sorry,
they are all 351s (with the black dot)

Greg,

Thanks for sharing this on the forum.
I have another general question, what did push you to choose the 351 for modifications ? why haven't you chosen the 350 ? Many people devalue the 351 in favor of the 350 for some reasons. In theory what you have done on the 351 could be done on the 350, could not it ? what is your views on that, would you approve the decision on starting the same kind of work on a 350 ?
Thanks a lot.

Alex

Hey greg,

Me again with another question, I am in the work of modifying on 350 with your schematics (thanks for this):

On the schematics, you kept the record calibrator, may I ask what is this for ? (it might be a stupid question but...). And since the pot must be kept, how do you have it set ?

Okay thanks for this.
Alex

There are three reasons that might've prompted Greg to stick with the 351's. First, the 350's require a dedicated power supply. The 351's have one built-in. The second reason might be that Greg found it easier to do a "mass modification" with preamps that employed circuit boards rather than the 350's point-to-point wiring. Third, it might be simply that the studio came across a large number of 351's at some point available from the same seller at a decent price.

The record calibration pot is there to provide an internal set gain function. I believe Greg has his set to provide up to 65db of overall gain (see his Tech Journal for more info).

Hope this helps a little...

I don't have any experience modifying the 350s. I would assume you could do it, but I don't know how different the job would be. I wouldn't use my schematics alone. Try to get the original 350, and 351 schematics so you can compare and contrast.
www.recordist.com
There are no stupid questions, just stupid people.
Pretty much what Dan said is true. That record cal is there to control the full gain of the preamp (which we set to 65 dB). I suppose I could get rid of it now, but we used it to tinker with in the past. You can cause early clipping if that is turned up.
I wasn't part of the decision process that led to the 351. That was done before I arrived. I think Steve and Bob were using an unmodded 351 as a preamp and liked it. We then bought a batch of them for really cheap.

What do people say is worse about the 351?

Hi,

I have difficulties to find the RELCAP 0.02uF/600V polypropylene (C 18 19 & 21).
Actually I can't find any. I found in TEFLON but it is very expansive.
Can you sugest me a dealer or a replacement ?

Also is C1 450V or 600V ?

Thanks a lot.
Alex

Idoia wrote:Hi,

I have difficulties to find the RELCAP 0.02uF/600V polypropylene (C 18 19 & 21).
Actually I can't find any. I found in TEFLON but it is very expansive.
Can you sugest me a dealer or a replacement ?

Also is C1 450V or 600V ?

Thanks a lot.
Alex

They may not be available anymore but you can get .022uF as well. Let google be your friend. Quick finds-
http://www.hndme.com/storeindex.html

https://secure.tubesandmore.com/

C1 is 400/450V

Thanks for the fast reply.
While I am at it,
- right above the meter the resistor is 3K9, is it a typo error and you meant 39K ?
- on the right of this there is the headphone Jack which has a capacitor in between its connectors, below is written 0.01 assuming this is uF what voltage is that cap and is it a polystyrene ?

Thanks for your time Greg..
Alex

The meter resistor is 3.9K

The headphone cap can be anything you want. 50V should be fine. Polypropylene is probably the best choice as it will be cheaper than a polystyrene.

Good luck with it.

For those who are interested in having an Electrical-style 351 without the hard work, my company is about 2 weeks away from releasing a modern copy of it with all the bells and whistles. Check out www.AnthropicAudio.com in a few days for info.

Me again,
I am sorry but I cannot find ANY Rel-Cap polypropylene 0.15uF 450V and 0.02uF or 0.022uF 600V. I had checked the links you gave me already Greg, and they don' t do them. Can I replace them with Mallory, AudiCap or Multicap with the same values ?

Also, I cannot find the electrolytic 4000uF 20V. You said that we should round up to the next standard value, so actually there is 4700uF but there is also 3900uF, should I go for the 4700uF anyway ?

Thanks again for your input, sorry to be such a pain.
Alex