Technical Question - Receiver amplifier circuit

caseymou

I have a NAD 7175PE int. receiver/amp which I absolutely love. The sound from it always impresses me but I cranked it today and noticed that the bass seemed to be missing from one of the channels. I thought I had noticed this before but ignored it thinking it was because of the recording or station. Tonite I tested it with a CD and FM stations. There is no question that the bass is missing from one channel. Years ago I had this receiver hooked to a set of Cerwin Vega's, one of which had a replacement 4 ohm woofer. Is it possible that driving an unbalanced load could have caused the problem? Is it even possible to partially blow a channel? I have some electrical background so don't worry about getting too technicial.

sgtgto

Hi:

Sounds like a speaker problem more than an amp problem. Have you checked your speakers?

Gary

caseymou

I have noticed this on a couple of different sets of speak's.

axeman

If it is an intergrated amp, I would think it to be suspect that a channel would "partially" blow, as most of these are from a stereo amp chip.

You say you drove a 4 ohm speaker in the past. What is the receivers amp rated at? If it is higher, then it is possible some damage resulted to the chip circuitry.

But it is still puzzling that you are only missing the bass.......

Joe

RuSsMaN

You should have a switch on the back of the Power Envelope series receivers, for 4/8 ohm AND for Soft Clipping. Regardless of what they are at now, try the opposite setting.


Cheers,
Russ

I have a 7220PE, and will never get rid of it.

caseymou

Thanx, guys. I will investigate further and try things mentioned. Why do the NAD's sound so good? This thing absolutely blows my Denon away in FM. Plenty of power and I bought the thing at a garage sale in a ritzy neighborhood for $100. Did I mention I found a set of Ohm Walsh 2's in good cond. for $50 at a pawn shop. These are what I am using for sound with the NAD. On Ohm's website they list nominal impedence at 6 ohms. Is it possible to measure total speaker impedence with a multimeter or does each speaker have to be measured and then calculated?

joe logston

try swiching speakers from right to left and see if its the speaker

caseymou

Update here... I swapped speakers and the problem followed the receiver. I tried changing impedence and nothing. I also tried swapping pos and neg of 1 speaker in case they were out of phase. Again, no change. I then tried swapping the pre outs from the preamp to the amp and the problem still followed the right channel. Also, I swapped the left and right channel input of the cd player and nothing again. The only thing I can think of is directly inputting the cd into the amplifier section but I don't have variable outputs on the cd. I pretty much think it is with the preamp section now but I don't know what it could be since it acts the same way with cd and FM. I guess I will have to find the users manual and hope there is a wiring schematic on it. Anyone else with ideas?

joe logston

to me its your pre amp thats starting to go in the right channel, if your fm tunner is going the same as the cd player, them it is your pre amp, the pre amp sends the low frequency from the cd player & fm tunner to the amp. and the right channel is starting to go out on the low frequency section of the prossesor, or that the power part of the amp is going out.

sgtgto

Hi:

I am not familiar with your receiver, but have you checked your setup for all channels with a test disk? That should tell you where your problem is.


Gary

caseymou

I'm feeling kinda stupid now. But in case this ever happens to anyone else I should pass on the info. When I sat down and really started thinking, it had to be in the preamp section. I thought I should eliminate the obvious and check the bass adjustment. Since it is stereo and both channels should be discrete I am guessing the bass knob is connected to two pots. Just turning the knob normally I could not hear any crackling and it seemed to be working correctly but when I really started jiggling and pushing on the knob the bass came back. I will have to take the cover off and squirt some contact cleaner in the pots. I guess I can quit shopping for another NAD on ebay now. I just couldn't live without my NAD!

shack

Hey - good deal - more money for other upgrades!

Glad you found the problem.

gidrah

And you helped us if we should ever come across this problem.

I'm glad you did all the troubleshooting to find this sneaky problem. Good job.:D

gidrah

I definately want to go pawnshop and garage sale hopping in your neighborhood. I always wanted to try a pair of Ohm Walsh for rears.