Its been a while since I have contributed to this forum so thought it could be useful and informative for others to post details about my recent Musical Fidelity A1 re-build. The re-built amp sounds pretty amazing and well worth the many hours of effort slaving over a hot soldering iron and emptying my pockets to buy replacement components
To summarise the re-build:
1) Replaced direct wire 2-core mains lead with proper 3-core mains cable attached to an in-line 3-pin IEC plug, PE connected to chassis. The steel case on this amplifier is really hard to cut so this mod gives a mains IEC connection with very little effort.
2) Fitted a decent Ground Loop Breaker (Rod Elliot ESP) to replace the original 3R3/100nF parallel circuit attached to the chassis green 4mm banana post.
3) Upgraded the original 06A10 6A rectifier diodes with 10A10 10A and fitted 47nF 250V capacitor filter across the AC on the board. Possibly, a high current bridge rectifier may have been even better.
4) Re-capped the PSU capacitors, with as much as I could squeeze in to try compensate for the rather puny mains transformer. This involved using my Dremel to drill new capacitor mounting holes - 12000u + 2200u + 2200u followed by 12000u + 2200u, the original 0.47R 3W dropper resistor was replaced by 0.56R 5W which I had available. The 2200u were low ESR, 105C rated however the main Nichicon capacitors were standard 85C (I know, I know!).
5) Replaced the signal input 1u electrolytics (C6 & C7) with 1uF MKT and other electrolytics with same or better value/rating 105C replacements.
6) Removed the quad TL084 op-amps and re-fitted in DIL sockets, just for fun.
7) Isolated the existing pre-amp output using a 2-pin shunt jumper (open) and fitted direct input phono sockets to the power amp section, connected across resistor R3, 100K. I fitted a 2K/1K resistor divider onto the phono sockets to match the signal levels from my source. NOTE: This must be connected to a pre-amp or an audio source with volume control/adjustment.
8) Replaced the original MJ2955/2N3055 with MJ15023/MJ15024 transistors and fitted new silica washers with heat-sink paste instead of the dry thermal Silicone pads. Its important to do this because the pads may have deteriorated due to the repeated hot-cold thermal cycling and will have loosened off the mounting screws anyway. I fitted a heavy-gauge silicon wire collector connection to the board.
9) Replaced the board to output speaker connector cables with similar heavy gauge silicon wire.
10) Resprayed the top heatsink cover with 2 - 3 coats of matt black high temperature "stove" paint, good for up to 600 deg so should be ok with the A1 toaster.
Probably the most important improvement was to by-pass the existing pre-amp circuit, which is well-documented to be a poor design and bad implementation. Secondly, the seriously beefed-up PSU supply does wonders for the low end bass performance and general mid-range dynamics. Its warm, lush sound may not suit everyone's musical taste but its getting plenty of playing time with my music collection, its a definite keeper. I am a Musical Fidelity convert and have just bought an el cheapo B200 and am in the process of yet another re-build
To summarise the re-build:
1) Replaced direct wire 2-core mains lead with proper 3-core mains cable attached to an in-line 3-pin IEC plug, PE connected to chassis. The steel case on this amplifier is really hard to cut so this mod gives a mains IEC connection with very little effort.
2) Fitted a decent Ground Loop Breaker (Rod Elliot ESP) to replace the original 3R3/100nF parallel circuit attached to the chassis green 4mm banana post.
3) Upgraded the original 06A10 6A rectifier diodes with 10A10 10A and fitted 47nF 250V capacitor filter across the AC on the board. Possibly, a high current bridge rectifier may have been even better.
4) Re-capped the PSU capacitors, with as much as I could squeeze in to try compensate for the rather puny mains transformer. This involved using my Dremel to drill new capacitor mounting holes - 12000u + 2200u + 2200u followed by 12000u + 2200u, the original 0.47R 3W dropper resistor was replaced by 0.56R 5W which I had available. The 2200u were low ESR, 105C rated however the main Nichicon capacitors were standard 85C (I know, I know!).
