DIY Audio Projects Forum

Hi all,
I have a stereo version of the Oddblock octal which is beautiful, and built exactly per Bruce's latest plan with Edcor iron, except stereo in one chassis. I was testing with a set of small speakers and even some cheap ex SS stereo shelf speakers and it sounds great. Now, I have built a set of Frugelhorn FHXL speakers using Alpair 10p drivers. On my friends SS home theatre amp they sound great. On my oddblock, they seem lack high end (normally bass is the issue in my experience). I am not an audiophile by any means, but they just sound dull at home compared to running in his shed on his amp. Now bear in mind my source is a cheap optical to rca DAC or my iphone 3.5mm output, and his is a PC with digital out to the amp, it could be my source that is the issue.

So , can this be the speakers don't like the oddblock? I note the impedance is 8 ohms and I have it on the 8 ohm tap on the opts should I try them at 4 ohm tap? (I don't think this would make a difference). Any opinions?

Thanks,
Glenn.

I'm no expert Glenn but I noticed a dip in the manufacturers freq v spl chart around 4.5 k to 6.5k or so. Not sure how much music is up there though. Good ears may notice. I recently moved my speakers to almost on axis toed only slightly inward and moved the boxes away from the walls a bit to better balance the bass. I am still evaluating that but so far it's good. My speakers are ported two way though. The fullrange ones are being contemplated. It's good to know I'm not the only brisbanite bitten by diy. I am sure there are others in the wild.

_________________
John

Thanks Woodo. I am thinking I might bring my crappy workshop speakers and sit the on top of the FHXL's for a direct comparison (remembering to power off the am first). If they sound the same, then input issue somehow.
One thing I just remembered after looking at the schematic, I have no volume pot on the input to my amp, so no resistor to ground except whatever is connected to it. Might have to check that out further in case the source can't deal with it.

Hi, I suspect that there is some sort of mis-match. It may be that there is an unusual impedance bump in the speakers. I don't know of anyone using Frugelhorns so I can 't compare your issue to a known one. There is no harm in trying the 4 ohm tap as there could just as easily be a dip. The amps are very flat responding to well past the top of the audio band (and below it as well) so I don't believe them to be the issue. They pretty much don't care what they are feeding (within limits). As mentioned in other posts...I believe I would move the speakers around a bit and see how that effects the sound. Some are quite directional and some don't like being near walls (either sides or rear). I use ESLs in a room 12 feet wide and 17 long and on the 12 wall they need to be nearly 3 feet from each side and 4 feet from the rear to have the propper response. Let us know how this works out so we can add it to the knowledge base.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:

• PoddWatt: 5751 / EL84 Push-Pull DIY Tube Amplifier Project
• OddBlocks: KT88 Push-Pull DIY Tube Amplifiers (Mono Blocks)
• ForeWatt: ECC802S (12AU7 / ECC82) DIY Tube Preamplifier Project
• GrooveWatt: Tube (Valve) RIAA Phono Preamplifier Project

manufacturers freq v spl chart normally isn't a accurate repersentative of the actuall product but close, I would expect +-30% of error
Typically being cheeky to make more money

Thanks for the responses. They do state that these drivers are for Audiophile use, not general use so maybe this is an example. I'll try the 4 ohm tap when I get a chance. I did connect an iPod instead of the DAC and it actually seemed much better, although I was prevented from turning it up to a decent level.

Hi, I would suggest trying a high quality source. That amplifier design was never intended to use those sorts of inputs. It is designed to mate best with sources in the 2K-10K impedance range. Typically input voltage for full output is around 2 volts. A line stage preamp is the preferred method to drive the amps. Adding controls to one of the amps for level input is possible, but it can cause issues with the mis-match of input impedances. The control will effectively alter the input impedance of the amp and can result in attenuation of portions of the frequency range. Particularly if it is from something like a low Z headphone jack on a phone or player. I wonder if this is what you are hearing.

The speakers and enclosures you used ought to be OK, not my first choice of type as the demands on the speaker are high and the enclosure has to be right on for best response. To be sure it is usually the bass that suffers so your apparent loss of top end is unusual and might not be related to them. Try other sources first.

EDIT: BTW IMO "audiophile use" is a nice phrase that sells things and allows the company to add cost to something. It is not a definitive term in any sense of the meaning. There was a recent discussion of this on another site that concluded the same thought. If your amp was built like you say, it is certainly equal to anything you might hook up to it. Several well known individuals in the audio field have used (and as far as I know still use) and or tested them and agree.


Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:

• PoddWatt: 5751 / EL84 Push-Pull DIY Tube Amplifier Project
• OddBlocks: KT88 Push-Pull DIY Tube Amplifiers (Mono Blocks)
• ForeWatt: ECC802S (12AU7 / ECC82) DIY Tube Preamplifier Project
• GrooveWatt: Tube (Valve) RIAA Phono Preamplifier Project

Thanks Bruce. Understood. I am working on your phono preamp design. Got the valves, power supply caps and a B+ transformer. Thinking about how to make a nice-ish case within the noise quality build constraints. That'll allow me to try some nice vinyl. Maybe I should change to a line stage preamp instead.

Hi, I would probably do a line stage first as it is generally needed for all systems.

The phono preamp can be a frustrating build as it requires a high level of understanding of grounding. Done wrong and all you will get is hum. Done right and it will sing. If you PM me with a email address I'll send a copy of an article I wrote on it.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:

• PoddWatt: 5751 / EL84 Push-Pull DIY Tube Amplifier Project
• OddBlocks: KT88 Push-Pull DIY Tube Amplifiers (Mono Blocks)
• ForeWatt: ECC802S (12AU7 / ECC82) DIY Tube Preamplifier Project
• GrooveWatt: Tube (Valve) RIAA Phono Preamplifier Project

Thanks Bruce. Forewatt here we come, will shelve the Groovewatt for the moment. Shame with the dollar and freight your kit is prohibitive to buy from here, but I am well capable of building from scratch.