recording setup

[molmes]

Well - I may have spoken too soon. The situation IS much better, when all inputs are muted on the mixer. But the same buzz/hum comes back when I un-mute the amplifier input, and a different (smaller in -db) buzz/hum when the reel-to-reel input is un-muted - - -

[steve]

My only concern is that the isolator might modify the data stream in some way (like maybe a lower frequency response curve for the transformers

Transformers do have non-linear characteristics. One of the more noticeable effects is the loss of low bass frequencies. Transformers that are substantially linear over the audio frequency range are not particularly cheap. The preferred solution is to try and eliminate the source of the hum (though not always possible).

This is one of those "hands on" jobs that it's difficult to help very much with over the internet, but I can try and throw a few ideas;

Have you got all the equipment plugged into the same socket?
Any chance you could beg/borrow a pair of headphones? (would be helpful in pinning down where the noise is coming from)
How long are your cable runs? (the longer the cable the better quality it needs to be).
All connectors need to be clean and untarnished - electrical spray can sometimes improve contact resistance, but it is usually only a temporary solution until the connectors can be replaced with nice shiny new ones.

[molmes]

This is one of those "hands on" jobs that it's difficult to help very much with over the internet,

I agree - and I appreciate the time that you have taken - sometimes it helps just to have someone to bounce things off - - -

I live in an apartment complex, so who knows what is hooked up to the power system - and I have a "whole bunch" of units hooked up to my receiver. Way too many to try the process of elimination. I think that I will simplify by purchasing a separate RIAA preamp to bypass the receiver. Do you have a favorite? A recommendation? I saw one today on the Internet from ART - - - a small unit for about $40, with a frequency response of 10hz - 50khz, with .01% THD.

[molmes]

Transformers do have non-linear characteristics. One of the more noticeable effects is the loss of low bass frequencies. Transformers that are substantially linear over the audio frequency range are not particularly cheap. The preferred solution is to try and eliminate the source of the hum (though not always possible).

I just received an e-mail back from Radio Shack. Here are the specs for their ground loop isolator:


Ground LP Isolator (270-0054) Specifications Faxback Doc. # 9542

ELECTRICAL DATA:

Impedance Ratio:
Z1:Z2................................................1000 Ohms:600 Ohms
Z1:Z2................................................1000 Ohms:600 Ohms
Frequency Response:.............................300 Hz to 4000 Hz +/- 3 dB
DC Resistance:[email protected] degrees C
Z1:....................................................200 Ohms +/- 20%
Z2:....................................................150 Ohms +/- 20%
Insulation:.........................500 VDC apply to primary and secondary
more then 100 Meg Ohms Min.


Not so hot, eh? It looks like I'll be returning it - - -

[waxcylinder]

... I think that I will simplify by purchasing a separate RIAA preamp to bypass the receiver. Do you have a favorite? A recommendation? I saw one today on the Internet from ART - - - a small unit for about $40, with a frequency response of 10hz - 50khz, with .01% THD.

I use the ARTcessories DJ-PreII for my vinyl transcriptions and I have been very pleased with it - well built, sturdy construction, good sound (and good pre/post-sales advice from the company). Have a look at this thread I started a couple of years ago when I was trying to decide what to buy: http://forum.audacityteam.org/viewtopic ... =recommend

I run all my recording gear (PC, monitor, pre-amp, TT, FM radio, active speakers) all from the same single wall outlet (3-pin grounded UK) and fed from a good quality power-surge/lightning protector distribution block. I am lucky in that this seems to deliver good hum-free signals - the TT is grounded to the grounding post on the ART pre-amp.

WC