Tape Delay Preamp HELP (Echo Dek)

[sevenisthenumber]

I have an old tap delay that I love the sound of plugged in at the front of my rig. Here is the schematic from the lid and the new schematic I drew of just the audio path on that preamp with a master volume added. My problem is that it has a little more BG noise than I want, white hiss. The actual unit doesn't really do this. Am I missing something? Adding the Master volume really helped decrease that due to the load but IM stumped.

[duck_arse]

seven - I can't see any of your images. is my interwebs broken again?

[wavley]

They were there yesterday.

Just like the flaw of the space echo, there is no buffer on the input, you run into a pot that if cranked wide open will give you an input impedance of 50K.  Google Billy Zoom space echo mod, I think I even have a thread here dedicated to playing around with this mod.  His is a simple Jfet input buffer in between the input jack and the input pot, I ended up using a modified Jack Orman Mini Booster as my input so I had some control of gain, this extra gain allowed me to play with the gain staging of the rest of the circuit so it wasn't amplifying as much noise.

[sevenisthenumber]

They were there yesterday.

Just like the flaw of the space echo, there is no buffer on the input, you run into a pot that if cranked wide open will give you an input impedance of 50K.  Google Billy Zoom space echo mod, I think I even have a thread here dedicated to playing around with this mod.  His is a simple Jfet input buffer in between the input jack and the input pot, I ended up using a modified Jack Orman Mini Booster as my input so I had some control of gain, this extra gain allowed me to play with the gain staging of the rest of the circuit so it wasn't amplifying as much noise.

So you think simply adding this right before the pot after the input will help the white noise?

[sevenisthenumber]

I also say where he stated this on an OLD forumn post:

"That's a FET follower mod to convert the input to high impedance so it sounds good with electric guitar. It goes right on the input jack, before the volume pot. The units came with about a 10K input impedance, which loads guitar pickups and makes them sound dull and fuzzy. This changes the impedance to a regular 1 meg guitar input and puts the tone back."

He doesnt mention white noise etc so I just wondered. Thanks for any help!

[anotherjim]

Our ears are very good at finding signal amongst noise, but also very sensitive around 1 to 2kHz, so if you don't have much signal around there, you will notice the hiss more. So adding an input buffer to get the brightness back from the guitar is a good thing, it won't really reduce the hiss, but will make it much less noticeable.

However, if the guitar is already being buffered by another device before the tape, adding one won't improve things.

[sevenisthenumber]

Im gonna try this simple 5089 buffer at the input. Thanks guys, here is a schematic.

[wavley]

It's just my opinion, but I really think for the best bang for your buck you should consider using a FET here.  The high input impedance is what you're looking for, if you don't want to do the Billy Zoom thing, there are lots of projects based on the input FET booster of the EP3 Echoplex.

But, as Jim pointed out, you don't really need to build anything if you have a good low output impedance buffer to put in front of this thing.

I would probably save the 5089s for replacing the noisy bipolars that are already there.  I did this with my 101 space echo and between the new input stage and using lower noise transistors in my signal path I reduced the noise to the point where I missed it when making echoes feed back on themselves.

[alfafalfa]

Thanks guys, here is a schematic.

Sorry but here I can't see the schematic!

Alf

[anotherjim]

Would this be it?

[duck_arse]

Thanks guys, here is a schematic.

Sorry but here I can't see the schematic!

Alf

me too - still. I can see anotherjim's posted one, but none before. (I have a feeling it's the dead hand of googoo sign-ins, strangling the webs for non-believers .....)

[bluebunny]

+1

The URL you posted gives a blank page: the HTTP response is zero-length.