Upupa Epops said:
Hi Pavel,
Consider me as just another guy who " likes to listen good music, but total " not technician type "... aren't preliminary impressed by some concrete technical solution, only listen..." 😉
BTW Spectral : These machines, which are really fast, may be probably sensitive to hf disturbing. Without good measuring technique may be interventions inside them very problematic...
Hi,
Somehow I feel I am not making myself clear here, unfortunately.
When I responded to a comment that Elma switches should sound as good as Shallco, there were no resistors (or whatever) involved in my listening trials here, and there was no possibility to solder the connections concerned, as this would defeat the object of adding a switch.
I needed to use a switch anyway to allow more inputs to a pre-amp, and the comparisons I made were:
1)Elma switch compared with no switch (quite noticeably worse detail due to some overall veiling).
2)Blore Ewards switch compared with Elma switch (considerably better, with much less veiling).
3) Shallco compared with Blore Edwards (very little, if any differences).
4) Shallco compared with no switch (a small deterioration in detail when using this switch, but so small, I decided to live with this).
I still feel this is as fair a trial between these different switches as practical, but when comparing any of the switches with nothing at all, one cannot ignore any small effects which may be due to the short extra wire necessary, and the 2 soldered joints.
🙂
The small differences between the Shallco and no switch, could well be due to Peter's suggestion that he feels silver has some overall effect on the sound, but in this application, I needed to use something.
Upupa,
I am sorry but I don't understand what you mean "at which chain you try this test".
Could you explain this again, please, and I will try to answer you.🙂
Somehow I feel I am not making myself clear here, unfortunately.
When I responded to a comment that Elma switches should sound as good as Shallco, there were no resistors (or whatever) involved in my listening trials here, and there was no possibility to solder the connections concerned, as this would defeat the object of adding a switch.
I needed to use a switch anyway to allow more inputs to a pre-amp, and the comparisons I made were:
1)Elma switch compared with no switch (quite noticeably worse detail due to some overall veiling).
2)Blore Ewards switch compared with Elma switch (considerably better, with much less veiling).
3) Shallco compared with Blore Edwards (very little, if any differences).
4) Shallco compared with no switch (a small deterioration in detail when using this switch, but so small, I decided to live with this).
I still feel this is as fair a trial between these different switches as practical, but when comparing any of the switches with nothing at all, one cannot ignore any small effects which may be due to the short extra wire necessary, and the 2 soldered joints.
🙂
The small differences between the Shallco and no switch, could well be due to Peter's suggestion that he feels silver has some overall effect on the sound, but in this application, I needed to use something.
Upupa,
I am sorry but I don't understand what you mean "at which chain you try this test".
Could you explain this again, please, and I will try to answer you.🙂
Upupa Epops said:
Depends on wiring technique. My old passive used a four-deck Grayhill make-before-break rotary, every second position a 100 ohm resistor wired to ground. Both ground and hot are switched. Any measurable crosstalk was down 110+ dB at audio frequecies and varied with movement of the wiring loom. That due to the selector was well below the resolution limit of any popular consumer audio source. Crosstalk is also, of course, dependant on the source impedance driving the selector.
I just read the HiFi technical description of the Lyra line stage and find it interesting the open-frame nature of the selector and attenuator in a sense echo the 'air dielectric' construction approach of the circuit path.
I'm asking, which boxes, CD player etc. do you have... To similar statements I'm very diligent, 'cos I know, which can cause psychoacoustic...
Don't forget at crosstalk between path and collector... It is nice to see with square signal...
Upupa Epops said:
Hi Upupa,
I'm sorry to say that I don't understand what you are getting at here either.
As far as my trials with the switches I have been talking about, and when comparing Elmas and Shallcos, I don't see how any switch or connector attached to the exterior of a pre-amp like this, can have any effect on its operation.
Spectral pre-amps are (or were!) not quite as mystical as maybe the makers might have you believe, and the DCM -10 I have had for nearly 20 years was certainly capable of being substantially improved, as I have found.
In fact, apart from the main circuit board and some very good Vishay resistors and teflon caps in the RIAA circuit, I have replaced almost everything else in this pre-amp since its purchase.
