Hello
Here am I again with my problem. Still present ...
What I've done so far :
Turntable side
Checked wires, cables and carts. Every resistance of cables and cart are the same on right and left channel. On the 3 carts I own. So far, so good.
Holman preamp side
Cleaned all switches and pots. Cleaned all adjustable pots. Device seems to be untouched, electrolytic caps are original (as far as I can judge, from the photos on Internet).
The left channel is still lower in output than the right channel even using a mono record (I own a couple). More importantly, the default is present on Phono 1 and on Phono 2 input !
So any advice and troubleshooting tips are very welcome !
Thanks a lot in advance !
Here am I again with my problem. Still present ...
What I've done so far :
Turntable side
Checked wires, cables and carts. Every resistance of cables and cart are the same on right and left channel. On the 3 carts I own. So far, so good.
Holman preamp side
Cleaned all switches and pots. Cleaned all adjustable pots. Device seems to be untouched, electrolytic caps are original (as far as I can judge, from the photos on Internet).
The left channel is still lower in output than the right channel even using a mono record (I own a couple). More importantly, the default is present on Phono 1 and on Phono 2 input !
So any advice and troubleshooting tips are very welcome !
Thanks a lot in advance !
Take a systematic approach:
1) Skip the turntable, feed it a high level source: CD, tuner, etc
If problem gone, problem is in phono stage. If problem persists ...
2) disable "Infrasonic Filter" switch on back of unit (button out).
If problem gone, problem is in infrasonic filter circuit. If problem persists ...
3) Flip both "R>L" and "L>R" switches up.
If channel imbalance changes to other channel, problem is in Tape Monitor or Ext Processor switches. If no change in channel imbalance ...
4) flip "Tone Defeat" switch up.
If problem gone, problem is in the tone control stages
If problem persists, it could be in the Volume , Mode or Balance control stages, or the final output buffers/relay, and further testing needed.
So I tried to put a CD with 1kHz mono signal in. Both channels are OK on whatever high input I use.
So IMHO, the problem lies in the phono input circuitry.
I'll try to put a signal generator at the phono input and check the infrasonic switch and/or the left level at the output of the phono preamp.
Thanks for your help !
So IMHO, the problem lies in the phono input circuitry.
I'll try to put a signal generator at the phono input and check the infrasonic switch and/or the left level at the output of the phono preamp.
Thanks for your help !
The infrasonic switch comes AFTER all the inputs, so if CD was OK, the infrasonic filter is not the cause.
Does your turntable/cart work OK with other preamps?
How bad is the imbalance? You haven't said if it's small or large.
If small, it's possible that the previous owner may have adjusted the phono balance trimpots to match his cartridge. Have you tried adjusting these? (try to remember their initial setting if it doesn't help).
Hello,
First, the turntable played good on a Luxman L-2 integrated amp. I bet I unsoldered one wire when I switched to the Holman. Now this is repaired. Both cables and carts are OK. Switching input cables right/left make no change. The left channel is still the lowest.
Next, I tried various High level sources : Tuner, set top box, CD player and all high level inputs (tape untested) are OK.
The Phono input left channel loudness is very low compared to the right channel. On both phono channels. (it is sufficiently lower to be easily heard on every record played. be it stereo or mono).
I've cleaned ALL switches using KF Contact F2 product, and all pots and adjustable.
The balance adjustable resistor in the phono preamp where set at the middle. I cleaned them, and set them back to middle. I tried to fiddle with them to correct the imbalance but to no avail.
I've repaired the BF Philips gen and made the Tektronic scope back in use by removing and plugging back all cards. It runs fine now.
If tme permits, I'll try to set up a measuring jig and troubleshoot it tomorrow...
All idea you may have won't be overlooked ! Thanks for your response.
First, the turntable played good on a Luxman L-2 integrated amp. I bet I unsoldered one wire when I switched to the Holman. Now this is repaired. Both cables and carts are OK. Switching input cables right/left make no change. The left channel is still the lowest.
Next, I tried various High level sources : Tuner, set top box, CD player and all high level inputs (tape untested) are OK.
The Phono input left channel loudness is very low compared to the right channel. On both phono channels. (it is sufficiently lower to be easily heard on every record played. be it stereo or mono).
I've cleaned ALL switches using KF Contact F2 product, and all pots and adjustable.
The balance adjustable resistor in the phono preamp where set at the middle. I cleaned them, and set them back to middle. I tried to fiddle with them to correct the imbalance but to no avail.
I've repaired the BF Philips gen and made the Tektronic scope back in use by removing and plugging back all cards. It runs fine now.
If tme permits, I'll try to set up a measuring jig and troubleshoot it tomorrow...
All idea you may have won't be overlooked ! Thanks for your response.
Thread bump. I just got one of these, and it needed quite a bit of going through to get it into service. First, my power supply was dead, one of the 18v regulators was toast, and someone had put 15v regulators in instead of the 18v the circuit calls for. So fixed those. It worked.
Next problem was tone control circuit. I got buzzing when Tone defeat was off (tone circuits engaged). Couldn't find anything wrong with the circuit, until I realized that there were metal washers on the three screws where the circuit board attaches to the faceplate. One of the metal washers was touching the main ground of the circuit board and the solder mask had worn off there. This created a ground loop. The main ground for that board is at the back and screws into the transformer housing. Eliminating the metal washers so the screws were now not grounding eliminated the ground loop and solved the buzzing when tone circuit was engaged.
