Owen Y Posted September 13, 2010 Posted September 13, 2010 Did you mention an finger-lift, James? Definitely a good idea. if you can later salvage an armlift (the usual dashpot lever type) from an old arm, that will just make lowering esp, safer & more gentle.
Omegaspeedy Posted September 13, 2010 Author Posted September 13, 2010 Owen Y;132931 wrote: Did you mention an finger-lift, James? Definitely a good idea. if you can later salvage an armlift (the usual dashpot lever type) from an old arm, that will just make lowering esp, safer & more gentle. Owen, I want to add a finger lifter but I'm worried that it might roll the arm in that direction, though I can add an adjustable out rigger to compensate (extra weight) Tonight I put a slight tapper on the arm and I looks good. Still very rigid. I also twisted the tone arm cable. I'm just going to put one coat of Danish on as I don't want to add to much weight. Cable is tacked in with PVA which can be picked out if required. Owen I have an idea for the lifter. I'm going to make one with 8mm dowel on a cam arrangement fitted in a wood block:) Fiddly again but it will be worth it. I'll show pics when it' finished. Re the new arm board I'm not certain it will be final. It's made from oak which is very hard. Not sure if the acoustics will be right for what I'm doing and I want to add the lifter and RCA point integrated. Time will tell. Cheers James.
Owen Y Posted September 13, 2010 Posted September 13, 2010 A simple balanced finger lift could be a pin/brad projecting ea side. Or a bar across h'shell. Looking forward to seeing your unique solution tho!
Omegaspeedy Posted September 15, 2010 Author Posted September 15, 2010 Owen as you suggested a finger lifter is good and makes life easier. Noise still a slight problem and I think purpose designed tone arm cable will fix it and also a well screened RCA cable. Still it sounds great. I'll re-wire it next week.
Owen Y Posted September 15, 2010 Posted September 15, 2010 How's the sound? Hum pickup from mtr or nearby PTXs: Maybe strip some RF cable & use the braid &/or a metal tube in the arme groove? Grounded to the TT RCA outputs. Wood is self damping, nice.
Omegaspeedy Posted September 15, 2010 Author Posted September 15, 2010 Sound is very nice. Open, good bass, clear midrange... I stuck some aluminium tape in the groove and grounded it to RCA, took a lot of the hum away and grounded metal spike, that took more away. I think that the tone arm cable is not insulated enough and is too sensitive to RF. Proper arm wire will have a good dielectric coating. Would still like to get it quieter though. I'm 80% happy and happy enough to put my good cart on it and remove the SME. Still room for improvement as always:)
Owen Y Posted September 15, 2010 Posted September 15, 2010 Ah good, the longer tonearm => lower distortion => an 'easier' more natural tone. Also, the Unipivot bearing => bearing chatter eliminated => beautiful HF rendition. The hum is LF, usually (i) EM pickup from PTXs etc and/or (ii)Ground 'loops'. PS. The way you have the cartr mounted, their should be little, if any, azimuth correction needed. PPS. That alumin tape is handy
Omegaspeedy Posted September 15, 2010 Author Posted September 15, 2010 Owen Y;133092 wrote: Ah good, the longer tonearm => lower distortion => an 'easier' more natural tone. Also, the Unipivot bearing => bearing chatter eliminated => beautiful HF rendition. The hum is LF, usually (i) EM pickup from PTXs etc and/or (ii)Ground 'loops'. PS. The way you have the cartr mounted, their should be little, if any, azimuth correction needed. PPS. That alumin tape is handy The hum is funny Owen, when I put my hand on the arm, it increases in loudness, if I touch the metal pivot, it disappears all together. I know most TT's have a bit of hum but how much is acceptable (if any:)). I put a mirror down on the platter and it sit level which is a sweet surprise considering the finger lifter. I wonder if the cart mounting compensates it. All is good in that area anyway.
paul300b Posted September 15, 2010 Posted September 15, 2010 omegaspeedy;133095 wrote: The hum is funny Owen, when I put my hand on the arm, it increases in loudness, if I touch the metal pivot, it disappears all together. I know most TT's have a bit of hum but how much is acceptable (if any:)). I put a mirror down on the platter and it sit level which is a sweet surprise considering the finger lifter. I wonder if the cart mounting compensates it. All is good in that area anyway. Maybe try grounding the metal part of the tonearm base to the turntable? Nice arm, and so green. How much did it cost you?