For example, in the input stage I replaced the cascoded NPD5566s with cascoded 2SK389s, as these are sonically better, in my opinion. In the next stage I replaced MP350s, initially with SSM2220s, and then later I used the slightly better MAT03s here. The Original MP310s were similarly replaced with SSM2210s, and then MAT02s, but the output mosfets VP1304s (x2) and single VN1304 I retained, as they are a good choice here.
Every resistor, including several presets I replaced with Vishay bulk-foils, and all caps have been changed through many 'iterations' to mainly Black Gates and MIT RTX polystyrenes.
One of the most noticeable sonic improvements was to the first-stage output DC blocking cap, for which I tried many variations before being satisfied. I made many changes to the PS including Shottky diodes and better smoothing caps than the stock IC types, and added additional discrete on-card regulators on sub-boards etc.
I must say that they are not bad circuits, but with more recent developments in active devices/components, and increased knowledge, my unit is quite different-sounding from what it was originally.
😉
Regards,
For me, Bob, is this company very symphatic, but I never hold these machine in my talons... 😉 Only one thing was for me barely beliveable, that they recomend to their machines speaker calble with build in choke ( ! )... But later I was understand - owner of cable company is ( ? ) brother-in-law of owner Spectral company... 😉
Hi Upupa,
In case my comments were misunderstood, I am not knocking Spectral, and I am sure when my DCM-10 pre-amp was designed, it was ahead of its time in concept and execution. It was the finest-sounding pre-amp I had come across at that time, too, and had huge gain to accomodate even for low-output MC cartridges.
My comments were intended to counter your apparent suggestion that there was something almost mystical and way out of the ordinary with these units, and that any changes I had made would likely unsettle my unit's operation for some reason.
At no time did I ever experience any instability, or at least if there ever was any, it was never audible, and was beyond the 'reach' of my digital 'scope, even though over the intervening years I made numerous changes to it.
Doubtless the design (mainly due to Demian Martin, I believe) was carefully considered, with all balanced circuitry using dual devices everywhere (even for current mirrors) and these dual devices were considered 'cutting-edge' at that time. I had not previously seen the use of 2x 'P' channel mosfets in the outputs partnered with 1x 'N' channel, presumably to 'equalise' gain (transconductance) characteristics, and when modelled in Number One Systems Linear Circuit Analysis Programme, the RIAA response was extremely accurate, within 0.25dB IIRC, at worst case.
Unusually, there were no stability/compensation caps to be seen anywhere, but there was a sophisticated protection circuit, which I never once saw operate.
However, I noticed after a subsequent factory update, that some R/C networks had been added underneath the PCB, I guess to curtail some of the claimed (and possibly excessive) HF bandwidth, which was supposedly in excess of 1MHz, originally.
I cannot comment on the cables and 'relationship' issues between the two companies, MIT & Spectral, other than to say that Rick Fryer was then the head of Spectral, and I understand that Richard Marsh was largely responsible for MIT's operations. I never found the need for any 'special' cables in use, myself, and I tried out many variations when I used that pre-amp, and never had any problems.
After I had the unit for a few years, I sent it back to the factory for updating to the latest spec., during which time the vol. control was swapped from an Alps to a Noble pot. Subsequently, I replaced this with a hand-selected Penny & Giles pot, but by far best 'sonic' result was experienced when I made up the Vishay/Shallco switched attenuator, and installed this.
Regards,
In case my comments were misunderstood, I am not knocking Spectral, and I am sure when my DCM-10 pre-amp was designed, it was ahead of its time in concept and execution. It was the finest-sounding pre-amp I had come across at that time, too, and had huge gain to accomodate even for low-output MC cartridges.
My comments were intended to counter your apparent suggestion that there was something almost mystical and way out of the ordinary with these units, and that any changes I had made would likely unsettle my unit's operation for some reason.
At no time did I ever experience any instability, or at least if there ever was any, it was never audible, and was beyond the 'reach' of my digital 'scope, even though over the intervening years I made numerous changes to it.
Doubtless the design (mainly due to Demian Martin, I believe) was carefully considered, with all balanced circuitry using dual devices everywhere (even for current mirrors) and these dual devices were considered 'cutting-edge' at that time. I had not previously seen the use of 2x 'P' channel mosfets in the outputs partnered with 1x 'N' channel, presumably to 'equalise' gain (transconductance) characteristics, and when modelled in Number One Systems Linear Circuit Analysis Programme, the RIAA response was extremely accurate, within 0.25dB IIRC, at worst case.
