Studiomaster 16-4-8 restore
Hi, so I’ve just picked up an old Studiomaster 16-4-8 in great condition. Its just a bit noisy, Id like to recap it and mod it.
I have some info such as:
I went through a few of these around 20 years ago. Installing local .1 uf bypass caps on the power rails does help. All feedback loops need to have a small cap across, most stages had them. Use Wima FKP-2 or MKP-2 polyprop caps in the EQ, especially the hi mid and hi shelf. Opamps can be the older OPA 2134 BurrBrown stuff, the LT1358, the OP-275, the AD 8599 (with a brown Dog adaptor) or the National LME49720/LME49860, balanced outputs can use the National LM6172 for great output drive. Also check out the new AD8510 series, a BurrBrown fet input sub for the OPA134 series. Mic pre transistors can be 2SA1316 or 2SA1083’s to lower front end noise and add some HF air. A nice big Power One HDD-15-5A will be a good power supply if you add the small 1/2 amp 48 volt supply for phantom. Then you can play with opamps all day long. The summing amps in the master should be the National LME part due to it’s large open loop gain, = a clearer mix buss.
I started by the power supply caps; major improvement in noise and hum. I found out that most original caps were rated low, like 16 volts for a 15 volt power supply, so I used 25 volts throughout (except where the design called for higher voltage).
Replace with the same type of capacitor to the one you remove. So, if you remove a 10uF or 22uF tantalum capacitor, you do NOT replace it with an aluminium electrolytic!
2. Neve designers were restricted back then on the size of capacitors and, in the case of the power decoupling to the 183/283 (fitted to the frame of the module), fitted the largest value that could fit in there… usually 640uF. I personally recommend fitting the largest capacitor that you can now fit in there… like a 4,700uF which may be the same size now as the original.
There is nothing to be gained (and, indeed factors may go against you in extreme cases) by using a much higher voltage electrolytic capacitor. You should fit one as close to the operating voltage as you can. 35v is probably a good, top limit, value.
3. As for capacitors on circuit boards… remembering the warning about substituting tantalums for other types… there’s no harm in fitting bigger value capacitors if they will fit. If it’s decoupling the power rail, it will decouple slightly better. If it’s decoupling between two amp stages or an emitter bypass, it will improve the bass response marginally.
Here are the links to pics: