf
405 is very similar to 606.
Cheers
I would suggest to remove cap from ''positive'' side. I would suggest checking it by scope. It might be responsible for that crossover node. There still might be some oscillation.
Things are going to improve if you mount amp in proper case etc. Good wiring is essential especially grounding.
I'm not sure about idle current but 112 mA seems reasonable. If you want know more about 606 check this.
http://www.desmith.net/NMdS/Shack/Bernd Ludwig 405 Modifications V13.pdf
405 is very similar to 606.
Cheers
Truth is I need to check again. The node I saw a the crossover point was on the first channel I tested. I'm not sure the second channel had it. I'm not sure the amp will ever see a chassis. Most amps I build don't. I'll do more testing and get back to you.
Juan,
I can't speak to the sound yet. I have only been playing one channel at a time so far and through my test speakers. I have to free up some heatsinks so I can hook it up to my A/B setup and then I will be able to give a more informed listening test. Square waves are just so-so. I'll post some scope shots soon.
Blessings, Terry
ok got it, I totally forget about the heat sink unusual settings making it difficult to test, ok when you get a chance no hurry take your time, I think because is current dumping design is way too different to check
stuffBest Regards
Juan
OK, I clamped it to some heatsinks and hooked it up to my A/B setup. I don't believe it is oscillation. I don't see any hash of the like on the scope but the amp sounds like it is distorting to me. Not grossly but there. Especially noticeable at low volume. Of course I can't say if it is because to the parts choices I've made or not. I may try swapping out the 2N5551/5401 for MPSA42/92. I still can't help thinking that the bias is too low. The heatsink is barely warm. I checked this morning and I do see a node at the crossover point on the scope on both channels. That usually means low bias. Any ideal how to raise the bias on this circuit?
Thanks, Terry
Thanks, Terry
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Hey Terry
Are you sure about that E701 and J503 swap? E701 seems to pass more current. It might be responsible for that distortion.
About idle current. It is normal to be really low with current dumping circuit. There is only T7 running in class A ...all the rest is basically closed at idle. I mean all the rest of the output stage.
I'm attaching photo(sadly I can't find the file I have just print) of old 520 circuit. There is solution without J503 and LM334. If you decide to put the amp in chassis when everything solved I could send you J503-s. I must still have some.
One more thing. Is everything fine with your psu. I mean do you have that floating ground? Have you connected the speaker in the middle of both smoothing cans?
Cheers
Are you sure about that E701 and J503 swap? E701 seems to pass more current. It might be responsible for that distortion.
About idle current. It is normal to be really low with current dumping circuit. There is only T7 running in class A ...all the rest is basically closed at idle. I mean all the rest of the output stage.
I'm attaching photo(sadly I can't find the file I have just print) of old 520 circuit. There is solution without J503 and LM334. If you decide to put the amp in chassis when everything solved I could send you J503-s. I must still have some.
One more thing. Is everything fine with your psu. I mean do you have that floating ground? Have you connected the speaker in the middle of both smoothing cans?
Cheers
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I am not certain about anything.
I could not find the J503 and just did some googling to try and find a replacement. You very well be right about that. Maybe the node I see on the scope is not audible. I like to mention things when I see them to aid in troubleshooting. That may just be the nature of current dumping amps.
I cheated a little on my PSU. I am using a 40-0,40-0vac transformer and just putting the secondaries in series to give me 40-0-40 and then not connecting the CT. I used a conventional PSU board with 6-6800uFx63V caps and connected only the two 40vac wires and then connected from those to the Ground plane with 470n caps. The output is +-57v with star ground.
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Hey Terry
Such crossover node is not the nature of 606. Believe me on that one. Picture on scope should be perfect. Overall 606 is one of the best amps I ever see. It is also one of the best sounding. Fast, clean, nice...everything. Far from distorted..
You could try modify it to that old 520 circuit and you will see how it behaves. It seems you just remove J503 and stick 47K resistor inside. It probably won't do any harm. I would still suggest to use some 40W bulb and connect it in series with primary of power transformer for first start.
Once again check that all grounds are connected. I have some bad memory about it and somehow I think I have had similar problem with 606 and somehow I think it was something wrong with grounding...you know many grounds at 606 and it is really easy to forget something.
Happy hunt..
Taj
Such crossover node is not the nature of 606. Believe me on that one. Picture on scope should be perfect. Overall 606 is one of the best amps I ever see. It is also one of the best sounding. Fast, clean, nice...everything. Far from distorted..
