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Post by karma67 on May 1, 2020 16:27:58 GMT
LED's are lit in MM mode, that is with the relays energised. The design has the relays unpowered in MC mode so there is no possibility of any ripple on the relay supply from coupling into the sensitive MC input. The MC input isn't switched btw. Don't throw the switch unless the volume is at minimum, there is a large perturbation in output when switching. ive been having a lot of them lately  |
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Post by Deleted on May 1, 2020 16:36:39 GMT
LED's are lit in MM mode, that is with the relays energised. The design has the relays unpowered in MC mode so there is no possibility of any ripple on the relay supply from coupling into the sensitive MC input. The MC input isn't switched btw. Don't throw the switch unless the volume is at minimum, there is a large perturbation in output when switching. Thanks Alan. I normally flick the mute switch on the preamp before switching anything having learned the hard way in the past! LED's on it is then for this evening's test. I'll soak test everything for a few hours first. |
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Post by electronumpty on May 1, 2020 16:47:55 GMT
Great looking build, love the copper shield!
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Bigman80
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Post by Bigman80 on May 1, 2020 16:57:26 GMT
Thanks Oli and thank you for all your responses to queries on some of the techy bits. Bending the copper plate: A big vice and nylon fronted hammer with a block of scrap plywood between it and the copper.We have power and everything lights up....a big bonus is that I didn't turn to a toasty crisp when I switched it on! Earth continuity between panels testes and within 0.1 Ohms all round. Close up, and I mean with my ear a few inches from the case I can hear a slight hum of the transformer but you wouldn't be able to hear this from a metre or two away.  
I assume that the red LEDs are lit in "MC" mode? They go off if I throw the switch anyway. I just have the front panel decals and some lettering for the rear of the casework to finish all off to do now. As i suspected. I now need a big Vice lol |
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Post by antonio on May 1, 2020 17:06:20 GMT
Very tidy work, I like it. Next up a review.  |
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Post by Deleted on May 1, 2020 17:12:47 GMT
Just played the first track and something's not right at all. Sound is massively bass heavy and there's no HF detail. Checked the wiring and all is present and correct. Valve positions PCC88 to top, ECC83 middle and PCC88 bottom (as you look at them in a line). Are the valve positions right?
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Post by firebottle on May 1, 2020 17:19:05 GMT
Valve positions are correct, what cartridge are you using Paul?
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Post by electronumpty on May 1, 2020 17:20:01 GMT
is this in MM?
When I first put mine on (in MM) it sounded a bit dull with a lack of the hf detail that the mk1 has from the off. After 2-3 sides it became more apparent and now sounds very good. I used Mundorfs for the main and 2.2 uf caps though. give it a side or 2 and see?
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Post by Deleted on May 1, 2020 17:34:08 GMT
Slaps head...then a headbutt to the wall!
Right...I'm the numpty. I'd soldered in 330 Ohm load resistors thinking that the switch flicked between circuits. It doesn't, so I need to remove the load resistors to use in on MM. I guess it just uses the relay to switch gain through the JFETS for the additional 28dB or whatever MC needs?
One change I'd suggest perhaps if there was ever to be a V4 would be a simple one....it would mean the need for a second switch but what I'll do is mount a breadboard piece on some standoffs and have a 2A LV switch in line with the load resistors with the return going back to the PCB. That way I can switch in and out the MC stage without needing to desolder anything.
I may also add a jumper panel to the rear for a resistor netwirk to allow for adjustable loading.
I guess the load resistor in circuit is the candidate for muffled sound...bass nearly blew the windows out mind....
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Post by Deleted on May 1, 2020 17:49:52 GMT
Ok..order restored. Offending load resistors clipped off for now and all is back to normal.
First impressions are good. To early for any sort of review but with volume turned up to normal loudsih listening position there's only the slightest breath of audible hiss evident through the speakers....bear in mind that I'm listening on 93dB/1w/1m speakers though so with most speakers anywhere in the 80's sensitivity, there's be no audible hum at all.
First few tracks the overwhelming impression summed up in one line would be "smoothness and balance but with detail". It's evident immediately that it is more refined than the little giant killing Hagerman Cornet stage I built some years back but that was compromised by its power supply.
Well done Alan and Oli....it's a good design, very quiet indeed. You should publish a build guide, when opened reads in big letters only "Remove the loading resistors you Numpty!"
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Post by hammer on May 1, 2020 18:06:41 GMT
Nice job Paul
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Post by Deleted on May 1, 2020 18:13:09 GMT
Thanks hammer.
Forgot to answer Alan's question....valves are all NOS Phillips short plate. I do have a few others here but initial impressions with these are very good indeed.
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Post by firebottle on May 1, 2020 18:32:38 GMT
The design was really intended for loading sockets to be used, so any loading, resistive for MC or capacitive for MM could be plugged in as required.
Glad you have it running Paul and thanks for the vote of confidence.
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Post by Deleted on May 1, 2020 18:55:17 GMT
Thanks Alan
Yes, I can see how loading sockets would make sense. Is there any "standard" load already set for MM capacitance? (ie without any load caps additive to a standard say 150pF?)
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Bigman80
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Post by Bigman80 on May 1, 2020 19:54:56 GMT
Thanks Alan Yes, I can see how loading sockets would make sense. Is there any "standard" load already set for MM capacitance? (ie without any load caps additive to a standard say 150pF?) 150pf sounds recognisable |
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Post by gninnam on May 1, 2020 20:34:06 GMT
Fantastic work and it looks brilliant - great work and glad it sounds good.