It worked for a little while, and after a recap, I was getting relay buzzing. I removed the relay to inspect, and the plastic base crumbled when I pulled it out (maybe I was a little too forceful). I only had 12v low signal relays on hand from a spare pcb out of a Rotel reciever. So I put the new relay on some perf board and wired a 750 ohm resistor in series with the relay coil. I also inspected the mute circuit and found that the circuit in mine varied significantly from the schematic in the service manual, and on the base of the case. I drew up the circuit following traces and measuring resistances. It appeared that one of the capacitors, (no cnumber marking) was in backwards according to my schematic, despite the cap being inserted per the polarity markings on the actual PCB. So I flipped it around, and still, the relay buzzed. So looked at the schematic I drew up again, and decided to flip around one of the transistors, so it went against the markings on the pcb... Board was marked with an E where the emitter of the transistor was, so I rotated it 180 degrees, and bingo, that did the trick. Now the muting circuit worked perfectly. 4-5 second delay on power up, then click. Instantaneous click on mute button press and depress, and instant disconnect at power down. Measurements show the relay and resistor dropping 19.2v, and drawing 11ma. This puts my relay voltage drop at 10.9v, and the resistor at 8.3v.
Now that the unit was working perfectly, I replaced the opamps with opa2134, and the volume opamp with tle2072 (because someone in here said that one is better in the volume location). I couldn't be more pleased with the unit. Looks and sounds fabulous.
I have attached my drawing of the mute circuit on my unit, as well as a couple pics of the mute circuit. The cap and transistor in the 4th pic both needed to be flipped around to get it working.
Next problem was tone control circuit. I got buzzing when Tone defeat was off (tone circuits engaged). Couldn't find anything wrong with the circuit, until I realized that there were metal washers on the three screws where the circuit board attaches to the faceplate. One of the metal washers was touching the main ground of the circuit board and the solder mask had worn off there. This created a ground loop. The main ground for that board is at the back and screws into the transformer housing. Eliminating the metal washers so the screws were now not grounding eliminated the ground loop and solved the buzzing when tone circuit was engaged.
It worked for a little while, and after a recap, I was getting relay buzzing. I removed the relay to inspect, and the plastic base crumbled when I pulled it out (maybe I was a little too forceful). I only had 12v low signal relays on hand from a spare pcb out of a Rotel reciever. So I put the new relay on some perf board and wired a 750 ohm resistor in series with the relay coil. I also inspected the mute circuit and found that the circuit in mine varied significantly from the schematic in the service manual, and on the base of the case. I drew up the circuit following traces and measuring resistances. It appeared that one of the capacitors, (no cnumber marking) was in backwards according to my schematic, despite the cap being inserted per the polarity markings on the actual PCB. So I flipped it around, and still, the relay buzzed. So looked at the schematic I drew up again, and decided to flip around one of the transistors, so it went against the markings on the pcb... Board was marked with an E where the emitter of the transistor was, so I rotated it 180 degrees, and bingo, that did the trick. Now the muting circuit worked perfectly. 4-5 second delay on power up, then click. Instantaneous click on mute button press and depress, and instant disconnect at power down. Measurements show the relay and resistor dropping 19.2v, and drawing 11ma. This puts my relay voltage drop at 10.9v, and the resistor at 8.3v.
Now that the unit was working perfectly, I replaced the opamps with opa2134, and the volume opamp with tle2072 (because someone in here said that one is better in the volume location). I couldn't be more pleased with the unit. Looks and sounds fabulous.
I have attached my drawing of the mute circuit on my unit, as well as a couple pics of the mute circuit. The cap and transistor in the 4th pic both needed to be flipped around to get it working.
Attachments
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No, not saying that, but it wasn't working properly when I got it, and now it seems to work beautifully. It did certainly appear that the capacitor in the picture was labeled incorrectly. I'm not an electrical engineer, just a hobbyist, but the changes I made, made sense to me based on looking at the circuit I had drawn out. I completed the relay circuit work a few days ago, and it works great now, with 5 or 6 hours of play time yesterday, and a couple more already today. I saw pictures of other mute circuits, and none of them looked like this. It also didn't match the schematic on the case or the service manual. So I had to sketch it out and figure out what looked off myself.
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The parts that were installed, were installed per the markings on the pcb. But flipping them around against the markings, per the notes in my schematic made the circuit work. I think the pcb was marked incorrectly. Not sure what else to say, the capacitor and the transistor in the close up pic both needed to be flipped around from how you see in the pic for me to get the relay to work.
Here is a crappy video where you can hear the relay clicking when it should.
apt holman mute relay click test - YouTube
Here is a crappy video where you can hear the relay clicking when it should.
apt holman mute relay click test - YouTube
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In the previous video, I was just trying to show that the relay works with my circuit mods. I wasn't trying to open a can of worms. Mine is different than other images I have seen of the mute circuit, as well as different than the service manual and schematic. I just wanted to share what I found, and what worked in case others see theirs and it doesn't match up to the schematic.
This video gives a better short demo of the unit with audio
apt holman preamplifier demo - YouTube
This video gives a better short demo of the unit with audio
apt holman preamplifier demo - YouTube
Post 26 in this thread spells it out, and has pictures. I let my kids mess with my stuff, so it needs to be able to power up and down pretty simply, and I don't want my system to have any pops or clicks, so for mine, it doesn't really matter what you turn on or off first or last, there are zero pops, clicks, or any unpleasantness regardless of power up/down procedure. I couldn't imagine trying to get my wife to follow a set procedure, so I have made sure that it doesn't really matter how you do it.
My biggest problem is that when the 8 year old and the 5 year old come bounding into the room, sometimes the cd player will skip. Grrr.
My biggest problem is that when the 8 year old and the 5 year old come bounding into the room, sometimes the cd player will skip. Grrr.
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This does not take into account power line dropouts, etc. Not enough for reliable protection.
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