I posted a photo of a planned PCB loading board back in post #290. Since then I've decided I'd investigate the PP999 (Pyle, gasp!) phono preamps I read about elsewhere. Because my phono loading board would make a most excellent addition to this preamp, they're almost designed for one another. Of similar proportions, the the PP999 is held in with a screw in each of four corners. So I can replace the screws with stand-offs and simply design my board to mount right above. In the meantime I've gotten a lot of help @ another forum on mods. I've replaced the RIAA components with those suggested in the OPA164x documentation, so my RIAA should be (in theory) +/- .18db from 100-Hz to 20k. I've also replaced the electrolytic coupling caps with polyester, and installed a socket/replaced the stock JRC4458D with an NE5532. I'm not even troubled by the fact that the board says it is a "PHONE AMPLIFIER." But the goal here is my ultimate MM phono stage, which conforms to RIAA standards AND allows lots of loading flexibility. Hopefully more to come.
I'm sure we'll all be looking forward to your progress on this Phil. I've done a little reading about phono stages and RIAA just because it's interesting (even though I don't own a turntable) and will be glad to see what you do with this. Is the Pyle active or passive RIAA filter?
The clue being only one dual opamp in the circuit for the two channels, so would have to be in feedback loop
I'm in the process of modifying one of my studio 1/4" 2 track analog tape machines to operate at 30 ips / 15 ips instead of the 15 ips / 7 1/2 ips it previously operated at. The equalization has been changed from NAB to AES for 30 ips and IEC-1 (CCIR) for 15 ips. My Ampex 354 already operates with IEC-1 equalization. This is the front of the transport. I had a new capstan sleeve (to the right of the head block) machined out of stainless steel to double the speeds. I had to reject quite a few attempts from the poor machinist to get one with acceptable runout and precise enough inner diameter. The capstan sleeve is held in place with a set screw. This machine has had several previous modifications to accommodate whatever madness I had at the time. This is the back of the transport. The wires dangling at the top are for a soft start relay. Machines operating at 30 ips have the problem when pressing 'play' that of the tape being propelled by the capstan faster than the takeup reel can get up to speed. A tape loop is thrown and the transport stops. There are two solutions I could use, one being temporarily bypassing the torque limiting resistor on the takeup reel by a relay until it gets up to speed. The other solution is the one Ampex used on their Model 300 machines where the capstan is motionless until the 'play' button is pressed. The capstan motor takes a second or so to get up to speed, and by that time the takeup reel has enough torque to avoid a thrown tape loop. This is the solution I am using because it's more historically accurate and slightly easier to implement. Of course on 'newer' machines, this whole process is done with digital logic. While I was working on the back of the machine, I got rid of the cable ties in several places which were used on previous mods and replaced it all with new period-correct cable lacing. I'm getting better at lacing, but there's room for improvement before I can work at Bell Labs or NASA. Not related to the 30 ips speed change but interesting nonetheless, this is a closeup of the record and playback heads. I replaced them several years ago with premium quality 'butterfly' metal heads made by PhotoVox. These heads have a profile which allows smoother and more extended low frequency response than conventional profile heads. PhotoVox heads are among the best you can get. Finally this is the first-run frequency response at 30 ips. I have some fine tuning to do with capacitive loading of the head to smooth out that peak beyond 20kHz, but the response goes all the way to 30kHz and is very flat. There is almost no sign of the usual 'head bumps' at low frequencies - the PhotoVox heads are largely responsible for this. Ignore the roughness in the trace in the lower frequencies since this was done using pink noise. Now the question is what am I going to record with this machine? Honestly, I have no idea! I guess I could make some damn awesome sounding mix tapes....but a 10 1/2" reel of taps zips by in 16 minutes at 30 ips, so they would be really short mix tapes.
Nice. Latching relays? How I would do it. One can select with only momentary power from an inert source like battery. But then you want a separately-selectable rec-out = 8 more relays to pick off the input bus. Zone 2 = 8 more and another ladder. No load isolation. Mono, another per input or output, phase, another, eq loop, etc. One finds that cost per input port overtakes a top differential 8-in ADC like CS5368 pretty quickly, which opens up massive mux and routing abilities with mixing, along with multi-out DACs with attenuator, and infinite DSP options. More digital ins are low cost. Put a flat phono pre in front of a few inputs. Maybe time for the first all-digital stereo preamp - doubling as 16x8 PC/MADI interface but with standalone controls.
A bit of a photo dump for the amp I am working on. Getting very close now. Next step is to put the finishing touches on the PCB's I'm designing and then (after my wallet recovers from these purchases) order the boards. Here is a photo of the iron. Output transformers in the back corners, power transformer in the back middle and the two power supply chokes in the front. This photo is only a fraction of the parts for the amp. The highlights really. Led power switch, external heatsink for the shunt regulator, main output cap for the regulator, Duelund tinned copper coupling caps as well as their Duelund silver bypass caps, Clarity TC2 caps (bigger blue ones) for the high voltage power supply for the output tubes and Clarity TC4 caps (smaller blue ones) for the high voltage supply for the input/driver tubes, half of the speaker jacks, RCA jacks, Tent Labs output tube bias supply, power supply bypass cap, Amtrans feedback caps, Takman circuit resistors, and lastly Ametherm thermistor. One thing I forgot to put in the picture was the Vishay Z-foil signal resistors.
I think i may have confused you with my post on the previous page of this thread. I have 2 projects going on. One is in the acquisition phase. An amplifier which some of the parts are in the above post. The other a preamp, in the design stage, which I posted about on the previous page for the switching and volume board. That project will assuredly be using a microcontroller for the switching and volume as well as the display. Is that what you were referring to?
Cautionary tale: look at this Pro-Ject phono - and the noise: A Tale of Two Phono Preamps, Part 1: Pro-Ject Phono Box DS+ You could use an 8 bit up-down counter for volume (accelerating clock only when dpdt pressed), and pushbuttons in a diode isolation grid for selection set/resets. Readout the relays and set as power-on memory in a presettable. Even a tri-state parallel ADC with reference generator and a volume knob, change comparator to enable update.
A friend of mine just gave me these large Advents he bought new in 1975. I’m definitely going to restore them
What model are they? I brought back to life a pair for my neighbor a while back. Reworked the crossovers, dampened the cabinets and so on. I might be able to give some suggestions if it is the same model.
I just looked up the FRD and ZMA files for that project, it appears to have been the Advent 1. I don't know if that was a bigger or smaller speaker. None the less since it appears to be a different speaker. The concepts would be applicable but not the actual component values.
Wow I like these Forums. I have never been here I don't think. This is an awesome site. I love the photos people. Anybody tell me how to post pictures on here? Thank you in advance.
Welcome to the forum! The opening post in this thread attempts to guide you through one method of posting images at SHMF, but maybe not as successfully as I'd hoped There are a few threads in the Forum Business section that go over other methods.