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Bigman80
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Post by Bigman80 on May 1, 2020 20:47:35 GMT
The design was really intended for loading sockets to be used, so any loading, resistive for MC or capacitive for MM could be plugged in as required. Glad you have it running Paul and thanks for the vote of confidence. 100% on the loading plugs vein That option really gives ultimate flexibility and whilst initially may be a bit of an extra spend (on sockets and plugs) it's worth it IMO. I'd take a plug over a switch btw...just never keen on switches in the signal path. |
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Post by Deleted on May 1, 2020 21:06:57 GMT
True...but it's switched through a relay and you can get low noise switches. It's more the convenience if you have a few arm/cart combos to avoid taking the top off but agreed. loading sockets are the obvious and simple answer.
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Bigman80
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Post by Bigman80 on May 1, 2020 21:18:31 GMT
True...but it's switched through a relay and you can get low noise switches. It's more the convenience if you have a few arm/cart combos to avoid taking the top off but agreed. loading sockets are the obvious and simple answer. I believe LDA does a rotary switch on the back of his phonostages and in reality, that is probably THE most convenient way, but i didnt understand how he did it so i left it alone lol. Maybe one day when i am clevererer i can do the same hahaha Anyway, that's the beauty of a project like this, you can tailor it to do whatever you want, however you want it. |
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Post by Deleted on May 1, 2020 21:50:13 GMT
is this in MM? When I first put mine on (in MM) it sounded a bit dull with a lack of the hf detail that the mk1 has from the off. After 2-3 sides it became more apparent and now sounds very good. I used Mundorfs for the main and 2.2 uf caps though. give it a side or 2 and see? Hope you put them in the right way. |
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Post by Deleted on May 1, 2020 21:52:05 GMT
Did you not consider using rubber stand-offs for isolation? I would.
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Post by electronumpty on May 1, 2020 21:53:34 GMT
is this in MM? When I first put mine on (in MM) it sounded a bit dull with a lack of the hf detail that the mk1 has from the off. After 2-3 sides it became more apparent and now sounds very good. I used Mundorfs for the main and 2.2 uf caps though. give it a side or 2 and see? Hope you put them in the right way. They are fine, non directional  |
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Bigman80
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Post by Bigman80 on May 1, 2020 22:02:56 GMT
Did you not consider using rubber stand-offs for isolation? I would. Got a link to any nice ones? |
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Post by electronumpty on May 1, 2020 22:15:54 GMT
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Bigman80
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Post by Bigman80 on May 1, 2020 22:41:13 GMT
How on gods earth do you order those? Sorted, quote requested Fantastic website for oddities. |
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Post by Deleted on May 1, 2020 22:59:11 GMT
Hope you put them in the right way. They are fine, non directional Ah! Not that straight forward! Once upon a time, some film caps used to be banded with an identification mark to identity which connection was the outer and which was the inner. The outer connection going to the preceding circuit and the inner connection going to the proceding circuit. This was done to minimize noise. So there you go. Trouble is, manufacturers don't bother with an identification band now, and even if there is one, it's not a guarantee that it's correct. Love his deadpan expressions and deliveries. |
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Post by Deleted on May 1, 2020 23:02:01 GMT
Did you not consider using rubber stand-offs for isolation? I would. Got a link to any nice ones? Not right now. Just search on eBay for rubber standoff. ebay.co.uk/itm/283857495223Packs of 4 for £3.30, I think. |
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Post by Deleted on May 2, 2020 6:46:34 GMT
Did you not consider using rubber stand-offs for isolation? I would. Yes, of course I did . It's a little odd to assume what you might or might not do, isn't it, without first the knowledge of the transformer details and behaviour under load? How many pieces of hifi kit do you own that use stand offs for the transformer? I've checked and the only other piece of kit that I own that uses any is the Radford STA25 Series 5. It's good practice to have the traffo case grounded to chassis earth....not strictly necessary, but this can still be done well enough with rubber washers or isolation stand offs and ensure earth continuity via the fixing threads and star washers. In this case, as it is a properly (over) rated transformer, it isn't saturating or having any electrical buzzing to cause vibration so in this case no transformer isolation is needed. None. It weighs as much as a small boat anchor! Oli, if you need the details of the feet I'll PM you the details. |
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Post by Deleted on May 2, 2020 7:05:34 GMT
What's odd about it? It's a simple enough question. You could have said yes I tried it but there was no benefit or no I didn't think it would make that much difference. If you had considered it I just thought you would have mentioned it. Hardly a unique position not having vibration isolation. I can't actually recall seeing any preamp using such mounts, which, with valves, has always struck me as a bit "odd"!.
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Post by Bigman80 on May 2, 2020 7:09:43 GMT
What's odd about it? It's a simple enough question. You could have said yes I tried it but there was no benefit or no I didn't think it would make that much difference. If you had considered it I just thought you would have mentioned it. Hardly a unique position not having vibration isolation. I can't actually recall seeing any preamp using such mounts, which, with valves, has always struck me as a bit "odd"!. I think it is a valuable idea for the PCB and is one i looked at, but those you've linked to are too big. However, Electronumpty has located some very suitable ones. €35 for 12 though......ouch |
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