Good news. 
Ok. I tested it with the resistors in place, installed it into the test system (a bunch of old components - MF P3a preamp, NAD 5200 CD player, Tannoy 603's) All good, old '80's components...
With the preamp hooked in, the max dc on either channel was 6.3mv. the channel I repaired was close to 0.0mv
With the CD playing on low volume (resistors, no speakers), I had AC on both channels.
I powered down, waited for the voltage to drop, and hooked up the speakers.
Power-on, we have sound, and it's clean!
This CD player is narky, it just won't play modern pressings, but I have one of the first all-digital recordings in Australia on CD - Vince Jones 'For all Colours" (1984) http://www.vincejones.com.au/albums/for_all_colours.html Even with the new caps, it sounds pretty good. I _think_ the sound has improved while we listen to it. (maybe it's the wine...) there is a sublime sax solo on this album (in 'Straighten up and fly right') and even with the old and scratchy CD player and limited speakers, it shines. In fact, I'm surprised at the bass, the Tannoy's have only a 5" bass driver, but they sound more than that in this system. Maybe the pine table that everything including the speakers is sitting on is adding to it.
Very happy. I'm off interstate in a couple of days for a week. When I get back, if it hasn't blown up, I'll be doing the OP627's. It occurs to me that since the opamps are socketed, I can just bend the pins out of the way on the DIP to disconnect the LM318-required circuits.
So. Thanks to all for your advice and help. I'm enlightened by the level of knowledge and support and humbled by the way in which that you offer it openly and freely. I'm bitten also, I have one of BrianGT's Gainclone kits on order. My journey has just begun
Michael
Ok. I tested it with the resistors in place, installed it into the test system (a bunch of old components - MF P3a preamp, NAD 5200 CD player, Tannoy 603's) All good, old '80's components...
With the preamp hooked in, the max dc on either channel was 6.3mv. the channel I repaired was close to 0.0mv
With the CD playing on low volume (resistors, no speakers), I had AC on both channels.
I powered down, waited for the voltage to drop, and hooked up the speakers.
Power-on, we have sound, and it's clean!
This CD player is narky, it just won't play modern pressings, but I have one of the first all-digital recordings in Australia on CD - Vince Jones 'For all Colours" (1984) http://www.vincejones.com.au/albums/for_all_colours.html Even with the new caps, it sounds pretty good. I _think_ the sound has improved while we listen to it. (maybe it's the wine...) there is a sublime sax solo on this album (in 'Straighten up and fly right') and even with the old and scratchy CD player and limited speakers, it shines. In fact, I'm surprised at the bass, the Tannoy's have only a 5" bass driver, but they sound more than that in this system. Maybe the pine table that everything including the speakers is sitting on is adding to it.
Very happy. I'm off interstate in a couple of days for a week. When I get back, if it hasn't blown up, I'll be doing the OP627's. It occurs to me that since the opamps are socketed, I can just bend the pins out of the way on the DIP to disconnect the LM318-required circuits.
So. Thanks to all for your advice and help. I'm enlightened by the level of knowledge and support and humbled by the way in which that you offer it openly and freely. I'm bitten also, I have one of BrianGT's Gainclone kits on order. My journey has just begun
Michael
p 170
Have you fitted the new 326 op amp to your p170. I have just obtained a p170 and some of its internals look a bit different. Have seen pics of other p170's all a bit different. Mine might have been an earlier model, its transformers say 1986. Any way mine works ok but i would like to improve the sound quality. it has had the 2 sets of four resistors (next to the mosfets) replaced with 2 47 ohm resistors on each side. Any help with an upgrade would be appreciated. ie if i replaced the 318 op amps with 326's would i have to remove pins 1 & 5, mine has a resistor or cap soldered across 2 pins not sure of thier no's. thanks rob
Have you fitted the new 326 op amp to your p170. I have just obtained a p170 and some of its internals look a bit different. Have seen pics of other p170's all a bit different. Mine might have been an earlier model, its transformers say 1986. Any way mine works ok but i would like to improve the sound quality. it has had the 2 sets of four resistors (next to the mosfets) replaced with 2 47 ohm resistors on each side. Any help with an upgrade would be appreciated. ie if i replaced the 318 op amps with 326's would i have to remove pins 1 & 5, mine has a resistor or cap soldered across 2 pins not sure of thier no's. thanks rob
Yes, I replaced the 318's with OP627's as detailed earlier in the thread. The sound is clean and sweet.
