6N1P or EF86 for bass guitar preamp?

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Mikael Abdellah

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Joined 2003
Hi again guys

I need some help to decide wether I should go for the 6N1P wich I am quite familiar with or the EF86 wich I have NEVER played with before. Right now I have a 6N1P connected to a BUF634 buffer. It sounds awesome, but gain could be a bit higher. I was thinking about using the EF86 i pentode mode.
 

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Mikael Abdellah

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Joined 2003
I just got the EF86 connected to my buffer on the bench. Now we're talking! The gain is just what I was looking for. I used the same RC filter as I assembled some time ago for my 6N1P. That gives me closer to 300VDC than the 250VDC for the 6N1P since the current draw is much lower. Also the heater current is lower wich pushes the heater voltage close to its limits at almost 6.9VAC. I will probably start soldering everything together in my new chassis some time pretty soon. I'll post a few more pics as the work continues.
 
Trout

Trout

Member
Joined 2004
The EF86 is very popular in Marshall style preamps. I know the guys over at 18W.com have several schematics posted in their library that utilize them. If memory serves there were several variations posted over the the AX84 website also.

The Clips of the 18W amps I have heard sounded very good especially if your into that heavy Marshall overdriven sound.

http://www.18watt.com/files/ef86_layout.jpg

I have seen little mention of the Russian version.

Trout
 
M

Mikael Abdellah

Member
Joined 2003
I have connected everything except my VU meter and fired it up about 2 hours ago. It works! :D

A s*itload of gain just like I wanted. I have a bit of hum that I will try to erradicate, but the biggest problem now is "scratches" when I turn my potentiometers. I bought really cheap pots, but I realize it was a bad misstake. Where can I find very, VERY good potentiometers with 500k and 1M resistance?
 
Trout

Trout

Member
Joined 2004
Mikael Abdellah said:
I have ordered Alpha and CTS potentiometers that should arrive in the middle of next week. I have decided to change all my internal signal wiring to a highly shielded cable that should reduce the hum a lot! I will post pictures as the work progresses.
Click to expand...


Speaking of scratchy pots,
I generally buy Alpha's because I can get them fast and easy.

On more than 1 occasion, I have had freshly built guitar amps that appeared to have a scratchy pot on the Hi Bright channel.

If I turned/increased the pot REALLY slow it would not make any noise, If I turned it fast it sounded really dirty.

It turned out to not actually be the pot but actually the tube in the V1 position. I replaced the tube, Noise gone.

Be careful adding shielded leads, I would only add them 1 at a time and test between additions. I as well as others I know have experienced that in some cases they actually induce noise.

That has never really made a lot of sense to me, Yet it does happen.

Trout
 
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Mikael Abdellah

Member
Joined 2003
The preamp is almost finished. At least the first stage of it. I chose the CTS potentiometers and the beautiful corona cable took care of most of the humm. There is a small amount of hum even with the HV switched of so I guess it's either from the heater supply or stray leakage from one of the, so far, not twisted AC leads. I will try and make a complete schematics later. I will also post some new pictures shortly. The only big thing left now is the VU meter. I still haven't decided how to build it but it will NOT be with 3914/3915 IC's.
 
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