Omegaspeedy Posted September 15, 2010 Author Posted September 15, 2010 paul300b;133099 wrote: Maybe try grounding the metal part of the tonearm base to the turntable? Nice arm, and so green. How much did it cost you? Cheers Paul, I've got it grounded at the moment and it did help reduce some of the noise. At about 90dB output volume position, you can hear the hum 4m away. You can't hear it over the music though. Still the SME 3009 was dead quiet once I sorted that out so my expectation is the same. I'm reasonably confident that the arm wire is at fault with its very limited dielectric. I'm hoping the Audio Consultant silver wire will be more quiet though it's got a thin dielectric too but a totally different geometric configuration (solid core 0.15mm I think). The arm cost about $50 (spike set of HAS) to make but about 40 hours labor so far. When I add the silver tone arm cable with cardas cart pegs that will add another $60.
Vitesse Audio Posted September 15, 2010 Posted September 15, 2010 2) I haven't drilled the head shell mounting screws yet. What should the offset angle be. (longitudinal axis of cart to longitudinal axis of tonearm)? Note it is a straight arm. Distance from stylus to pivot = 12". For an arm of Effective Length say 305mm...for Baerwald Alignment, Offset Angle should be 17.8mm (allow some angular adjustment, via slots or hole tolerance), Overhang 13.35mm / Pivot-Spindle 291.6mm. The easiest way to verify is to measure your own pivot to stylus length, go to Vinyl engine and feed that into their calculator by clicking effective length & type 305(??)mm: Tonearm Alignment Calculator I've been through this, just couldn't get the null points in the right place on a custom gauge I drew up. It seems the overhang and pivot-spindle spec given by an arm manufacturer was wrong, wish I'd found it earlier.
Omegaspeedy Posted September 15, 2010 Author Posted September 15, 2010 Vitesse Audio;133124 wrote: The easiest way to verify is to measure your own pivot to stylus length, go to Vinyl engine and feed that into their calculator by clicking effective length & type 305(??)mm: Tonearm Alignment Calculator I've been through this, just couldn't get the null points in the right place on a custom gauge I drew up. It seems the overhang and pivot-spindle spec given by an arm manufacturer was wrong, wish I'd found it earlier. Thanks for that, it's a cool calculator. The offset angle is within 0.6 of a degree to what I've set it to and there is enough movement to re-adjust. Cheers James.
Owen Y Posted September 15, 2010 Posted September 15, 2010 Vitesse Audio;133124 wrote: The easiest way to verify is to measure your own pivot to stylus length, go to Vinyl engine and feed that into their calculator by clicking effective length & type 305(??)mm: Tonearm Alignment Calculator I've been through this, just couldn't get the null points in the right place on a custom gauge I drew up. It seems the overhang and pivot-spindle spec given by an arm manufacturer was wrong, wish I'd found it earlier. That page is easy to use & handy. I use the John Elison spreadsheet which appears to be in agreement with the above pg & the graphs there are also a v good illustration of the effect of the diff alignments. Tonearm manuf's instructions are not always along the lines of the conventional alignment (ie, Baerwald alignment)... eg SME, also Rega too I believe. Incidentally, these tools just make it easier for you to get the right alignment quickly, when you use the parallel line protractors. Check the arm mounting distance, calculate the Overhang... then the alignment geometry should be spot-on at the 2 null pts on the protractor.
Owen Y Posted September 15, 2010 Posted September 15, 2010 For anyone interested, my take on the differences in the 3 alignments: (Refer to the Vinyl Engine graphs.) Stevenson alignment: Accepts some higher distortion at the beginning & towards the latter half of the record, for zero distortion at the IEC standard 60.3mm inner groove. (Problem is, inner grooves vary between 57.5 to 87.5mm from spindle. However, this alignment is probably intended to achieve min. distortion at the orchestral climax at the end of classical recordings.) Baerwald alignment: This is based on achieving equal peak distortion at the 3 pts across a record - the outer groove, middle & 60.3mm inner groove... ie. averages pk distortion across the record. Lofgren 'B' alignment: Accepts higher distortion at the beginning & end of a record, in favour of lower distortion over the broad middle section of the LP. The thinking is that the latter is of longer duration than the short pks of higher distortion at beginning & end. My experience is the Baerwald is best for shorter arms, (9-10"), for most music. YMMV of course PS. There are other alignments too, eg. the Allen Wright 'Guru' alignment!