It's sitting dormant now though, waiting for me to get around to replacing the main PS Caps. I've been using a Mauro LM3886 amp for a while (There's a monster thread about it in the chipamps section)
Regards,
Michael
It's sitting dormant now though, waiting for me to get around to replacing the main PS Caps. I've been using a Mauro LM3886 amp for a while (There's a monster thread about it in the chipamps section)
Regards,
Michael
Hi,
Maf's schematic posted way back for the P170 showed pencilled in the corner 270,370,470.
Does that mean that all these series of amps had a similar schematic. Basically just altering the PSU and output pairs?
Or were the changes between models a lot more complex.
I remember hearing a 470 at an audio show driving a pre production ARCAM speaker. It sounded absolutely superb, even for an hotel room.
Down to more techy.
The second stage appears to be some kind of diamond connected cascode with bases referred to ground. Is that correct?
Does it produce voltage gain?
Which components determine the gain?
Why the big difference in dropper resistors between +Vrail and -Vrail? Is the current draw much larger in the -Vrail?
Maf's schematic posted way back for the P170 showed pencilled in the corner 270,370,470.
Does that mean that all these series of amps had a similar schematic. Basically just altering the PSU and output pairs?
Or were the changes between models a lot more complex.
I remember hearing a 470 at an audio show driving a pre production ARCAM speaker. It sounded absolutely superb, even for an hotel room.
Down to more techy.
The second stage appears to be some kind of diamond connected cascode with bases referred to ground. Is that correct?
Does it produce voltage gain?
Which components determine the gain?
Why the big difference in dropper resistors between +Vrail and -Vrail? Is the current draw much larger in the -Vrail?
Well, the chip replacement worked out not too expensive in the end. I landed up with a bunch of 627's from ebay at a good price for my other projects which brought the unit cost down.
The amp got sidelined because I got interested in building my own, and had great success. I'll get back to it, but time is limited at the moment.
Don't get me wrong. The P170 is a great amp, and the addition of the OP627's opens it up some. If you have one, make sure you replace all the caps, they are getting quite old, but they are cheap to replace, and if they let go, you risk the MosFets which is a lot more complicated and expensive.
Getting my fingers dirty in the repair got me interested in building the kit amps. If you read about the origins of Mauro Penasa's amp that I have built, you will see that it was inspired by the Musical Fidelity current pump arrangement, and that shows in the quality of the output.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=54571
It's a monster thread though...
Michael
The amp got sidelined because I got interested in building my own, and had great success. I'll get back to it, but time is limited at the moment.
Don't get me wrong. The P170 is a great amp, and the addition of the OP627's opens it up some. If you have one, make sure you replace all the caps, they are getting quite old, but they are cheap to replace, and if they let go, you risk the MosFets which is a lot more complicated and expensive.
Getting my fingers dirty in the repair got me interested in building the kit amps. If you read about the origins of Mauro Penasa's amp that I have built, you will see that it was inspired by the Musical Fidelity current pump arrangement, and that shows in the quality of the output.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=54571
It's a monster thread though...
Michael
p170 opa627 chips
please can someone tell me where to buy opa627 chips for my p170. I need the pinned, plug in type. What is the model no. Ive seen some on e-bay, with end prefix of au, but these look like solderd jobs. if someone could give me the part no's for the plug in types i would be grateful.
thanks rob
please can someone tell me where to buy opa627 chips for my p170. I need the pinned, plug in type. What is the model no. Ive seen some on e-bay, with end prefix of au, but these look like solderd jobs. if someone could give me the part no's for the plug in types i would be grateful.
thanks rob
Hi.
Sorry, got your email and hadn't replied.
Yes, I just bent pins 1, 5 and 8 out of the way so they never entered the socket. It gave me an out in case the 627's sounded worse (unlikely) or I needed them for something else.
As I understand it, at the time the differences between the circuits were just in the PSU and MosFets. You have probably gathered that the circuit design was a bit of a moving feast, so it's quite likely that refinements were introduced to the design as time went on. I also understood that there were factory mods applied to some early amps that failed in the field.