5) Replaced the signal input 1u electrolytics (C6 & C7) with 1uF MKT and other electrolytics with same or better value/rating 105C replacements.
6) Removed the quad TL084 op-amps and re-fitted in DIL sockets, just for fun.
7) Isolated the existing pre-amp output using a 2-pin shunt jumper (open) and fitted direct input phono sockets to the power amp section, connected across resistor R3, 100K. I fitted a 2K/1K resistor divider onto the phono sockets to match the signal levels from my source. NOTE: This must be connected to a pre-amp or an audio source with volume control/adjustment.
8) Replaced the original MJ2955/2N3055 with MJ15023/MJ15024 transistors and fitted new silica washers with heat-sink paste instead of the dry thermal Silicone pads. Its important to do this because the pads may have deteriorated due to the repeated hot-cold thermal cycling and will have loosened off the mounting screws anyway. I fitted a heavy-gauge silicon wire collector connection to the board.
9) Replaced the board to output speaker connector cables with similar heavy gauge silicon wire.
10) Resprayed the top heatsink cover with 2 - 3 coats of matt black high temperature "stove" paint, good for up to 600 deg so should be ok with the A1 toaster.
Probably the most important improvement was to by-pass the existing pre-amp circuit, which is well-documented to be a poor design and bad implementation. Secondly, the seriously beefed-up PSU supply does wonders for the low end bass performance and general mid-range dynamics. Its warm, lush sound may not suit everyone's musical taste but its getting plenty of playing time with my music collection, its a definite keeper. I am a Musical Fidelity convert and have just bought an el cheapo B200 and am in the process of yet another re-build
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Any connection to chassis would require any paint or anodizing to be removed to ensure a good electrical connection.
As the original design is double insulated you can not rely on different parts of the chassis being in good electrical contact with other parts due to paint and anodising... such as sides, top etc.
Remember the PE was not part of the original design and so is not needed for safety.
As the original design is double insulated you can not rely on different parts of the chassis being in good electrical contact with other parts due to paint and anodising... such as sides, top etc.
Remember the PE was not part of the original design and so is not needed for safety.
I repaired one of these for a friend (actually my wife's hairdresser ) when living in Taiwan. A seriously nice sounding amp (warm and lush are the right words) that got me into my class A amps.
In my case it was the filter resistors (1 Ohm IIRC?) that had burnt out. Replaced them and redid the heatsink compound and it was good to go. It does run hot.
I got him to position a desk fan over the top to keep it cool. When we left about 2 yrs later he was still enjoying it.
) when living in Taiwan. A seriously nice sounding amp (warm and lush are the right words) that got me into my class A amps.In my case it was the filter resistors (1 Ohm IIRC?) that had burnt out. Replaced them and redid the heatsink compound and it was good to go. It does run hot.
I got him to position a desk fan over the top to keep it cool. When we left about 2 yrs later he was still enjoying it.
Ok clear... well i see that PE was not present in the original scheme so i agree is not needed....
About heating... yes it runs pretty hot... but i solved without fan as it can bring some noise\disturbance etc... so i just removed the 2 sides and it does not go over 50\55 (which is acceptable i guess)))
About heating... yes it runs pretty hot... but i solved without fan as it can bring some noise\disturbance etc... so i just removed the 2 sides and it does not go over 50\55 (which is acceptable i guess)))
Musical Fidelity A1
Hi Aurgolo - in case you hadn't already found it, just wanted to point-out Mark Hennessy's excellent A1 pages:
Hi-Fi › Musical Fidelity A1
I've always really liked these - hope you are enjoying it!
Rgds/paul
Hi Aurgolo - in case you hadn't already found it, just wanted to point-out Mark Hennessy's excellent A1 pages:
Hi-Fi › Musical Fidelity A1
I've always really liked these - hope you are enjoying it!
