[Sean H]

I've got parts to make an RA-1 clone and intend to use it with both Grado's and HD650's. I once owned the RA-1 and found, like others, that oddly enough it mates quite well with the HD600/650. Now I see Grado has a new "high voltage" version of the RA-1 meant for higher impedance cans and I'm wondering if anyone knows what it is they changed in the design to get higher voltage and if I can implement this into my RA-1 clone I intend to build? Also, any sense if the higher voltage would be too much for Grado cans, I'd hate to lose the ability to use them with a higher voltage version? WARNING: inexperienced newbie when it comes to technical stuff, please put in "dummy" terms.

Thanks.

 

[Sean H]

I just realized that the new "high gain" RA-1 is AC only and am getting the idea that it achives the higher gain due to the AC in some way. So in that regard is my inquiry here null and void in that a clone'd RA-1 with batt supply likely can't be modified for higher gain?? Anybody?

 

[tangent]

"High gain" suggests that they simply increased the gain of the amp, which is a single resistor change per channel in that type of design.

The reason it's probably wall-powered (besides wall power being convenient) is that that offers more voltage to the amp stage, which is needed to swing the output voltage higher. To do the same trick with batteries, you'd have to add more batteries in series, which works against the semi-portable nature of the original RA-1.

 

[Sean H]

Thanks a lot for the reply, tangent, I appreciate it. Ah, I see, this makes sense. Do you think the RA-1 has the most gain possible that is still in line with what the batteries can supply for voltage swings or do you think the gain could be tweaked a hair?

 

[tangent]

I don't know, but it's easy to find out. If you can't turn the volume knob up all the way before it gets too loud, the question is moot. If you get clipping (very easy to hear distortion) if you turn the volume knob up past a certain point and it's not yet too loud, you need more supply voltage to make use of the amp's current voltage gain. If you don't get enough volume with the knob turned up all the way and you don't hear distortion, you can reasonably try tweaking the gain.

I seem to recall that current RA-1s are potted in epoxy, though, so changing those two resistors may not be trivial.

 

[Sean H]

Quote:

Originally posted by tangent I seem to recall that current RA-1s are potted in epoxy, though, so changing those two resistors may not be trivial.

Thanks again for the help. Again, I'm constructing an RA-1 clone so changing the resistors would be easier than messing with a stock RA-1, but I'm inclined to just stick with the standard gain. I don't know maybe I'll try it. First I have to learn how to build this thing! This will be my first amp, with experience only in building cables but I have done many of them.

 

[mclaren20]

maybe you can just socket the resistors, so you can try higher gains?

 

[davei]

You could also replace the gain resistor with a pot.

 

[tangent]

Quote:

I'm constructing an RA-1 clone

Oh. I don't know why we're talking about Grado's products at all, then. Build it however you want. Grado's choices do not limit you.

One thing I just thought of: I seem to recall that the NJR op-amp Grado used is a bipolar-input chip. If you use that chip or another bipolar, you usually have to change at least two resistors per channel to keep the input section of the circuit balanced. Read the TI app note Op-Amps for Everyone or another good text covering op-amps if you don't know what I'm talking about. Or, stick with the standard resistor values.

 

[GWN]

My RA1 clone uses the same configuration as the standard RA1 with the exception of a better volume pot. It works well with my SR200's and my HD600's. For me it has more than sufficient volume even with the 600's. I really don't see the need for a higher gain version unless you have headphones that are particularly hard to drive.

 

[PeterR]

I found the standard RA-1 (the real one) to work quite well with HD-600s. No need for more gain at all.

 

[Sean H]

Ok, thanks guys. I thought the RA-1 drove my HD600's quite well too. Sounds like I shouldn't fuss over this and just build the clone as planned.

Hey, one other question that I have asked in another thread, would going to something like an Alps pot change the sonic signature too much or ... ??? Seems like it would be a smart thing to do given the better quality of an Alps Blue but I'm just wondering how much of a factor the cheaper pot is on the sonics and the synergy of the parts.

 

[GWN]

If you want an exact match, go for the Radio Shack pot (no longer available here in Canada), Radio Shack battery clips, Switchcraft 1/4 inch inlet. My original clone was built with the Radio Scap pot when it was still available here. Tracking a low volume was useless. The second unit I built I used a pot from Mouser with little change if any in the sound and much better tracking. A long time RA-1 user friend liked the pot so much that he asked me to remove the Radio Shack pot from is real RA-1 (also problematic at low volume) and replace it with the Mouser pot. My current personal unit has an Alps Black Beauty, Kimber internal wiring (instead of the computer ribbon cable used in the RA-1) and a Neutrik locking inlet. It sounds great but can no longer be called an RA-1 clone.