I don't know if the change in my FETs was part of a factory fix or some independant work after they failed. The person I bought it from said that it had come with the HiFi shop when he bought it, so there is no history. It may have been a trade-in, or maybe it had never left the shop from new. In any case, the repair was pretty shonky
Michael
Sorry, got your email and hadn't replied.
Yes, I just bent pins 1, 5 and 8 out of the way so they never entered the socket. It gave me an out in case the 627's sounded worse (unlikely) or I needed them for something else.
As I understand it, at the time the differences between the circuits were just in the PSU and MosFets. You have probably gathered that the circuit design was a bit of a moving feast, so it's quite likely that refinements were introduced to the design as time went on. I also understood that there were factory mods applied to some early amps that failed in the field.
I don't know if the change in my FETs was part of a factory fix or some independant work after they failed. The person I bought it from said that it had come with the HiFi shop when he bought it, so there is no history. It may have been a trade-in, or maybe it had never left the shop from new. In any case, the repair was pretty shonky
Michael
Summary of suggested mods anyone?
Hi Every one
I have just been given a P170, an early variant with the red lettering on the case and the wider transformers but the circuit board is a mess. Parts burned out and missing. The power supply seems ok on both channels and it seems a waste to throw it out.
What I have in mind is etch a circuit board, any one been down this route?
Can any one let me have a copy of the circuit diagram please ??
Any one able to summarise the key component changes recomended -
what about output protection and suggestions that dont affect the sound too much?
Many thanks in advance
Ian
( to.ian@ntlworld.com)
Hi Every one
I have just been given a P170, an early variant with the red lettering on the case and the wider transformers but the circuit board is a mess. Parts burned out and missing. The power supply seems ok on both channels and it seems a waste to throw it out.
What I have in mind is etch a circuit board, any one been down this route?
Can any one let me have a copy of the circuit diagram please ??
Any one able to summarise the key component changes recomended -
what about output protection and suggestions that dont affect the sound too much?
Many thanks in advance
Ian
( to.ian@ntlworld.com)
Re: Summary of suggested mods anyone?
Have a look in post 22 of this thread, here: http://www.diyaudio.com/forums/showthread.php?postid=673432#post673432
I haven't heard of anyone making their own circuit board, but it would certainly be do-able, as the board is uncomplicated.
Another option would be to retro-fit the Mauro circuit into the case, it is based on the current pump principle and applied to the LM3886. I have one and the sound is in the same league as this amp. A great kit is available from Russ White in the chipamp section of this site.
Regards,
Michael
ianfromnotts said:
Have a look in post 22 of this thread, here: http://www.diyaudio.com/forums/showthread.php?postid=673432#post673432
I haven't heard of anyone making their own circuit board, but it would certainly be do-able, as the board is uncomplicated.
Another option would be to retro-fit the Mauro circuit into the case, it is based on the current pump principle and applied to the LM3886. I have one and the sound is in the same league as this amp. A great kit is available from Russ White in the chipamp section of this site.
Regards,
Michael
Replacing LM318 in MF A1 Final Edition
Hi Maf_AU,
I was reading this thread very interested cause it initiated again
my thoughts of swapping the lm318 in my musical fidelity A1 Final Edition (board is an B200, with LM318 but with BUZ900 Mosfet)...So Circuit is very close to this http://www.mhennessy1.f9.co.uk/mf_a1/mf_b200.jpg
What do you think...is it oussible to replace the LM318 just in the way you did it with the P170....
I mean...there are many guys who´re warning cause of calibrated oszilation fitting to the lm318.......
But in the end you were lucky by just ´cutting of´ 3 pins out of the curcuit.....
What do you think...
Best regards Marcus
Hi Maf_AU,
I was reading this thread very interested cause it initiated again
my thoughts of swapping the lm318 in my musical fidelity A1 Final Edition (board is an B200, with LM318 but with BUZ900 Mosfet)...So Circuit is very close to this http://www.mhennessy1.f9.co.uk/mf_a1/mf_b200.jpg
What do you think...is it oussible to replace the LM318 just in the way you did it with the P170....
I mean...there are many guys who´re warning cause of calibrated oszilation fitting to the lm318.......
But in the end you were lucky by just ´cutting of´ 3 pins out of the curcuit.....
What do you think...
Best regards Marcus
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