Rgds/paul
The power amp stage of this integrated amp was designed by Tim De Paravicini
https://www.musicalfidelity.com/news/65/15/Tim-De-Paravicini-1945-2020
and
https://www.whathifi.com/features/that-was-then-musical-fidelity-a1-1985
and as I know one of any few solid state amplifiers (additional I know EAR M100A - go to
https://www.diyaudio.com/community/...former-coupled-single-ended-amplifier.391567/
and the amps mentioned here:
https://www.diyaudio.com/community/...o-those-from-passlabs-overview-wanted.317489/)
For me MC's A1 is one of the best sounded solid state resp. transistorized integrated amplifiers.
Circuit descriptions are here:
https://www.markhennessy.co.uk/mf_a1/technical.htm
and some descriptions regarding refurbishing in German are here:
https://ftbw.de/xp/amplifier-xp/musical-fidelity-a-1x.html
https://ftbw.de/xp/amplifier-xp/musical-fidelity-a-1.html
https://ftbw.de/workshop/hifi-highend-service/musical-fidelity-fix-price/david2-revision.html
Here some measurements:
https://www.audiosciencereview.com/...-mk3-and-b200-vintage-amps-measurements.3141/
Now the question: exist anywhere a description from Tim De Paravicini itself (for the circuit of power amp unit) ?
I want to realize some other own ideas/variations (e. g. adding a adjustment for idle current in the output stage and a variation of open loop gain etc.).
Maybe Tim De Paravicini's circuit description explain more details than those from Mark Hennessy.
https://www.musicalfidelity.com/news/65/15/Tim-De-Paravicini-1945-2020
and
https://www.whathifi.com/features/that-was-then-musical-fidelity-a1-1985
and as I know one of any few solid state amplifiers (additional I know EAR M100A - go to
https://www.diyaudio.com/community/...former-coupled-single-ended-amplifier.391567/
and the amps mentioned here:
https://www.diyaudio.com/community/...o-those-from-passlabs-overview-wanted.317489/)
For me MC's A1 is one of the best sounded solid state resp. transistorized integrated amplifiers.
Circuit descriptions are here:
https://www.markhennessy.co.uk/mf_a1/technical.htm
and some descriptions regarding refurbishing in German are here:
https://ftbw.de/xp/amplifier-xp/musical-fidelity-a-1x.html
https://ftbw.de/xp/amplifier-xp/musical-fidelity-a-1.html
https://ftbw.de/workshop/hifi-highend-service/musical-fidelity-fix-price/david2-revision.html
Here some measurements:
https://www.audiosciencereview.com/...-mk3-and-b200-vintage-amps-measurements.3141/
Now the question: exist anywhere a description from Tim De Paravicini itself (for the circuit of power amp unit) ?
I want to realize some other own ideas/variations (e. g. adding a adjustment for idle current in the output stage and a variation of open loop gain etc.).
Maybe Tim De Paravicini's circuit description explain more details than those from Mark Hennessy.
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Dear @tiefbassuebertr!
Unfortunately, there is no detailed and readable description of how the A1 Power Amplifier (by Tim de Paravincini) works. But there doesn't have to be, as the circuit is self-explanatory.
Yesterday, by chance, I stumbled across a fellow countryman of ours once again, in his world he is the master of knowledge, see for yourself:
Meisterwerkstatt Kühne
"Musical Fidelity A1 - oft kopiert, nie verstanden" [Zitat M.K.]
He announces the airing of a secret that has been kept for well over four decades. As I said, he announces it and rambles a lot.
Nothing more needs to be said. But all this (unqualified) rambling does more harm to this beautiful little amplifier than anything else.
I really like the A1 and every incorrect attempt to explain this simple circuit really bothers me.
#
The only other thing that interests me about the A1 is the current modifications that have been made to the model currently available.
Does anyone have a service manual or a current circuit diagram of the complete new A1 that they could publish here?
Regards,
HBt.