You could try modify it to that old 520 circuit and you will see how it behaves. It seems you just remove J503 and stick 47K resistor inside. It probably won't do any harm. I would still suggest to use some 40W bulb and connect it in series with primary of power transformer for first start.
Once again check that all grounds are connected. I have some bad memory about it and somehow I think I have had similar problem with 606 and somehow I think it was something wrong with grounding...you know many grounds at 606 and it is really easy to forget something.
Happy hunt..
Taj
No,no,no...don't put just diode there. It will probably result in ''bang''
That thing that J503 is such element which holds constant current through wide range of voltage in contrast to ordinary resistor which will pass certain current at certain voltage. But let's assume that you have quite constant psu voltage at your amp. Let's leave aside other benefits...basically that J503 acts very similar as resistor.
In case you put 4148 there it will pass all current which won't be blocked by R3 and R12...circuit still might survive but it won't operate properly. Far from it.
Cheers
That thing that J503 is such element which holds constant current through wide range of voltage in contrast to ordinary resistor which will pass certain current at certain voltage. But let's assume that you have quite constant psu voltage at your amp. Let's leave aside other benefits...basically that J503 acts very similar as resistor.
In case you put 4148 there it will pass all current which won't be blocked by R3 and R12...circuit still might survive but it won't operate properly. Far from it.
Cheers
I will try replacing E701 with 47k and see what happens. Besides the distortion the square wave show a weakness in the bass response.
I always use a light bulb and variac in circuit for testing. It stays on the bench at all times.
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Hi Taj,
I installed the 47k and that is a great improvement. The sound is much clearer. I hooked it back up to the A/B setup and comparing it to the Symasym, it is voiced around the midrange. The Symasym has a more full sound and bigger soundstage which seems right because the Quad shows in the square waves to be a little light in bass response. I will post some scope shots in a few minutes. The node is gone in the sine wave and clipping is very even and nice.
Blessings, Terry
I installed the 47k and that is a great improvement. The sound is much clearer. I hooked it back up to the A/B setup and comparing it to the Symasym, it is voiced around the midrange. The Symasym has a more full sound and bigger soundstage which seems right because the Quad shows in the square waves to be a little light in bass response. I will post some scope shots in a few minutes. The node is gone in the sine wave and clipping is very even and nice.
Blessings, Terry
Hey Terry
Nice to hear that.
About bass. You could try different value of input cap.It is C2, 100nF...later models 707 and 909 use 330nF there.
My guess is that 100n will cause some dB drop at 20Hz. My impression with 606 was actually tat it has really fast and deep bass. I compared it to my restored Phase Linear 700b which was hooked up in my living room at the time. I must admit that I used really big transformer for 606 and 2 boards of capacitors each 2x10pcs of 2700uF....and also quite decent wiring...I don't know what's the reason but it sounds really nice...like some really expensive, good quality amp..hehe
About that 47k resistor...it is probably not perfect solution. I would suggest buying J503 somewhere..maybe try ebay...other solution is of course P.M. me your address and wait few days.
Cheers
Nice to hear that.
About bass. You could try different value of input cap.It is C2, 100nF...later models 707 and 909 use 330nF there.
My guess is that 100n will cause some dB drop at 20Hz. My impression with 606 was actually tat it has really fast and deep bass. I compared it to my restored Phase Linear 700b which was hooked up in my living room at the time. I must admit that I used really big transformer for 606 and 2 boards of capacitors each 2x10pcs of 2700uF....and also quite decent wiring...I don't know what's the reason but it sounds really nice...like some really expensive, good quality amp..hehe
About that 47k resistor...it is probably not perfect solution. I would suggest buying J503 somewhere..maybe try ebay...other solution is of course P.M. me your address and wait few days.
Cheers
The bass is not at 20hz. You can see it even at 1khz. I will post some pics. I just found some J503s on ebay and ordered them. My guess is that without having a good A/B setup, you may not notice the difference. With the low current draw I'm not sure a huge transformer is really needed. The one I'm using is 600vA.
Blessings, Terry
Blessings, Terry
Aha..
If it is at 1KHz than something else is still wrong...and it might be result of that 47k resistor instead of j503
600VA should be enough for stereo
One more question. Do you have any power out from it...I mean like at least 20W or so to be sure that op stage is operating and it is not only that T7 class A amp via 2x22E resistors?
If it is at 1KHz than something else is still wrong...and it might be result of that 47k resistor instead of j503
600VA should be enough for stereo
One more question. Do you have any power out from it...I mean like at least 20W or so to be sure that op stage is operating and it is not only that T7 class A amp via 2x22E resistors?