You can see my full build thread HERE
There are two awesome TTSH threads in Muffs.
2600 clone - Two Thousand Six Hundred (TTSH)
and
Two Thousand Six Hundred (TTSH) Project General Build Thread
The DSL-Man site has a very good TTSH thread
And of course the official build thread is here
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The unpopulated rear section of VCO 1
Install the IC headers, resistors & caps first.
This is the front view of VCO 1
These headers connect the VCO submodules to the motherboard.
I'm installing these on the motherboard as high as as I can to
provide as much room as possible between the two boards.
Connecting VCO1 to the PSU.
I'm soldering the connections directly to the PSU, though you many wish to use MTA connectors.
+15V needs to be applied there for testing.
If all is working you should see a square wave from this pad and a saw from the pad above.
The VCO uses fairly inexpensive LM301 op amps which can be found in many vintage ARP 2600s:
This is the pinout:
I might in the future try replacing these with more modern 711's, LF351s or 411s. ???
It's probably not a matter of simply swapping the chips. Maybe the 301's are better left in the VCOs and changed in the filter ??? These 301s are everywhere. They can be found in the VCOs, the filter, the EGs and the VCA.
This modification is just a personal idea and I haven't tested it yet.
I don't recommend any modifications unless you are a qualified technician.
In Mark Vail's book "Vintage Synthesizers" he discusses the SL19986 describing it as "nothing more than a selected LM-301. He goes on to say that" The reason ARP selected them was for their DC performance. But because they aren't of very high input impedence .... they are not as good as an LF-351,411, or other high-performance op-amps."
Anyway, I'm a bit undecided about changing op-amps. New op-amps may clean the path but I kinda like dirt and noise. Maybe ill keep the old 301's in the end.
Another ARP guru, Phil Cirocco, has some great info on this website:
To quote him:
"...The 2600 uses microchip technology in all of its gain stages! The first 2600's .......used hi-fi chips (Teledyne 1339 octal op-amps) with a high slew rate. Although these chips sound great, they were very unreliable and prone to latch up. Around 1972, plagued by failures in the field, ARP was forced to change these chips to a much more reliable type (National Semiconductor LM-301 or SL-1998) The problem is that they slew the wave shape producing a muffled sound. The LM-301 is classified as a general purpose amplifier, and is considered inadequate for audio by present standards. Nearly all the standard production gray-face 2600's use the LM301. This is the main reason why the legendary Blue Marvins sound better!
So I wonder what he replaces the 301's with today ???
***********************
Many thanks to "unknown" for his comment re the MC1439
"I've seen picture of 2500 modules where the 301s had been
replaced by MC1439. The PCB looked like it could accommodate
either; the 301, according to the older schematic only used
a cap whereas the 1439 looks like it use series RC for
compensation."
Yes it looks like the pinouts for the LM301 & the MC1439 are identical. Ins are on pin 2 & 3. Out on pin 6.
I'll give this a try on one of my next builds.
It's probably not a matter of simply swapping the chips. Maybe the 301's are better left in the VCOs and changed in the filter ??? These 301s are everywhere. They can be found in the VCOs, the filter, the EGs and the VCA.
This modification is just a personal idea and I haven't tested it yet.
I don't recommend any modifications unless you are a qualified technician.
In Mark Vail's book "Vintage Synthesizers" he discusses the SL19986 describing it as "nothing more than a selected LM-301. He goes on to say that" The reason ARP selected them was for their DC performance. But because they aren't of very high input impedence .... they are not as good as an LF-351,411, or other high-performance op-amps."
Anyway, I'm a bit undecided about changing op-amps. New op-amps may clean the path but I kinda like dirt and noise. Maybe ill keep the old 301's in the end.
Another ARP guru, Phil Cirocco, has some great info on this website:
To quote him:
"...The 2600 uses microchip technology in all of its gain stages! The first 2600's .......used hi-fi chips (Teledyne 1339 octal op-amps) with a high slew rate. Although these chips sound great, they were very unreliable and prone to latch up. Around 1972, plagued by failures in the field, ARP was forced to change these chips to a much more reliable type (National Semiconductor LM-301 or SL-1998) The problem is that they slew the wave shape producing a muffled sound. The LM-301 is classified as a general purpose amplifier, and is considered inadequate for audio by present standards. Nearly all the standard production gray-face 2600's use the LM301. This is the main reason why the legendary Blue Marvins sound better!
So I wonder what he replaces the 301's with today ???
***********************
Many thanks to "unknown" for his comment re the MC1439
"I've seen picture of 2500 modules where the 301s had been
replaced by MC1439. The PCB looked like it could accommodate
either; the 301, according to the older schematic only used
a cap whereas the 1439 looks like it use series RC for
compensation."
Yes it looks like the pinouts for the LM301 & the MC1439 are identical. Ins are on pin 2 & 3. Out on pin 6.
I'll give this a try on one of my next builds.
I've seen picture of 2500 modules where the 301s had been
ReplyDeletereplaced by MC1439. The PCB looked like it could accommodate
either; the 301, according to the older schematic only used
a cap whereas the 1439 looks like it use series RC for
compensation.
Thanks heaps for this bit of info.
ReplyDeleteYes it looks like the pinouts for the LM301 & the MC1439 are identical. Ins are on pin 2 & 3. Out on pin 6.
I'll give this a try on one of my next builds