Unusually, there were no stability/compensation caps to be seen anywhere, but there was a sophisticated protection circuit, which I never once saw operate.
However, I noticed after a subsequent factory update, that some R/C networks had been added underneath the PCB, I guess to curtail some of the claimed (and possibly excessive) HF bandwidth, which was supposedly in excess of 1MHz, originally.
I cannot comment on the cables and 'relationship' issues between the two companies, MIT & Spectral, other than to say that Rick Fryer was then the head of Spectral, and I understand that Richard Marsh was largely responsible for MIT's operations. I never found the need for any 'special' cables in use, myself, and I tried out many variations when I used that pre-amp, and never had any problems.
After I had the unit for a few years, I sent it back to the factory for updating to the latest spec., during which time the vol. control was swapped from an Alps to a Noble pot. Subsequently, I replaced this with a hand-selected Penny & Giles pot, but by far best 'sonic' result was experienced when I made up the Vishay/Shallco switched attenuator, and installed this.
Regards,
Hi Bob,
thanks for explanation 😉 . About this machines I was only reading and I know anybody who have it... Words at prospects was typed such that I should can to sigh it... 😉 . Mr. Martin probably know his job very well, any redundant blables... Thank you again,
Pavel
thanks for explanation 😉 . About this machines I was only reading and I know anybody who have it... Words at prospects was typed such that I should can to sigh it... 😉 . Mr. Martin probably know his job very well, any redundant blables... Thank you again,
Pavel
Mr. Martin is actually a member of this forum: http://www.diyaudio.com/forums/member.php?s=&action=getinfo&userid=13612
Upupa Epops said:
Hi Pavel,
You are welcome, and I am glad you understand the matter now.
I also think the designer knew what he was doing, and this pre-amp was very well constructed with a lot of attention being paid to every small detail. The PCB layout was tidier than anything I had previously seen, and star-earthing, which was not generally adopted then, was used throughout, for example.
There is (nearly) always room for improvement, though, as I have found if you are prepared to spend a lot of time and money on these 'upgrading' projects. Many potential improvements which an enthusiast (who has the skills, the time, and some knowledge) might contemplate, would just not suit OEM production techniques.
Also, in this case, I took advantage of later-developed semi-conductors etc., which were not available to the designer when the unit was originally being developed. Additionally, in those days, it was not generally appreciated that power supplies are just as important for good sound as the rest of the circuitry, and I was able to make many improvements in this area. Simply replacing a few LM317/337s with many discrete on-card regulators, gave a very worthwhile boost to the overall performance, alone.
For what it is worth, I believe that the later Spectral units were designed by some other people, as Demian Martin left Spectral and went his own way, or so I understand.
Although I don't use this pre-amp much nowadays, I am still very fond of it, and for me, it performs very well.
Regards,🙂
Edit: I have just read Peter's comment, and it is interesting to know that the designer (to the best of my knowledge it was Demian Martin, as I said) is a member here. Maybe if he sees this he might make some comment?
Hi Bob,
do you have some schematic or service manual ? In this time, when people like only as possible simply circuits ( 'cos they have heads exploited by " Apostles of simplicity " 😉 ) it sound for me like " Music from paradise..." 😉
Regards,
Pavel
do you have some schematic or service manual ? In this time, when people like only as possible simply circuits ( 'cos they have heads exploited by " Apostles of simplicity " 😉 ) it sound for me like " Music from paradise..." 😉
Regards,
Pavel
There is a very nice internal photo of the DMC-10 at crustyloafer > Electronics > Hi-Fi, full size its about 4.5 Meg.
Regards
James
Regards
James
Hi Pavel,
Regrettably I don't have either as Spectral would not allow me to have a service manual nor any circuit information when I requested it many years ago. All I had was the owner's booklet, which merely indicated which pots need to be adjusted for DC output offset, and Iq etc., but no circuit information.
I therefore needed to reverse engineer anything I wished to work on when carrying out the 'upgrades' I mentioned, and this was made rather less easy due to the double-sided PCB.