Omegaspeedy Posted September 15, 2010 Author Posted September 15, 2010 Owen Y My experience is the Baerwald is best for shorter arms, (9-10"), for most music. YMMV of course Would you suggest a different alignment for a 12" arm or stick with Baerward?
Owen Y Posted September 15, 2010 Posted September 15, 2010 Not sure, James. I haven't experimented. Technically, a 12" arm has 1/3rd less distortion than a 9" arm, but as zero distortion is the benchmark, I would think that Baerwald is still best. Incidentally, some Antiskating is still useful for a 12" arm...altho a lot of people don't bother as side-force is less (~30%) than for 9" arms.
Omegaspeedy Posted September 16, 2010 Author Posted September 16, 2010 Hummmmm gone! thank christ it nearly drove me nuts:) Removed earth from TT mains and earth chassis to phono stage. Gone! Earth loop as Owen said. The SME wasn't affected by this which made me not try this earlier.
Owen Y Posted September 17, 2010 Posted September 17, 2010 So, James... TT mtr still has 3 pin plug earthed? I may have put you wrong initially, grounding TT sub chassis to tonearm works best - logical really.
Papa Hemi Posted September 17, 2010 Posted September 17, 2010 Thanks OS, looking (thinking) at all projects in gestation, this should find a place. It will definitely be a unipivot and closely modelled on yours.
Omegaspeedy Posted September 17, 2010 Author Posted September 17, 2010 Papa Hemi;133366 wrote: Thanks OS, looking (thinking) at all projects in gestation, this should find a place. It will definitely be a unipivot and closely modelled on yours. Sweet Papa! It's well worth it and sounds so good. Looking forward to seeing what you come up with. Feel free to ask any question re design. Cheers James.
Omegaspeedy Posted September 17, 2010 Author Posted September 17, 2010 Owen Y;133346 wrote: So, James... TT mtr still has 3 pin plug earthed? I may have put you wrong initially, grounding TT sub chassis to tonearm works best - logical really. no, when I got it the earth on the three pin was cut so I re-wired it when I put in the IEC socket in. This introduced noise. It is disconnected (Death trap??) now but is very quiet. If it shorts for any reason, it will fry my phono stage via earth cable, then fry my RCA's to the amp. The amp is the only earth. What do you think, is it risky?
Owen Y Posted September 17, 2010 Posted September 17, 2010 Lemme see if I understand correctly... I would do it like this: TT mtr is earthed with 3pin plug. TT chassis is now connected to tonearm grounding via IC to preamp ground. Do you think this would introduce hum? (TT mtr should only be connected to preamp via wall mains, ie. no loop?)
Papa Hemi Posted October 16, 2010 Posted October 16, 2010 Hey OS - have you seen this thread on DIY arm, I'm thinking of adapting the pivot bearing set up (although the detail of the female part seems a bit sketchy), what do you think?
Omegaspeedy Posted October 17, 2010 Author Posted October 17, 2010 Papa Hemi;135691 wrote: Hey OS - have you seen this thread on DIY arm, I'm thinking of adapting the pivot bearing set up (although the detail of the female part seems a bit sketchy), what do you think? Hi Papa, sorry I missed this, and the thread, can you point me to it? Cheers James.
Omegaspeedy Posted October 17, 2010 Author Posted October 17, 2010 Papa, here are the latest pics with some more info on my bearing. The bearing uses a hardened disc about 3mm thick with a 2mm hole drilled and dressed in the middle. The disc is then set into a pre-drilled hole and set with PVA. prior to the PVA setting (Just after the point it wont run) I assembled the arm and reset if required the bearing so that the arm hung very close to the correct position. With the cart in place it tended to roll anti-clockwise (looking at the cart end). This was fine because I added the brass counter weight. You will also note that the counterweight is as low as I could get it with the use of the spacer. I need to weigh the arm to check the resonance frequency with the Denon cart. The arm was too heavy for the Ortofon. Arm effective mass vs cart compliance graph with the aim of 12Hz shows an arm effective mass required with the Ortofon of 7grams!! With the Denon 28 grams:) I'm guessing that this is just about spot on.
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