There is a conceptual diagram of the initial stage including RIAA, shown on page 211 of John Linsley Hood's book "Valve & Transistor Audio Amplifiers", if you are interested. This was derived from information which I provided to this author, who was a long-term friend and mentor of mine, until his regrettable demise a couple of years ago.
Incidentally, I was not aware that this information was ever going to be published, and to respect the manufacturer, Spectral, I don't think it would be wise for me to show any other specific details. I am sure this Forum would not permit me to do this, anyway.
There is a second stage in this pre-amp which has an identical topology except for the RIAA components in the feedback path, and in between these 2 stages, is the volume control and some inputs for auxillary/tape etc.
As there was merely one aux. input and I had several analogue sources, this gave rise to the need for me to add an external switch to expand this capability, and hence the trials I conducted between the various types of switches I mentioned before.
I hope this helps.
Regards,🙂
Regrettably I don't have either as Spectral would not allow me to have a service manual nor any circuit information when I requested it many years ago. All I had was the owner's booklet, which merely indicated which pots need to be adjusted for DC output offset, and Iq etc., but no circuit information.
I therefore needed to reverse engineer anything I wished to work on when carrying out the 'upgrades' I mentioned, and this was made rather less easy due to the double-sided PCB.
There is a conceptual diagram of the initial stage including RIAA, shown on page 211 of John Linsley Hood's book "Valve & Transistor Audio Amplifiers", if you are interested. This was derived from information which I provided to this author, who was a long-term friend and mentor of mine, until his regrettable demise a couple of years ago.
Incidentally, I was not aware that this information was ever going to be published, and to respect the manufacturer, Spectral, I don't think it would be wise for me to show any other specific details. I am sure this Forum would not permit me to do this, anyway.
There is a second stage in this pre-amp which has an identical topology except for the RIAA components in the feedback path, and in between these 2 stages, is the volume control and some inputs for auxillary/tape etc.
As there was merely one aux. input and I had several analogue sources, this gave rise to the need for me to add an external switch to expand this capability, and hence the trials I conducted between the various types of switches I mentioned before.
I hope this helps.
Regards,🙂
tvi said:
Hi James,
From the look of that pic, I would say it is an early version without the Vishay resistors and teflon caps in the RIAA section, but I am sure that the bank of 16 smoothing caps on the right, have been modified.
It looks like two caps have been replaced with a slightly different type/colour, and two more have been added, which puzzles me as the lower 2 rows of caps are only for the Left channel. The upper 2 rows cover the right channel, and normally the entire bank of electrolytics is in a square outline, with 4 rows of 4 caps.
Maybe there was a problem with some caps and the repairer couldn't obtain similar types/values, but I am sure it never left Spectral in that state, looking rather odd and untidy, and with possibly different total capacitance for each channel.
You can readily see how much care has gone into designing and making this pre-amp, though, and the gold-plated double-sided PCB is obvious here.
Regards,
Hi Bob,
I can't to do some reverse ingeneering ( nice word for normal thievery 😉 )... If you can, send me a mail, I will post you some my circuits for your inspiration 😉 - you will see, why I like this firm...
Regards,
Pavel
P.S. : Many thanks to James, photo is wonderfull...
I can't to do some reverse ingeneering ( nice word for normal thievery 😉 )... If you can, send me a mail, I will post you some my circuits for your inspiration 😉 - you will see, why I like this firm...
Regards,
Pavel
P.S. : Many thanks to James, photo is wonderfull...
Hi,
thievery it's not.
One has already paid for a piece of equipment and one want's to understand how it works.
No worse than dismantling a bicycle to understanding it's internal workings.
Maybe Bobken is good at this but I have found it very time consuming. I have only done four so maybe I need more practice, but I'm NOT volunteering to do your's.
Maybe it depends on what one plans to do with the information. I hope the "thievery" comment does not indicate you intend selling on that reverse engineered knowledge!
thievery it's not.
One has already paid for a piece of equipment and one want's to understand how it works.
No worse than dismantling a bicycle to understanding it's internal workings.
Maybe Bobken is good at this but I have found it very time consuming. I have only done four so maybe I need more practice, but I'm NOT volunteering to do your's.
Maybe it depends on what one plans to do with the information. I hope the "thievery" comment does not indicate you intend selling on that reverse engineered knowledge!
- Status
- Not open for further replies.